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Damp Proofing

What is causing this damp?

Hi, my parents bought a mid terrace house (victorian) about 11 years ago - no problems. The only issue at the time was that there was mould on the walls & ceiling in the downstairs bathroom - which was due to lack of ventilation, plus the previous occupier had wallpaper in there. Anyway fastforward to 3 - 4 years ago - in two of the bedrooms (front and back) we noticed that there were black mould spots appearing on the walls (the walls by the windows). I spoke to a surveyor at my work and he advised that it looked like it was due to condensation and to ensure that the rooms were kept ventilated and at a consistant temperature esp in winter (he also mentioned to wipe the mould off with a fungicidal wash and that we could paint the walls with the anti mould paint).

Since then its got worse, mould has now started appearing in the middle bedroom in the top corner of the wall again near the window, dining room underneath a window and in the living room by the bay window (where the roof bit is). We had a damproof company come round who tested the walls and they confirmed that water was getting in (though in the bathroom and the middle bedroom they didnt detect anything). so they sprayed the outside of the house with a chemical, i think it was called Aquabac? (or something like that) to make the property water tight and the back bedroom which was the worse affected, they removed all the plaster down to the brickwork and replastered it with a different type of plaster (cant remember what it was called though) as they said it would be harder for water to penetrate it. Anyway they said to leave it for a year for the house to dry out and that we should notice some improvement, however its been a year and a half since that was done, the other rooms dont seems any worse, however the back bedroom is really bad again - the walls that run along the eternal side have loads of black mould again.
The bathroom, where we first noticed a mould issue is fine though.

What could be causing this?


8 Answers from MyBuilder Damp Proofing Specialists

Best Answer

Hi Charlie

Its all down to ventilation! As you have stated the wall in question is a external wall i imagine its a cold area!
Being a victorian property it is of solid 225mm brickwork and with this in mind it doesn`t hold the warmth like a cavity constructed property.

One of two things you can do:
1 Insulate the internal wall with a insulated board.
2 Fit a Heat Recovery unit to expell the musty damp air and introduce fresh clean and heated air into the room.

Good luck
Scott Cannon.


Answered 21st Aug 2011

Hi Charlie,
i am RItesh, It seems that house is detached or Semi detached with solid brick works (not cavity)

In UK houses 3 things are very important 1) Heat 2) Insulation and 3) Ventilations All of them have to be in same proposan.

After reading what you have wrote above it feels that windows are always closed and heating is always on. What i can suggest is please insulate walls and Heat recovery pumps. Please try this with one room. If it works than try try with other effected room.

Please contact me if you want me to descuss this in details


Answered 21st Aug 2011

I have worked in the damp industry for 30 years and i am pretty confident the problem is condensation try heat recovery ventilators they are excellent for curing condensation


Answered 21st Aug 2011

Hi, have you checked roof to ensure no leaks with water managing to get into the cavity? I have a house I rent out that had problems with mould, tiny leak in one corner of roof was letting water into cavity. We also got cavity wall insulation done, this stoped the internal Walls getting too cold and letting condensation build up. If you have new windows they will have trickle vents, allows a good air flow. Bathroom if in middle of house should have mechanical extraction, if possible keep room doors open as much as much as you can to allow good flow of clean air.
Hope this helps.

Kenny McMillan
Edinburgh builder


Answered 21st Aug 2011

hi charlie ,

It does sound like there is water coming from the roof , mainly the roofline area which is common as thats where the felt under the tiles starts to rot upwards. It seems like you might need the botton few courses of tiles removed then replace the felt. This should solve the problem.

Regards fraser


Answered 21st Aug 2011

Does sound like a condensation problem,if there is no signs of water penetration, if this is the case on external walls you need to stick on thermal boards [ polystyrene backed ] to stop the condensation
we carried this work out on many council flats which do suffer from this problem


Answered 21st Aug 2011

If the issues were addressed with regard to ventilation then it may still be down to damp walls. Is there any mould in the areas that were hacked off and re-plaster. I am assuming that the walls are 9" solid walls without a cavity. If so what is the condition of the pointing on the outside of the property? Check the condition of pointing by seeing how easy it can be scratched out with a screwdriver. If it is quite soft and easy to remove then there be a need to repoint. Check different areas around the property. Another common reason for walls to be damp is overflowing/leaking/blocked gutters. If you can inspect the outside of the house when it is raining. Check if water is overflowing or running down exterior walls. It could be down to poor guttering (sometimes an easy fix). It could be a combination of both. This type of damp is penetrating damp as opposed to rising damp (which has been addressed by the work carried out).

Let me know about what you find out after inspection,


Briner & Sons


Answered 21st Aug 2011

would need to view this to assatain the problem as there could be many differant reasons, guttering,badly fitting windows, poor pointing, post this in the jobs section and get a few local tradesmen round to find the cause


Answered 21st Aug 2011

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