Damp-proofing Basement : Any Experts out there ?

TonyCat

Hello. Recommendations for the following : Basement flat ( 50% at front 100% at rear, below ground level ) with history of serious damp. Poor render on externals ( due to be done next year ) plus I think penetrating damp from ground. Basically coming in everywhere atm. I thought tanking was the way to solve it so I'm trying to get 3 companies round to quote. The first company to respond however said they haven't tanked in 10 years, what they do it put a waterproof membrane on the wall then dryline, membrane on floor with pump, sump & channels in floor & cover with whatever ( cement or hardboard ). Water collects in sump, fills up and gets pumped out. I got the impression tanking is old fashioned, this is THE new right way to damp proof a basement. Except I know a neighbour just used a combination of tanking external walls and injecting internal walls. So is it a sales pitch ? or is it really the new right way ? Is it any better ?

Any thoughts or recommendations appreciated. Any websites that I should/could look at please.

Canucklehead

Good morning: The option described by the installer is becoming more popular...one of my OH's clients had this solution used in her old coal store (understairs). More info here... http://www.safeguardeurope.com/applications/basement_waterproofing.php
This method also allows for fixings to the wall without voiding the warranty e.g. radiators, sanitaryware etc.

HTH

Canucklehead

TonyCat

Thanks Canucklehead that link is useful. I think I'll just listen to the sales pitch from the different salesmen and then have a think and decide.

HugoSP

I have recently tanked our new basement, some of which we excavated ourselves.

For the new utility room that was literally dug out before underpinning the house, as we had reduced the internal ground level by some 5 feet. This is underground at two sides, the third side is above ground and the 4th side abuts onto the basement kitchen.

We used a product called Thoroseal. This involved painting a cement based compound onto the two underground walls and part of the third solid wall that abutted an underground wall. Where these walls were not concrete (from the underpinning) or concrete blocks we had to render to give a sound base for the thoroseal.

The concrete acted as a sound damp proofer in its own right but it was thorosealed anyway.

A concrete floor was laid with the DPM coming up inside the room, so it was overlapping the thorosealed walls. hence any damp that could run down underneath te thoroseal on the walls would run underneath the membrane.

The floor was solid concrete with some 3" of insulation and screeded on top.

The walls were then drylined.

For the basement kitchen that is next door to the utility room we used a different approach.

The wall that was 100% underground had a thick grade tanking membrane hum on it that went under the floor membrane

Then we built a 4" concrete wall infront of it leaving a minimum gap of 2 inches. This was also to support the floor joists in the room above, taking them out of the original wall that is subject to some damp. Thus the tanking membrane is between the two walls, so any damp will hit the membrane and run down under the floor membrane.

This same tanking is also inside the wall that joins onto it at the corner.

We are going to build a garage on the side of the house so that the side wall that would normally be partly underground will not be. The new garage will be extensively tanked as it is built.

There is not a sump pump in sight.

TBH tanking has to be got right. It is very difficult to make sure there are no leaks and the consequences of having a hole in the wrong place can be dire. I suspect that this is why tanking companies, who have to guarantee their work, will go for an option that allows for damp to flow into a pumped membrane system, such as what the OP has described.

Having said that we have not had any damp since the damp proofing was done, and we have had one of the wettest summers on record.

TonyCat

Saw the surveyor from the damp proof company Discussed the merits and disadvantages of both tanking and membrane, they're approx the same price He came up with a third option - which surprised me What he's suggested is taking down the stud/drylined inner wall and putting up a block inner wall with vents. Reasoning - ventilation is the key. The inner block wall will provide a cavity/space. The current stud wall doesn't work because of it's material plus wooden baton fixings. This solution only applies to the walls /external walls. The party wall still damp injected and floor to be decided later. The final decision on the external walls ( 3 ) to be taken once area's completely stripped out ie plaster hacked off and stud walls removed. The 'selling' point of this solution for me is, if it works, it'll be a forever solution whereas tanking approx 10 years & membrane approx 30 years.

I know every property is different and needs it's own approach, but anyone have any thoughts on this approach ? Has anyone done the same and did it work ?

TonyCat

Any thoughts anyone about this solid internal perimeter wall ?

dampdaveski

hi Tonycat,
get a quote from a surveyor who has the following qualification C.S.S.W and ask them to design a scheme that complies with BS8210. You can then make an informed decision on what system to use.
If you don't want to go for an ultra failsafe system then you can go for a cheaper more risky system, but at least that will be your decision.
As a surveyor with the above qualification, i can't think of a worse system that relies on any water 'running behind the membrane' under the concrete floor! great if you live at the top of a hill (maybe) and great if you want to run the risk os subsidence when the running water has washed the soil away from your foundations!
might take years for that to happen, but is it possible YES!
If you want to do it yourself, just put cavity membrane systems or basement conversion in the search engine, most are pretty good, i'll not embarress anyone by mentioning trade names
hope this little rant helps ;-)