"Lobster" wrote in message
...
I've got an old brick shed with a concrete slab roof; watertight at the
mo, but in one corner (external) the surface of the concrete has broken
up under the influence of weather; probably an inch deep? in a 4-5 inch
slab. Think it's got visibly worse over the winter.

If this was an indoor repair, I'd be brushing out the loose stuff,
treating with PVA solution, put some shuttering around the corner, and
then fill and seal with mortar or concrete; however PVA presumably won't
cut the mustard here.

So how would this best be repaired? I'm sure some form of treatment of
the old surface would be in order, but what? And can I use just a
sand/cement mix (easier) or would concrete be needed?

Cheers
David

Knock off any loose concrete

Wire brush any steel you can seal and paint it. With hammerite or similar if
you have some.

erect your formwork.Not forgetting there may be a 'throat' on the underside
to stop water tracking back to the walls.

mix sand, cement and grano with diluted PVA in the water.

Spay some WD40 on the inside of your formwork and fill with the grano mix.

Tap sides of formwork as you fill and trowel of level with roof.

When dry, 48 hrs. Strip form.

Clean rest of roof and apply bitumen type sealant to whole roof.