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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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1,189 Damp Proofing questions

Damp wall

I recently took fixed wardrobes out of my bedroom and found damp on the outside north east facing wall. It appears to of dried out but had to get someone to look at the corner t cause the new lining paper was slightly browning in the corner. The bedroom next door is on the same wall and the bed when moved from that wall I could smell a musty smell and the damp meter is picking up damp although there is no damp patches but the wall is very cold. (1937 built home) Tried the damp machine at the top of the wall but no noise. Not sure what to do cause I'm decorating. Is it because I'm putting furniture on this cold outside wall or have I a problem. Please help!!

Potential rising damp

Hi and thanks in advance for your advice,

I have a small terraced property c1840s with only 2 rooms on the ground floor

- small kitchen (8m2) and
- living room (18m2)

The house has been empty for 4 years with no heating. Previous to that it was occupied sporadically. It has no GCH, only a gas fire in the living room. A window in the kitchen was broken for a year, hence giving a form of ventilation ;-)

I have now taken the responsibility for renovating it. I have had a professional re-point the entire back wall, front seems fine. There is no water ingress from the roof/chimney stack. The ground floor has an uneven but 'fairly' level concrete surface with probably the old flags under that.

The wallpaper was hanging off the rear wall and side party wall to a lesser degree. A damp meter indicates rising damp. No real salt tide marks.


1. Is the damp cause likely to be because it's been vacant so long with no heating?

2. If I have to go to the degree of putting a DPC in, via a professional, are there any ways I can do some labouring prep to make a material difference to the cost?

3. If it has to be the, knock plaster off to 1.2m solution and then render/skim, how long after that job is completed can I paint the walls? (Nb not planning on wallpapering)

4. Will a dehumidifier help to get the current dampness out or post remedial work, to help to dry the plastering out?

Many thanks for your help!

Are air bricks required below wooden flooring?

I have discovered the joists under the wooden floorboards in my 1880's house have wet rot and historical woodworm infestation. We pulled up the boards and to my understanding, there should be air bricks on the outside, above the floor level, and then air bricks on the inside, below the floor level, to aid ventilation. There are no air bricks on the inside (just on the outside), the walls are narrow cavities - what is the purpose of having air bricks just on the outside and not flowing inside the house? Should their be air bricks to aid ventilation under the floors? Some of the timber below the main joists are touching the soil, hence probably a contribution also to the wet rot problem, which to my understanding needs to be dug deeper and the joists replaced with treated timber, is this correct?
Thanks in advance for any advice.

Damp patches and black spots on the wall

We bought our 2 bedroom house last July 2012. We noticed to the one room we are using is having damp patches on the wall by the window and to one side of the room, some of the patches are developing black spots, started when the weather get colder and worsen by winter. The new paint was ruined as elevating. I'm quite disappointed as we don't know what to do to stop it and who to contact to solve it. I searched the internet the possible cause and it looks like condensation. Is there a connection that our house has no exhaust or because its flat roof?is it condensation or any problem? Please help.

Best was to removing / preventing mould on rafters?

I've noticed what looks like superficial mould growth on my loft rafters since the rain got in (ridge tiles now fixed).
What's the best way to clean and treat them afterwards.
There seems to be some conflicting info on the web.
Many thanks

spreading damp

i noticed a damp patch in my bathroom next to the window (black mould) this has slowly spread along the other wall and is now in my bedroom. Next door is a rented property and they suffer terribly from damp. I have had my roof checked and guttering done so its not a problem from my roof. I have ventilated the bathroom which has helped the problem. I also notice water on the worktops in the kitchen occasionally and i am getting damp in my kitchen cupboard. Next doors guttering is old and rotten could this be the source of the problem? Also what tradesman do i need to solve the problem? Please help i am at my wits end with this and had only recently redecorated the bedroom abnd the plastering is getting ruined.

Mould on Carpet following laying of screed floor

In May/June we had repairs done to our property including brickwork repairs, laying of a screed floor on top of an existing concrete base and redecoration to our dining room.

Since that time we have noticed areas of mould (white, furry patches or darker dust like patches) on the carpet in this room. Since the work was completed the room has been empty of furniture, the curtains have been put back up and the room hasn't been used.

A fortnight ago I went in there to find these patches on the carpet. I immediately vacuumed them up, went on holiday for a fortnight, have come back and mould has regrown but not as extensively as it was a fortnight ago.

There isn't any evidence of mould anywhere else in the house and is only on the carpet in the room, and we haven't had this issue prior to the work being done. Logic tells me that it is to do with the floor. The screed was laid 18 days prior to the carpet and underlay being relaid. I don't know much about the screed other than it contained fibres and was like a dry cement substance.

Any advice?

Since this posting, we have now lifted the carpet and underlay and there isn't any sign of mould either on the back of the carpet, underlay or on the surface of the screed!

We have now a hygrometer and humidity in the room at the moment is around 67% and going up. As the only thing new is the floor, what should our next step be? There are obviously raised moisture levels in that room causing mould to grow on the surface of the carpet. As this work was done as part of an insurance claim, we are not sure what our next steps should be. The builder who the insurance company appointed arranged for the carpet to be lifted and is now happy that there is no obvious sign of moisture. However, from our part this problem has only arisen following the laying of the floor. Any further advice for me?

i had damp in my kids bedrooms out side walls,my housing came round and put up stud walls,but i can smell the mold and there is spoills on the new walls,what should i do?

my houseing said its condansation but why did thay put up stud walls?

Is it normal procedure to fill outside drilled holes with sand af end of job?

Hi, I have recently had a damp proof course done af my home. The guys that did it have filled the outside holes that were drilled with what looks like sand. I only noticed this when I brushed my finger over the area & the substance just came away. I am concerned that when it rains this will all just wash away exposing the holes. Can filling the holes with a sand like substance be a temporary measure & do they return to fill with cement or something more permanent at a later date?

Mould behind wardrobe

i have a rented flat where if a wardrobe is placed along a wall mould grows and clothes go musty. Tenants complain if they have to move furniture away from walls as bedroom is quite small.. I have put in extra vents in other external walls etc. if i put in a built in wardrobe with insulation in the back and vent holes in the doors would this solve the problem? There isn't room between the houses (victorian) to get down side to put in air bricks on this wall inside wardrobe..

Thankyou Annabelle, I'll give it atry then!

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