Great News for Lime Lovers

At last the revolutionary lime product that we have all been waiting for:

From: https://vivus.solutions

I have known for sometime that someday, someone (well I knew whom) would create a special lime product that would answer all the concerns that people have about lime on their buildings. Well folks, that day has arrived.

Vivus Solutions have just launched their website to you access to their amazing materials. Have a look at www.vivus.solutions. Lime has never been easier, quicker, better. Forget all your prejudices, this is a series of products that can be used by virtually anyone on virtually any old building.

We have known for many years that we have been ruining older solid walled buildings by applying modern non-breathable to them. Almost every traditionally built solid walled house is covered with hard cement render or an impervious paint, walls have been re-pointed with cement mortars that lock in moisture and cause the bricks and stones to spall. This has been due to a large amount of ignorance in the mainstream industry and a lack of awareness from owners. Time and time again I, and many others, have stated that lime mortars and renders need to be used on projects, but clients end up listening to mainstream builders and surveyors rather than conservation specialists.

For years, the industry has moaned about the fact that lime is slow, difficult to use, expensive, unreliable and just out of reach for most. Well I think that this is a game changer.

As well as being an Air Lime (which provides a highly breathable mix) this new series of products are sent out dry. No longer will we have to pay for wet mixes to be delivered. So already it is money saver. The 20kg bags are designed to be mixed up in a standard mixing tub with a plaster whisk.

The small bag sizes are important for two reasons. Firstly Health and Safety but also the fact that each mix will be dry in a day. So you don't want to have it sitting around for long.

Dry in a day! That is truly remarkable for a non hydraulic lime. However, it will still carbonate like a putty over time, so it will still absorb CO2. So the trick has been to get an Air Lime to set this quickly. Great stuff. This means that suddenly you are not there waiting around for days for first sets / coats to dry etc. As I say, a game changer.

I would highly recommend that people have a look at all the products available - there are internal plasters, external renders, mortars and even some pre-formed laths. Spread the news!

Note: We do not benefit commercially at all from this product, or from Vivus Solutions, I just think that it is great.

Limewashing the west facing wall

Limewash picture from Heritage Directory

I have spent a lovely few hours yesterday painting the rear of my house using some limewash. I made the limewash using some mature lime putty mixed up with water. The mix is around 60:40 water to putty. I used a plaster whisk to mix up the solution (a very quick job) and then up the ladder.

The first job was to get the masking equipment out. Dust sheets over the ground and windows all taped up and covered with some protective sheeting (old compost bags). If you have never attempted lime washing before it is a splashy business. Limewash has no binders in it like normal paint, so it doesn't really hold together when being applied. This issue was also made the more extreme as my walled are rough cast (so quite textured). The limewash was more slopped on using a large brush than any more glamorous process. Many professional limewashers use large soft floor brushes to apply it as it really is a case of just getting it onto the wall. 

When using lime you should also be careful with your skins and eyes as lime is caustic. I had a small cut on my hand and this 'burned' when limewash got onto it. So, don't do as I do and just get on with it, you should wear goggles and gloves and appropriate clothing.

The process was to start from the top of the wall and work down. The limewash can form quite thick patches due to the roughness of the wall. These will crack as they dry out to form the characteristic limewash finish. These are not a problem at all as they will effectively just create thicker pieces of limestone on the wall, however it is better to apply two thinner coats rather than one thick one. As this was just a quick top up I only did the one coat, but it is possible to apply two in one day and in total many people might find that they have to put on 3 or 4 coats to give them a good period of maintenance free finish.

I am always amazed by limewash and how durable it is. Some old splashes on the ground are still there (from being painted last year) and looking really fresh. So don't think that it is a job that you need to do every year.

The limewash is quite translucent when it is applied and with our lime render being quite red underneath the render does show through when wet. However, as the limewash dries and carbonates it turns much more opaque. So when I looked out this morning it was looking lovely and matt.

In all I did two fairly small walls and I needed one 20 litre pot of lime putty (thus using around 50 litres of limewash). A 20 litre pot of putty costs around £15. So it is really cheap (if you have white walls!) but expect to pay more for made up limewash or for colours / pigments. Even so, it is a really cheap way of painting your house.

So that is the house protected for the next few years, so feeling OK about life at the moment. 

Sand and lime

When building we use the term 'sand' a lot for mortars, but what do we mean by it and is sand what we really need for lime renders and plasters?

