On 8 Nov 2005 01:27:02 -0800, wrote:

So are
you saying under the plaster there are just slats of wood? How can I
really tell for sure?

What do you mean by a "crumbly wall" ? If you poke a hole into it,
what do you find ? (the first 1/2 is always likely to be plaster and
doesn't count).

Thick grey or pink plaster - this is just thick plaster, impossible to
hang a weight off . You need to drill deeper.

Grey cement block dust, where the material is to hard to push a steel
spike into by hand. These are breeze blocks. They'll take a screwed
fixing and a reasonable weight, but usea plug that doesn't expand too
much or else you can crack them.

Red brick dust, hard or soft. This is brick and you should get a firm
fixing into it. Crumbly bricks will form oversize holes and will need a
"sticky" plug material in them, not just a plastic plug.

If you hit dark mortar on some holes, you've drilled betweem two bricks.
Best to simply move along a bit and try again.

Open airspace, or wood fragments. This is lath and plaster. It's very
dificult to hang a heavy shelf off it, but you can use toggle fittings
to hang something light, like a light fitting.