As you may have gathered by now I have an issue with damp proof courses in older walls, however they do have their place and one of these is in brick walls. Here damp proof injections stand a chance of working as long as they are applied correctly. The silicon creams can flow into and along the mortar layers (in lime mortar) or into the bricks (in cement mortars).
The process for this is to drill out a hole for the injection gun and then to inject the cream or liquid into it. The treatment will then go into the structure and create a water proof layer (well in theory, there are some issues here with how totally effective it is, but that can wait).
All well and good, one might think. However I have seen time and time again a major flaw. Contractors, having created this water proof layer, are then meant to back fill the hole with a sealant (this might be cement, lime, plug or a silicone filler) but so many do not. This this effectively creates a system where rain water is allowed into the structure above the water proof layer! How ridiculous is that?
So if you do have a damp proof course injected into your wall, just check that the holes have been back filled. Also because most often they use cement to backfill this can often be pushed out of the hole as it is incompatible with the underlying mortar or brick.
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