There are two reasons for wanting to dry-line. First to
provide a good, flat, clean surface, and second to help
insulate the house, which gets extremely cold in Winter.
The walls are very old, stone / lime mortar / clay / rubble
infil and about 2 feet thick. They are nice and dry, no
damp to contend with, just cold. The existing lime plaster
has become a bit grotty and crumbly in places since it was
done on the 21st August 1892 (according to a date marked on
What size gap should there be between the plasterboard and
wall? Should I put some insulation material there? What
sort - there are lots to choose from? Preferably not too
expensive as I'm on a tight budget. I'd guess that foil
based perhaps would not be a good idea as it may prevent
the walls from breathing and trap moisture?
As this is upstairs, can the plasterboard sit directly on
top of the floorboards or does it need to be suspended a cm
or something above the floor on wooden battens?
All feedback, suggestions, tips, URL's etc welcome please.
David in Normandy. Davidin...@yahoo.fr
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There is plasterboard with poly foam bonded to the back of it -
available in various thicknesses. Makes for a fairly quick job -
depending on how 'sound' and 'true' the existing surface is.
I used to work for the people that made the stuff (Britich Gypsum) -
their preferred technique for applying it was to trowel plaster dabs
onto the wall, then press the cut sheets of board back onto the dabs.
If the existing plaster's not strong enough to support this then you
could clean back to something solid (bolster / sds chisel) and sit
your dabs on that.
The 'de-luxe' application method (particularly good if the underlying
surface wasn't true / level) was to use thick dabs of plaster to stick
small pads of plasterboard offcuts to the wall - and level / true
these with a long spirit level. Once you've done this, and it's gone
'off', you can then proceed as above, but pushing the large sheets of
plasterboard back against the pads, so the finished surface ends up
true - and, better still, the edges of adjacent boards are at the same
If possible, get the tapered-edge plasterboard, as it's easier to get
an 'invisible' joint. If you're plastering the finished wall anyway -
don't bother. Use the proper tape on all joints - otherwise they'll
crack open (after you've decorated!)
Hope this helps
> There is plasterboard with poly foam bonded to the back of it -
> available in various thicknesses. Makes for a fairly quick job -
> depending on how 'sound' and 'true' the existing surface is.
> I used to work for the people that made the stuff (Britich Gypsum) -
> their preferred technique for applying it was to trowel plaster dabs
> onto the wall, then press the cut sheets of board back onto the dabs.
> If the existing plaster's not strong enough to support this then you
> could clean back to something solid (bolster / sds chisel) and sit
> your dabs on that.
> The 'de-luxe' application method (particularly good if the underlying
> surface wasn't true / level) was to use thick dabs of plaster to stick
> small pads of plasterboard offcuts to the wall - and level / true
> these with a long spirit level. Once you've done this, and it's gone
> 'off', you can then proceed as above, but pushing the large sheets of
> plasterboard back against the pads, so the finished surface ends up
> true - and, better still, the edges of adjacent boards are at the same
> If possible, get the tapered-edge plasterboard, as it's easier to get
> an 'invisible' joint. If you're plastering the finished wall anyway -
> don't bother. Use the proper tape on all joints - otherwise they'll
> crack open (after you've decorated!)
> Hope this helps
Plaster isn't a good idea as an adhesive, dry wall adhesive is made for this
purpose and most normal plaster has the words printed on the bag, 'not be
used as a dry lining adhesive'
On Sun, 02 Mar 2008 17:11:57 GMT, "Phil L" <neverc...@hotmail.com>
You're right, of course.....
sloppy language - should have said 'plaster' - that's what they always
used to call it at BG....
The 'official' instructions (at the time - and we're talking a few
years back) required that each sheet was also given a mechanical
fixing with a 'frame fixing' - apparently in case there was a fire,
and the poly foam melted, allowing the plasterboards to fall off the
I remember very well trying to get these darn fixings into the wall -
in the days before I had an SDS !
Then infill with 50mm celotex, and plasteboard over.
The walls are certainly uneven and crumbly in places. I
don't think I'd trust adhesive / plaster to stick to the
walls. Looks like the stud wall solution would be best with
SDS drill at hand to put in some long screws - it is pot
luck when drilling if I hit clay, sandstone or granite,
small rocks through to large boulders.
I forgot to mention in the original posting that I'd
already bought a big pile of plasterboard, so using one of
the pre-foam backed alternatives isn't an option.
I just googled 'Celotex', it seems there are several
different types and this is the name of the manufacturer.
Is it some sort of rigid foam insulation? The manufacturers
are a bit coy about the price implying it is expensive?
