How to waterproof garage wall?

[Rossute]

I have soil against garage wall with the garage slab below the ground level. In heavy rains I can see water seeping through the break wall. I was planning to dig a trench and put agi pipe around the garage walls. Just wondering how deep I need to dig and what is the process of water proofing the break wall from outside. Which products should I use?   Thanks.

 

[JacobZ]

Hi @Rossute,

Thank you for your question and welcome to the Bunnings Workshop community, it is great to have you with us.

It sounds like the problem is that the water is sitting in the soil and not draining away. Best practice would have the line of the soil well below the top of the slab, so any sitting ground water is below the level of the slab.

Lowering the level of the soil to below the slab would be the best way to reduce the water ingress, however a trench with agi pipe will help to bring down the water level in the soil and divert it somewhere else. 

I would suggest that the trench should be at least 300mm deep and filled with a base layer of compacted drainage gravel at least 50mm thick.

You would also benefit from applying Crommelin 2L Dampstop Concrete And Masonry Damp Surface Moisture Barrier And Primer to the outside of the brick below the soil line. This will prevent the water seepage through the brick diverting it to the agi pipe where it will subsequently be carried away.

Ideally, the agi pipe would be connected to a stormwater outlet so the water is drained away to the council stormwater services. This, however, would require the assistance of a suitably licenced plumber.

Let me know if you have any further questions.

Jacob

[Rossute]

Hi @JacobZ 

Many thanks for the response.  A few basic questions:

To lay an agi pipe, how deep the trench should be? Is it 300mm below the footing?

Do I need to use silicon between the footing and the first layer of bricks or Crommelin would be enough?

How should I apply Crommelin? Do I need to wash the bricks first and wait until they are dry? 

Is it better to use corflute after waterproofing?

Sorry for so many questions. 

Cheers, Ross

[JacobZ]

Hi @Rossute,

I've given 300mm as a general number that should cover most situations. It doesn't look like the concrete slab is too far below the level of the soil so this should be adequate for you. If the photo is deceptive and the concrete slab is much lower, then you would need to go deeper. The goal is to give the ground water a point below the brick line to drain to. If the drain is above the brick line, then water will still be present in the soil at the brick line, meaning it will find its way into the garage.

Silicone such as this Sikaflex 11FC Plus between the bricks and slab would also be beneficial as it is adding another layer of protection that will stop the water finding an entry point.

The bricks should definitely be cleaned down, preferably with a pressure washer, but if you don't have one available to you, a stiff bristled brush with hot soapy water should be fine. The idea is to remove any loose material or dust that can limit the waterproofing membrane's ability to stick.

Once clean, paint the Cromellin Dampstop on following the manufacturer's instructions for best results. The idea is for the membrane to form one solid barrier the full length of the wall which will stop the water touching the bricks making it run down into the drain. 

In other situations that are different to yours I would recommend corflute, but in your situation the Cromellin's Dampstop should be adequate by itself.

No need to apologise for asking questions, that's the goal here. If I can answer your questions, it will help you, and may help others in the future.

Let me know if there's anything else I can assist with.

Jacob

[JacobZ]

Hi @Rossute,

Just to add to my earlier response, you might also like to check out How to install garden drainage for some guidance on installing the drain.

Let me know if you have any further questions.

Jacob

[Rossute]

Thanks @JacobZ . I will follow your suggestions. 

For the water proofing product, I also came across this: 

https://www.bunnings.com.au/gripset-betta-4l-bitumen-rubber-waterproofing-membrane_p0960166?store=62...

Any difference between this and Crommelin? 

[JacobZ]

Hi @Rossute,

The Crommelin Dampstop I have linked to is specifically formulated for use on concrete and masonry substrates, this is why I linked you to this product.

The bitumen waterproofing membrane that you've linked to is a general use waterproof membrane that can be used in a variety of applications including this one.

In hindsight, the product you have linked to is likely more cost effective and easier to use in your application as it is thick and can be painted on whereas the Dampstop is far more liquid. I would suggest the bitumen waterproofing membrane is the way to go, but be aware, it is extremely sticky and will not wash out if you get it on your clothes. Make sure to wear some old work clothes that you can afford to live without as well as gloves and a mask to avoid fumes.

Let me know if there's anything else I can assist you with.

Jacob

[Rossute]

Appreciate it @JacobZ . One final question, how deep I should dig the trench? Does it need to go below the footing? 

[MitchellMc]

Hi @Rossute,

@JacobZ mentioned that he recommended the trench be 300mm deep, which I'd agree with. It doesn't specifically need to go below the footing, but 300mm is a good depth to capture both surface and sub-surface water.

Mitchell