silicone covering for external wall

[thursdaycat]

In previous posts I have been advised to "avoid like the plague" silicone solutions to coat the outside of our stone walled house. They are supposed to stop water coming in through the stone.

Please can someone spell out for me why they are to be avoided? This product for example says it stops water ingress but still allows the wall to breathe - isn't that OK?. http://www.decoratingdirect.co.uk/viewprod/b/BITSUWS/

I know I've asked before about this but my Dad is going on and on about it and I need to understand more...

 

[Nemesis]

Can you explain the science of why it claims that it is waterproof one way and not the other?

Any sort of seal like this should be avoided. It's a bodge job which isn't good for buildings. In any case old buildings move, and creating a total seal isn't possible or desirable.

Stone in general isn't in need of waterproofing - it's not very porous.

If you are having problems with water coming in it's better to fix the problem - leaking gutters, pointing which is in poor condition or has been done with hard material such as cement.

The ad says for brickwork, concrete and cement. These (unless you have very historic soft brick) should all be 'waterproof' materials anyhow.

 

[MdB]

Can you explain the science of why it claims that it is waterproof one way and not the other?

Same principle as Gortex. You have a water repellent material which is full of microscopic holes. Rain drops are much larger than the holes so are repelled by the bulk of the material. Water vapour on the other hand can go straight through. The science is sound but whether or not it works in this application and wether or not it is a good thing for the wall is a completely different question.

Stone in general isn't in need of waterproofing - it's not very porous.

Hmm. Not sure if that is true for the rock that my house is made of. It looks like it will soak water up like a sponge.... Will have to do a few experiments.

 

[Gervase]

Gore Tex talks a better game than it plays (says the Paramo fan and MLTB trainer - but that's another hat...).
But, aside from that, I tend to rest my faith in what has been shown to work over time. The great thing about the IHBC, SPAB and other like-minded conservation groups is that they are populated by terminal anoraks who will test any such claim until it squeaks - and invariably it is found wanting. Every couple of years there's a new miracle cure on the market, and each and every time someone's bitter experience becomes everyone else's lesson learned thanks to such groups.
My own advice is never to be in the vanguard of any new technique. Me? I'm just about (grudginglyl) to accept hydraulic lime! :wink:

 

[NT]

Nearly all these old buildings were designed to handle damp just fine, and when they dont people want to put a plastic mac on them. What they tend to not notice is that evaporation is key, and is how the walls get a soaking yet the damp doesnt come through, it evaporates off again.

AIUI silicones require reapplication to stay effective, and reapplication leads to clogging of the stone pores, leaving you in a much worse position than you started.

As Nemesis says, why not fix the problem, the cause. In almost every case the cause is ignorant changes to the building or failure to maintain.


NT