I shall be plasterboarding the ceiling of a dining room extension to my
property soon.

I recall reading somewhere that the best approach for a good ceiling that
doesn't crack is to put up two layers of 3/8" plasterboard with staggered
joints.

There is also a loft conversion above, and I recall someone in this ng
saying it is good practice to have a DPM above the ceiling, but below the
joists, to avoid condensation in the loft.

My proposal is to use one layer of 3/8" foil-faced plasterboard put up first
(foil-face down); then to tape the joints with aluminium foil tape; then to
put up a second layer of plain 3/8" plasterboard with staggered joints.
This will/should give me a strong, 3/4" plasterboarded ceiling with an
integral DPM.

Is this a good plan, or is there a downside (other than the cost).

When fixing the first layer of plasterboard, should I butt the edges, or
leave a small gap?

Same question for the second layer of plasterboard.

I'll be having a smooth skimmed plaster finish (not Artex). Which side of
the lower layer of plasterboard should face downwards - the white or the
grey? The joints will be taped, probably with open weave fibreglass
adhesive tape, rather than paper tape.

Any comments/advice/warnings appreciated.

TIA
--
Mike
-Please remove 'safetycatch' from email address before firing off your
reply-

mlv wrote:
I shall be plasterboarding the ceiling of a dining room extension to
my property soon.

I recall reading somewhere that the best approach for a good ceiling
that doesn't crack is to put up two layers of 3/8" plasterboard with
staggered joints.

you only need one layer of PB with staggered joints

There is also a loft conversion above, and I recall someone in this ng
saying it is good practice to have a DPM above the ceiling, but below
the joists, to avoid condensation in the loft.

There is a habitable room above the dining room?
- in which case you don't need a DPC

My proposal is to use one layer of 3/8" foil-faced plasterboard put
up first (foil-face down); then to tape the joints with aluminium
foil tape; then to put up a second layer of plain 3/8" plasterboard
with staggered joints. This will/should give me a strong, 3/4"
plasterboarded ceiling with an integral DPM.

Is this a good plan, or is there a downside (other than the cost).

Yes, the aluminium foil should be joist side up, that is, touching the
underside of the joist, but as I've already said, it's not required.

When fixing the first layer of plasterboard, should I butt the edges,
or leave a small gap?

Butt all PB's up and keep all gaps as small as possible.

Same question for the second layer of plasterboard.

I'll be having a smooth skimmed plaster finish (not Artex). Which
side of the lower layer of plasterboard should face downwards - the
white or the grey? The joints will be taped, probably with open
weave fibreglass adhesive tape, rather than paper tape.

The white side is for plastering

Any comments/advice/warnings appreciated.

TIA

I you are getting a plasterer in for the ceiling, it may be wise to let him
plate it for you as well

mlv wrote:
I recall reading somewhere that the best approach for a good ceiling that
doesn't crack is to put up two layers of 3/8" plasterboard with staggered
joints.

That sounds like a spec for fire-resistance, which wouldn't normally be
required for an "ordinary" property. Would also be good for
soundproofing if that's an issue; however if all you're worried about is
cracks, then I'd say it was overkill to put up two layers of pb.

There is also a loft conversion above, and I recall someone in this ng
saying it is good practice to have a DPM above the ceiling, but below the
joists, to avoid condensation in the loft.

If the loft conversion is immediately above the dining room and is
living accomodation, then it doesn't make sense to have DPM below
that... you want a vapour barrier above/outside the loft conversion, not
below it.

How many storeys do you have? Is the loft conversion directly above the
dining room? (Just wondering whether there are indeed fire regs to
consider).

When fixing the first layer of plasterboard, should I butt the
edges, or
leave a small gap?

Same question for the second layer of plasterboard.

That's a question to ask the plasterer who's doing the work. I've used
two in recent years; one said he wanted a 1/8" gap between the boards,
the other said butt them up tight.

I'll be having a smooth skimmed plaster finish (not Artex). Which side of
the lower layer of plasterboard should face downwards - the white or the
grey? The joints will be taped, probably with open weave fibreglass
adhesive tape, rather than paper tape.

White I think (the stuff I use is coloured the same both sides) - isn't
"plaster other side only" emblazoned over one face?

David

"mlv" wrote in message
...
I shall be plasterboarding the ceiling of a dining room extension to my
property soon.

