External Masonry paint finish damaged by failed Cavity Wall insulation?

24 Aug 2010
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United Kingdom
Hi everyone.

Odd ball question, I would be interested in sensible input as to the following problem, not my property!

The cavity wall was retro-filled with the Dreaded Cavity Wall insulation, on this property the Cavity Wall Insulation failed, damp patches have developed in the usual form, here and there.

This post is NOT about the pros and Cons of Cavity Wall insulation [everyone has an opinion about that] Also the post is not about the damage that can ensue internally, damp walls peeling paper loss of heat Etc. Etc. Etc.

This post is aimed at, the External Roughcast render? The internal Plaster and décor finishes affected will be addressed, but the external roughcast render [looks like a so called “Wet Dash?”] is the area I am interested in any information at all about.

Externally, the roughcast render has had multiple coats of presumably various types and Quality of external masonry paint applied, in dozens of areas of this external wall at all levels, the applied paint finish is De-bonding or bubbling away from the top external surface of the Roughcast Render. If these areas are touched, the paint film is noticeably hollow, having totally De-bonded from the surface of the roughcast render, the paint film even crackles.

Now for my Question, sorry it has taken this long to cut to the chase?

Has anyone undertaken Cavity Wall insulation removal? And tried to re-decorate the external surface of the affected walls, if so what was the result? I am seriously concerned that, the paint is being De-Bonded and forced off the external surface of the Roughcast Render by the Soluble Salts emanating from the Mortar and bricks on the outer leaf of the affected walls, all four walls of a detached two story property are affected. I am considering that the removal of the Roughcast Render, never mind just the blown external paint finishes is a potential requirement, because the application of new paint to Roughcast Render that is Saturated with Soluble Salt [at all heights, not just the ubiquitous 1.0m above DPC] will seriously affect any new external paint finish that is applied?

I am considering the removal of the damaged EXTERNAL PAINT by Scaffold and Soda Blasting.

I am struggling to find anything meaningful on Google? .

Thanks for reading, are you still awake?

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Joe, good evening.

On this project, it is on-going, and is the subject of an Insurance claim against the so called Insurance backed guarantee scheme that the installer had at the time the cavity was filled.

Some small areas of the external brick work was removed and the insulation was removed, it when squeezed allowed all the trapped water to run out of the insulation, no need to say more??

As for remedial work? using external holes remove the Saturated fill, leave the external holes open, internally form some holes on the inner surfaces of the upper bedrooms, using suction draw the air out of the cavity for a period of time, and using hygrometers from time to time test the volume of free water emanating from the suction devices placed in the bedrooms.

In this case it appears a so called no brainer as to the causation?

I would agree that in some cases, I surveyed one this week as it happens, that jumping to an incorrect conclusion can be a false diagnosis the one I saw this week had a leaking rain water down pipe, the joint at high level on this pipe was allowing all the roof rain water to cascade on to the external surface of an old pebble-dashed wall surface, the result was that on the ground floor the internal wall plaster had been damaged severely by the cascading rain water somehow getting through the external leaf, running down the inner surface of the external leaf, then either hitting a load of crap in the cavity or bridging over at a horizontal row of wall ties, who knows? need a Bore-Scope to find out for sure.

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I have first hand experience of failed cavity insulation ,the house we have moved to and are renovating has such an issue.
We installed twin wall flue, wood stove, patched blown plaster and decorated the dining room only to find a patch of damp to the side of the window had come through
I suspected the insulation as the house is very exposed and removed bedroom window cill to gain access to the cavity.
I vacuumed out the rockwool which was damp in places and when I exposed the downstairs window catnick lintel, it was part rusted away so thats another job to
place on my list.
just read the title, I would have thought it was the failed paint that let the rain in rather than the failed insulation damaging the paint that started the process.
BTW,is the damage on one of the southern elevations?
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lostinthelight, hi.

The rational is that because the wall and the damp / saturated Cavity wall insulation both absorbs rain water and gets rid of the slowly accumulating water load in the fabric, especially on the outer leaf, the constant flow and ebb of water molecules passing through the paint, and the render can affect the render, making it de-bond from the sub strat, likewise the more fragile external paint finish will fail long before the external render begin to become detached. lets not forget, the Cavity wall insulation was [in this place] installed many years prior to the damage manifesting itself internally, in patches similar to the problems you are having.

The external paint finish has de-bonded in large sheets, up to about half a Meter Square, what appears to happen is that the rain water enters externally via cracking and micro cracks in the paint finish and render, As the wind passes over the wall surfaces the trapped rain water in effect evaporates to air, much the same effect as rain cloud formation over an ocean?

One other point worth noting, your internal walls may appear to be un-affected, but it will take a survey with a moisture meter to determine the true internal damaged areas

If you could possibly find out who installed the Cavity Fill, and then go on to find out who the insurance guarantor / backer was then it is just possible to intimate an Insurance Claim on that Guarantee?? This Insurance claim if successful would fund all requisite repairs to your property?


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