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!

[boxer-brass_09]

Hi Dave,

The efflorescence on the flooring is from when I put down vinyl backed carpet tiles. When I realised what was happening between them and the slab they were gone pretty quickly and replaced with rugs. The only thing between the Davco K11 and them was Davco 173 floor leveller. It always thought it was a result of temperature differences between the slab, vinyl backed carpet tiles and the room itself.

When you say the concrete squares, do you mean the many smaller slabs that make up the big one?

Would you have any advice on any products to use, and/or an order to to it all in?

Thanks in advance!

[Dave-1]

Good Evening @boxer-brass_09 

Yes I was talking about the many smaller slabs making up the larger one and sadly I dont know what you could use to seal between them as its only going to seal the top and not the sides.  😕 

The only time ive seen efflorescence like yours was from water pushing through the concrete more then sitting on top and then draing away. I dont think the vinal backed tiles would cause that look. I have had the same issue with my garage right down to the vinyl backed carpet tiles getting super wet/going under and the concrete didnt have the efflorescence look (my water came through the soil outside and then through the brickwork.)

One of the other members may have a suggestion on how to seal the concrete blocks, but remember its going to be a multi pronged solution I would suggest.

Dave

[EricL]

Hello @boxer-brass_09 

In your second proposed option - Take out the baseplate studs, put waterproofing on the slab, then damp proof course and H3 timber, then refit some villa board or wet area gyprock in the lower levels. Unfortunately, I'm not aware of a product that can withstand extreme hydrostatic pressure. Your concrete floor is showing signs of strong water ingress and anything placed on its surface will meet up with that hydrostatic pressure and get peeled off. 

Waterproofing is only effective if it is applied on the correct side or surface. In this instance it's highly probable that putting a waterproofing membrane on top of your floor will get pushed off. 

Eric

[boxer-brass_09]

Hi @EricL and @Dave-1

Thank you for your responses.

Davco/Lanko K11 is what I used for waterproofing the main area (I didn’t do below the studs because they’d been installed before I knew better). It’s a cementitious Class 3 membrane that reacts to water present and forms crystals, essentially creating a uniform slab. Sika K10 or Sikalastic are other options sold by Bunnings, or were last time I checked. 

Excavating the external side and waterproofing is the ideal option, but not feasible right now as the aircon unit is on the ground not on the side of the building.

[Dave-1]

Afternoon @boxer-brass_09 

As in interm measure then I would try and create a way the water will flow away from the edges of your building as much as possible until you go through the steps you want.

Dave

[boxer-brass_09]

Hi @Dave-1,

There isn’t much I can do at the moment, unfortunately. 

In terms of products that would be suitable, I’ve been looking at Sikalastic 1-Komponent and Dunlop Damp-proof Waterproofing. I’ve also come across Gripset Betta Water Plug.

Would you have any recommendations between the these, or any other products?

[Dave-1]

Good Evening @boxer-brass_09 

I just had look at the Dunlop 4L Damp-Proof Waterproofing you mentioned and the first part that jumped out at me is

"An acrylic brush-on membrane, Dunlop Damp-Proof Waterproofing will prevent rising damp, efflorescence and will resist negative hydrostatic pressure"

This I thnk means that it would go on the soil side of the wall to stop water coming through. 

I have only used a thick black tar like substance to stop water traveling through the soil then brickwork into my garage It worked but it was messy. I had also permantly removed the soil from against the outside of the wall. 

Fixing water ingress issues in garage and in particular Gripset Betta 4L Bitumen Rubber Waterproofing Membrane This is the black tar like substance, Its meant to go on the soil side so water dosnt get a chance to seap through the brickwork. I only include it as an example of how a negative hrdrostatic material works. A positive one (which I dont know of any 😕 )you could paint on the inside of a wall to hold back the water.

I dont have any other knowledge of types of products that you could use. @EricL , @MitchellMc may.

Dave

[MitchellMc]

Hi @boxer-brass_09,

As I mentioned in the beginning of this discussion, Sika 10kg Sikalastic Waterproof Membrane (1-Komponent) would be a suitable product to use. It's suitable for inside waterproofing of negative water pressure of walls and floors in basements.
 

Remember, the entire floor needs to be coated, even under the walls. 

Mitchell

[boxer-brass_09]

Thank you @MitchellMc 

I spoke to a concrete specialist who recommended using that and Xypex in the problem areas and wall/floor joints. I can’t find who sells Xypex in Brisbane, or if there is a similar product sold by Bunnings?

[MitchellMc]

As that product is not something we sell @boxer-brass_09, it's difficult for me to suggest an equivalent. Sikalastic can also be used on joints between walls and floor when used in conjunction with Sika SealTape S. However, in speaking with Sika again, since the moisture is pushing up from below, they recommend enlisting the services of a professional.

Mitchell