How to waterproof base of rendered blueboard?

I have installed blueboard sheeting to the exterior of an old garage, sealed the corners and joins, and then rendered it. It looks fantastic but I am getting water penetrating under the sheets into the garage. The blueboard sheets sit directly on top of the concrete foundation which is about 30-40mm above paving surrounding the garage. I have not installed any weatherproofing/dampcourse and this is what I've been told I need to do. How can i go about this with everything already in place whilst also meeting required build code requirements for South Australia?

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MitchellMc

Welcome to the Bunnings Workshop community @BenR. It's splendid to have you join us and many thanks for your question on waterproofing a wall.

It sounds like the water is wicking up or finding its way in where the bottom edge of the blueboard meets the slab. Normally, those sheets should be held slightly clear of the concrete with a flashing or dampcourse in place to prevent exactly this issue.

Can I just check whether you’ve left any gap between the bottom of the sheets and the slab, or are they sitting hard down on the concrete? If there is a gap, you could look at sealing it with a flexible, exterior-grade product such as Sikaflex 11FC or a similar polyurethane sealant. That would help stop water tracking in at the base.

That said, because you’ve already rendered the sheets and they’re sitting directly on the slab without a dampcourse, you’re right to be thinking about compliance. The safest step now is to seek advice from a qualified builder. They’ll be able to confirm what, if anything, can be done to retrofit a compliant barrier or flashing to meet code requirements. Sometimes a simple sealant will help manage the water, but for peace of mind (and to avoid future damage), it’s worth getting professional guidance.

Please let me know if you have any questions.

Mitchell

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