How to repair concrete?

Question

Hi

I had a leaking pipe that required fixing. By coincidence it is next to 2 different concrete pours merging with lots of movement.

Appreciate tips for tools, concrete type, power of grinder required, float types, whether some concrete should be knocked out from hole. Etc etc really  - essentially tools, products and methods. Thank you.

MitchellMc · Answer

Hi @BigCheesey,

There's always movement between slabs and that is why an expansion gap has been added there. It's a small gap to allow movement and prevent an unsightly crack in that area. The expansion gap is visually intrusive but is required.

Expansion gaps are filled with a flexible filler like Sikaflex 11FC. Generally, this filler sits below the surface and can be a bit of a dirt and debris trap. What was the issue you wished to repair? Did you want to fill the area to prevent leaves from being trapped? Apart from that, there's no repair as such required.

Filling the expansion gap with anything non-flexible, like mortar, would most likely result in the patch cracking and falling out, due to the movement.

Please let me know if you have any questions.

Mitchell

BigCheesey · Answer

Thanks Eric. I’ll look for a smaller mortar bag as the hole isn’t too big. Any suggestions please on what is required to address the other issue, which is the movement between the two slabs? For wattage grinder/disc/filler required? My Bunnings shopping list will be sure to grow.

EricL · Answer

Hello @BigCheesey

Welcome to the Bunnings Workshop community. It's sensational to have you join us and thanks for sharing your question about patching your concrete slab.

I suggest removing all the debris and dust in the cut-out section of the slab. The hole must be totally empty, and any loose or compromised concrete will need to be removed as well. I propose using Dunlop 1L Multipurpose Water Based Primer to prime the cut face of the concrete slab. Once the primer is ready, I suggest using Dingo 10kg Mortar Mix. Before putting the mortar into the cavity, I recommend putting a square piece of cardboard on the left-hand side of the hole (2nd picture). Spray the cardboard surface with WD40 and then put the mortar into the hole. The WD40 serves as a release agent and will not stick to the mortar. Once the mortar dries, pleas remove the cardboard divider.

The reason for the cardboard is to provide a gap between the slabs. This will prevent your patchwork from cracking should there be any movement in the slab. I suggest using a Trojan to a150mm Pointing Trowel to mix and level the mortar.

Please remember to wear personal protection such as gloves, goggles and a mask.

If you need further assistance, please let us know.

Eric