How to fill gap between concrete slab and external wall
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How to fill gap between concrete slab and external wall

by pe+e » Sun Jun 07, 2009 11:39 pm

The screed and concrete around the edge of my concrete slab (where the slab meets the external cavity wall) was cracked. I poked at it with a chisel and removed the loose material. this has left a channel of about 1" wide all the way around the edge of the wall.

I notice that the plastic DPM is doubled up/not pulled up properly to the top level of the slab. Therefore if i just fill the gap back in with concrete, it will be touching the brick that is below the wall's DPC...thus effectively connecting the slab to the damp side of the brickwork.

Given that this is only a couple of inches deep (although along about 5m of wall) should i just fill the gap back up with concrete and not worry about the potential for damp getting to the slab? Or is this a bad idea.

I thought about trying to paint a liquid DPM onto the brick before pouring the concrete in- but being only a thin gap, this would be very difficult.

Also considered using silicon to fill the gap- but this will use a good 10 tubes + and the floor will not be solid at this point. Are there any hard materials that i could fill the gap with that dont allow water to penetrate through?

or does anyone have any other ideas?

many thanks

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by stoneyboy » Fri Jun 12, 2009 8:24 pm

Fill it with a sharp sand/cement mix but make the mix fairly dry.

the specialist
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by the specialist » Mon Jun 22, 2009 6:53 pm

polymer modified water repellant cement. It wont crack or shrink and it works - I have used it several times for sealing a wall to floor joint. Triton Chemical sell it - They call it Triton Fillet seal. It's not cheap. The advantage of this over ordinary cement based products is that it copes with the differential movement all buildings experience due to warming up and cooling down (expansion and contraction)

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