The picture above shows some 'soft sand' on the right and 'coarse / sharp sand' on the left. It is really important that any render is mixed with a coarse / sharp sand. This is often termed 'Builders' sand. The angular nature of the aggregate is important, however it is not the only important factor in choosing the best aggregate for the work.

Two other major factors are:

Grade of the mix. It is really, really important that any aggregate is well graded and this means that it has a wide range of particle sizes in it. You need a variety to ensure that it is well bonded with minimal air gaps. Dust is therefore key to a good render mix. Many mixes are just a combination of different uniform sized particles (e.g. 2mm mixed with 1mm and 0.5mm). These mixes do not give the variety needed.

Type of material. Many mixes are sands or crushed quartz. These rocks are not very porous in themselves, they rely on water moving around them to give the porosity needed for a lime render. Using a porous rock, like limestone, as part of the aggregate mix allows water to pass both through and around the aggregate.

We would therefore recommend that you use well graded limestone aggregates for renders.

Note that there are other issues as well like colour of aggregate, amount of pozzolans in the mix etc as this affects the colour of the render and also the amount of 'free lime' in the mix. Care is therefore also required on these fronts.

Brick face failure

This is quite common to see bricks suffering from old age (and occasionally poor pointing)

This is the type of wall that is commonly rendered over (using cement) because the bricks have lost their faces and hence are much more prone to the weather.

The rendering over can of course cause many more problems due to old bricks (with lime mortar) not being compatible to modern waterproofed cements. The obvious answer, assuming that you are happy to render over, would be to use a compatible lime render. This will work with the wall to help keep it dry and also provide it with the necessary protection from the elements.

What to do though if you want to save the look of your home?

Well, getting the same bricks to match is difficult and would require lots of research as many of the old bricks were made by small local factories that have now succumbed to nationals and multi-nationals. Getting a colour and texture match is therefore a bit tricky.

The answer, though, is staring us in the face (apols for the pun). Each of the damaged bricks will have a perfectly preserved face on its other side, so all we need to do is to turn it around! Easy (said.)

Removing the mortar can be a bit tricky, but where the original lime mortar is, it should be much easier as the mortar is softer than the brick. Where it has been re-pointed using cement the opposite is true and this causes more problems. The use of lime mortar is important for this very reason. Mortar in old houses was there more to keep the bricks / stone apart rather than to stick them all together. When we started building thin walls (cavity walls are effectively two very thin and unstable walls) we needed to stick them together using strong cement mortars and wall ties.

Anyway, back to the point. How to get them out. Well there are a couple of tools that are generally used: Angle Grinders and also Masonry Plunge Saws. The main issue is minimising dust. Silica dust can be nasty and so make sure that you wear a mask. Personally I think that it is worth hiring a Masonry Saw (also known as Wall Saws).

Wall saw

Basically, you then cut around the brick(s) in question and then you can remove them, flip them around and reset it back into the wall using a matching lime mortar. Good luck!

Brick turning

I can't afford lime render!

Lime rendering done by Welsh Lime Works in Cardiff

Lime rendering is a specialist trade (not to be confused with lime plastering or cement rendering!) and as such it takes time served craftspeople to do it well and it also takes more time to do. These two factors mean that many people who need to have their houses re-rendered choose the cement route. Using cement, of course, represents a higher long term cost. The render will crack and, most likely, damp will be re-introduced to the walls. This will need to be addressed again in the future, whilst a lime render should last the lifetime of the building.

A customer of ours choose cement render over lime due to the cost, however within 8 months the cement had failed, the wall was still wet and she has had to do it again. So the difference in price has already been negated due to failure.

However, this article is about what to do if you cannot afford at the moment to replace the cement with lime.

My recommendations (in general) would be as follows:

• Keep the existing cement render on
• Regularly check the walls for failed render (tapping the walls will audibly indicate where the render has become separated from the wall)
• Repair any cracks (even the small ones, especially if facing the prevailing winds and rain) and any blown areas of render
• When replacing blown areas, it is better to cut around the render to be removed so that the process of removal does not dislodge any of the surrounding render
• Use cement render to replace / repair
• Check for failure of seals around doors, windows, pipes etc and repair as necessary
• Save up and when you can afford it, replace the cement with lime.

Enlarging cracks allows for a better repair as the new render will fit into it

The rationale behind this recommendation is that where you have a structure that has been altered to try to keep water out then as long as this philosophy is being maintained then it will have a better chance of working than when it is not. Cement render and masonry paint is designed to keep water out and as long as it is doing this then it will provide some protection from wind driven rain, however it needs to be uncompromised. So maintenance of its integrity is really important. The more water that gets behind it, the worse the wall will perform and the more likely damp issues become.

