Cement Rendering / Damp

[meow2222]

a> >

That's one lousy answer. Or are you really claiming the basics of physics have changed lately

[harry]

Showers kitchen and bath rooms of course. When the warm damp air encounters a cold surface, it condenses.

[harry]

ter vapour into the indoor air.

xtent out through walls.

Clearly a topic you have zero knowledge about.

[harry]

ave the concrete floors.

It is very likely condensation especially if it is worse on the kitchen side and the extension is a cold room.. I'm surprised you don't also have condensation on the outer wall(s) of the kitchen but some surfaces don't show it or maybe are insulated.

Do you have a cooker hood to take away cooking vapours? If not, that is the likely cause of your troubles. The chemical DPC should be good if properly done.

[polygonum]

"Normally" seem to imply an ongoing, more-or-less permanent state of affairs. Our kitchen and bathroom might transiently have RH towards the high end - but very rapidly reduce - we do have opening windows! Hence ours are not running in condensation, are not coated in black mould, etc.

[stuart noble]

changed lately

We have insulation and central heating these days. That is what has changed. Breathing, washing and cooking just aren't a problem in the modern home.

[stuart noble]

vapour into the indoor air.

out through walls.

Turn your heating on, Harry. You know it makes sense!

[stuart noble]

Well exactly. What's so complicated about that? You get rid of condensation either by ventilation or by raising the air temperature so that it can carry more moisture (i.e. it dries) or, shock horror, a combination of both. Yes it hurts to have the windows open and the boiler on but it's not for long.

[meow2222]

have changed lately

Indeed, which doesnt change the above one iota.

AFAIK they've never been a problem in any home. Excess water vapour however is in some old houses that have been wrongly modified and are now borderline in terms of how they handle water vapour.

NT

[meow2222]

Nothing. It seems to confuse increased RH with condensation & mould. Conden= sation only happens where RH locally reaches 100%. Mould only happens where= condensation happens so much the wall is too damp over time.

Most of the time such meaures aren't being taken, and water vapour is being= put into the air all the time a house is occupied. Heating enables it to c= arry more water vapour, but obviously that alone wouldnt keep it dry for lo= ng, there is then ventilation which replaces interior air with greater vapo= ur content with outdoor air with lower water vapour content.

In walls without a VB, you also have higher water vapour content on one sid= e than the other, so the vapour slowly migrates through the walls from insi= de to outside.

Its basic physics.

[stuart noble]

Obviously it would. With the thermostat at 20 degs the air will carry more water than you can produce by breathing and cooking. That is precisely why it isn't a problem for normal people in normal houses.

It's interesting that tropical hardwoods grown where the RH is damned near 100% dry out too quickly when they are felled. It's all about temperature

How much vapour content there is, in or out, depends on temperature. You can't just say that the interior has a higher vapour content.

Fortunately the average housewife knows perfectly well how to keep a house dry and healthy without your in-depth knowledge of physics.

You continue to adopt this high handed and patronising attitude to anyone that disagrees with you, which I don't find at all constructive

[Phil L]

In which case the horizontal row of holes must still be visible both inside and outside the house? If not then they are plastered over inside and rendered over outside - they should not be covered, they can be filled in, but the brick that has been injected should be visible (provided you've removed the skirting boards)

I think it needs injecting again, the rendering and internal plaster completely removing and fresh render applied inside and out, stopping

*above* the DPC in both cases....chances are he's used browning or other similar inappropriate plaster internally.

I assume the dividing wall was once an external wall prior to the extension being built?

[meow2222]

Even if heating increased vapour carrying ability by 10 or 100x, the amount= of water vapour it can carry is always finite. But the addition of vapour = to the air by living is endless. Its patently obvious that air can't carry = an endless amount of vapour, so heat alone doesn't resolve things.

Lordy. We take in the outdoor air and add more vapour from breathing, cooki= ng and washing. Do you think that dries the air?

Whether a home stays dry is more to do with its design & construction. Only= a minority of buildings require significant care over interior activities.

Well, you demonstrate a determined failure to grasp the basics, you can't b= e bothered to read up on the subject, yet you insist your confusion is righ= t. Lets just agree to disagree, its easier.

NT

[stuart noble]

You are forgetting that outdoor air is normally cooler than indoor. When it enters the house, it is heated and, what was a high RH outside, quickly becomes a low RH inside. Buildings with modern standards of heating and insulation will invariably be too dry in winter. Ask anyone who owns a piano. The RH in my house is between 40% and 60%. Lower than that you get static problems, and higher than that you can get thrush and similar ailments.

On that we agree! The only insurmountable problems I have encountered were in a 60s concrete north facing flat that was in constant shade and should not have been built in the first place. Low RH is a major problem in offices, despite the occupants breathing in and out all day. It's only a slightly lesser problem in modern houses where kitchens and bathrooms raise moisture levels, and it probably isn't a problem at all if you live in a listed building on Dartmoor.

The lack of comments from anyone else suggests that is probably a good idea. Actually it's QI that there is no interest from a group that will argue the toss about virtually anything :-)

[meow2222]

Of course i'm not forgetting it, its totally obvious. You only show your position to be foolish by such suggestions.

Correct. Then you add the usual indoor vapour sources, and the result can only possibly be more water vapour in the air than outdoors (unless you're using ac).

Some are, some aren't

Yes, when a/c is used. It extracts water vapour.

NT