I recall reading somewhere that the best approach for a good ceiling that
doesn't crack is to put up two layers of 3/8" plasterboard with staggered
joints.

There is also a loft conversion above, and I recall someone in this ng
saying it is good practice to have a DPM above the ceiling, but below the
joists, to avoid condensation in the loft.

My proposal is to use one layer of 3/8" foil-faced plasterboard put up
first (foil-face down); then to tape the joints with aluminium foil tape;
then to put up a second layer of plain 3/8" plasterboard with staggered
joints. This will/should give me a strong, 3/4" plasterboarded ceiling
with an integral DPM.

Is this a good plan, or is there a downside (other than the cost).

When fixing the first layer of plasterboard, should I butt the edges, or
leave a small gap?

Same question for the second layer of plasterboard.

I'll be having a smooth skimmed plaster finish (not Artex). Which side of
the lower layer of plasterboard should face downwards - the white or the
grey? The joints will be taped, probably with open weave fibreglass
adhesive tape, rather than paper tape.

Any comments/advice/warnings appreciated.


Use 50mm joint tape. It is an open nylon mesh that is put over all the
joints and stuck on with plaster. It is supposed to be self adhesive but
don't believe that. It is used to stop cracking. Two layers are unnecessary
in my view.

mark

Phil wrote:

I wrote:

I recall reading somewhere that the best approach for a good
ceiling that doesn't crack is to put up two layers of 3/8"
plasterboard with staggered joints.

you only need one layer of PB with staggered joints.

That's what I have in the existing rooms, and they have all cracked along
the joints. I read about the two x 3/8" layers of plasterboard method in a
technical book some while back.

I agree the first layer of plasterboard has the joints staggered (like brick
courses), but the second layer is put up with an opposing stagger, if you
see what I mean. Consequently, no joints in the first layer coincide with
any joints in the second layer.

There is also a loft conversion above, and I recall someone in this ng
saying it is good practice to have a DPM above the ceiling, but below
the joists, to avoid condensation in the loft.

There is a habitable room above the dining room?
- in which case you don't need a DPC

The property is a bungalow with a loft conversion. Part of the ceiling is
beneath a habitable room, whilst the rest is beneath the insulated roofspace
(eaves).

My proposal is to use one layer of 3/8" foil-faced plasterboard put
up first (foil-face down); then to tape the joints with aluminium
foil tape; then to put up a second layer of plain 3/8" plasterboard
with staggered joints. This will/should give me a strong, 3/4"
plasterboarded ceiling with an integral DPM.

Is this a good plan, or is there a downside (other than the cost).

Yes, the aluminium foil should be joist side up, that is, touching the
underside of the joist, but as I've already said, it's not required.

I thought the important point was that the DPM had to be beneath the joists
(as mine would be) and not above. The DPM doesn't actually have to touch
the joists and 3/8" of plasterboard between the DPM and the joist should be
irrelevant. Using my method (foil-face downwards) gives me the opportunity
to tape the joints to give a continuous membrane. I couldn't tape the
joints if the first plasterboard layer was foil-face upwards.

If you are getting a plasterer in for the ceiling, it may be
wise to let him plate it for you as well

I wouldn't attempt the plastering myself, but I can recover the extra cost
of two layers of plasterboard by fixing it myself ;-)
--
Mike
-Please remove 'safetycatch' from email address before firing off your
reply-

Lobster wrote:

I wrote:

I recall reading somewhere that the best approach for a good ceiling
that doesn't crack is to put up two layers of 3/8" plasterboard with
staggered joints.

That sounds like a spec for fire-resistance, which wouldn't normally
be required for an "ordinary" property. Would also be good for
soundproofing if that's an issue; however if all you're worried about is
cracks, then I'd say it was overkill to put up two layers of pb.

Additional soundproofing is always welcome between living rooms and
bedrooms. As I'm doing the work for myself, the potential overkill isn't an
issue, especially if I end up with a ceiling that doesn't crack.

There is also a loft conversion above, and I recall someone in this ng
saying it is good practice to have a DPM above the ceiling, but below
the joists, to avoid condensation in the loft.

If the loft conversion is immediately above the dining room and is living
accommodation, then it doesn't make sense to have DPM below that... you
want a vapour barrier above/outside the loft conversion, not below it.

Yes, I have a vapour barrier on the warm-side of the loft walls and ceiling.

How many storeys do you have? Is the loft conversion directly above
the dining room? (Just wondering whether there are indeed fire regs
to consider).

