I'm fitting a mirror in my bathroom which, due to the lights built into
it, is designed to be recessed into the wall. So, by Aldi Fein-alike and
SDS, I'm cutting out a wide shallow space in the wall. Most of the depth
is taken up by tile and plaster, but I am taking off a very thin layer
of the hard concrete block that forms the wall itself.

Does the group think it's worth somehow sealing the face of the block?
There shouldn't be any actual splashing water here, but it's a bathroom
with a sometimes very humid atmosphere. Or am I worrying about nothing?

Cheers,

Pete

On Sat, 17 Oct 2009 13:40:35 +0100, Pete Verdon
d wrote:
I'm fitting a mirror in my bathroom which, due to the lights built into
it, is designed to be recessed into the wall. So, by Aldi Fein-alike and
SDS, I'm cutting out a wide shallow space in the wall. Most of the depth
is taken up by tile and plaster, but I am taking off a very thin layer
of the hard concrete block that forms the wall itself.

Does the group think it's worth somehow sealing the face of the block?
There shouldn't be any actual splashing water here, but it's a bathroom
with a sometimes very humid atmosphere. Or am I worrying about nothing?


I think that would be wise. I would probably use bitumastic paint,
but it might be subject to condensation. Perhaps a skim of plaster
over the cut block, and several coats of emulsion paint?

PVA is not suitable, because the adhesive "re-activates" when wet. SBR
is waterproof but too expensive by virtue of its 5L unit quantity.

Mapei Primer G is a good water resilent primer, priced at £4 from
Screwfix - basically not much more expensive than PVA. Mapei Primer S
is a fully waterproof version, but you're not planning on a swimming
pool I assume :-)

If you can, consider getting a quiet humidistat controlled fan in the
bathroom. Whilst some condensation will still occur since it can't
keep pace, it will reduce it somewhat.

The lights incidentally will provide some heating which may mitigate
condensation (just a thought).

js.b1 wrote:

Mapei Primer G is a good water resilent primer,

Ah ha! I actually have a few bottles of that in the shed left over from
the tiling. Of course, I've installed the mirror frame in the cavity now
so it won't be quite as easy to apply, but if the consensus is that I
need something that's probably what I'll use.

If you can, consider getting a quiet humidistat controlled fan in the
bathroom. Whilst some condensation will still occur since it can't
keep pace, it will reduce it somewhat.

Yep - got one, but not wired up yet. (Actually, it's not humidistat
controlled, it's on an overrun timer off a flow switch in the shower
supply, but same idea.) Hopefully once that's in action there'll be less
condensation about.

The lights incidentally will provide some heating which may mitigate
condensation (just a thought).

Indeed, the lights (fluorescent tubes, so presumably not *hot*) are
supposed to be warm enough to stop the mirror fogging.

Pete