This patching and maintaining is really important to allow the wall to perform as well as it can before the ultimate solution of the lime render is applied. So don't waste your money on putting a new coat of cement render over your pre 1919 solid wall house, repair what you have and save your money up so that you don't waste it on an unsustainable, and still quite expensive, piece of cement based sticking plaster!

If you have a 'rising damp' problem (this is rare to occur in most untreated houses, but can be caused by the introduction of cement based renders and plasters onto a breathable wall) then another cheaper option is to remove the cement render up to around 1m above ground level. This wall might then need to be repaired using lime mortar (re-pointing) or it could be lime rendered. Doing this at ground level means that there is no need for scaffolding and the area involved is much less, thus keeping the costs down. You will need a good drip above this so that any water running down the upper wall is not fed directly into the lime or onto the exposed wall.

If you need to put up expensive scaffolding to do the repairs then this brings an extra dimension as the lime rendering becomes more cost effective in the longer term. So any initial repairs to the cement are best done off of a tower scaffold or ladders.

I have written at length before about lime rendering, but it is worth re-iterating at this point the things to remember when looking for a good lime renderer.

• Use a company that both supplies and installs the render (this can get over the issue of where, if there is a problem with the final work, you are not inbetween a rock and a hard place where the installer blames the manufacturer and the manufacturer blames the installer!)
• Remember that rendering is not the same as plastering. So use an experienced renderer.
• Ask for references and a good portfolio of completed works
• If it is new company then you will need to ask about the experience of the tradespeople and where they served their time. You can then investigate this company.
• Read up about lime from trusted sources like CADW, Historic England, Historic Scotland etc (depending on where you are)
• Ask about the mix that they will use and the finish that will be applied. I am a believer in aggregate being really important. I think that the aggregate needs to be a mix of sizes and also that it contains a high proportion of permeable stone.
• The finish needs to be appropriate. So a lime putty and permeable stone mix can be easily covered with a lime wash, a less breathable combination of NHL lime and sand will probably work better with a mineral paint.

Vapour Control Layers in Insulation

From RIBA

The pressure for energy saving in solid walled buildings is real and tangible. Green Deal and rising energy bills are encouraging us to insulate our walls. Where we have external features / facades that we want to keep we are forced to choose internal wall insulation (IWI).

BS5250 (the British Standard) for moisture control in buildings recommends a series of potential interventions (but crucially it also says that this is NOT a recommendation for breathable walls - which are virtually all the solid walls). One of the main recommendations (and hence common practice) is to install a Vapour Control Layer on the warm side of the insulation.

If there is no water in the wall then this works fine, but it is now becoming common knowledge that virtually all the UK's solid walls must be seen as 'moist'.

This is starting to create problems for the vast majority of the solid walls fitted with VCLs or non-breathable insulations due to Reverse Condensation (or Summer Condensation). This is a phenomenon that occurs when external temperatures and hence humidity levels are greater than the internal environment. Higher external pressures associated with temperatures forces this moisture laden air into the wall and when it cools and hits a water proof membrane or insulation the vapour condenses and runs down the back of the barrier. This concentration of moisture deep into the wall structure also means that joists and other wood is more at risk of damage.

The answer is to carefully read BS5250 and listen to what it says, which is, for breathable walls take professional advice from specialists. The best to provide this are bodies like National Trust, CADW, English Heritage and Historic Scotland. Thankfully all these sources of specialist advice are members of the STBA (as indeed RDE is) and their advice / case studies etc are available from http://www.stbauk.org.

The best advice recommends using a fully breathable insulation (wood fibre for example) with a lime / clay plaster and a breathable paint finish (like our Earthborn Claypaints or Auro Lime Paint). 

So beware of advice and common working practices that are based on half-true information. 

Damp proofing a typical Welsh terrace wall

Typical streetscape in Cardiff

Can you stop stone and brick walls from getting damp?

The simple answer is YES, but there are a range of issues surrounding the question and the answer!

The main issue around whether a wall is damp or not is that diagnosing damp is an art not a science per se. Common damp meters use electrical resistance to measure damp and this is fine for timbers, but for walls it requires a lot of interpretation. High readings can come from salts in mortars, old lead based paint etc, so not always water. So where you take measurements can radically affect the advice that you are given. So some companies who are trying to sell you damp proofing measures can use these meters to show that you need treatment when you might not.

So that's the issue with defining whether you have damp, but assuming that you do actually have a damp problem the next issue is where is it coming from.

