Hi All

Just wondering if any of the more experienced out there know if its ok
to repair blown patches of original sand / cement under coat plaster
with thistle hardwall?
I need to repair several large patches which will be taken back to
bare brick before skimming the whole walls. Not sure if this will just
crack at the join?
Hoping to save a little time and effort by not having to hand mix up
loads of sand / cement under coat (plus a friend has some spare bags
of thistle hardwall going free!)
Obviously this will be a massive false economy if it all cracks after
skimming! so any advise before i start will be much appreciated

Mike wrote:
Hi All

Just wondering if any of the more experienced out there know if its ok
to repair blown patches of original sand / cement under coat plaster
with thistle hardwall?

You can use hardwall, or any of the other thistle backing plasters -
browning, bonding etc

I need to repair several large patches which will be taken back to
bare brick before skimming the whole walls. Not sure if this will just
crack at the join?

You need to damp down the brickwork before starting, and where the patch
ends and the existing plaster begins, give this a coat of PVA, so that any
backing plaster that gets onto the existing wall is well adhered.

Hoping to save a little time and effort by not having to hand mix up
loads of sand / cement under coat (plus a friend has some spare bags
of thistle hardwall going free!)
Obviously this will be a massive false economy if it all cracks after
skimming! so any advise before i start will be much appreciated

Skimming sticks to almost everything, but the existing plaster will need a
coat of PVA prior to commencing.

NB. New backing plaster like this should be skimmed the same day, or the
next day at the very latest....any later than that and the skimming dries up
and cracks off almost immediately.

--
Phil L
RSRL Tipster Of The Year 2008

In article ,
"Phil L" writes:
Mike wrote:
Hi All

Just wondering if any of the more experienced out there know if its ok
to repair blown patches of original sand / cement under coat plaster
with thistle hardwall?

Yes, unless the wall is damp, in which case you can't use any
gypsom based scratch (under) coat. It might have been done with
sand and cement originally for this reason.

You can use hardwall, or any of the other thistle backing plasters -
browning, bonding etc

I need to repair several large patches which will be taken back to
bare brick before skimming the whole walls. Not sure if this will just
crack at the join?

You need to damp down the brickwork before starting, and where the patch
ends and the existing plaster begins, give this a coat of PVA, so that any
backing plaster that gets onto the existing wall is well adhered.

Hoping to save a little time and effort by not having to hand mix up
loads of sand / cement under coat (plus a friend has some spare bags
of thistle hardwall going free!)
Obviously this will be a massive false economy if it all cracks after
skimming! so any advise before i start will be much appreciated

Skimming sticks to almost everything, but the existing plaster will need a
coat of PVA prior to commencing.

NB. New backing plaster like this should be skimmed the same day, or the
next day at the very latest....any later than that and the skimming dries up
and cracks off almost immediately.

I would phrase that a bit differently (but with same end result)...
Finish coat doesn't actually stick very well, except to the previous
plaster or sand/cement coat providing it's still wet (and ideally
almost but not quite fully set), and to tacky PVA (so you can plaster
anything if you paint it first with diluted PVA and let it almost dry
before plastering).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Mike wrote:
Hi All

Just wondering if any of the more experienced out there know if its ok
to repair blown patches of original sand / cement under coat plaster
with thistle hardwall?
I need to repair several large patches which will be taken back to
bare brick before skimming the whole walls. Not sure if this will just
crack at the join?
Hoping to save a little time and effort by not having to hand mix up
loads of sand / cement under coat (plus a friend has some spare bags
of thistle hardwall going free!)
Obviously this will be a massive false economy if it all cracks after
skimming! so any advise before i start will be much appreciated

Use whatever you've got. There's no essential difference between any of
them, and anything will crack if the surface underneath it is too
porous. Pva the wall, and then the undercoat when it's dry, and you
can't go wrong. Always worked for me anyway.

Andrew Gabriel wrote:
In article ,
"Phil L" writes:
Mike wrote:
Hi All

Just wondering if any of the more experienced out there know if its ok
to repair blown patches of original sand / cement under coat plaster
with thistle hardwall?

Yes, unless the wall is damp, in which case you can't use any
gypsom based scratch (under) coat. It might have been done with
sand and cement originally for this reason.

You can use hardwall, or any of the other thistle backing plasters -
browning, bonding etc

I need to repair several large patches which will be taken back to
bare brick before skimming the whole walls. Not sure if this will just
crack at the join?
You need to damp down the brickwork before starting, and where the patch
ends and the existing plaster begins, give this a coat of PVA, so that any
backing plaster that gets onto the existing wall is well adhered.

Hoping to save a little time and effort by not having to hand mix up
loads of sand / cement under coat (plus a friend has some spare bags
of thistle hardwall going free!)
Obviously this will be a massive false economy if it all cracks after
skimming! so any advise before i start will be much appreciated
Skimming sticks to almost everything, but the existing plaster will need a
coat of PVA prior to commencing.

NB. New backing plaster like this should be skimmed the same day, or the
next day at the very latest....any later than that and the skimming dries up
and cracks off almost immediately.

I would phrase that a bit differently (but with same end result)...
Finish coat doesn't actually stick very well, except to the previous
plaster or sand/cement coat providing it's still wet (and ideally
almost but not quite fully set), and to tacky PVA (so you can plaster
anything if you paint it first with diluted PVA and let it almost dry
before plastering).


This is the old argument about whether you should allow the pva to dry
or not. It's never made any difference IME.

New backing plaster like this should be skimmed the same day, or the
next day at the very latest....any later than that and the skimming dries up
and cracks off almost immediately.

Thanks everyone for the advice. i'll crack on with the hardwall stuff
then. (damp areas already done with sand/cement & waterproofer)
One last question, if i don't have time to skim within a couple of
days applying the new backing plaster, do i just treat it the same as
the old plaster before skimming - weak pva to seal, let it dry,
second stronger coat of pva and skim while still tacky?

Thanks again

Mike wrote:
New backing plaster like this should be skimmed the same day, or the
next day at the very latest....any later than that and the skimming dries up
and cracks off almost immediately.

Thanks everyone for the advice. i'll crack on with the hardwall stuff
then. (damp areas already done with sand/cement & waterproofer)
One last question, if i don't have time to skim within a couple of
days applying the new backing plaster, do i just treat it the same as
the old plaster before skimming - weak pva to seal, let it dry,
second stronger coat of pva and skim while still tacky?

Thanks again


Tacky doesn't matter IME. Seems like nitpicking but, if it means
committing yourself to plaster at a certain time, it can be a pain. Pva
works by reducing suction, which it does equally well when dry.