damp proofing internal wall

[jocollett]

Hello hope someone can give me some tips.

I'm renovating a house and the kitchen has been knocked through by previous owners into a pantry/ toilet area. This area was very damp and had a concrete floor, the rest is suspended timber. The damp wall was originally just painted brick. I've removed the concrete floor and clay soil lowering it by about 2 ft. I've also installed airbricks. The L shaped section of wall around the old concrete is the only bit of the house without blue bricks, its about 3 meters total length.

I was thinking of using some damp proof cream with 12mm holes and wondered if this sounds like a good idea to anyone here.

Ta for any tips.

Jo

 

[tommyl18]

if its rising damp from the floor then hack off a metre high back to the brick work apply sika damp proofing render

http://www.sika.co.uk/uk-home/uk-con/uk-constr-waterproofing-2.htm

 

[ajrobb]

I've removed the concrete floor and clay soil lowering it by about 2 ft. I've also installed airbricks. The L shaped section of wall around the old concrete is the only bit of the house without blue bricks, its about 3 meters total length.

Have you replaced the concrete floor with a suspended wooden floor with air bricks underneath?

I was thinking of using some damp proof cream with 12mm holes and wondered if this sounds like a good idea to anyone here.

If there is no damp course and you have a solid wall you could have the elusive rising damp. One clue is if you see any efflorescence (salt crystals) growing out of the wall. However, if the old larder air brick was blocked up then you could just have condensation, which also affects the bottom of the wall.

Heritage House hate any waterproof treatments, including chemical DPC and waterproof renders.

There you go, clear as mud.

 

[jocollett]

Thanks tommy and ajrobb!!

I'm fairly sure it's rising damp. The concrete I removed was very wet and there's no one living there so I don't think condensation is to blame.
I thought of tanking but not until after I battoned plasterboard to the wall and I don't really want to remove it.

Yeah I've replaced with joists and air bricks and it's an ex council house so I don't think heritage house will mind id I use chemicals javascript:emoticon('')

 

[ajrobb]

A cold, empty house with a damp mud floor will be very humid and likely to suffer condensation. Heritage House don't like chemicals because they can damage the fabric.

This photo shows a chemical damp course - the bricks below are dry but the wall above is still wet from condensation!

Have you put any insulation behind the plasterboard?

Did you use Duplex plasterboard with a vapour proof layer (VPL)? Without a VPL, moisture from the warm house can seep through the plasterboard and condense on the cold bricks. It could make the problem worse.

If you have left a cavity next to the bricks and you have a VPL at the plasterboard, you could make sure the cavity is open to the underfloor to allow moisture to escape and help the bricks dry out.

 

[jocollett]

Thanks Ajrobb just looked at the Heritage House website, very interesting stuff.
I can see what your saying about rising damp and condensation.

unfortunatly i didn't use a vapor barrier plasterboard or insulate behind it. We do have cavity wall insulation which should help keep the bricks warm.

The wall seems dry at the moment but it's completly open now without a floor. I'm fairly sure there was damp rising under the concrete as it had rusted some plaster beading up to about 5cm from floor level. Also the previous owner had simply screwed plasterboard to the bricks and the the screws were rusty.

There was however leaking radiator pipes burried in one section that could have spread laterally to the beading and given the surveyor the high moisture readings.

I could, like you suggest allow free air movement behind the plasterboard (it's currently open at the top into the floor space above) to help any moisture move away.

 

[ajrobb]

Damp can take months (or even years for thick walls) to dry out once the source is treated. Now you have removed the leaking pipes and wet mud, I'd wait a year to see if the damp comes back in the winter.

If the pointing needs redoing, lime mortar helps moisture wick out of the bricks so they dry out and resist frost damage (spalling) and is softer than brick so protects them from cracking. On the other hand, cement mortar blocks the evaporation and can cause spalling, can be harder than brick and cause them to crack.

If you haven't painted the plasterboard already, you can treat it with a sealer that should reduce the water vapour getting through.

If you've already painted, I think acrylic paints also make a pretty good vapour barrier in case the damp comes back.

I could, like you suggest allow free air movement behind the plasterboard (it's currently open at the top into the floor space above) to help any moisture move away.

Old houses tend to leak quite a lot of air between floors, which is good for ventilation in this case. CWI can reduce that, but you can probably still feel quite a draught coming between the floor and skirting board in the room above. (Modern house construction is supposed to reduce air leaks and the ceilings are sealed to the wall as a fire barrier.)

 

[jocollett]

I've used a plasterboard primer and will be painting it with kitchen paint so hopefully that will prevent condensation getting to the bricks.

Think I'll take your advice and leave the chemicals alone for now and check the wall next winter.

Thanks very much

Jo

 

[ajrobb]

Good luck with your damp. I hope it goes for good over the summer.

 

[jocollett]

Thanks ajrobb! I'll let you know what it's like in winter.