We have all heard of rising damp, but many houses in Wales suffer from penetrating damp. This is water that is blown, or diverted into the structure. This can be through cracks in pointing, cracks in render, leaking rainwater goods, blocked guttering, failed seals around doors and windows, ...

Damp can also be caused by condensation. This might be due to poor heating, ventilation, high humidity from indoor activities. Again this needs to be assessed by looking at heating and ventilation strategies and infrastructure. Do the windows have trickle vents, have the chimneys been blocked??

Rising damp might be due to a range of factors including external ground levels, the presence of replacement concrete floors, blocked under floor ventilation, ... 

As you can see, damp can be difficult to diagnose. However, it is really important to ascertain where the source of any unwanted water is coming from.

Once you know what the problem is, you can start to find the cure. However, the cure will be influenced by the history of the building and the materials that were used to built it in the first place. This means the make up of the basic structure and also the materials used to repair, maintain and develop it over time. This building pathology work is key to refining the diagnosis and will hence help lead to an appropriate solution being found.

I cannot go into any great detail here as each building is different and requires specialist individual advice. However, the question was is it possible to damp proof these old buildings. The answer you might remember was yes, so what are the solutions?

1. Rising damp

If you do indeed have rising damp then you might need to:

• Lower the external ground level
• Re-instate ventilation under the floor boards
• Remove cement render from the outer walls
• Re-point the bricks / stone with a lime mortar
• Re-render using a lime render

All of these are potentially permanent solutions, however they are fairly major bits of work, so most people just want to inject something into the wall. This is potentially possible and it depends on a range of factors, one of which is whether the wall is made from solid brick or stone. These walls are fundamentally different in their nature and it is easier to apply modern injection treatments to brick walls. 

Damp that is rising in a brick wall can be treated quite effectively using creams like DryZone. However even here you see companies injecting the damp proof cream into the bricks rather than the mortar. So with care this type of product can be part of a solution (but not if your damp is due to condensation or penetrating damp). However it won't work in stone walls (unless you have an even mortar bed at the correct height - like in ashlar walls).

Stone walls are fundamentally 'moist' in nature and so need a more holistic approach that is based on material science. The solutions here are much more likely to follow the bullet pointed measures above. It might also need to be combined with addressing ventilation issues, as stone walls need to dry out by the movement of water from the water to the outer and inner surface. 

2. Condensation

This tends to be more due to high humidity in the building and so a balance needs to be found between energy efficiency, ventilation, insulation and behaviour. It may be that a house needs positive input ventilation, or that the old chimneys need to be unblocked and vented, trickle vents on windows need to be opened, humidity controlled extractors fitted, or just a clothes dryer installed in the garden / room with an extractor fan. 

3. Penetrating damp

Penetrating damp is generally caused by issues around poor maintenance of a property. However, it can be down to the use of inappropriate materials like cement render. Seals like silicon around doors and windows fail over time and rainwater runs down the surfaces and straight behind the sill. Cement render (is fundamentally inappropriate, but nevertheless covers the majority of stone and brick houses) cracks due to its brittle nature and traps water behind it. Gutters and downpipes need to be clear otherwise they can easily poor high volumes of water against (and into) walls. Poor drainage around the building can lead to water sitting against walls,  I could go on.....

As you can see, diagnosing damp and finding the correct solution is a bit more involved that just pumping in a load of chemicals. However, pumping in chemicals and using water proof cement is what we do in the UK to the vast majority of our solid walled houses. In fact many mortgage lenders insist on this type of damp treatment. What a shame, it is generally a complete waste of money and resources. A typical damp treatment costs around £4 to £5,000. Don't be fooled by guarantees and assurances, many are meaningless. A recent customer had a injected DPC installed and when it failed dismally she was told that it had been installed correctly and so she couldn't claim against the warranty!

We would always recommend that you use your money wisely and this means that it is better to find a permanent solution to damp. This requires time and knowledge to get to the correct diagnosis, It is not a quick trip around with a damp meter and a bill of £5,000. The answers are there, but you will generally need some independent guidance to find the right ones for you and the house.

Where has that damp smell gone?

No need for these now!

The was always a certain smell when we came back home. That slight dusky smell that reminds you that there was damp in the house. Well, I am glad to say that when we returned from being away at Christmas there was no such gentle reminder.

The mould that has been growing (thanks to the original builders who left the house renderless and with some major defects exposed to some pretty awful weather in the late summer) has been stopped in its tracks. Now, all I need to do is to repaint all the internal areas that have lost their paint / been affected by mould etc.

