Screed damp proof a concrete clay Subfloor which has a suspended timber floor

Skoolz

New Member
Hi All,

I'm in desperate need of your help and advice on a damp issue I need to resolve. I have had various diagnosis by surveyor specialists confirming lateral and rising damp (I'm not going to debate the whole it's a myth concept so if you don't believe it exists then please spare me and yourself by not replying).
It's due to my house, a semi, on a down hill slop, is attached to my neighbours house which is on the uphill side, meaning they are on higher ground. Their ground and DPC is about 1 metre higher above ground than mine.

This means that their foundations, mainly clay soil are butting against the party walls on my living room walls and chimney walls. This means everytime we get rains, their ground water is seeping into my living room walls and soaking them. I've hacked off the plaster months back and have had the brick walls bare and dried out so I've literally been witnessing the bare bricks get soaked following rainy days and dry out during dry days. I then decided to open the timber floor to clear the subfloor which was also full of concrete and earth type screed which was heaped/lumped against the party wall subfloor footings. Turns out this was done to seal the ground water seeping from lower party walls and also from under the subfloor because the moment I removed this, water started seeping through the loose mortar areas of the lower party wall as well as rising from the subfloor ground and pooling where i had removed the heaped earth.

So to remediate this, I can't really build drainage to take away this water as the outside is slightly higher ground ( I have dug out drain trenches around the whole house to lower ground and let the bricks breath) This has reduced /stopped the rising damp so the only issue remaining is this lateral damp from next doors raised ground against my party wall. So the only option I'm now going for is tanking/rendering the party walls.

1. I need block/seal the seeping water from my subfloor mortar first (scrape about 20mm or more reporter with water proof mortar)
2. I need to also create a concrete screed to stop the ground water rising and pooling, so it spreads through the clay downhill rather than up to my subfloor. The subfloor has some cement and some clay areas. The water is pooling in the clay areas areas that don't have cement (it was cracked and I've dug it out).

Questions
1 So what's the best mix for the waterproof mortar to seal out the seeping water from the few mortar areas of the lower party wall subfloor? Sbr ratio to cement? or Sika slurry etc? I know sealing the water rather than draining, will mean it will rise on the wall hence why I'll tank the party walls. I have drilled a cream DPC (Dryzone) which I'm not convinced works TBH.
2. What's the best screed mix for the subfloor ground which will bond to clay and cement and soil areas to seal the groundwater from rising and pooling?
 

Attachments

ChrispyUK

Well-Known Member
Hi All,

I'm in desperate need of your help and advice on a damp issue I need to resolve. I have had various diagnosis by surveyor specialists confirming lateral and rising damp (I'm not going to debate the whole it's a myth concept so if you don't believe it exists then please spare me and yourself by not replying).
It's due to my house, a semi, on a down hill slop, is attached to my neighbours house which is on the uphill side, meaning they are on higher ground. Their ground and DPC is about 1 metre higher above ground than mine.

This means that their foundations, mainly clay soil are butting against the party walls on my living room walls and chimney walls. This means everytime we get rains, their ground water is seeping into my living room walls and soaking them. I've hacked off the plaster months back and have had the brick walls bare and dried out so I've literally been witnessing the bare bricks get soaked following rainy days and dry out during dry days. I then decided to open the timber floor to clear the subfloor which was also full of concrete and earth type screed which was heaped/lumped against the party wall subfloor footings. Turns out this was done to seal the ground water seeping from lower party walls and also from under the subfloor because the moment I removed this, water started seeping through the loose mortar areas of the lower party wall as well as rising from the subfloor ground and pooling where i had removed the heaped earth.

So to remediate this, I can't really build drainage to take away this water as the outside is slightly higher ground ( I have dug out drain trenches around the whole house to lower ground and let the bricks breath) This has reduced /stopped the rising damp so the only issue remaining is this lateral damp from next doors raised ground against my party wall. So the only option I'm now going for is tanking/rendering the party walls.

1. I need block/seal the seeping water from my subfloor mortar first (scrape about 20mm or more reporter with water proof mortar)
2. I need to also create a concrete screed to stop the ground water rising and pooling, so it spreads through the clay downhill rather than up to my subfloor. The subfloor has some cement and some clay areas. The water is pooling in the clay areas areas that don't have cement (it was cracked and I've dug it out).

Questions
1 So what's the best mix for the waterproof mortar to seal out the seeping water from the few mortar areas of the lower party wall subfloor? Sbr ratio to cement? or Sika slurry etc? I know sealing the water rather than draining, will mean it will rise on the wall hence why I'll tank the party walls. I have drilled a cream DPC (Dryzone) which I'm not convinced works TBH.
2. What's the best screed mix for the subfloor ground which will bond to clay and cement and soil areas to seal the groundwater from rising and pooling?
Similar (ish) issues with my house I'm, renovating, although no gradient. My house (30's) is built on a concrete raft and clay soil. Water has been getting in, which lies on the raft and although does eventually drain, it starts to evaporate causing all the timbers to be continually soaked in condensation. Solution...well previous solution (previous owner) was to get in a 'damp 'company' to inject DpC, hack off 1m and re plaster with 'damp proof plaster' and re-timber the floor. Obviously all was well for 20 yrs, till it all rotted again as they never cured the problem of the water getting in because most damp companies are f**k**g idiots. Ive dug down to the raft externally and let brick work dry out, re-pointed and tanked with Remmers MB2k which will hopefully stop the water getting in. Will have another physical membrane attached to help prevent hydrostatic pressure and prolong the tanking and french drains. Its pretty much all i can do.

Problem you have is you're trying to waterproof from the inside and you're at the bottom of the slope. Unless you can solve the problem from the other side, concreting the floors may be a better option, but there is a risk of pushing the water elsewhere and causing issues.
 

Skoolz

New Member
Thanks ChrispyUK,
Appreciate you taking the time to respond. Yeah, the odds are stacked against me in respect of doing the ultimate right thing which would be to dig up neighbours foundations or dig beneath my subfloor and install some french drains , but I can't so those aren't even options.

I'll have to remorter and concrete/screed so hopefully someone can help with the best mix product. I'll look up Remmers MB2k for pointing as I was thinking KA Tanking as a mortar but not sure and no info on this.
 

ChrispyUK

Well-Known Member
Thanks ChrispyUK,
Appreciate you taking the time to respond. Yeah, the odds are stacked against me in respect of doing the ultimate right thing which would be to dig up neighbours foundations or dig beneath my subfloor and install some french drains , but I can't so those aren't even options.

I'll have to remorter and concrete/screed so hopefully someone can help with the best mix product. I'll look up Remmers MB2k for pointing as I was thinking KA Tanking as a mortar but not sure and no info on this.
the problem you have is that you don’t have access to the source of the water so to speak, so it’s a bit like putting a patch on the inside of a boats hull, rather than the outside. The Remners is a 2 part tanking Compound to waterproof the walls. Not sure if it’s the right product or approach in your situation but could be. Goggle Permaguard who specialise in these types of products. May be worth giving them a call.
 
Top