damp report

[Dave Plowman (News)]

Yehbut, do you really want a de-humidifier in a living area? Might be ok in a garage or workshop.

[dennis]

With damp a fan on its own is close to useless.

You need to reduce the humidity and that can only be done by letting in less humid air (which doesn't work all the time in the UK), heating it up, or extracting the moisture.

A dehumidifier will both extract the moisture and heat up the air. The heating effect is quite a bit if its really damp as you get the latent heat back.

[tabbypurr]

t more energy efficient in winter.

cobblers

NT

[tabbypurr]

I've not found it a problem.

NT

[Dave Plowman (News)]

I'd rather fix the damp at source especially if it's a renovation job anyway. It's not impossible to tank out a basement so damp doesn't get through the walls. Obviously, it will still need suitable heating and ventilation like any room.

Put it this way. If I were buying a house meant to be in good condition and I saw a dehumidifier in a basement room, I'd be put off. Or expect to adjust the price to pay for the proper repairs.

[Tim Lamb]

In message , dennis@home.?.invalid writes

It would only extract vapour from cooking. Clothes washing/drying is done elsewhere. Although I suppose a dishwasher must generate some moisture during the drying cycle.

Understood.

[Peter Parry]

Depends on the damp. In this vintage of house they were designed to cope with damp by evaporating moisture from walls and venting it through open windows and chimneys/open fires. It is only when you take away the ventilation by fitting double glazing and not having open fires that problems occur.

Using a continuously running low power low noise fan can create the same ventilation environment the house was designed for and keep humidity to acceptable levels.

[tabbypurr]

but is not a great solution.

NT

[Dave Liquorice]

How old is it? Coatings fail, full stop. With a non-breathable coating any moisture that gets behind it only has the small hole(s) it got in by to get back out, or it can take the much easier route through the wall to the inside. Remember the relatively warm and dry interior will tend to draw damp towards it.

[tabbypurr]

the warm dry interior is where most of the damp comes from. It may feel dry but it holds more water vapour than cool outside damp air. So many people think the problem is rain moving inward, and coat the exterior, when really that's only going to make the problem worse.

NT

[Tim Lamb]

Not certain. Recent re-paint (post renovations) with a Farrow and Ball product.

>

[stuart noble]

So a modern house should generate huge amounts of damp then? The RH in such houses is invariably too low in winter, and humidification equipment is the norm in continental climates. You're on thin ice with your pronouncements, which is why you have to resort to abuse when anyone disagrees

[Tim Lamb]

Now, now gents. this is a zero abuse thread:-)

So far we have acceptance that even basement walls not in contact with surrounding soil are likely to be cold and prone to condensation from kitchen use.

Direct ventilation of cooking area is going to help but not necessarily cure.

A de-humidifier would probably solve a condensation issue but may not be practical in a galley kitchen.

Moisture trapped in a wall through using impervious paint is very bad news.

Battening off may side-step the problem.

I am unclear if the surveyors recommendation of re-plastering/rendering with lime based materials will solve a condensation issue? The party garden wall should be repaired/re pointed anyway.

[Peter Parry]

It doesn't, by itself, solve the condensation issue. In conjunction with better ventilation it prevents the mould growth associated both with condensation and the moisture permeable wall. With the type of construction you most probably have the walls are not completely waterproof, some moisture will track through the bricks and cement. They are also not insulated, even by a cavity, so are colder than other surfaces. If you use a waterproof plaster the moisture builds up behind it and eventually it breaks off. To prevent condensation damage to the plaster it needs to be capable of adapting to the humidity which lime plaster does. This prevents the surface film of water which would occur on impermeable surfaces such as gypsum plaster forming and promoting mould growth.

Using Lime plaster and adequate continuous ventilation creates an environment where the natural moisture through the walls and through condensation evaporates harmlessly without damage occurring.

Trying to use techniques appropriate to a condensation problem in a modern better insulated house with a cavity wall won't necessarily be successful.

[tabbypurr]

huge is a bit vague, but houses do generate water vapour from breathing, cooking, bathing and sometimes clothes drying. This is of course added to what started out as outdoor air.

Yes, as you warm air up it can hold more water vapour, so even though the air feels drier it still contains more water vapour than cool outdoor air

it's basic physics, which you consistently refuse to go get yourself informed on

maybe you're thinking of someone else

NT

[tabbypurr]

it helps sometimes. Run all the time it just costs in heating. When it does & doesn't help depend on water vapour concentration, which can be calculated from on indoor & outdoor temp & RH.

1. maybe in the next room it is.
2. you can get tiny peltier powered dehumidifiers

battens & DPM prevent evaporation from wall into the room. But by preventing evaporation they increase water content in the wall, and sometimes this can result in damp patches appearing in other areas nearby as the dampness spreads.

Doing that to the exterior increases evaporation, so is a win. Liming the interior is less clear cut & more complex.

NT

[stuart noble]

In the real world people heat their houses to a comfortable level so that the air is able to hold all the available moisture most of the time. I dry washing outdoors and stop breathing when the humidity is high. Rain that pisses through 9" walls does not respond to your laws of physics.

[The Natural Philosopher]

yes, but most of the time has an exception which is contact with very cold exterior walls, cured by insulating them.

May not be your problem, but dont discount it.

Well it does, but is that the issue? If you have solid 9" walls then condensation will be a huge issue.

If you have such the answer is to use foil backed celotex and plasterboard to dry line the wall inside

And that wull also stop the rain if it is that getting any further than the wall, which can dry outwards when the rain stops..

[Dave Liquorice]

A modern house will have warm interior walls due to insulation(*) so won't fall below the dew point and get condensation. A modern house will also be designed to have suffcient air changes based on room use, ie extractors in kichens and bathrooms.

(*) One part of the building here has a block work wall built inside the orginal solid walled structure with a 3" uninsulated cavity at ground floor level. The inside face of the blockwork wall is at least

room). In winter the temperature difference can exceed 10 C.

[Chris French]

In message , Tim Lamb writes

Wall mounted? A 200 a 10-12L one isn't that big