retrofit cavity wall assumption inaccuracies

[Harry Bloomfield]

http://www.stormdry.com/applications/wet-cavity-wall-insulation

That web site is selling a water proofing cream to be applied to the outer face of the wall, supposed to stop rain getting through to the inner leaf and the CWI. My home is brick built, solid floors and had fibre CWI put in around 35 years ago. We live atop a hill, in what is often a quite windy location and have suffered no damp problems what so ever in that time. The cavities were checked and cleaned out around 40 years ago, plus having a chemical DPC added to the existing DPC.

 

[mikeey84]

That web site is selling a water proofing cream to be applied to the outer face of the wall, supposed to stop rain getting through to the inner leaf and the CWI. My home is brick built, solid floors and had fibre CWI put in around 35 years ago. We live atop a hill, in what is often a quite windy location and have suffered no damp problems what so ever in that time. The cavities were checked and cleaned out around 40 years ago, plus having a chemical DPC added to the existing DPC.

Oh I'm sure it's snake oil, but gives an account of where the water goes.

If you have a poor outer leaf, lots of wind driven rain etc, then cavity wall could cause issues, but in a "typical" house, with good condition brick work, how much water do you expect in a cavity?

And how does adding water proof insulation affect water running down the brickwork. If there are torrents of it, then maybe you'll have an issue, but how much soaks through brickwork, or gets into the top of the cavity?

Edit- this is a genuine question. I don't know!

 

[mrrusty]

http://www.stormdry.com/applications/wet-cavity-wall-insulation

QED - "if it fails, it isn't us guv, it's the brickwork".

That said problems of damp penetration can occasionally occur. Most commonly these pertain to the state of repair of the wall or the cavity debris has not been noticed

 

[Harry Bloomfield]

And how does adding water proof insulation affect water running down the brickwork. If there are torrents of it, then maybe you'll have an issue, but how much soaks through brickwork, or gets into the top of the cavity?

Edit- this is a genuine question. I don't know!

Unless there are actual large gaps, I would expect zero running water, otherwise at most a little moisture will get through which will quickly evaporate through both brick leafs. Sealing the outer, rather than improving the situation, may well encourage the moisture to evaporate via the inner leaf.

 

[johnny2007]

Unless there are actual large gaps, I would expect zero running water, otherwise at most a little moisture will get through which will quickly evaporate through both brick leafs. Sealing the outer, rather than improving the situation, may well encourage the moisture to evaporate via the inner leaf.

This is correct.
However, the brickwork sealers have their use.
I used them on chimneys for example because it protect the pointing and the chimney breathes from inside where there's a constant draft.
Also on the last 2 courses of bricks where the dpc is too low, although this is not a permanent solution.

 

[DIYedboy]

Cavity walls were 'invented' to stop penetrating damp associated with 9" solid walls cos that naughty moisture can run inside the cavity..............but..............if you live in a low wind/ rain penetration area, have good pointing, weathertight roof n downpipes, you don't need the 'defence cavity' and it would be financially advantageous (in the heating bill dept) to fill the cavity