Suitable damp proofing for walls?

travel_freak

Hi,

I have what is an outside toilet which hasn't been in use for a long time and I'm planning to make an entrance to it from inside and make it usable again.

At the moment there is the basic brick structure with old quarry tiled floor - so there is no damp proof layer on walls or floors.

I've had a few builders in to quote for the work (cutting in new doorway, bricking up old one, preparing walls/floor and putting in loo/basin) and asked how they would damp proof the walls - one builder whose quote is favourable said he would use black bitumen paint on the walls. Is this adequate or should I be seeking something better than/alternative to this?

Would it be normal to have the damp proof layer on the walls then plaster over or put up plasterboard?

Many thanks for any advice to help me know what is correct here and what I should be seeking from the builders here - at the moment it's a typical disused, damp, outside loo.

travel_freak

Hi,

Please can anyone comment on this? I'm now wondering whether I should be getting one of those injectible damp proof courses but not sure as these are at the moment bare brick walls - not sure what the correct procedure is and I'm worried that just painting on black bitumen paint sounds like a shortcut.

On the other hand this builder can start early February and I'd love to get everything underway as the house looks like a bombsite at the moment!

Regards,

Canucklehead

Good morning: Useful info here... http://www.bricksandbrass.co.uk/diyelem/extwalls/damp/dpdamp.htm and here http://www.safeguardeurope.com/applications/applications_menu.php

You could also post on forum. We did what you are planning to do but dug out solid floor and created a suspended floor...hired chemical injector and DIYed. damp course. Dabbed plasterboard on walls...cloakroom extractor installed and radiator as well. My OH is a very handy guy!

HTH
Canucklehead

PS. A bodger who had the property before us used bitumen without success elsewhere in the house (Victorian stone semi)

HugoSP

Without seeing the property for myself it's difficult to comment.

Bitumen based products are fine but a little old fasioned. There are better products on the market. Although some of these are more expensive the extra cost makes little difference on the price of a job.


Floor
The proper way to do this would be to replace the floor with a screeded concrete floor and lay new tiles. Building regs require 70mm of celotex insulation or 100mm of jablight (polystirene sheet). The floor and the sub base would need to be excavated to at least 10 inches below floor level to provide depth for insulation, concrete slab and sand/cement screed, unless he can get a level finish on the concrete - easier on a small area, which it sounds like this is.

Walls
You don't say where the damp is coming from.

Rising damp.
First make sure you haven't got a damp proof course in there. A lot ofolder houses have very effective slate damp proof courses that have been bridged by people raising ground levels outside.

Penetrating damp.
This is a scurge of properties without cavity walls. The damp enters the outside of the wall then tracks through. The bitumen idea suggests that the builder thinks this is what you have. This is called tanking, ie providing a water barrier on the inside of the property so that penetrating damp can't affect the decor on the inside. The bitumen is usually applied to a height of around 3 to 4 feet above ground level.

Applied on its own this can have either one of two effects.

1. It works, the property is then dry
2. In cases of severe hydrostatic pressure (a lot of rain, damp in the ground etc) it can breach the tanking and come over the top. we had this in a house we bought and had to strip all the render off the affected wall and dry line.

If the property needs protection against penetrating damp, my take would be to tank it using Thoroseal, not bitumen, as the latter can cause issues with adhesion of the top coat of render/plaster if not keyed properly.

However, to offer some protection against the tanking being bridged, I would also make sure you have an effective damp proof course. Inject one if necessary.

Then, with the floor fully excavated, tank the walls in accordance with the manufacturers instructions. This will ensure that the floor membrane has a good overlap with the walls.

Then the damp proof membrane for the floor should be lapped inside but adhered to the tanked walls.