In article ,
Stephen writes:
Hello,

I have been stripping some wallpaper and some plaster has come of from
behind it. I did use a steamer, is this to blame? I would have thought
that a steamer would cause air bubbles trapped under the plaster
(between layers?) to expand and cause the plaster to crumble, so is it
a sign of the plaster being bad, rather than the steamer's fault? How
could a steamer damage good plaster?

I don't think I held the steamer too long in one place as three walls
escaped without injury but the fourth wall had a few areas where the
plaster fell off. It's only the top layer of plaster that fell off,
leaving a very sandy render underneath. I tapped it to see what was
hollow and picked off the loose bits by hand.

I used to buy Wickes ready mixed tubs for about £7 but they are now
nearer £12! I saw that a small bag of plaster powder was only a few
pounds so decided to try and mix my own.

The instructions were a bit vague so I wasn't sure quite what
consistency I wanted. I thought if it was too runny it might take
forever to dry and might slide off the wall. I thought if it was too
dry it might be lumpy and crack.

Drying and setting are two different things. The plaster must
stay wet until it has set, or it will stop setting -- setting
is a chemical reaction with the water. Once it's set, it can
then dry out, and it doesn't matter how long that takes.
Finish coat plaster is mixed up quite sloppy -- more sloppy
than you might imagine if you've not done it before.

I mixed some that seemed to apply ok but overnight it has cracked. I
understand this means it dried too fast. (I did not have any heating
in the room: the rad was removed for decorating).

Does this mean I need to make the mix a bit wetter next time?

You haven't said what plaster you used and how you applied it,
so it's difficult to help. Plaster shrinks as it sets (finish
coat particularly), so it will crack if applied too thickly.
2mm is probably about the safe limit for one finish coat.

How do I treat the cracks? Ca I just fill them with more
plaster/filler?

Plaster doesn't make a good surface filler. Use something
like pollyfilla.

--
Andrew Gabriel
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