Options for waterproofing the inside of a concrete block garage

Forums › Home Workshop DIY › Options for waterproofing the inside of a concrete block garage

joshtnx

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#303139 19-Jan-2023 11:30

Hi all. Browsing through the diy Reddit and these forums I have seen a range of advice on waterproofing the inside of garages/concrete walls. Example photos of the walls are here: [https://imgur.com/a/zog4MK8] - these are just small sections as I need to move a bunch of shelving etc.

While eventually I'd also like to do work on the outside, the garage is hard up against the neighbour's boundary and garden, so am focusing on internal options for now that I'll be able to do this summer.

Water seeps in both at the join with the concrete floor, but also down the walls, in heavy rain. I basically want a product that will minimise this, if not entirely eliminate it. I need to do two of the full garage walls (approx 6mx3m) so am also looking for something relatively affordable. I also know I need to be looking for something that is appropriate for negative pressure waterproofing. I'm not super handy, so something that can be applied by a total novice would be ideal.

Previous posts (e.g. here: https://old.reddit.com/r/diynz/comments/zr0qb2/filling_crack_in_concrete_stop_water_getting/) suggest a combo of products including hydraulic cement and a waterproofing paint. This post focused more on the exterior of the garage: https://www.geekzone.co.nz/forums.asp?forumid=141&topicid=161817

I've also found this interesting Cemix product Aquastop which looks ideal as my garage walls are cinderblocks. I am currently leaning towards this. A bit more info here https://www.cemix.co.nz/products/aquastop/

I guess my questions are:

what products would you recommend?

what prep do I need to do for the walls? (waterblast, scrub, etc)

is there anything I should definitely avoid doing?

Any advice would be great thanks in advance

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#3023662 19-Jan-2023 11:48

my Dad used like a black tar (sika product) that you brush on which has done well for a similar issue

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Silvrav

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#3023664 19-Jan-2023 12:01

This is the heavy duty stuff, which you could apply outside as well - there is a video down below that show you prep and application - https://nzl.sika.com/en/diy-trade/waterproofing/basements/concrete-block-concreteexteriorwalls/sika-blackseal-elastic.html

timmmay

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#3023668 19-Jan-2023 12:18

Sto Protect or similar is clear. I used it outside over existing artwork on a concrete block wall and it seemed to help. Not sure how useful it is, given you will likely drive a wet car into the garage anyway, making the whole place fairly damp.

timmmay

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#3023772 19-Jan-2023 12:48

Also, if you manage to keep the water in the wall, the wall will fill up with water. It might drain out somewhere, outside maybe, or may sit there. I'm not sure that's an improvement on draining.

Bung

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#3023870 19-Jan-2023 13:07

Is the neighbour's garden built up against the wall? How does the roof meet with the wall? Does the top of the wall have a flashing? Is there an internal gutter?

Slasher

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#3023888 19-Jan-2023 13:26

Good water blast/scrub and acid wash before applying any of these in general, some products have specific wall prep instructions.

If you have no option to remediate from the outside, the best option would be to use something like Xypex which seeps into the concrete pours and seals it. However, this is not sold to the public and needs a trained applicator. Thinking long term solution.

joshtnx

19 posts

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#3023901 19-Jan-2023 13:48

Bung: Is the neighbour's garden built up against the wall? How does the roof meet with the wall? Does the top of the wall have a flashing? Is there an internal gutter?

That's the roof of the side at the neighbours. The garden is slightly built up, probably six inches or so and the leaking is definitely worse in those areas. Very minimal flashing. But the main leaking is seepage through the wall rather than from the top (as far as I can tell).

No internal gutter. The roof is slightly sloped to the south and there's a gutter on the south running West to East.

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joshtnx

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#3023902 19-Jan-2023 13:50

timmmay:
Also, if you manage to keep the water in the wall, the wall will fill up with water. It might drain out somewhere, outside maybe, or may sit there. I'm not sure that's an improvement on draining.

Yep, this is definitely a concern. Longer term I'd like to dig and waterproof from the exterior and lay some drainage too, but trying to find relatively affordable options for at least reducing the seepage through the interior at the moment. It's definitely not ideal!

joshtnx

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#3023904 19-Jan-2023 13:54

Slasher:
Good water blast/scrub and acid wash before applying any of these in general, some products have specific wall prep instructions.

If you have no option to remediate from the outside, the best option would be to use something like Xypex which seeps into the concrete pours and seals it. However, this is not sold to the public and needs a trained applicator. Thinking long term solution.

Yeah the cemix product seems to me the best consumer-grade version of something like that - but definitely not a permanent or perfect fix. Longer term I do want to waterproof the outside of the garage for sure.

mrdrifter

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#3023938 19-Jan-2023 14:45

I was recommended to try the Regis Coatings Duromastic HiBuild for Negative Pressure protection. https://www.regiscoatings.co.nz/Products/Instance/Waterproofing/Duromastic-EP-Hibuild/ . It was easy enough to apply a couple of coats following their instructions. I had to do 60sqm of floor with two coats and so far seems to be doing what I need. For walls I would be keeping an eye on where the water will find it's next weak spot though.

mdf

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#3023952 19-Jan-2023 14:54

You're definitely on the money with the negative pressure point. There are a few products available for this, but the key requirement for most is that the wall hasn't been treated or painted previously. I've just been through this with a painted concrete block wall and ended up doing it with the Cemix Aquastop product you mentioned. This was the only product I could easily find that was at least a little tolerant of previous coatings. Everything else wanted something pristine. I spend a very long time painstakingly heat gunning and scraping off the majority of the previous paint (and diamond grinding the worst bits) but impossible to get it all.

Aquastop itself was pretty straightforward to use and gave a pretty good finish. You can overcoat it with paint afterwards. But do watch the application videos on youtube - for best results, you need to apply a coat in one direction only (i.e., left to right, not left and right) then another coat at 90 degrees to the first. This wasn't completely possible in my situation and was very difficult in terms of muscle memory of how to apply, I very much wanted to paint backwards and forwards. Kind of weird stuff to apply too, it was sort of a foamy toothpaste consistency but I sort of troweled it on with a wide brush.

Technofreak

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#3024020 19-Jan-2023 15:29

For my money I'd be putting my efforts into doing the outside. Anything thing going on the inside is not going to last as well as it should with moisture pushing through from underneath. Sealing the outside will give you the best long term outcome.

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johno1234

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#3024023 19-Jan-2023 15:38

I don't have any optimism that waterproofing the inside will work, long term. The right way to fix is to dig down below the floor slab the length of the garage walls outside and put a drain in.

I realise that this might not be possible though, unless your neighbour is cooperative.

Or, if you are lucky, there might be a drain already there that is just blocked... in which case a CCTV drain unblocker might be able to get it working again.

Bung

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#3024041 19-Jan-2023 15:53

Internal treatments can work. Years ago a cousin had a block wall pit in his garage that was sealed with Aquella, supposedly developed to waterproof the Maginot Line, and that stopped the water.

I'd be looking at the flashing on top of the wall. Weeds are growing, it could be full of holes.

johno1234

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#3024172 19-Jan-2023 18:41

Trouble is, if water is building up behind the wall it is going to build hydrostatic pressure. It will perpetually try to find a way through, even if it has to push the coating off the wall. A membrane on the outside encourages the water to find a path of less resistance.

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