Concrete floor dpm above wall bitumen causing rising damp. Also quarry tiles on earth.

[timbikeshed]

I have been investigating the rising damp in my Victorian mid-terraced house. All walls have the original bitumen damp proof treatment. In the kitchen I noticed that the 80's concrete floor has a dpm that is above the bitumen.

I suspect that damp is rising through the earth below the dpm and into the bricks.

Rather than digging out the whole floor, would it be possible to dig a trench along the wall, below the bitumen, and reconcrete with a dpm? - in order to stop the bridging.

The photograph shows a trial trench that exposes the bitumen layer. You can also see the dpm under the concrete. The earth I have dug out is not dry but farly damp. There are salts accumulating on the exposed bricks that were under a skirting board.


We also have original quarry tiles in the hallway that probably don't have a dpm - they are causing rising damp on the internal walls during wet weather.


You can also see where the quarry tiles meet the kitchen concrete.

These tiles were covered and sopping wet - they dried out really well during the summer and damp in the walls dried out too.

Any advice would be gratefully received.

Thanks

 

[Feltwell]

The problem with the trench idea is how you seal a DPM to the bitumen DPC in the wall - and also how you create a trench without destroying the DPM that's there now, you inevitably will, then hod you join a new one back to the DPM under the central remains of the slab.

Your quarries have dried out well, so I presume they are no longer a problem? The kitchen concrete wouldn't have been helping that either - the water under the kitchen DPM can be pushed up under surroundings areas.

 

[timbikeshed]

Thanks for your response.

My thinking was just to encase the trench fill in a dpm. That would put a barrier between any damp soil and the bricks above the dpc. I suppose capillary action could allow moisture to rise but I thought that might be acceptable improvement.

The quarries are dry but moisture is still rising along adjacent internal walls - as you can see by the discoloured paint. The hall way damp we can live with but the other internal wall is adjacent to a wooden joist floor and damp is migrating along the wood the joists sit on and will eventually lead to further problems.

We have only been in since May - and the sodden hallway only allowed to breathe since then - perhaps further drying out will happen over time.

 

[Cubist]

May be a couple of silly questions but... what is the overall area of the concrete floor and what proportion have you already broken up?

Could it be worthwhile just taking the remainder out?

 

[Feltwell]

Thanks for your response.

My thinking was just to encase the trench fill in a dpm. That would put a barrier between any damp soil and the bricks above the dpc. I suppose capillary action could allow moisture to rise but I thought that might be acceptable improvement.

The quarries are dry but moisture is still rising along adjacent internal walls - as you can see by the discoloured paint. The hall way damp we can live with but the other internal wall is adjacent to a wooden joist floor and damp is migrating along the wood the joists sit on and will eventually lead to further problems.

We have only been in since May - and the sodden hallway only allowed to breathe since then - perhaps further drying out will happen over time.

Capillary could be my concern to.

How gutting would it be to do all that work and still find you've got a damp problem?

Personally, I'd bite the bullet, hire a heavy duty breaker for a couple of days, buy the neighbours earplugs and chocolates and take it out!

 

[malcolm]

While things might be improved with a damp course I'm not sure I understand the whole story here. Is the damp course much lower than the floor (ie originally a suspended floor)?

You can treat internal and external walls differently. The rising damp on the internal wall is easier - waterproof coatings and the water is trying to find a way out by going upwards. If all else is good there shouldn't be much water trying to get out so make the coatings not waterproof to fix the problem.

 

[timbikeshed]

While things might be improved with a damp course I'm not sure I understand the whole story here. Is the damp course much lower than the floor (ie originally a suspended floor)?

You can treat internal and external walls differently. The rising damp on the internal wall is easier - waterproof coatings and the water is trying to find a way out by going upwards. If all else is good there shouldn't be much water trying to get out so make the coatings not waterproof to fix the problem.

I think the original floor would have been quarry tiles (same as hallway) but I'm guessing about this. In the 1980s this was concreted. The concrete is only about 2" thick with a dpm underneath. This is about 3 courses of brick above the bitumen dpc. (maybe it was a suspended floor - as the adjacent front room is suspended)

It is a problem with internal walls - so are you saying it is best to allow the moisure an escape? - as the moisture should be limited (as long as there are no other water problems such as drainage or leakage)

 

[malcolm]

In my place where the damp was on an interior wall with ground levels the same on each side I've got away with removing the waterproof paints and wallpaper and the wall has dried. I don't think there is a high rate of water ingress. I think the problem was that water couldn't get out.

A damp membrane is a good idea in new houses where it can be properly joined to a good damp course in the wall. I don't think you have a good damp course and it would be tricky to extend that bit of plastic. There is a risk that all a damp membrane attempt would achieve is to let water in and stop it getting out again. If it were me I would remove any accessible plastic sheet and re-lay the floor without a membrane.

I've got concrete floors downstairs with no membranes. They don't seem to cause much bother so long as you remember that concrete is not perfectly impermeable and it's best to avoid putting plastic or rubber floor coverings on top of it.

 

[timbikeshed]

Thanks for the advice. This is the first time I've used this forum. It is really useful to get the insight of others.

I think I'm going to backfill the area I dug out without a membrane and monitor it until next summer. (basically put the whole thing off!)

We've only been in a few months so there might be some natural drying that could help our situation. I also need to investigate drainage - to check there is no ingress of water that is the real cause of this.

Thanks again

 

[malcolm]

Sounds like a good plan. It's worth an investigation into the wet wall and maybe try an experiment there. I'd chip a hole in it back to the brick to find out what it's been plastered with. If it's soft it'll be lime and it's the emulsion paint causing the problem. If it needs a breaker then cement.

 

[jibbers91]

Did you get to the bottom of this in the end? I have rising damp on internal walls in my kitchen which also have quarry tiles!