Supports for concrete reinforcing mesh.

On Sun, 24 Jan 2010 17:46:11 +0000, "David WE Roberts" wibbled:

Many people use broken 1/2 bricks (about 2" up from base) or bits of roof tiles or paving slabs (good for 1" up).

I wouldn't be too pedantic. Unless you wire and support the mesh in a fairly thorough way, you'll just be glad if it all gets covered and most of it is approximately at the depth you intended. It's not a precise art unless you really go to town. The mesh may start out flat, but it will have a few undulations by the time the merchant has bent it, you've cut it and walked on it a few times and that makes it a difficult to be utterly precise.

In article , Tim Watts writes

That's a good summary.

Broken bricks do work in spite of looking a bit gash but people will stand on the mesh while the concrete is being poured and I think those plastic supports wont last 2mins.

FWIW, I think your 4" slab with mesh in the middle will be fine.

On Sun, 24 Jan 2010 22:34:52 +0000, fred wibbled:

That's an very good point. It's easy to forget that one must walk all over it whilst the pour is going down. When I did my shower room floor slab (3m2 in a confined space) I used broken 1" quarry tiles at regular grid spacings so I could guess roughly where to stand even when they were covered. It's slightly easier to stand in wellies on a bit of masonry than an unsupported section of mesh, though the mesh won't care either way.

I think those plastic chairs are intended for proper building site use where you have concrete pumps and long reach pokers and floating tools (ie can work from the sides) - not for a bloke with wellies and a shovel in hand.

Timber merchants Lawsons do a special cement jobby spacer for the purpose...Google Lawsons

Years ago, probably in the late 70s/early 80s, we used to make our own spacers on site using hand batched concrete (with 10mm maximum aggregate size) and tying wire - the stuff that was used to tie reinforcing bars together.

Yeah. That's more or less what the builders merchant (Jewsons) said. Certainly they don't stock any so they are not in common use. Half bricks it is, then. Can't help feeling that this reduces the integrity of the base of the concrete, though (but by how much?).

On Tue, 26 Jan 2010 12:53:15 +0000, "David WE Roberts" wibbled:

Deck of the QEII bridge - maybe. Your workshop - no. Stop worrying ;->