Hello,

This is my first post, I did a quick search to see if this question has already been posted, but I could not find anything (quite possible that I missed something though!). I am getting clued up on laying a damp proof membrane in a cellar and then a concrete floor on top of it.

A problem that I foresee is that there are 2 supporting walls which jut out in to the middle of the square-shaped cellar, which mean I will have to cut in to my piece of membrane in order to fit it around these walls. Will damp be able to penetrate the membrane if I cut and then lay pieces of the membrane over each other?

If cutting is not a problem, can someone recommend a type of damp proofing membrane that can be cut and then sealed with some kind of adhesive?

Next questions: I have removed the old brick floor already, but some bits of brick and stones remain. Before I lay the membrane should I first cover the floor with sand to prevent a sharp piece damaging the membrane? Once the membrane is in place can concrete be poured directly on top? Typically what should the depth of concrete be?

I'll also be looking to fix the rather powdery walls too. Should I do this job at the same time?

Thanks & happy new year to all,
Dave

the floors no problem but if your thinking of turning it into a habitable room and completely eliminate the damp theres a lot more to it...

concreting on top of the soil may or may not work, ideally you should have at least 100mm (pref 150mm) of compacted (wacked) hardcore under your concrete and in addition to that, if you want to keep it warm then add another 50mm (at least) of cellotex (or kingspan, the foil covered foam insulation) or 100mm (at least) of jablite (polystyrene sheet)..

if the soil is loose it will crack the concrete when it settles thats what the hardcores for... might be teaching you to suck eggs a bit here but for the benefit of others....

yes, blind any sharp edges with sharp sand and if possible give it a wack with a wacker plate and blind it again then wack it again...
lay your 1200 guage dpm down (any builders merchant or diy shed), snip down to the corners and fit so it laps up the wall past where the top edge of any screed would be but where the cut line is just use some low modulus neutral cure silicon and gook some more dpm round it to seal it like a patch, it wont go anywhere once the concretes on it..

all that said, ideally, rather than use standard dpm you need something like this

http://www.safeguardeurope.com/applicat ... oofing.php

that'll cover floor, walls, and damp proofing... very effective system although can be quite costly...
in certain circumstances you need to install a sump with a submersible pump that cuts in when the drained water reaches a certain level and pumps it out to a waste drain...

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Thanks for all of your kind information, it will prove to be useful.

For my cellar, I will just be using it for storage. Luckily the cellar is already pretty dry, so I think I will go for the cheaper DPM system, to keep something in the 'war-chest' for the next job on the list... The other system that you gave a link to seems very good though.

Since I'm doing a cheaper job on the floor that means I have to find another way of covering the cellar walls and coping with the powdery mortar. Perhaps I can remove the old powdery mortar and replace with new? It's possible that the original mortar is 100 years old, hence it has degraded over time. My garden walls were powdery and I used a fixative to improve the surface prior to painting. Perhaps the same stuff would work for the cellar walls? Or is there a better method that springs to mind?

For the cellar walls I would like some sort of plaster or rough rendering on them, just something functional rather than pretty. Hopefully since the walls seem pretty dry already this won't be a problem. I'm aware of course that if there is any damp in the walls in will affect any plaster/rendering.

Thanks again,
Dave

if the surface is just powdery i.e not friable / crumbly then a coat of stabilising solution such as artex stabilex may give you a good enough surface to apply something else..
the 'tanking' solution is one way to stop the damp, or you could just knock it all off back to brick and re-render with sand and cement containng a waterproofing additive but be advised, 'waterproofing additive' doesnt completely waterproof a wall, it slows the moisture penetration right down but on a cheap job for storage would probably suffice...

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Hello again,

I just re-read my last post and realised that I was not clear in my description of the cellar wall surface, sorry about that. The surface is crumbly, in the worst places the old paint and mortar (from between the bricks) comes away very easily when touched. There is no rendering on the walls, they were just painted.

Based on your previous advice, I am now looking to remove all the old crumbly paint and mortar, using an angle grinder with a steel brush attachment. After the dust settles and can see what I'm doing again, I will wash off the walls. I am worried that the surface adhesion will remain a bit weak and that the new render won't stick all that well, since some dust will likely remain. How should I best wash the walls off, will just water do or is there a chemical solution?

There will be gaps between bricks where old mortar has fallen away, do I need to fill in these gaps before rendering or is it fine to fill these gaps with the new rendering?

Your description of the render sounds good enough for my purposes. As for the composition of the rendering, what ratio of cement:sand is recommended. I imagine that the 'waterproofing' additive will come with some instructions of how much to add.

Since I've ended up in Belgium (Belgian girlfriend & half Belgian child) I have to find a waterproofing additive that I can buy over here, one that has been mentioned to me is called Compaktuna. Does that look as though it would do the job?

http://www.compaktuna.be/pdf/CompaktunaPROengels.pdf

Final point before I start preparing my walls tomorrow: I've read a bit about an older, traditional kind of rendering before Portland cement was used. I think it is called Lime mortar (? ), I have had it recommended by my father-in-law, but he, like me, is no expert!

Would you recommend the sand & cement & waterproofing additive over the Lime mortar? Maybe this last question is not too much to worry about, although by chance my father-in-law is also renovating a dry cellar, walls in v good condition, at pretty much the same time as me. He is using the lime cement option, not sure who recommended this to him though. So all the more reason to make sure that mine turns out well

Thanks for your patience with my questions, I am a complete beginner with this lark, so I appreciate it very much! I'm starting the preparation in the morning, time to get dusty...

cheers
dave

have found that the walls are chalky rather than painted . I guess this would be some kind of lime-based whitewash.

I am thinking of getting rid of the loose, dusty bits and washing off, then cement rendering it, even if some of this chalky/lime stuff remains on the wall surface. Does concrete readily adhere to a chalky surface? If not then I'll have to wire-brush it all.

cheers
dave

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Dave

stablising solution might work..
http://www.diy.com/diy/jsp/bq/nav.jsp?a ... =266888182

or a needle gun..
http://www.--------.co.uk/hire/tools-equi ... 22211.html

or better still..
http://www.brandontoolhire.co.uk/direct ... roduct=450

_________________
http://www.peterborough-plasterer.co.uk/