How to fix gap between outdoor concrete slabs and the house?

Terrancele

The concrete slabs outside the house have tipped down overtime, which created a 2cm gap with the house as in the photo.

Should I do something about it? Please guide me through: some video would be great and what materials to use. Many thanks.

The gaps collect falling leaves and ants runjing somewhere down there too.

MitchellMc

Welcome to the Bunnings Workshop community @Terrancele. It's fantastic to have you join us, and many thanks for your question about gaps.

What you’re seeing there is fairly common as slabs settle away from the house over time, and while it’s not usually structural, it is worth sealing. Leaving the gap open allows water, debris, and insects to collect right against the wall, which can lead to damp issues and ongoing pest problems.

The usual fix is to treat it like an expansion joint rather than trying to pack it solid. Push a gap filler rod down into the gap so it sits below the surface. This takes up most of the depth and stops you wasting sealant, while also allowing some movement between the slab and the house. Once that’s in place, apply a flexible polyurethane sealant such as Sikaflex 11FC over the top, tooling it so it bridges cleanly between the concrete slab and the wall. This creates a weatherproof, flexible seal that won’t crack as things move.

Before sealing, clean the gap out thoroughly so there are no leaves, dirt, or ants left inside, and make sure it’s dry. The finished joint will stop debris building up and block insect access, while still allowing the slab to move independently of the house.

There’s a very helpful step-by-step guide on How to fill a joint in a concrete slab, which shows the exact process and tools used, and it’s well worth a look before you start.

Please let me know if you have any questions.

Mitchell