Tanking Slurry Failed?

[Adam Bill]

I have a garage that is built into the earth on 3 sides, ever since I have moved into my house I have had issues with damp and mold in the garage and so I decided to try tanking to prevent water ingress through the walls.

I used Febtank Tanking Slurry and this appears to have dried well on 1 wall however the other 2 walls have still not dried out (after over a month) and now on those walls it appears like the tanking is cracking and falling off (pictures attached). I do not know why this hasn't worked and was wondering if anyone could give and advice on this or how to fix this?

 

[mikeey84]

Due to hydrostatic pressure, tanking like that is always at risk of failure.

You would be better digging back the ground outside and waterproofing the outside of the wall

 

[Ivor Windybottom]

That was never going to work.

Is it a solid wall into the soil? If so then you need a radical plan involving a second wall, either on the inside or outside of it.

 

[Adam Bill]

Thanks for the replies. Yes it is a solid wall into the soil. About 3/4 of the wall is in the soil and the remaining 1/4 of the wall is above ground. Would any ventilation help solve this if was to put in air bricks in the wall that was above ground?

 

[mikeey84]

Not really.

Easiest way to make it better (probably not solve it), would be a trench all round the outside to bellow the DPC.

Then tanking slurry or paintable DPM, then backfill with gravel.

But if it wasn't built to be surrounded by soil in the first place, it can be very difficult, if not impossible, to make it less damp afterwards

 

[Adam Bill]

I've just had a look again under the decking where the garage meets and taken a couple of pictures. Does that look like it would be soil touching the wall? If so it would need a trench digging all the way round. So really it should have been built 2 bricks thick to begin with?

 

[mikeey84]

That looks like a fairly modern build with a cavity wall, not single skin.

That should have been built to withstand the soil touching it, if was always going to be built into the side of a hill

It looks like a DPM is there just above the soil level, so it could be your decking that is causing the issue, as it could be causing water to get above the DPC

 

[Adam Bill]

Thanks. It is pretty modern and actually now that you mention it the wall that doesn't have decking is the one the tanking has stuck to and doesn't appear to be failing whereas the two walls with the decking next to it are the ones where it is still wet and tanking appears to be failing. Do you think of I cut back the decking away from the wall that could help?

 

[freddiemercurystwin]

No, it needs tanking internally, either a bituminous layered system on the walls held in place with a skin of masonry joined to a membrane under a screed from the likes of Synthaprufe or RIW or a drained cavity system from the likes of John Newton or similar.

A render system only works where the hydrostatic pressure is very low.

 

[Adam Bill]

So is the cementous tanking I have done known as a render system and so it be better to get something like Synthaprufe instead?

Now the tanking has failed is there a way that I can go about getting this off to then apply something like Synthaprufe?

Going back to @mikeey84 comment the garage was built into a hill and the only walls that are getting damp are the ones with decking either side which makes me think it could be something to do with that, if so would there be a better/easier solution to deal with this such as cutting the decking back so it's not as close to the wall? (Apologies if you can't tell I am a real novice when it comes to this)

 

[freddiemercurystwin]

I suggest you read up on Synthaprufe and the others mentioned, essentially it's a membrane applied to the exisitng wall and then a skin of blockwork built to hold it there, same for the floor, it's not a cheap method but if you're sure you appiled your render/tanking slurry meticulously as per manufacturers instructions (?) then the only reason it would fail is the pressure is too high so if you really want a waterproof method you'll have to splash out (arf). I suspect the decking is a red herring.

 

[Ivor Windybottom]

It doesn't look new to me, I'm guessing it's decades old so has had plenty of time for people with clever landscaping ideas to have ruined it!

Have a dig down in one spot, if it's all facing brick then it was probably never intended to have been buried in the first place.

If this was the intended design then it was a rubbish one.

You will not fix it with any miracle super-goo. It needs a retaining wall on the outside, or just removal of the soil - possibly back to how it was after it was built.

 

[cdbe]

Personally I blame the workman. It hasn't failed because water has pushed it off the wall, it's failed because it hasn't adhered properly in places.

This stuff requires meticulous preparation. You need to strip it back to the brick, clean the bricks till they're spotless and try again - follow the instructions to the letter, they usually say you have 30 minutes to use a batch, I prefer a maximum of 15 minutes.

If you're not 100% confident in the background you could try a few coats of SBR cement slurry as a primer, again following the instructions, you really can't mix a bucketfull and spend the afternoon painting it on. You should extend it across the floor 300mm and pay particular attention to the wall/floor join - a small sharp sand and cement fillet (primed below) will fill any voids and provide a nice base for subsequent coats. You could render the whole walls before tanking but that's an expensive job unless you can do it yourself and you should find the SBR will do the job.

 

[Adam Bill]

@cdbe any idea how I go about stripping it all back to brick?

 

[freddiemercurystwin]

Personally I blame the workman. It hasn't failed because water has pushed it off the wall, it's failed because it hasn't adhered properly in places.

This stuff requires meticulous preparation. You need to strip it back to the brick, clean the bricks till they're spotless and try again - follow the instructions to the letter, they usually say you have 30 minutes to use a batch, I prefer a maximum of 15 minutes.

If you're not 100% confident in the background you could try a few coats of SBR cement slurry as a primer, again following the instructions, you really can't mix a bucketfull and spend the afternoon painting it on. You should extend it across the floor 300mm and pay particular attention to the wall/floor join - a small sharp sand and cement fillet (primed below) will fill any voids and provide a nice base for subsequent coats. You could render the whole walls before tanking but that's an expensive job unless you can do it yourself and you should find the SBR will do the job.

But you don't know anything about how it was applied or how meticulous whoever did it was. The OP could strip it, re-render then reapply the tanking meticulously and it may still fail again, if the pressure is too great. That's the big problem with this method, it's the cheapest solution if it works but the most expensive solution if it fails, like here and it all has to be re-done.