I am really pleased that our efforts (and that of Welsh Lime Works) have paid off.

In summary we have:

1. Created a drain all around the building so lower the external ground level - this will allow any moisture from the ground to be vented off before reaching internal floor levels

2. Opened up a blocked chimney on the first floor to create a better airflow through the house (the ground floor chimneys house wood burning stoves and so are already open)

3. Removed the cement render from the solid walled and early cavity walled elements of the house and replaced this with a lime putty / limestone dust render. Finished with a white limewash (applied in a hot mix)

4. I have also reset all the guttering to ensure that it is not leaking anywhere

So effectively the house is now functioning as closely to its original design as it is economically viable to do (note that we have not replaced the cement floors with the original suspended floors).

We have experienced some pretty wet weather at times since the work was finished and it should be noted that some areas (concrete block substrate) is still drying out, but the internal walls are now dry and the render is slowly releasing all the trapped water to the outside. 

I had imagined that the drying process would take a lot longer, given that the walls were exposed for so long and that the limewash was only put on late last year, but the project has worked really well and we now have a dry and smell free home. So all bodes well for the future as, apart from routine maintenance on gutters etc, the actual structure of the building is now working in a way that will keep the whole house dry inside for many decades to come. I am expecting that I will need to re-limewash every 6-8 years one the southern and western elevations, but more like every 10-15 years to the north and east (and this is down more to issues of traffic fumes rather than the weather).

Given that I have seen replacement cement render failure in a significant number of solid walled houses within a year of application I think that the added expense of doing it right will soon pay off. It really is a false economy to use cheap materials when all you do is store up more hassle and expense for a future date. So, if you have an old house with a damp problem why not give us a call and we can help you out.

Lime wash on, it can be hot in the winter!

Welsh Lime Works have finished my house!! Hooray. They have managed to work around the scaffolding and all the problems left by the last lime company to produce a lovely white house.

The final coat to this lime putty render has been the limewash. There are a number of special properties to this covering, firstly it is the same lime as was used in the render mix, i.e. a limestone derived lime. This is important when rendering (as opposed to plastering) as it is a hard wearing material. Some limewashes in the past were chalk based as they expected them to be used internally, but you will need a limestone based limewash.

Secondly, the boys (and girl) put the limewash on as a 'hot mix', so basically they used quicklime to make up the limewash just before it was applied and this meant that the limewash went on hot (due to the slaking process). Welsh Lime Works think that this provides a better longer lasting finish due to the reaction that is ongoing when it is applied, so it bonds better with the underlying render. Great to see steaming 'paint' being applied to your house, especially in the winter months (mine you it was still above 5 degrees when it was done).

I have been very impressed with the level of skill and knowledge from Welsh Lime Works and their attention to detail. The house was also left nice and clean.

Plastering. Is it the same as Rendering?

Plastering with gypsum is obviously different from rendering with sand and cement

When doing 'conventional' works to buildings it is a clear distinction of trades between internal and external works. This is because there is a difference in some of the materials used and also because there is a large enough market to have specialist firms doing one operation or the other.

In the lime world, it tends to be that people do both rendering and plastering. This is driven by the fact that the materials used can be much more similar. Most people will use a NHL Hydraulic lime for both internal and external works.

If you look for a Lime Render course you will generally find one day courses that cover both plastering and rendering as well as everything else lime!

Given that plastering and rendering courses are normally at least two years long it seems a bit much to expect people to be able to render and plaster with lime after a couple of hours. Maybe this is why lime can have an application issue attached to it. After all lime is a much less predicable material than cement and gypsum. 

Having seen the boys from Welsh Lime Works doing a very professional job on my house you realise that that there is no substitute for experience and knowledge. There have been a number of key points in the work where you just know that someone who has just done internal lime plastering would have made some fundamental mistakes.

Welsh Lime Works are keen that their workmanship and knowledge that has been built up over the years is not shared carelessly, so if you want any info I would recommend getting in touch direct with them. http://www.WelshLimeWorks.com. However I think that it is fair to say that the key points around door and window reveals, wall corners and floor junctions are where their work stands out and will pass the test of time where others may well fail. Not to mention the issues around potential lamination of the render. All of these key factors require a professionals eye and years of experience in order to get right. So it has been fascinating seeing the process, the method of application, the changes in mixes, the subtlety in timings etc.

So if you have been on a lime plastering course be very aware that applying lime externally is very different from doing the same internally. The effects of the weather, temperatures, orientation and the various pressures on the fabric due to the use of the building all need to be taken into account if the job is to be a long lasting and high quality one.