I had to do this for a whole cottage - 1800's farm cottage in
Scotland, refurbished in 1928, suspended floor with oodles of
ventilation and lath and plaster on the walls with all the ventilation
passing up behind the plasterwork into the roof space !!! COLD !
So we stripped off all the plasterwork, making sure none of it went
down under the floor, new 2 x2 studding, rock wool bats, and very
importantly a polythene membrane on top of the studs before the
plasterboard. It is essential this membrane as any moist air passing
through the insulation will condense if the stone wall is cold and
saturate the insulation. This was done 20+ years ago and has been
It's cheap, see some prices here http://www.bmdinsulation.com/insulation-special-offers.html.htm
Yup rigid foam with foil facings. For your application you could use
sheets butted together and jointed with foil tape behind stud, and
either vapour shield plasterboard or a separate membrane behind the
All the product numbers are misleading. There really isn't much
variety, just thickness and sheet size.
Excellent tip about the membrane. I hadn't thought about
David in Normandy. Davidin...@yahoo.fr
Its polyisocyanurate foam boartd covered with aluminium foil.
Kingspan and Celotex are the two brands I know of. It is ****ing
expensive..about a quid a square foot, but its the best insulant bar
none in terms of heatloss per unit thickness.
Consider using epoxy mortar and screw fastening if you run into trouble.
BUT a stud wall is more or less self supportng so it doesn't need to be
as firmly attached as other things do.
Celotex has its own foil vapour barrier, and should be taped over with
special aluminium foil tape as well to both hold it to the studs and
provide a continuous barrier. Its about twice as good as rockwool at the
> Kingspan and Celotex are the two brands I know of. It is ****ing
> expensive..about a quid a square foot, but its the best insulant bar
> none in terms of heatloss per unit thickness.
Ecotherm is a cheaper (i.e. half the price) brand for much the same thing...
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I have just done precisely this in a cottage in N Wales with 600 mm
rubble walls in lime mortar. I chose to ignore the technical advice
to put insulation on inch battens to leave a ventilated gap at my own
risk and very sucessfully adapted to the following method
Apply dry wall adhesive to the plaster with a serrated trowel, say,
ditto to the 2" Kingspan TP10 or whatever PU equivlent is cheaper but
Put the board on the wall and tap in in place with a plank and lump
drill 12 mm holes - about 5 of them in through the insulation into
the stone of the wall (use the stone unless the mortar is not friable)
such as to enable the insertion of the 2" diameter pink plastic washer/
plug fixings used for external attachment of boarding to walls and
insert the stainless steel nail in with a lump hammer. Hit until it
just indents the insulation
Next ( and this is good for you as you have the plaster board) put on
plaster board and staggered centres in exactly the same way but this
time (having noted where the original five fixings were by photo or
diagram) aplly another five fixings in different places.
Next skim the whole lot
next apply drywall top coat vapour check
Then any picture rails architraves etc have to be fixed with really
long thin 5" or so screws or glued in place!
I have a series of photos if this would be of interest
should a drainaway option be left,
or is it best to try to make everything watertight?
what about having two vapour barriers
as in one of the posts,
wouldnt this mean any moisture then has nowhere to escape to
and so will linger and rot wood?
is it cheaper to use glue or wooden battens?
there's a coldbridge issue with battens isnt there?
Any damp is a sign that tiou need to strip the while lot of anything and
Rockwool tends to sag in vertical cavities..
> should a drainaway option be left,
> or is it best to try to make everything watertight?
> what about having two vapour barriers
> as in one of the posts,
> wouldnt this mean any moisture then has nowhere to escape to
> and so will linger and rot wood?
No. Any vapour in the wall area can escape via the wall.
> is it cheaper to use glue or wooden battens?
? Glue, but its harder on a undeven wall, to get things staright.
> there's a coldbridge issue with battens isnt there?
Some, but not major.
Thank you for the replies everyone. Much appreciated.
ISTR some sorts of foam insulation plasterboard act as their own
vapour barrier too - is it "closed cell" foam or somesuch (as opposed
to the "open"ness of say, polystyrene?
I used some on our solid brick walls a few years ago was pink foam
sheets glued to 12.5mm pboard - dotted and dabbed with pboard
adhesive, then when set, added a couple of suitably long frame anchor
type things through into walls at abt 6ft to secure in case of fire -
no obvious probs and a helluva lot warmer since! :>))
I could take up some unevenness in walls with thicker adhesive dabs as
necessary but when I did it no more than a couple of inches over 2.4m
(mixed units are my forte!)