Damp walls but only when it's sunny !!

[wwwebber]

Strange one this !!!.

Just before Christmas We bought a house that needed extensive refurbishment. The DPC was re-done under the existing 22 year old warranty - yes the company is still going !!. In addition to this all internal plaster was removed and the first metre treated with a salt / water retardent scratch coat. 50mm Thermaline Plus was then applied to the inside of all externally facing walls.

Now here's the strange bit :- we get damp when it is sunny but not whilst it is raining !. At various points around the front of the house - the internal floor (no carpets yet) has darkened and is wet to the touch. Last week dirung the hot & sunny period I put my hand under the bottom of the thermaline plus and touched the external wall and it feels damp / wet to the touch !!.

I have still to drop the external soil levels as they are apparently too high but you'd expect this damp to occur when it is raining if this is the fault.

My only thought is that this might be condensation from the still damp walls and the thermaline plus vapour barrier is holding it in. Maybe the walls still have some drying out to do ?? - the whole house was without heating until about 6 weeks ago and the interior was very damp.

Any ideas would be much appreciated.

 

[ajrobb]

It can take months to dry out a house and condensation sounds a likely culprit, possibly made worse by the scratch coat as this prevents it escaping into the wall. Maybe some more information would be helpful.

• When was the house built?
  Is this a solid brick wall?
  Is the DPC a chemical treatment or a traditional impervious layer?
  Is the room well ventilated or have all draughts been well sealed?
  Are the air bricks OK?

 

[wwwebber]

It can take months to dry out a house. Maybe some more information would be helpful.

• Is this a solid brick wall?
  Is the DPC a chemical treatment or a traditional impervious layer?
  Is the room well ventilated or have all draughts been well sealed?
  Are the air bricks OK?

Apologies - here you go :-

Yes, solid brick walls
The DPC is a chemical treatment
Ventilation hasnt been changed - although there doesnt appear to be any anyway !!
As above - no air bricks as far as I can see

If it helps any - the house was built in 1895.

Thanks.

 

[ajrobb]

Please check the edit of my previous post. I suspect this house was sealed by previous owners and they created a condensation problem. This could have been misdiagnosed as rising damp as both occur at the bottom of the wall. One suggestion I have seen is to look for the presence of nitrates in the wall to indicate rising damp rather than condensation. I've found the Heritage House site informative. I assume you had a structural survey before you bought such an old property. Did the report mention air bricks?

 

[stuart45]

Google reverse or summer condensation.

 

[wwwebber]

Please check the edit of my previous post. I suspect this house was sealed by previous owners and they created a condensation problem. This could have been misdiagnosed as rising damp as both occur at the bottom of the wall. One suggestion I have seen is to look for the presence of nitrates in the wall to indicate rising damp rather than condensation. I've found the Heritage House site informative. I assume you had a structural survey before you bought such an old property. Did the report mention air bricks?

Yes, various reports undertaken. No mention of airbricks just that damp had been found in various areas of the house and that some external ground levels were too high. We got the DPC people back in who re-did the chemical DPC after testing damp levels in the mortar.

I will be digging away the sides of the house soon to lower the ground levels and then filling with gravel to ensure good drainage. This should remove this issue from the equation. I've already ruled out penetrating damp due to broken guttering etc

Could this simply be the house continuing to dry out then ?. I suppose this would explain the damp occurring only when it is sunny as this causes much more condensation - especially as the interior will likely to be cooler.

 

[JohnD]

"in case of condensation, add ventilation"

 

[foxhole]

The damp proofing was more than likely a total waste of time, higher ground level outside would give damp low down, if it had been sorted there would be no need for treatment and any treatment without solving the problem completely pointless. Lack of ventilation will only increase the problem.

 

[ajrobb]

The insulation and VPL should prevent condensation on the walls. I'm a bit confused/concerned that you can touch the scratch coat from the room. Ideally there should be no gap between the floorboards and wall insulation (consider closing the gap with foam and/or mastic). Otherwise warm damp air can reach the coldest part of the wall and cause condensation in just the right place to collect and rot the joists. Also, there should be several air bricks at the front and another several at the back of the house and the underfloor should be unobstructed to allow free flow of air between the front and back.