Concrete blocks full of water

I hope that you can see from this photo that in the corner of the wall there is a dark rectangular patch. Under here is where an old doorway was blocked up using concrete blocks. The first coat of lime render is finding it hard to dry in this area and another similar one. Where it is on bricks and stone the render is rock hard and curing, but it is amazing how much water is being retained by the blocks.

The lime render will of course allow this area to dry out fully in time, but for the time being it is holding up work a tad as the amount of water that needs to be removed is astonishing.

Part of this problem is that since the first lime renderers walked off site it has been raining quite a lot and hence the blocks became sodden. One of those issues that you cannot really foresee, but it does mean that I am even more annoyed with that original company. Very irresponsible and unprofessional.

This acts as a warning to others that if you are lime rendering concrete blocks make sure that you do not wet them too much. It also highlights that when people cement render over these blocks that, if they are wet, they will trap a heck of a lot of moisture in the structure for a long time.

The house is coming along, the base coat is on all over as can be seen in the following shot:

The strength of cement

Look no hands! Nine bricks being supported by their edges by a 10mm thick piece of cement render.

I was planning on capping the wall that abuts into my house (this was to reduce the amount of water that is being channeled into the main house from the wall's poor structure). So I started to rake out the pointing where there was a loose brick. One of course lead to another and before I knew it I had taken down four courses of bricks and it didn't stop there.

The neighbours side had a lovely big ivy growing out of it (unknown to me) and this had blown the render on their side and so I had to remove this (a quick yank on the ivy sufficed!) The missing render can be seen on the left hand edge of the picture. The rest of their render was basically intact and so I left it.

I returned to my side and continued to identify the loose bricks. As it turned out this was a further twelve - all the roots from the various plants that were growing out of the wall had destroyed the mortar between the bricks. As I removed the bricks one by one I was amazed as the top two rows of bricks didn't move at all. As you can see from the picture this meant that the two courses ended up being suspended in mid air just by the cement render on their sides. Needless to say I then had to quickly replace the bricks (this time using a lime mortar) to ensure that it all stayed there.

The great thing of course with the old mortar was that it had left the bricks intact and it was easy to dust them off and re-use them. So I have rebuilt the wall and am now awaiting the caps to ensure that the wall stays a lot drier than it has been for the past couple of decades. More on this with the next post!

Lime render and doors

Replacement doors tend to be held in place by screws, not inbuilt frames

The door on my house has seen a lot of changes. Since I have owned it we have had 2 doors. The removal of the render showed that the original door and frame must have been at least 10cm wider (there is a pillar of bricks on the far side in this photo).

When we changed the door we fitted a new frame as well. However, this frame is held in place using screws set into rawl plugs in the wall. This gives a firm enough finish, but it does move when slammed, so what to do with the new lime render, will this get affected by repeated use?

Well the thought is that yes the door will effect the render. As the door vibrates the render can be weakened and a really hard slam could shift and crack the new finish. So the plan is to counter this by using a cement and mesh to really tie the frame into the wall. With a firm and secure frame in place the covering render will be protected from any movement.

Purists might be up in arms about this as it is not lime (well cement is a lime, just a particularly hard and strong type), however this is about being sustainable and I feel that having something that will last longer in a potentially susceptible zone is better than having a purer version fail. The other important element to remember here is that the cement will be covered with the lime putty render, so this will be effectively buried into the wall and the lime will keep it dry.

Brick detailing ruined by cement

Lovely brick arch revealed on front of house

If it weren't for the addition of cement render over the years I think that this detail would have been recoverable, however the cement has pulled off the surface of the bricks and also caused them to break over time.

This detail would have been nice to re-instate on an otherwise bland looking terrace house, but without replacing all of the bricks it is just not possible.

The use of inappropriate materials therefore has an aesthetic effect on older properties as well as the fundamental damage that they cause by changing the way in which they work.

The damage is caused by the cement being too hard and strong. Basically the mortar and / or render should be weaker than the underpinning structure. Having a harder material means that it is the structure that is damaged when the outer coating is removed. Mortars should just be there to keep the main structural blocks apart and the render is there as their protective external wearing layer. Instead cement changes this to a system where the render is the dominant player and the main structure becomes it servant. Surely we can see that this is fundamentally wrong.

Anyway, my wall will just be a plain render finish (as planned), but seeing that lovely level of detail that was in the original house just illustrates to me what has been lost through the use of modern building materials on an old property. Shame.

