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Do you need mesh or rebar for a small concrete void?

I've hear conflicting stories on this, so need advice from locals.

I've recently removed a bathtub and had the plumbing capped, and now need to fill the void with concrete. The area to fill is small, just 1.4m x .85m and after compacting it will be around 10cm deep.

My plan is to concrete up to about 10mm short of the height of the existing tiles, and and then use levelling compound for the remainder so it's as close as possible to the existing floor (and then extend the existing tiling).

My question is: Do I really need to mesh or rebar first? Some forums say yes, some say no if the area is small.

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MitchellMc

Will you be using tile underlay on this area once filled, @mikeyo?

There's no harm in popping in some reo mesh and it will certainly assist with the structural integrity. However, the more important thing to consider is whether you are going to experience movement in this area that could cause the tiles or grout above it to crack. What probably should happen here is that you drill into the existing slab on all sides and chemically glue in a rebar that extends out into the new slab. This joins it to the old and ensures it doesn't move. Say, for instance, your new slab section sinks as it is unsupported, all the tiles and grout above the joints will crack.

Personally, I would add reo mesh and tie it to the rebar you've anchored into the surrounding slab. Sounds like a bit of overkill, but much better than having to rip it all up again to fix the issue in the future.

Please let me know if you have any questions.

Mitchell

mikeyo

Thanks, that's helpful. I don't anticipate any movement in the area (we built about 15 years ago, no issues so far), but I also know that's not a guarantee something won't happen in the future.

I forgot about the underlay. I'm assuming the order is...

concrete
levelling compound
underlay adhesive
underlay
tile adhesive
tiles

Please correct me if that's wrong.

MitchellMc

That's the correct method @mikeyo.

It's not so much about the movement of the house, more so that you have two separate slabs. Any time you have two concrete slabs next to each other they move independently and require an expansion joint to accommodate this or they need to be mechanically joined together so they move as one. This is less of a concern since you'll be using tile underlay.

Mitchell

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