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Damp Proofing Questions

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2,253 Damp Proofing questions

How to prevent and stop mould and dampness.

My windows in my flat are not the best they are the old double glazing style with wooden frames and from time to time they get all mould and its making my blinds mouldy. I also had a problem with mould growing at the corners of my bedroom and anything that was sitting close by got affected. There is a built in cubboard in the room and a lot of clothes and shoes which were in it went al l mouldy. In the other bedroom there is a big wooden cubboard and bookshelf and I noticed everything inside the cubboard and the books were getting mouldy so i took them out and saw the wood was covered at the bottom. The bookshelf was black and the cubboard all green mould. I have also recently noticed the wooden frame of my couch is getting quite mouldy. Can anyone advise the best thing here? Also I have quite a lot of animals. Do you think this will be the cause of any problems?

How to get rid of mould and condensation?

I live in a 1930's semi detatched home. A couple of years ago, we had the house re-insulated, including cavity wall and in the loft.

Since then, we have had issues with condensation on the windows, between the double glazing and small black moud growing in several places in the house...mainly in my son's bedroom. We removed the mould with diluted bleach and painted over it with a special paint. It seems to be coming back though.
My son has a skin condition which seems to worsen when he comes home from university, so it is essential that this is sorted out quickly.

We were told by the insulators that we would need to have the existing vents opened or some fitted perhaps, but we never got round to it. Before having the insulation done, we hardly had any condensation and NO mould whatsoever. This suggests that it is definitely a ventilation problem, but I'm not really sure about what the exact solution is, and would greatly appreciate some help/advice.

will the Holland damp proofing air vent system work?

Do you need to remove plaster in order to put in a injected damp proof course? Alternatively is installing solid wall insulation at the same time a good idea?

We've been advised to reinstate injected damp proofing a 1920's semi. Previously undertaken about 30 years ago. We understand we need to remove the plaster to a meter up to guarantee the work. Is there anyway to avoid this?

Alternatively, we are considering taking it all off and fitting internal (solid wall) insulation. We are only really considering this for a staircase wall - how long would a job like this take and what kind of prices might we be looking at? Any advise would be welcome.

Finally, I have come across injection damp proofing that goes into mortar rather than a course of bricks, any experience, knowledge or advise on this would appreciated?

Many thanks in advance

Penetrating damp on rendered gable end wall in Victorian end of terrace


We are having an issue with damp patches appearing on internal walls of our Victorian end of terrace house. The exterior wall is rendered in what appears to be concrete (browney-sand coloured) which when tapped doesn’t appear to be blown. The patches started in an upstairs bedroom about mid-height on the wall and with the recent rainy weather have spread to cover most areas of this wall. The patches are a tan/brown colour and in some places there is black mould or white fluffy areas (plaster salts?). The damp is now starting to show at ceiling level at the room directly below on the ground floor with the same brown-ey patches.

We’ve had several “damp specialists” round who don’t seem to want to deal with the work upstairs and will only do a damp proof course. Only one person who has been out to survey the area has made a suggestion which was to use thermal boarding on the interior wall and re-plaster it then paint the outside render.

If we went ahead with this would this actually solve the problem? Surely the damp would still come through but we would no longer see it?

As there are floor joists in this wall, is there any chance that these may become damaged from the dampness in the wall?

Could anyone give us some pointers on what the issue may be?

Thanks in advance for your help.

Rising damp & penetrating damp

What's the difference, how can I identify both, are there tell tale signs?

How worried should I be about the timber joists and flooring in a new extension touching the wall below the dpc?

