Plaster Skim Tips
 

I have been practicing skimming onto some scrap pieces of plaster
board which I have taped together and temporarily fixed to a wall.

I'm using Thistle Multi-Finish and was hoping for a few tips.

1) One coat or two ? From other postings in this group it would seem
that you should apply two coats in fairly quick succession. This will
increase the time it takes to dry out and give you more working time.

2) How long to wait between applying the second coat and starting to
polish ? Does this just come down to experience ? I probably waited
about 1/2 hour.

3) When you are polishing should you be using the trowel flat against
the wall or at an angle ?

4) During the polishing I seem to keep ending up with a small amount
of sludge on the trowel which constantly needs to be cleaned off. Is
this normal ? I am keeping the trowel wet and using an old paint brush
to dampen the plaster on the wall before polishing ?

5) Does the plaster change colour once it's polished ? Seemed to turn
a bit darker after a few passes of the trowel.

Any help is much appreciated. The ultimate aim of this "practice" is
to skim a plasterboarded ceiling. Is this much more difficult than
working on walls ?

Plaster Skim Tips
 

Best tip is to use Gypsum Easy-Fill for the final coat. About five times
more expensive in B&Q (£10/10kg) but a hundred times easier to get a good
result. Also it is a lot stickier so you plaster the ceiling, not yourself.


"Andy Hide" wrote in message
m...
I have been practicing skimming onto some scrap pieces of plaster
board which I have taped together and temporarily fixed to a wall.

I'm using Thistle Multi-Finish and was hoping for a few tips.

1) One coat or two ? From other postings in this group it would seem
that you should apply two coats in fairly quick succession. This will
increase the time it takes to dry out and give you more working time.

2) How long to wait between applying the second coat and starting to
polish ? Does this just come down to experience ? I probably waited
about 1/2 hour.

3) When you are polishing should you be using the trowel flat against
the wall or at an angle ?

4) During the polishing I seem to keep ending up with a small amount
of sludge on the trowel which constantly needs to be cleaned off. Is
this normal ? I am keeping the trowel wet and using an old paint brush
to dampen the plaster on the wall before polishing ?

5) Does the plaster change colour once it's polished ? Seemed to turn
a bit darker after a few passes of the trowel.

Any help is much appreciated. The ultimate aim of this "practice" is
to skim a plasterboarded ceiling. Is this much more difficult than
working on walls ?

Plaster Skim Tips
 

In article ,
(Andy Hide) writes:
I have been practicing skimming onto some scrap pieces of plaster
board which I have taped together and temporarily fixed to a wall.

I'm using Thistle Multi-Finish and was hoping for a few tips.

1) One coat or two ? From other postings in this group it would seem
that you should apply two coats in fairly quick succession. This will

I usually apply 2 coats, but I'm rarely working on a surface as
good as new plasterboard. I have done just one coat when the
underlying surface was good, and that one coat went on well.

increase the time it takes to dry out and give you more working time.

That's not the reason (and I don't think it's actually true either).
When you do 2 coats onto rougher surfaces such as a scratch coat,
the first coat goes on and pretty much fills in the surface bringing
it all up to the level of the highest peaks on the surface. You
couldn't polish this because in places it will be level with the
peaks of the scratch coat. The second coat then goes on to make
sure there's a layer of finish plaster over the top of all the highest
peaks in the scratch coat, and this can be polished without the
scratch coat peaks showing through.

2) How long to wait between applying the second coat and starting to
polish ? Does this just come down to experience ? I probably waited
about 1/2 hour.

You start by just getting the plaster on the wall, as evenly as
possible, but ignore the trowel marks which you can't do anything
about at this stage. When the plaster has gone off a little and
got a bit thicker, you will be able to re-trowel the surface and
produce smaller trowel marks -- if you can't, then leave it a bit
longer. At each stage in the 'going off' process, you will be able
to improve the surface a bit, but no more. An important part of the
process is not to carry on trying to improve the surface past what
is possible at any particular point in the 'going off' process -- all
that can do is make it worse. You must leave it to 'go off' some
more before you can improve on it any more. Constantly over working
an area in an effort to try and improve it is a very common reason
for poor outcome.

