Damp Proof Membrane - Standards & Repair

[bogwort47]

Hi Everyone

I am in the process of re-doing our cloakroom which apart from a splash of paint is as built in 1978. Because the soil pipe is virtually in the middle of the room I have planned to move the pan back to the wall. So far I have excavated the 4" concrete floor to 6" in depth to the level of the top of the black joint collar and removed the top section of the crock soil pipe from the collar.

I now have 2 problems which in spite of research I have not been able to solve:

1. How to repair the DPM

The floor is very hard with filler in the mix of rounded pebbles and quartz so I ended up hiring a power impact hammer. Necessarily, no matter how careful I was I ended up damaging the DPM. This was not helped by a very thin blinding layer over a mix of soil, broken chalk and flint. The DPM appears to be a clearish polythene showing aging embrittlement not only where exposed around the soil pipe top but on the the blinding layer - not what I expected.
Repair schemes say to take the floor back to 150 mm of good DPM. Frankly, I feel this will be impossible to achieve due to the nature of the materials involved unless I take out the whole ground floor and start over. There was a time when I would have used Waterproof PVA but what it says on the can now has changed.

Any suggestions would be much appreciated please.

2. Damp

The wall behind the soil pipe, single breeze internal, has been showing efflorescence for some time. Damp testing shows it to be dry now and so also the surface of the floor but the in fill is showing wet. The mains water inlet runs low along this wall also and I found a very small leak from the S/C gland and also evidence of a small but long term leak from the cistern/down pipe. Carpeted, these leaks have gone unnoticed for some time. After about 3 weeks the ground fill is still wet. I am confused - I would have thought it would perhaps have dried out by now, particularly as it has been dry here for some weeks. I have a water meter, recently fitted, so I am checking for a supply pipe leak tonight after shutting off the internal S/C. Initial indications are for a zero leak rate - no movement on the 'spinner'. The house is built on a sloping site on chalk.

Any suggestions would be much appreciated please.

Thanks - sorry, I seem to have gone on a bit.

 

[bogwort47]

Update:

1. Overnight test of water supply pipe from road showed absolutely no movement of 'spinner' or smallest digit - phew! This comes up in the cloakroom.
2. Mains S/C in cloakroom opened and 30 min test showed zero movement.
Now plan to do an overnighter.
3. 2 x soil pipes from cloakroom (1 from bathroom above) and 1 from kitchen drain close by, all plugged at manhole, filled and checked over 30 mins each - result no movement - so all look OK.
4. All internal drains behind kitchen units exposed and visually inspected for any sign of leakage.
5. Subject to 2. above, overnighter, it looks like ground water - weird. Soil is still wet, but damp test meter shows sides of concrete floor hole to be dry - so also skirting and wall above which shows efflorescence, most likely from the long term small leak from the cistern down pipe.
6. Now trying to find somewhere to carry out soil test to determine source of water - has anyone got any ideas please?

 

[LMuschialli]

Hi there

Re point 1 - Yes DPM's that have a break in them are very difficult to repair, Do you have the room to lay a small dimpled profile dpm or a grooved say 2000 gauge flooring membrane over the existing cloak room floor? If so you could prime the soil pipe with a bitumen based primer paint up say 150mm from internal floor levels and then loose lay this 1mm grooved or nearly 3mm dimpled sheet above the existing floor and seal to the pipe. The downside would then be having to raise internal floor levels to accommodate a floor finish (probably 18mm with a T&G floor or you may get less with a decoupling membrane and tiles) The other option if you do not have the head height would be to lay an epoxy layer over the exiting floor. You may even be able to get a high quality epoxy to do a patch repair.

Re point 2 - I would monitor this longer and see if it improves before going further. Just out of interest is the soil pipe or the internal breeze block bearing near a retaining wall?

 

[bogwort47]

Hi Warren

Useful response - thanks

The ground floor throughout the house is concrete with thermoplastic tiles laid on what appears to be a bitumen based adhesive - so far there have been no other damp problems. I understand that some properties built in the 70s with concrete floors only had this and no underlying DPM

Head room is a problem as the cloakroom is squeezed in under the stairs.

I will leave it for longer as you suggest and monitor the damp levels.

Given the current standard of waterproofing, as originally built, thin DPM with bitumen over concrete, my feel is that any waterproof layer I can seal to the existing DPM could well be an improvement if after I make good the floor tiles etc.

The nearest retaining wall is 2' - 3' high about 5' - 6' to the North of the house. The cloakroom is about 15' South of the house North wall and bordered by the external East wall of the house, outside of which is a concrete drive up to the outer brick wall but below the DPM of the wall and sloping both South and East away from the house. The manhole collecting all 3 soil pipes is in the middle of the drive and at the same latitude as the cloakroom.

Just thought, I must check the relative heights of the inner and outer DPMs. I have already noticed that that the internal breeze wall, which had the efflorescence is built directly onto a standard wall strip DPM on the main concrete floor of the house.

There have been too many comings and goings lately to carryout an overnight supply leak test - must do soon.

Will keep you posted - thanks again.