I'm having a single storey extension built (approx 4m x 5.8m). The builder inserted the air bricks and dpc too high which meant that, when he put in the floor joists (hung off ledger boards bolted directly to the blockwork), the ledger boards covered the air bricks and all the timbers were below the dpc.
He admitted this was wrong when I pointed out to him that this couldn't possibly be right.
They have now put in new air bricks lower down so they vent underneath the floor joists.
With the dpc the builder suggested either injecting a dpc lower down or inserting a length of damp proof membrane between the ledger boards and the wall. I sought advice from a surveyor friend who said that neither of these options was acceptable (the injection system isn't that reliable and adding a membrane between the timber and walls was flawed because every bolt hole would puncture the membrane and allow damp through the hole). He said the ledger boards should be scrapped and the joists should be hung from the blockwork using S type joist hangers so that at no point does any wood touch the walls below the dpc. This is what the builder has now done.
However, the joists are so tight in the hangers that some still touch the blockwork and none of them are more than 1-2mm away from the blockwork. How worried should I be over this? What's the minimum gap you would recommend between the wall and the joists? And between the wall and the floorboards themselves (as they will also be below the dpc)?
Would a solution be to build a sleeper wall (with dpc and wall plate) at each end and rest the floor joists on this so that they are not connected to the blockwork at all? As the sleeper walls will then be taking the full weight of the floor, do they need some sort of foundation or can they just be built directly onto the oversite concrete?
I'd be really grateful for any advice please.
P.S. I'm on the west coast of Scotland if that makes any difference in terms of building regs, etc.
P.P.S. Before anyone else assumes I went for the cheapest dodgy builder, he's a well-established local firm, recommended by the architect & was main contractor on building works at a private school in the area!

How can I tell what is the cause of mould in my house? Two different companies have said different things...and I don't know which is right!

Having stripped wallpaper in my dining room there is black mould in the corner. It is over two walls and comes up to about metre. The water pipe for the house comes along the wall and up the other wall (upto boiler upstairs) but there is no sign of water, wood damage to skirting etc. I have had two cupboards up against the wall...for about 5-6 years but when I did a quick decorating fix 6 months ago I didn't see lots of damp/mould.
One tradesman has said it is definitely not rising damp and it is just caused by condensation (being near the back door, covered by cupboards etc). He wants to sell me a basement damp machine but I don't want this and if it is condensation I'll use cleaner and solution in paint/paste.
The other tradesman said it was rising damp (though he didn't seem to want to offer any other solution and didn't really speak - he just poked the wall and made a hole in it with a screwdriver!) and he quoted me £1000 to do damp proofing.
I'd like to be able to know what the mould is caused by and how to identify it given that the experts in my area can't agree!

Methods for installing a damp proof course

What's the best method of installing a damp proof course?

Damp patches around chimney breast

I think I have an interesting one for you all...

I have had a problem with damp patches appearing around my ground floor chimney breast and I would have though I first noticed an issue around 2 years ago. This is an INTERNAL wall and the construction is SINGLE SKIN brick. In June 2011, I commissioned an independent damp survey (CSRT qualified surveyors independent of any supplier) to try and identify the root cause of the problem.

The surveyor took damp measurements of the affected wall and created a damp profile. The moisture meter indicated elevated readings ranging from 70 - 90% in the plaster of the chimney breast and 40 - 60% in the plast of the adjacent wall. The skirting boards were 20%. Up to 1m the readings are fairly consistent and at approx 1m the damp readings stop entirely.

At my instruction floorboards were not lifted due to an existing laminate floor that I can't afford to replace at present. Samples of brickwork were not taken and the surveyor inspected the house from the outside but did not get up onto the roof or go into the loft.

The survey report identified the "cause" as being rising damp due to a missing or ineffective dpc in the chimney breast. Also possible bridging from the concrete hearth and associated earth mound allowing moisture to track up the brickwork and plaster. Unable to confirm whether the hearth is insitu due to the flooring.

Recommendation is to install a dryzone or vandex dpc in the bottom row of brick above floor level and replaster with sand+cement incorporating salt inhibitor. Plaster not to project more than 25mm below top of new skirting and min gap to floor of 25mm.

HOWEVER, from visual inspection over a period of time, the damp patches on the wallpaper gets worse very quickly during periods of heavy rain and gradually dries out over a period of several weeks when there is a dry spell (all too rare in north Manchester!).

The gas fire came out today and the hearth behind was full of rubble and soot. I have cleaned all of this out. I have had a couple of lads come out to quote for the

So then based on the above, is my problem:

a) Rising damp as diagnosed by the surveyor

b) Penetrating damp from a leaking chimney

c) Condensation being hygroscopic salts in plaster drawn through from brickwork behind.

d) Some combination of the above/ other

And based on that diagnosis. Do I:

a) Hire a dpc Contractor as per recommendation

b) Get a roofer to see what is what up top and fix any problems there as a first try.

c) Buy a dehumidifyer and run it hard for a few weeks.

d) Other.

Sorry for the essay, hope you found it an interesting one, any more info just ask, look forward to seeing responses.


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