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Damp Proofing Questions

Our expert damp proofers have kindly agreed to share their wisdom on such topics as removing mould patches, rotten timber, causes of mildew, damp basements, rising damp, floor construction, flooding and waterproofing and much more.

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763 Questions: Damp Proofing


damp chimney breast in bedroom

the chimney breast on the gable end of my house (bedroom) has damp patch at the top where it meets the ceiling and the top part of the wall itself is wet. how do I solve this issue ?

Yspitts 20th Jan, 2013 Damp Proofing
1 Answer u1

Heat Recovery Ventilation System for Condensation in home

I am living in a mid terrace house and have bad condensation in two of the bedrooms - upstairs exterior walls above double glazed windows. The condension has lead to black mould growth which i now want to deal with urgently before it affects my daughters health.

I do not have any ventilation currently in the bathroom and also dry washing in the house, which i know are both adding to the situation.

I have been looking into Posative Input Ventilation systems and also Heat Recovery Ventilation systems.

Can anyone give any comments on which are the best systems to use, average price for installation in a three bedroomed mid terrace approx 1940s property and also any reviews on whether the systems have helped clear up the problems/saved on energy bills/or left properties feeling draughty would be useful.

Yeperry79 20th Jan, 2013 Damp Proofing
1 Answer u1


The wall was tanked 1year gone September, the builder was called out within a year as damp appeared he said it is due to lack of venatlation. The problem is now the same as it was before he tanked the wall the plaster/paint is bubbling off the wall and is black. He gave me a certificate of guarantee 30yrs+ He is coming to see the wall again this week. Can you advise me on what action we need to take to correct this problem. We have concrete floor with laminate on top we do have airbricks and the doors are always open.

Ylynnwhite62 17th Jan, 2013 Damp Proofing
1 Answer u1

Mould cleaning/prevention on rafters


After some recent water ingress due to ridge tile cement coming loose (now fixed), I have noticed what looks like superficial mould/mildew on the rafters in the loft.
Please advise on the best way to clean this, and treat the wood for prevention afterwards.
There seems to be some conflicting information on the web.

Many thanks


Ymarkj_49 4th Jan, 2013 Damp Proofing
1 Answer u1

damp in bedroom

I live in a house about 300 years old on the bottom, 22 inch thick stone walls. It was built up in 1924 to become two storey. Upstairs is not stone, think it is brick and all has been rendered and Sandtexed. Main bedroom is damp, and grows black mould. DPC Inspector came and said DPC working well, but it was condensation, we needed to ventilate more. We have had the wall paper taken off the walls, and a "barrier" of a PVA glue and water mixture put on the walls in July. Then painted over the top to allow it to breathe. An elderly parent has the room, with a night storage heater on low, so opening windows is a problem. There is a dehumidifier going 24 hours a day. Still we have black mould appearing and I'm thinking now of putting another "PVA barrier" on top of the paint, then the 2mm polystyrene on top of that, and then paint it again. Do you think this will help? I cannot afford to have someone in to re-plaster. Can anyone help please with any further ideas? Many thanks.

Ycarol_577 29th Dec, 2012 Damp Proofing
1 Answer u1

New damp patch on upstairs bedroom ceiling

I noticed a large damp patch on the upstairs bedroom after coming back from holiday. It seems dry to touch and I cant find any wet areas in the attic. What is the likely cause? Which tradesman would normally deal with this issue?

Ycmahindra 4th Dec, 2012 Damp Proofing
1 Answer u1

9inch wall block then rendered wall. Will it always be cold and continue then to have a condensation problem?

Hi I work in the trade doing property repaires, I have found a bungalow to rebuild, just had a survey done and it notes that it isn't cavity wall just build in 9 inch brick/ block then rendered. What does this really mean? Is it always going to be cold and continue then to have a condensation problem?

Ystuartrobinson 4th Dec, 2012 Damp Proofing
1 Answer u1

will plastered walls dry out?

My neighbours built up there path over my extensions damp course level,been like this i gusess for a few years and hence ive got damp walls(damp meter readings,)ive since removed the obstruction to below the dampcourse recently and was wondering will it dry out in time?how long? or does the plaster need to come off,the plasters still sound,the wall is blockwork and pebb dash finish,thanks for any help.

Yfritzy 17th Nov, 2012 Damp Proofing
1 Answer u1

Solid floor extension without air bricks for raised timber floor


We have a single story extension across the rear of the house built by the previous owner (we think about 10 years ago). The extension has a solid floor that butts up to the raised floor of the original building. The house is a 2 floor 1930s semi.

I've come to decorate the rear room that joins on to this solid floor and after raising the carpet noticed a musty smell. I lifted a couple of floorboards in the corner near the floor and noticed the ground was damp (which we expected as everyone else on the road gets this due to high water level/being at the bottom of a hill). The thing that concerned me is that what looks like condensation/water droplets at the end of a joist near the party wall - I believe this is due to the lack of air flow underneath the rear of the building. The joist still appears solid and looks like it is sitting on brick with a rubber mat (dpm?) and some slate.

What would be my options here? Would I have to excavate the kitchen floor to lay ducting (which sounds expensive and messy!) or is there another way?


Ystevendavis 10th Nov, 2012 Damp Proofing
1 Answer u1

yellow spots on walls

Hi hoping someone might be able to help. Discovered today that there are yellow spots pretty much all over the walls which are the external wall (north facing) in 3 rooms in our house. We live in a 1930s house so have to be careful not to put furniture too close to these walls as have had issues with black mildew in past (we assume due to condensation). These spots are all over the wall & not just where furniture is near. The walls are painted, no wall paper.

Firstly what could be causing this and do we need to get someone in to rectify/monitor the problem?

Secondly, if it's not something we need professional help with how can we remove these spots and ideally prevent them reoccuring?

Thanks for your help

Ybuilding_26 23rd Oct, 2012 Damp Proofing
1 Answer u1
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