Steel reinforced lime

Stainless steel EML screwed into place over areas with different materials / old cracks

I have been busy on the house preparing it for its new coat of lime putty render. One of these jobs has been to mesh over any major cracks in the sub-structure and where there are different materials exposed. This is because the movement in the house may crack the new render. Whilst this is not catastrophic for the render, it is always better to have an uncracked surface aesthetically.

So I have been using stainless steel EML (Expanded Metal Lath) AND stainless steel screws and washers. So I have been drilling into bricks, mortar and an occasional stone to ensure that the mesh is tight to the wall.

The high spots of the dubbing out had to be rubbed back (using a nasty looking studded float) so that the EML would sit quite flush to the wall.

The only major issue was that I was doing this on my own and the EML is really sharp, even on the main surface, so I have managed to cut my fingers quite a lot!

So the EML now covers the main wooden lintel at the front of the house, a thin brick pillar that was constructed to make the door opening narrower, the zone between an old extension where the bricks were not tied in very well, a wooden strip that runs horizontally along the first floor and the junction between a brick element of the house and an infilled concrete block area (an old door way).

So the wall is getting there for being ready for the render. Welsh Lime Works starting today!!

Cement render = Rotten wood

Removing render exposes timber issues under cracks

One of the other issues that the removal of the cement render exposed was the condition of the wood in the structure.

Admittedly the house has a strange array of wood that has appeared in the most unusual places - joists that go all the way through the house from external surface to external surface. The trouble is that this change in underlying surface meant that the cement render was more likely to crack here. Of course, being cement, it did and this in turn allowed water to get behind the render. This concentration in damp behind the cement of course then fed into the wood.

This is one of the big concerns with cement rendering old houses as it it not obvious until it eventually gives way. One of the many problems that we are storing up for the future generations, by not understanding older properties well enough.

So, if you do have a solid walled house make sure that you maintain any render really well - remove cracks when they form etc. If you do get around to needing to re-render, then do so using a lime based render but also expect to un-earth a range of problems.

I feel that this is a similar situation to the climate change arguments. It is out of sight and so out of mind. It is also largely controlled by large companies with vested interests and so they will not lead the way for change as their industry is profitable as it stands, so why rock the boat, even if you know what you are supplying is ruining the environment (the built one that is rather than the natural one).

Dubbing Out

Haired lime putty render thrown into deep holes in wall

One of the jobs associated with re-rendering the house has been to make good the walls before the main render coat is applied. This involves getting hold of some lime putty render (same as the top coat) and throwing it into the main holes that were left by the removal of the old cement render.

The walls were quite a mess after the initial removal. The cement render is far too hard for the walls and so it takes off lots of the underlying mortar and also breaks bricks etc when it is removed. The removal process also involved fairly heavy equipment in the form of breakers and if they are not used carefully then they too can remove parts of the wall. If using breakers then it is advisable to use lower powered ones rather than being all macho about it. So medium breaker, with a wide chisel end, used in as parallel an angle as possible is the way forward.

Anyway the upshot of the job is that rather than expecting some areas of render to be 10cm deep and others 2cm it is best to 'dub out' the holes to make the surface more even.

The process I have used is to throw the mix into the holes as this gets more air into the mix and hence it cures quicker. I have also had to replace some half bricks. Any exposed wood has been treated using Osmo 4005 and the windows have been insulated into any void reveals. Next will be to sort the various joints in the wall so that any variety in movement of the walls does not crack the new render.

A trip around the block in Canton Cardiff

Part of my walk around the block

We are based in a residential part of Cardiff. Lots of solid walled properties and also some newer infill houses with cavities. Despite the ravages of time that have been served out by well meaning but not necessary best informed builders and DIYers, it still has great character - lots of different colours, features etc all based on a common theme.

All looks rosy then and in fact it is an area in demand as far as estate agents are concerned. Can you feel a but.... coming on??

Letting my casual eye wander across the urban landscape I did spot lots of very common issues affecting the houses, so here goes:

No end of cement render (should be lime based and ideally the mix I advocate)
Cracked render everywhere (letting rain into the structure)
Re-pointing with cement (rather than lime)
Damp proof course injected into bricks (should be into the mortar - if used at all)
Damp proof course holes not filled (thus letting water into the structure above the DPC)
Ground levels clearly above the internal floor level (there should be a 15cm difference between inside and out)
Blocked vents for the floor (suspended floors require good draughts under them)
Paint peeling off of dress stonework (should be left bare, or painted with a breathable paint eg. silicate)
Guttering broken, warped, joints snapped, loose downpipes, .....
Window seals broken (they need to be checked and repaired regularly)
Phone and internet lines roughly drilled through walls leaving holes around them (should be sealed up properly)
PV panels covered in pigeon poo (aerials need to be moved to remove the temptation!)
Letter boxes broken (should be repaired to ensure better airtightness)

And that was a quick 15 minute stroll along three streets!!