The property is a bungalow with a loft conversion, so only two storeys and
Fire Regs don't apply as they would for a third storey.

When fixing the first layer of plasterboard, should I butt the edges, or
leave a small gap?

That's a question to ask the plasterer who's doing the work. I've
used two in recent years; one said he wanted a 1/8" gap between
the boards, the other said butt them up tight.

Tried that. I get the same inconsistent answers that you have experienced.
Perhaps it doesn't matter. Personally I would have thought a small gap to
let plaster in between the board edges when the open-weave jointing tape is
skimmed in place.

I'll be having a smooth skimmed plaster finish (not Artex). Which
side of the lower layer of plasterboard should face downwards -
the white or the grey? The joints will be taped, probably with open
weave fibreglass adhesive tape, rather than paper tape.

White I think (the stuff I use is coloured the same both sides) -
isn't "plaster other side only" emblazoned over one face?

Dunno! Maybe - I haven't bought it yet :-)
--
Mike
-Please remove 'safetycatch' from email address before firing off your
reply-

Mark wrote:

I wrote:

The joints will be taped, probably with open weave fibreglass adhesive
tape, rather than paper tape.

Use 50mm joint tape. It is an open nylon mesh that is put over all
the joints and stuck on with plaster. It is supposed to be self-
adhesive but don't believe that. It is used to stop cracking.

That's the tape I seem to have. It's a square, open mesh about 3.0mm x
3.0mm, allegedly self-adhesive and 50mm wide. However, it's definitely
fibreglass, rather than nylon or fabric.

Two layers (of plasterboard) are unnecessary in my view.

Well, I know you wouldn't normally get two layers if it was left to the
builder, but, as it's my own property...
--
Mike
-Please remove 'safetycatch' from email address before firing off your
reply-

mlv wrote:
Phil wrote:
I wrote:

I recall reading somewhere that the best approach for a good
ceiling that doesn't crack is to put up two layers of 3/8"
plasterboard with staggered joints.

you only need one layer of PB with staggered joints.

That's what I have in the existing rooms, and they have all cracked along
the joints. I read about the two x 3/8" layers of plasterboard method in a
technical book some while back.

Joists not substantial enough maybe, and flopping up and down under
weight from above? Is there mesh across the joints?

Whatever; use screws rather than nails to fix the new board up, they are
far less likely to loosen off and cause cracks.

(If you want to put up two layers for sound-proofing then that's
probably sensible enough, but for any other reason I think you'd be
wasting your time.)

David

mlv wrote:
Phil wrote:
I wrote:

I recall reading somewhere that the best approach for a good
ceiling that doesn't crack is to put up two layers of 3/8"
plasterboard with staggered joints.

you only need one layer of PB with staggered joints.

That's what I have in the existing rooms, and they have all cracked along
the joints. I read about the two x 3/8" layers of plasterboard method in a
technical book some while back.

I agree the first layer of plasterboard has the joints staggered (like brick
courses), but the second layer is put up with an opposing stagger, if you
see what I mean. Consequently, no joints in the first layer coincide with
any joints in the second layer.

There is also a loft conversion above, and I recall someone in this ng
saying it is good practice to have a DPM above the ceiling, but below
the joists, to avoid condensation in the loft.
There is a habitable room above the dining room?
- in which case you don't need a DPC

The property is a bungalow with a loft conversion. Part of the ceiling is
beneath a habitable room, whilst the rest is beneath the insulated roofspace
(eaves).

My proposal is to use one layer of 3/8" foil-faced plasterboard put
up first (foil-face down); then to tape the joints with aluminium
foil tape; then to put up a second layer of plain 3/8" plasterboard
with staggered joints. This will/should give me a strong, 3/4"
plasterboarded ceiling with an integral DPM.

Is this a good plan, or is there a downside (other than the cost).
Yes, the aluminium foil should be joist side up, that is, touching the
underside of the joist, but as I've already said, it's not required.

I thought the important point was that the DPM had to be beneath the joists
(as mine would be) and not above. The DPM doesn't actually have to touch
the joists and 3/8" of plasterboard between the DPM and the joist should be
irrelevant. Using my method (foil-face downwards) gives me the opportunity
to tape the joints to give a continuous membrane. I couldn't tape the
joints if the first plasterboard layer was foil-face upwards.

