Rising damp?? Maybe not!

The common thoughts about the cause of damp at ground level - rising damp

Damp - It is a problem for many houses. Trouble is that we have coined a phrase that clouds our thoughts - 'Rising'.

Damp is the presence of water in the structure. This water could come from a variety of sources, but we tend to assume that if it is close to ground level that it must be 'rising damp'. As you can see from the picture above there are a number of routes that 'rising damp' can take, however there is a blinding omission.

Lets assume that a wall has had a damp proof course (DPC) installed - this could be physical one (in the form of slates / bitumen / plastic) or an injected chemical one. Most walls these days have such a feature, although there are many reasons against having an injected solution in many solid walls, and we generally assume that they work to a certain extent. So effectively we have a water proof / resistant layer in our walls. Now this layer does not discriminate between water wishing to come up into the structure and that which comes downwards.

This is the missing link in the thought process when it comes to damp. What if it is not 'Rising Damp', but instead 'Falling damp'?

Many walls are covered with cement renders and also suffer from a lack of maintenance by owners leading to cracks and gaps around windows, doors, services etc. These faults lead to water entering into the main wall structure. The water cannot escape to the outside due to the cement render, so it succumbs to gravity and tracks its way down and into the wall. If this is happening around ground floor level (around windows, cills, plumbing etc) then it can easily find its way to the DPC. Then of course the DPC (assuming that it is doing its job) will stop it and the damp will appear just above the DPC in the inner wall. Also worth noting that the plaster on the face of the wall will soak up the water and hence track it below the DPC as well.

So when we get damp meters out it is very easy to diagnose rising damp, when in fact the DPC is working well and the water ingress is from defects in the wall above rather than any other source. So guess what? People are then recommended to have another DPC installed! This of course does not solve the problem.

We really need to get back to first principles, use our brains and diagnose our buildings correctly. Falling damp is very likely in the UK, especially with all the cement renders that have been applied to older solid walls. 

If you want a good and intelligent diagnosis on damp then give the Eco Home Centre a call and get a true independent assessment, do not rely on 'damp specialists' from damp proofing companies because, guess what, they have products to sell.

New drain around the house

As you know I am in the full flow of getting my house sorted for damp. One of the main problems has been the fact that the outside ground is at the same level as the internal floor. This means that any rainwater is encouraged to make its way into the wall and hence the inside because the lower levels are always wet.

On the south and west facing walls this is particularly difficult as this is where I get the wind driven rain issues. It just so happens that this zone is an area of concrete that has steadily built up over time. So I took the plunge (as I did on the north wall) and created a trench along the perimeter of the wall. I effectively lowered the ground level back to what it would have been when the building was constructed, but with the amount of water that accumulates here I need to ensure that it can drain away quickly and easily so that I don't get any standing water.

One choice would have been to remove the whole of the concreted yard and to lower this whole area, but given my resources and love of my back I decided to keep the concrete yard and create a graveled drain.

So I popped to a local DIY store and found that they didn't have any land drains in stock, I soon found that this was typical and so I improvised. I bought some downpipes and joints and used a 10mm drill to create a makeshift drain. Note that the holes are along the top (this was because it has a slight indent in its squareness and this would be exacerbated by the stones to be placed onto it) and along the lower edge. This means that any water that rises up from the ground will feed into the holes and then track down the drain and away.

My make-shift drain with 10mm holes drilled in

 I then used the trusty spirit level to ensure that it was running down to the main drain. I will be placing some sort of barrier across the top to ensure that the chippings don't fall into the drain and block it.

The outlet of the land drain into the main drains

The trench was then back filled with the 20mm limestone chippings. The 20mm chippings were used as they should not fall into the 10mm holes, thus creating a long term fix. I shall also at some point get some geo-membrane and put this down below the top layer of chippings so that any dust / dirt etc doesn't get carried into the drain and block it.

The trench back filled with 20mm limestone gravel

With the rain that we have had over the past couple of days it was good to see that the trench has not filled up with water, so I think that it must be working.

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.

