Advice on damp please.

[david1805]

Hi,

The house I'm renovating is suffering from penetrating damp. Is rendering or some kind of textured coating a suitable fix? I'd prefer to repoint except its been bodged so many times it will be difficult to end up with anything thats looks ok.

In other areas there is evidence of rising damp - tide mark on the plaster, rotten skirting etc. I know that you can get a chemical treatment followed by replastering with a special render up to a metre, but what if I intended to dry line?

 

[Tiso]

Any kind of so called waterproofing render will trap the damp permanately where ever it occurs. Your first course of action is indentify where the damp is coming from. Common problems include leaking roof, leaking of blocked downpipes which can lead to water soaking through the walls. Another problem is if the previous occupant was into gardening and has raised the levels so that you soil or a path higher than youe damp prood course in your walls. As for chemical treatment don't bother is a con, they come with their meter which makes all facy noises when it gets close to the damp. There is only one true test for where the damp is from, this involves drilling a hole and chemically testing the sample as ground water and rain water have differing chemical compositions. Good luck with finding out where the damp is coming from

 

[david1805]

Thanks for your reply.

I know what you mean about the damp proof people and their meters and I definitely don't want ripping off!

On the outside wall the ground level is only around 3" lower than the internal floor so presumably this could be a problem?

However one of the internal walls shows signs of rising damp and, curiously, so does the party wall, yet I have been round my neighbours and have seen that they have no signs of damp on their side and haven't had any treatment - at least not in the eight years they have lived there. The house has been unheated for a number of years - is it possible that the plaster has absorbed moisture form the cold atmosphere and would simply dry out with heat or a dehumidifier?

 

[Nige F]

very possible ........Hygroscopic salts

 

[noseall]

very possible ........Hygroscopic salts

could't agree more Nige.

 

[Nige F]

probably instigated by the plasterers themselves

 

[andy2306]

condensation?

or

I had the same problem and I had the gutters replaced and hey presto no more damp. It was weird how next door didnt have any damp on the same internal wall!!

 

[david1805]

Ok, so I've had an 'expert' round with his so called damp meter and guess what? They recommend chemical treating the whole house. Oh and by the way I'm not touting for work but the joists have got woodworm.

Any thoughts on this one... When I started this house a month ago there was a damp patch on an external wall about head height and I took the damp plaster off to bare brick leaving dry plaster surrounding it. Today I noticed that the dry plaster is now freshly damp. It hasn't rained since Saturday though we've had plenty of wet weather since I first took the plaster off.

Can it take several days for wet to make its way through?

And what I can do with the wordworm?

 

[rcs]

Had a similar scenario as did the neighbours 2o years ago. The fix was to improve the ground level drop away from the house, check that the external floor level is far enough below the dpc so rain doesn't splash up, ensure the dpc was not bridged with render and improve sub floor ventilation (clear vent bricks and any sleeper walls of clag/fit hi-flo vents).
The joists were rotten and had woodworm and weavel so had to replace most of them but from my experience, if you've got a slate dpc, you don't need any kind of chemical injection. The waterproof plastering to a metre high should probably be done (imho) and replace joists with tanalised wood with cut ends treated with Cuprinol 5 star where necessary. You could also wrap joist ends in polythene membrain where they are inserted into the damp wall.

Did the specialist actually look at the woodworm attack, i.e. remove floors/use borescope? Are there any pipes in the area of wall damp? Is there loose/leaking guttering above the suspect area?

Our house dried out after 3 months of decent central heating and improved ventilation. The floor levels were adjusted and the bridged dpc was hacked back. So far so good. The neighbours have been fine for 20 years now.
rcs

 

[david1805]

Thanks for your reply, RCS.

As far as I can make out this house has solid external walls with no obvious sign of a cavity or dpc. There is only 2-3" difference in height between the level of the floor inside and the ground outside - is this enough? Should it be 6"+? If this could be the problem with the outside wall, then great.

This, of course, doesn't explain the internal wall. When I removed the wallpaper, which had already detached itself at the bottom 2', there was a tide mark on the plaster. Having removed the plaster though the bricks appear dry. Having read the numerous posts regarding the non-existence of rising damp I am starting to think the apparent damp is due to the house being largely unheated for years, and that once I get some warmth from the central heating into the place the problem will go away.

As far as the woodworm is concerned he only did a visual inspection and then recommended some kind of pressure treatment - is there any DIY method? At the end of the day I could probably replace the joists cheaper than a professional treatment.

 

[Softus]

The house I'm renovating is suffering from penetrating damp. Is rendering or some kind of textured coating a suitable fix?

No. Removing the source of the moisture is the correct fix.

In other areas there is evidence of rising damp

If you have rising damp, then it is being caused by moisture rising between brickwork and its covering (i.e. rendering or plaster).

I know that you can get a chemical treatment...

These achieve nothing. You need to find the source of the damp and stop it from soaking the brickwork.

 

[rcs]

Solid brick walls act as heat stores (to a certain extent) and so maintaining constant central heating will dry out any damp problems providing sufficient ventilation is provided, and will stay reasonably warm once heating is removed. When we were doing the real messy work and so uninhabitable, we left the heating on between 4-7am and 4-11pm, which seemed to dry out a lot of our problems and now we have a new boiler, it feels really comfortable all day, whatever the weather.

 

[david1805]

The house I'm renovating is suffering from penetrating damp. Is rendering or some kind of textured coating a suitable fix?

No. Removing the source of the moisture is the correct fix.

In other areas there is evidence of rising damp

If you have rising damp, then it is being caused by moisture rising between brickwork and its covering (i.e. rendering or plaster).

I know that you can get a chemical treatment...

These achieve nothing. You need to find the source of the damp and stop it from soaking the brickwork.

Softus, the moisture can only be from the rain getting in through porous mortar- the damp areas are at head height on the external wall with no drainpipes etc. If this is the case then would render cure it?

 

[rcs]

Is the render removed in that area, cracked or blown? If it's just exposed 9" brick, it would be fair to say that render would fix penetrating damp.

 

[david1805]

Is the render removed in that area, cracked or blown? If it's just exposed 9" brick, it would be fair to say that render would fix penetrating damp.

Yes its exposed brick. Some of the faces have blown and its been very poorly re-pointed in some areas. It would be very difficult to make a nice job re-pointing which is why I'm considering render.