damp report

[Tim Lamb]

Second hand so bear with me!

Daughters Edwardian terrace, North London, has always shown evidence of damp in the basement area. Used as a kitchen/dining/living area and with no extract system in place hardly a surprise.

Some recent building work included re-plastering the solid brick wall next to the garden exit.

The skim coat blew off within a few months of the builders leaving site.

A firm specialising in damp consultancy were brought in and I now have a copy of their report. They *measured* relative damp and moisture content and did thermal imaging.

In view of previous adverse comment on damp investigation I thought running their recommendations though here worthwhile:-)

Basically, fit an extractor. OK

Also strip off exterior render made non-porous by non breathable paint. Replace with breathable lime based render and lime wash for decor.

Any internal plastering should be undertaken using a lime based plaster only.

I am no plasterer but visually it looked as if the internal plaster skim was not *attached* to the base coat either by scratching or unibond and that, while condensation is undoubtedly present, this is not the cause of the blowing.

Thoughts?

[Tim Lamb]

In message , Phil L writes

London basement:-)

Steps down from the highway to a tiny yard with similar at the back. The walls are not in contact with soil although the garden dividing wall is suspect: poor pointing, porous brick coated in Ivy.

They spotted some poor chimney pointing which is clearly leading to moisture penetration to the room below.

I wonder how significant the exterior non-breathable paint is?

[Bill Wright]

Had there been a particularly bad road accident?

Bill

[Peter Parry]

Sounds like they were one of the few damp firms that know what they are saying. Old London (in particular) houses are usually of no cavity construction (easily seen if you can see the exterior brickwork, it is often Flemish bond

It is impossible for this type of wall to be completely watertight. They admit moisture and were designed assuming open fires (and lots of air changes as a result) and unsealed windows. This kept the moisture penetrating the walls under loose control. Seal the walls and windows, take away the air changes and you have a problem.

Using Lime mortar allows the wall to breath as intended, the extractor gets rid of the moist air. Use moisture permeable paint on top. Sensible solution to the problem.

Trying to keep the moisture out by lining the inner wall usually fails. The existing plaster would have delaminated because the moisture penetrating the wall had nowhere to go and built up behind the plaster skim coat until it broke free from the brickwork.

[Tim Lamb]

I try to be succinct:-)

[Tim Lamb]

In message , Peter Parry writes

They do not offer to do repair work so more honest than most!

Right.

I'm not sure there is that level of damp. Wall feels cold certainly. Prior to the building work there was the same lack of ventilation and amount of cooking without the skim coat popping off.

[stuart noble]

Round here plasterers are using some kind of polymer render bonded to a steel mesh.

[Brian-Gaff]

I was wondering about that, unless its built on the side of a very steep hill of course.

Brian

[Tim Lamb]

I can't believe that lime based is the only plaster/render that is able to breathe.

For relatively small repair jobs, 3 visits at 3 day? intervals to allow drying time will be prohibitively expensive in London:-(

[Dave Plowman (News)]

Going back many years, I remember work being carried out in a Victorian house with the same problem in the semi basement.

The builders fixed a corrugated bitumin liner internally to all the exterior walls which was plastboarded over. This does reduce the internal size of the room and requires new skirting etc. But did seem to work just fine - as the place belonged to a pal and I'd have heard if damp came back.

Of course there may well be more cost effective ways today.

[tabbypurr]

It transmits a good deal more water vapour than cement

Is that what's proposed?

NT

[Tim Lamb]

The report recommends using a lime based plaster and for necessary pointing, lime based mortar. It is unclear what they propose for external render.

The times scales are culled from the *Lime Stuff Ltd* site.

[Tim Lamb]

In message , "Dave Plowman (News)" writes

Hmm.. I suspect the job may wait until they *re-model* the kitchen layout when an extractor can be fitted.

I am gathering knowledge:-)

>

[tabbypurr]

a dehumidifier makes more sense in most cases

NT

[Fredxxx]

That really ought to be a temporary solution!

[tabbypurr]

not for a damp cellar. It's no less or more permanent than a fan, just more energy efficient in winter.

NT

[Fredxxx]

The idea of running a 150-200W dehumidifier 24/7 isn't a cheap option at circa £200 per year, less if just run in the winter of course.

[tabbypurr]

more energy efficient in winter.

You'd have to be living in a swimming pool for it to run 24/7

NT

[stuart noble]

More to the point, a good deal larger than a fan and, in effect, another appliance that needs plumbing in. Where's it going to be located?

[Tim Lamb]

Floor standing would be a nuisance as the current cooking area forms a slot or *galley* leading to the patio access door.

I think a route for an extractor could be found through the tops of the existing wall cupboards but this solution does not appeal to the person trying to justify a new kitchen!