It's impossible to give timings -- depends on temperature, age of
plaster (how long in storage), how you mixed it, how long before
it went on the wall, absorbancy of the wall, phase of the moon, etc.

3) When you are polishing should you be using the trowel flat against
the wall or at an angle ?

Always at an angle. If you accidently get the trowel flat on the
wall, you'll be very lucky if you get it off without yanking off
a trowel shaped chunk of plaster.

4) During the polishing I seem to keep ending up with a small amount
of sludge on the trowel which constantly needs to be cleaned off. Is
this normal ?

Yes -- actually it's extremely valuable for filling in blemishes.
Polishing is all about scraping off the minute peaks and dropping
them into the minute troughs in the surface, so you don't want to
be wiping too much off the trowel -- it's part of the polishing
process.

I am keeping the trowel wet and using an old paint brush
to dampen the plaster on the wall before polishing ?

That's fine.
A misting spray can be useful too, although a professional wouldn't
be seen dead with one -- accurately aiming the water from a distemper
brush is more professional;-)

5) Does the plaster change colour once it's polished ? Seemed to turn
a bit darker after a few passes of the trowel.

No -- the change in colour is the plaster going off. It will
happen regardless of you polishing it -- it's a chemical reaction.
The plaster goes back to the lighter colour when it dries out
(which is nothing to do with hardening, except it mustn't dry out
until it has fully gone off).

Any help is much appreciated. The ultimate aim of this "practice" is
to skim a plasterboarded ceiling. Is this much more difficult than
working on walls ?

The hard part is stepping back to see how you're doing...

--
Andrew Gabriel

Plaster Skim Tips
 

Many thanks for the useful advice. My practice session proved most
successful and I was pleased with the results. However, things have
gone downhill since then. I had another go last night and something
has gone very wrong. As I spread the plaster across the board I am
getting scratch marks. It appears that the plaster has gone gritty and
the small pieces of grit are leaving scratch marks as I move the float
across the board.

I've concluded this could be because:

1) Plaster not mixed properly. I tried adding more water but this did
not seem to help. I threw out one mix and started again. Same problem.
Bucket was fully washed out between mixes.

2) Plaster has gone off. The bag of plaster was left open inside the
house without being covered up. Would it go off in a day ? The house
is not damp.

I am determined to master this!

Plaster Skim Tips
 

In article ,
(Andy Hide) writes:
Many thanks for the useful advice. My practice session proved most
successful and I was pleased with the results. However, things have
gone downhill since then. I had another go last night and something
has gone very wrong. As I spread the plaster across the board I am
getting scratch marks. It appears that the plaster has gone gritty and
the small pieces of grit are leaving scratch marks as I move the float
across the board.

I've concluded this could be because:

1) Plaster not mixed properly. I tried adding more water but this did
not seem to help. I threw out one mix and started again. Same problem.
Bucket was fully washed out between mixes.

2) Plaster has gone off. The bag of plaster was left open inside the
house without being covered up. Would it go off in a day ? The house
is not damp.

Most likely you did not completely clean your tools.
When I mix plaster and pour it out of the bucket onto the
board, I then immediately go and clean the mixing bucket
and wisk, before even applying the plaster. It's easy at
that point, and the plaster can happily wait the extra
time.

Other possibilities are that your mixing technique left
some dry plaster around the top of the bucket, on the
wisk, or at the bottom which you didn't mix in. The
surface you plaster onto is unstable -- seal it with
PVA first (not applicable if you are still using
plasterboard). This might be from one of the surfaces
you are plastering up against, rather than the one you
are directly working on too. There's some other source
of contamination with dust. One amusing(?) one I've had
is plastering a wall which runs up to an artexed ceiling,
where the artex is in the form of small stalactites. I
found it very difficult to avoid breaking these of and
dragging them down the wall when working along the top
edge...

When you pour the plaster out of the bucket onto your
plastering table, work the plaster on the table a bit
with the trowel. This is useful to check you don't have
any lumps, but also any grit in the mix should come to
light at that point too.

--
Andrew Gabriel