How to waterproof 1960s concrete slab & basement?

[boxer-brass_09]

  

  

 

 

 

  

I’ve got a late 1960s high set house, so the slab doesn’t have positive side waterproofing (pretty sure the original owners sorted the slab themselves).

The lower level isn’t legal height, but I’ve built another spare bedroom downstairs. Timber framed, gyprock sheeting, insulation. When the base plates for the stud walls were put in I didn’t put waterproofing down, so there is water coming up through the slab. The side walls have bitumen paint on them that seems to have worked. I initially did the same for the flooring, but with the rains back in early 2022, that was pushed up and had to be removed mechanically. Since then I put down Davco K11 - an alkali reactive cementitious waterproofing product. After Alfred came through recently, there was minor flooding coming through where the studs were drilled into the slab and under the studs. I know I’ll have to remove the baseplates of the studs and replace them.

I’m after advice on waterproofing products to use, whether or not the baseplates can be steel studs or I should go with timber again with adequate damp proof treatment between the timber and slab, or just any general advice. Waterproofing products would need to be negative side.

Thank you in advance!

[EricL]

Hello @boxer-brass_09 

It would be best to speak with a builder or waterproofing expert regarding these questions, as they fall outside the typical advice we can access from the manufacturer. I don't wish to advise you incorrectly, this type of repair falls under the scope of professional waterproofing experts. Their repair service will come with a guarantee which you can call upon should the waterproofing fail. 

Eric

[Nailbag]

Hi @boxer-brass_09 

I'm in agreeable with @EricL in that you're going to need some very expert advice here especially as much of the construction is illegally built. You're simply not going to get the right advice from an online forum as there will be lots of considerations outside our scope. Plus my top concern should anything happen to the home your insurance company will be looking for any excuse to void your claim.

Nailbag

[Dave-1]

Good Morning @boxer-brass_09 

I am thinking it may be a wiser choice to get a professional to step in over the general knowledge we have. As has been mentioned the specifics that you are wanting to do and what may need to be done beforehand is resonably large. I would err on the side of caution and have it rectified properly rather then a repair.

Dave

[boxer-brass_09]

Hi @Dave-1 @Nailbag @EricL @MitchellMc 

I’ve taken off the gyprock and sections of the stud work where the main problems were, and it looks like the culprit of water ingress was actually cracks in the mortar and insufficient application of the (wrong) product, rather than it coming up in the flooring. I’m going to have to mechanically remove the SikaTite BE, and I’ve been in touch with specialists who’ve recommended various Drizoro and Mapei products to fix the issues. Would anyone have any recommendations themselves for products that Bunnings stocks?

 

 

 

  

    

As an aside, I’ve noticed that Bunnings no longer stocks Drizoro products - would anyone happen to know why that might be?

[Dave-1]

Good Afternoon @boxer-brass_09 

Nice that you are narrowing in on the issue and its not coming up through the floor.

I dont know of any product you can put on this side of that wall that will stop water coming through, water will push out whatever you apply, sometimes slowly sometimes a lot faster but water will win.

I had the same issue with my garage leaking from water that was damming up on the outside brick wall that was covered in soil and builders debris

Fixing water ingress issues in garage  was how I stopped it and yeah it was a lot of work but after retrofitting my garage, no way did I want o loose that work,

Gabion Wall to stop water ingress to garage This was the retaining wall I built away from the wall so water couldnt run down the wall and enter by those very same mortar cracks/holes, mortar also is NOT waterproof lol

When I saw your wall behind the studs my head went to the same thing, water is building up like a dam and then either overtopping or forcing its way through. Or both 😕 The water can be subsurface water so it dosnt sit above the soil but the solution is going to be the same. And digging I would think will be involved 😕

You need to remove the soil behind that bessa block wall down to below the level of your slab in the garage, then seal it with that black bitument on the other side, You can backfill if you want after that depending on how you feel. The second part of the equation is what to do with the water that may build up in that area, do you have a low point outside the house you can knock a small hole in the wall for? If you leave the gap sealed but empty of soil for 6 months/a year you could determine if its only subsurface water or its inflow from storms.  I prefer dead man workings, (Something that keeps on keeping on even if you are not here ) so a pipe with external low point and probarly the wall left free. 

Dave

[EricL]

Hello @boxer-brass_09 

I'm sorry, but I am not familiar with the Drizoro and Mapie products. I agree with @Dave-1's recommendation especially if the water is coming from the other side of the wall. The soil will need to be dug up and the gaps in the masonry repaired. Looking at the picture it appears that fine sand has started to come through the gaps for the masonry blocks which is indicates that there are possible gaps on the other side as well.  

Once the wall has been exposed a waterproofing membrane such as Gripset Betta 1L Waterproofing Membrane Bitumen Rubber or similar can be used to seal off the entire wall. If you wish to take that extra step of protection you can emulate @Dave-1's solution as seen in Fixing water ingress issues in garage. It's an elegant solution to an otherwise troublesome issue. 

If you need further assistance, please let us know.

Eric