Correct maintenance is really important with buildings otherwise we shall see these houses slowly degrade. In the heart of the city we need a well informed population, but who apart from us is trying in Cardiff??

Lime and Steel

The difference can make or break (literally) your project

These products do the same job. 

They also look very similar

One will work, the other will not

Fixings are used a lot in the construction industry. My render job on the house is no different. I shall have the following types of metal in my wall:

Expanded Metal Lath (EML)

Stop Beads

Screws

Washers

The EML will be used to tie together those parts of the wall where there are junctions (points where the risk of movement and cracking is most acute).

The Stop Beads will be used around the base of the wall

The Screws and Washers will be used to hold the Beads and EML in place

The important thing is that they are ALL stainless steel. Lime (and cement) attack steel and galvanisation is only a thin coat of zinc over the top of mild steel, so any slight removal of this protective covering will allow the moisture in the render to rust the steel. The galvanised steel will also slowly react with lime and this will cause the structure to fail as the rust expands and cracks the render.

Using galvanised and stainless steel together also creates a electrolytic reaction between the two and this will also lead to the render failing.

So when you are using a lime product it is vitally important that you use ONLY stainless steel (and / or plastic) in your fixings. Don't think that you can get away with using good quality beads and EML and then fixing them with some ordinary screws / nails. It will not work.

Stainless is a bit more expensive than galvanised, but in the long term it is very much cheaper! No point having work done only to need it redoing in a couple of months / years.

It is also worth noting that on a recent visit to a newly built school they had the same problem. All the drip beads had failed and had 'blown' the cement render. So it is not just old buildings where care needs to be taken with regard to material selection and combinations thereof.

Lime philosophies leave me in the lurch

Lime is a interesting subject and one that I have covered on a number of occasions in this blog. The reason why it is a controversial topic that it is a really important one where there are lots of vested interests and little in-situ research. Lime is material that is a vital element to the construction industry, especially in the traditional building element of it. Lime, though has become a generic term. We use it all the time to express the need for a breathable mortar, plaster and render. You will commonly hear people use the term lime render, but do we actually know what it means?

Some people use cement and just add powdered hydrated lime into it and then refer to it as a lime mix. Others will use the other common powder form of lime (Natural Hydraulic Lime) and use it with a sand aggregate. The purists will stick to Lime Putty. However, even the purists then disagree with the aggregates that should be used and also on how to apply it.

All this is a bit more confusing and less clear cut than the term 'lime' conveys. This is why I worry sometimes about the conservation industry and its use of the generic term.

I have always been clear on my thoughts about lime render and the aggregates that support it. These are the reasons why. I believe that:

• The walls of houses, where rendered, should have the most breathable (porous) element on the outside. So one should create a gradient of porosity from the main structural wall to the outer finish. This means that the outer surface will always help to draw moisture away from the inner structure, thus keeping it as dry as possible
• The pressure to take the movement of water through a render should be shared as evenly as possible between the lime and the aggregate. This means that the lime is not taking all the responsibility for the movement of the water, thus allowing the water to move more easily through the structure
• Lime renders need a consistency of mix through the structure in order to minimise the risk of de-lamination. Using different mixes and limes can create this difference in the structure and so should be avoided.
• Application of the render is really important as one needs to apply the mix in such a way as to encourage the different coats to chemically bond together. This again minimises the risk of de-lamination in the structure

Having sorted a specialist order for a limestone mix from a local supplier, the combination of lime putty and limestone aggregate has proved too much of a leap of faith for my current lime specialists on site. They have backed out of doing the job (unless I forgo by principles and stick to the common knowledge of the 'lime industry'). This means that I have been left with a house that has been hacked back to the stone / brick / concrete blocks etc and no contractor to put a proper lime render back on. I was a tad 'hacked off' as you can imagine!

Knowing that I am right (see picture above) is proving to be a problem!

However, there is a knight in shining armour. Mark from Welsh Lime Works has offered to step into the breach and do the rendering. This means more of a wait, of course, due to his other commitments, but at least I will be able to get what I want and have it done by people who know what they are doing. A huge thank you to Welsh Lime Works for this, true saviours.