Tracking down lime sources

A limestone quarry

What a palaver! Being a bit of a fuss pot over lime I wanted to check the lime credentials of the lime putty that is being ordered for my render. I seem to have been around the proverbial mulberry bush, but at last I feel at ease with the source that shall adorn my walls.

The lime putty that shall be used will have come from Cheddar (an Oolitic Limestone) as a Quicklime and then slaked in Brecon (at Ty Mawr Lime), left for a minimum of three months and then mixed with an aggregate including limestone from the Cotswolds.

I feel it is really important to know the source of lime as some limes are made from chalk. I think that an external render needs to be made from a limestone base rather than a chalk one. Ultimately it will be harder and more durable. Chalk derived products are fine for internal applications, but I am not so convinced with being exposed to the winds and rains that we can get (only occasionally mind) in Cardiff.

The limewash will also be a limestone based product as well.

Windows shrink with age

Having knocked off most of the render around my house (we are leaving those walls that will not benefit from a new lime render) the original reveals for the windows and doors are fully exposed. This then gives one a chance to see how big the original frames would have been.

One downstairs window has a gap of 3 inches / 75mm each side, so over time my window has effectively been shrunk by 6 inches / 150mm. That's quite a lot of light that I have lost!

What happens is that when windows are replaced we don't hack off the render or plaster to see where the structure is. The windows are measured using the visible reveal. No installer wants to estimate depths that they cannot see and most people don't want to have their reveals knocked around just to get an accurate measurement. So windows get smaller.

When the windows are installed, they do have to 'mess' with the reveal and then you find out that you could have had a larger window, but by then it is too late. The new windows are fitted and the reveals are extended so that the window frame is enclosed with plaster etc. Next time, of course, your reveal is now smaller and the process repeats itself.

I would estimate that around 0.5 - 0.75 inches (12 - 18mm) is lost per fitting, so this would mean that this window has been replaced about 5 times since construction.

One of the other common occurrences with this process is that this gap is often filled with that days newspaper. So, you can often catch up on the news from a couple of decades ago! Nowadays fitters tend to use expanding foam to seal up these gaping holes around your windows which is not so much fun. I am not a fan of this foam and so I have used some fluffy insulation in the gaps to provide a little more warmth (and more importantly) fewer thermal bridges around the edge of the window.

So, if you want to keep your windows as big as possible, you will need to allow fitters to remove the plaster around the window so that they can accurately measure the size of the original window void. This is unsightly and dusty, but it is the only way that a company can reliably measure up. They are not keen on making windows too large or tight as it means that they are responsible for getting it right, so their eye on caution is understandable given the costs of re-making the frames and glazing.

Lime rendering my home

Money where mouth is moment!

I have long been an advocate of treating old solid walls correctly. This means allowing them to breathe using a lime based render (where render is needed of course).

Anyway my house has been suffering from damp for a while and so eventually we have managed to get enough money together to start to put it all right. So we are taking the correct approach of getting the outside done first before moving inwards. So, first part has been to remove all the old cement render from the solid walled parts of the building. Note that we are not taking off the render on the already lime renders timber frame walls, or the newer block cavity walls, that form the end extension on the property.

Front of house is stone, behind door is solid brick wall, next extension is early cavity, still rendered is block cavity at ground level and timber frame above

Front door separates different materials

First floor timber joist exposed. Southern side of building is suffering from rot due to trapped moisture from cement render

I have long been a follower of Harry Cursham at Traditional Technologies (http://www.tradtech.net/) and Welsh Lime Works (http://welshlimeworks.com/) and so I have been very specific about the type of render that will be used. I have chosen the following:

1:3 Mix of Lime Putty (from Limestone NOT Chalk) and Aggregate (and this is one of the keys!)

As you may have read in some of my earlier posts, I see aggregates as being the vital, but often overlooked, element to renders. The aggregate mix that I have chosen is:

1:1 Limestone (3mm to dust) with Sand (50:50 mix of coarse and fine)

The key ingredients are the limestone dust and the limestone putty with the sand acting as a filler. The limestone and lime will do all the work in the render as it is these two elements that will carry the water in and out of the wall. Getting consistency of material, avoiding weak points and ensuring that de-lamination is avoided mean attention to detail!