Whilst *air* tightness improves insulation, a continuos DPM is not
required. It's merely a VAPOUR BARRIER to slow down moisture bleed
through, so that loft ventilation is enough to cope, not hold a couple
of gallons of water ;-)

Foil taping is for airtightness, not actual water penetration.

It's also a neat way to hold celotex sheets in place



If you are getting a plasterer in for the ceiling, it may be
wise to let him plate it for you as well

I wouldn't attempt the plastering myself, but I can recover the extra cost
of two layers of plasterboard by fixing it myself ;-)

No bloody point. Use a single layer, foil backjed with scrim taping to
hold edges together. Thats MORE than good enough.

Lobster wrote:
mlv wrote:
Phil wrote:
I wrote:

I recall reading somewhere that the best approach for a good
ceiling that doesn't crack is to put up two layers of 3/8"
plasterboard with staggered joints.

you only need one layer of PB with staggered joints.

That's what I have in the existing rooms, and they have all cracked
along the joints. I read about the two x 3/8" layers of plasterboard
method in a technical book some while back.

Joists not substantial enough maybe, and flopping up and down under
weight from above? Is there mesh across the joints?


Good soundproofing, thats all, and fire barrier is increased.


Whatever; use screws rather than nails to fix the new board up, they are
far less likely to loosen off and cause cracks.


Not really. Depends on how artful you are in inserting them.


(If you want to put up two layers for sound-proofing then that's
probably sensible enough, but for any other reason I think you'd be
wasting your time.)


Agreed 100%.

David

Lobster wrote:


Joists not substantial enough maybe, and flopping up and
down under weight from above? Is there mesh across the joints?

Joists are correct size for application. Brown paper tape was used on
joints.

Whatever; use screws rather than nails to fix the new board up,
they are far less likely to loosen off and cause cracks.

Yes, I do intend to use screws.
--
Mike

mlv wrote:
Phil wrote:

I wrote:

I recall reading somewhere that the best approach for a good
ceiling that doesn't crack is to put up two layers of 3/8"
plasterboard with staggered joints.

you only need one layer of PB with staggered joints.

That's what I have in the existing rooms, and they have all cracked
along the joints. I read about the two x 3/8" layers of plasterboard
method in a technical book some while back.

I agree the first layer of plasterboard has the joints staggered
(like brick courses), but the second layer is put up with an opposing
stagger, if you see what I mean. Consequently, no joints in the
first layer coincide with any joints in the second layer.

It's up to you but it doesn't make any difference how many layers of P-board
you put up, if it's going to crack on the joints, it's going to crack on
the joints, the fact that there's another board above that is irrelevant.
The only advantages are soundproofing and fireproofing, but these weren't
mentioned in your OP.


There is a habitable room above the dining room?
- in which case you don't need a DPC

The property is a bungalow with a loft conversion. Part of the
ceiling is beneath a habitable room, whilst the rest is beneath the
insulated roofspace (eaves).


Still not required - it's only of any use in flat roof spaces, where the
insulation is bridging the roof and ceiling.

Yes, the aluminium foil should be joist side up, that is, touching
the underside of the joist, but as I've already said, it's not
required.

I thought the important point was that the DPM had to be beneath the
joists (as mine would be) and not above. The DPM doesn't actually
have to touch the joists and 3/8" of plasterboard between the DPM and
the joist should be irrelevant. Using my method (foil-face
downwards) gives me the opportunity to tape the joints to give a
continuous membrane. I couldn't tape the joints if the first
plasterboard layer was foil-face upwards.

But you are defeating the object.
The foil is a barrier against moisture coming from *above*! - if you have it
foil side down, the opposite side (the roof facing side) of the foilboard
could be soaked and will perish.


If you are getting a plasterer in for the ceiling, it may be
wise to let him plate it for you as well

I wouldn't attempt the plastering myself, but I can recover the extra
cost of two layers of plasterboard by fixing it myself ;-)

Phil L wrote:


But you are defeating the object.
The foil is a barrier against moisture coming from *above*!

It most certainly IS NOT!

If you are getting a plasterer in for the ceiling, it may be
wise to let him plate it for you as well

I wouldn't attempt the plastering myself, but I can recover the extra cost
of two layers of plasterboard by fixing it myself *;-)

Never underestimate the effort involved in attaching plasterboard to a
ceiling. I would recommend either using small boards (B&Q do some
called Handiboards 900x1500 I think) or getting one of those
extendable poles to help you. Working over your head is painful,
especially if you're not used to it.