IF you start lifting floorboards, you might want to add underfloor insulation. It must allow drainage of spills - use mineral wool and no VPL. Instead, add even more air bricks and remove any rubble from the sub floor to improve the ventilation of the cold space.

 

[wwwebber]

The insulation and VPL should prevent condensation on the walls. I'm a bit confused/concerned that you can touch the scratch coat from the room. Ideally there should be no gap between the floorboards and wall insulation (consider closing the gap with foam and/or mastic). Otherwise warm damp air can reach the coldest part of the wall and cause condensation in just the right place to collect and rot the joists. Also, there should be several air bricks at the front and another several at the back of the house and the underfloor should be unobstructed to allow free flow of air between the front and back.

IF you start lifting floorboards, you might want to add underfloor insulation. It must allow drainage of spills - use mineral wool and no VPL. Instead, add even more air bricks and remove any rubble from the sub floor to improve the ventilation of the cold space.

We have solid foors downstairs and the plasterers have left a 50mm gap at the bottom of the walls.

 

[wwwebber]

Google reverse or summer condensation.

Thats quite interesting - I'll look into that further. I'm hoping it's the high ground levels but the condensation occuring in hot weather does add weight to your theory !!

 

[wwwebber]

"in case of condensation, add ventilation"

How do you ventilate the gap between a solid wall and interior dry lining ? - the condensation is occurring here. Adding ventilation to the room wont help at all.

 

[JohnD]

well now that's an arguable point. Are you of the view that the air inside the house does not hold any more moisture than the air outside the house, and is at the same temperature?

Is condensation occurring on the outside of the walls?

usually human activity inside a house means there is more water vapour inside than out. Ventilation takes it away.

Also in an old house, moisture may be coming up through the floor, evaporating into the air, and then condensing on a cooler surface. Again, ventilation takes it away.

Also you say

Maybe the walls still have some drying out to do ?? - the whole house was without heating until about 6 weeks ago and the interior was very damp.

Ventilation is needed to get this moisture out

BTW you said

Any ideas would be much appreciated.

 

[ajrobb]

How do you ventilate the gap between a solid wall and interior dry lining? - the condensation is occurring here.

One method is Gypliner Universal so that the battens stand off the wall. Open a gap between the floorboards and the wall to ventilate the cavity to the under floor void. That requires enough airbricks to ventilate the floor though.

Although there is no mention of penetrating damp in this case, additional airbricks near the ceiling can promote wall ventilation even more.

Adding ventilation to the room wont help at all.

I must disagree. The requirement is to keep the wall at least 5°C above dew point. Ventilation in the winter will lower the dew point to about as cold as outside. Seal the house and dew point will rise towards the body temperature of the occupants. (The occupants would suffocate before it gets that bad though.) Add cooking and showers and things get moist quickly.

Forced ventilation is a very effective way of eliminating condensation.

 

[mac391]

So many mention "lifting floorboards" ?? It's fairly clear you have concrete subloors, which won't have a DPM. The walls will also be solid (no cavity). so no need for airbricks.

On a property with solid floors and walls it is pointless applying a chemical dampcourse and even more pointless rendering the outside. Both of these applications will most lkely worsen the problem. A dampcourse can't possibly work in a solid wall without a cavity and the render (with waterproffer) will only hinder the escape of moisture to the outside, pushind rising damp further up the walls.

The first thing that should have been done is remove the higher ground and infill with gravel. Second, romove the render !!. Thirdly, let the house dry naturally or install dehumidifiers at the same time as adding ventilation such as wall vents that you can open and close. Lastly, re-render using lime mortar (no waterproofer).

If the concrete floor remains damp adding a DPM will only push the moisture under it into the retaining walls so would have to be returned up the wall and incorperated into the brickwork, effectively creating a dampcourse. The only escape for the moisture then would be through the outside skin (wall) hence the need to remove external render..

Did someone mention dry lining ?? there should be no plasterboard in whatever shape or form on the ground floor of a property this old.