Jon.

The Natural Philosopher wrote:
Phil L wrote:


But you are defeating the object.
The foil is a barrier against moisture coming from *above*!

It most certainly IS NOT!

It most certainly IS.

I don't recall ever seeing anyone plastering the foil side of a foilbacked
PB ceiling, YMMV

"Phil L" wrote in message
. ..
The Natural Philosopher wrote:
Phil L wrote:


But you are defeating the object.
The foil is a barrier against moisture coming from *above*!

It most certainly IS NOT!

It most certainly IS.

I don't recall ever seeing anyone plastering the foil side of a foilbacked
PB ceiling, YMMV

Well, you wouldn't. The foil goes on top (NP never suggested otherwise) and
is NOT to form a barrier from moisture from above (as NP said) it's to
prevent moisture going up into the cold space above and condensing. Putting
polythene sheeting up first and then ordinary plasterboard just as good of
course!


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

Bob Mannix wrote:
"Phil L" wrote in message
. ..
The Natural Philosopher wrote:
Phil L wrote:


But you are defeating the object.
The foil is a barrier against moisture coming from *above*!

It most certainly IS NOT!

It most certainly IS.

I don't recall ever seeing anyone plastering the foil side of a
foilbacked PB ceiling, YMMV

Well, you wouldn't. The foil goes on top (NP never suggested
otherwise) and is NOT to form a barrier from moisture from above (as
NP said) it's to prevent moisture going up into the cold space above
and condensing. Putting polythene sheeting up first and then ordinary
plasterboard just as good of course!

It's all academic anyway as most builders don't do this, both small
companies and large housebuilders.

Phil L argued:

Natty Phil wrote:

But you are defeating the object.
The foil is a barrier against moisture coming from *above*!

It most certainly IS NOT!

It most certainly IS.

No, the foil is a barrier to prevent moisture rising up, through the ceiling
and into the cold roofspace where it could condense and cause problems.
That's why the foil (DPM) has to be below the joists. If the DPM is above
the joists, the condensing moisture will be trapped and rot the joists.

My proposed 2-layer plasterboard installation had the first (uppermost)
plasterboard foil-side down, but then covered by the second plasterboard
layer. Therefore the foil was sandwiched between the two layers of
plasterboard (and below the joists).

I don't recall ever seeing anyone plastering the foil side of a foilbacked

Me neither ;-)
--
Mike
-Please remove 'safetycatch' from email address before firing off your
reply-

Tournifreak warned:

Never underestimate the effort involved in attaching
plasterboard to a ceiling. I would recommend either
using small boards (B&Q do some called Handiboards
900x1500 I think) or getting one of those extendable
poles to help you. Working over your head is painful,
especially if you're not used to it.

Yes, I know from previous experience fixing 8 x 4s.

Family members, armed with soft brooms, are very useful in a supporting
role!
--
Mike
-Please remove 'safetycatch' from email address before firing off your
reply-

mlv wrote:
Phil L argued:

Natty Phil wrote:

But you are defeating the object.
The foil is a barrier against moisture coming from *above*!

It most certainly IS NOT!

It most certainly IS.

No, the foil is a barrier to prevent moisture rising up, through the
ceiling and into the cold roofspace where it could condense and cause
problems. That's why the foil (DPM) has to be below the joists. If
the DPM is above the joists, the condensing moisture will be trapped
and rot the joists.

You've misunderstood my post.
My idea was to place the foilside uppermost against the joist - just like
you would have to do if you were skimming the foil boards opposite side.

Either way it's not required.

Phil L wrote:

You've misunderstood my post.
My idea was to place the foilside uppermost against the joist -
just like you would have to do if you were skimming the foil
boards opposite side.

No, I understood what you meant - install the plasterboard foil-side up
against the joists, as I would have to do with a single-layer, foil-sided
plasterboard installation.

The orientation of the foil isn't really an issue, if it's on the uppermost
layer of a double-layer plasterboard installation.

Either way it's not required.

Well, that's debatable. I've installed a loft conversion and the roof
ventilation will have been compromised (although I have added the
appropriate ridge vents and additional eaves vents). For a small extra
outlay I can use foil-sided plasterboard to reduce the amount of moisture
passing through the downstairs ceilings, thereby minimising the possibility
of condensation.

Whilst the foil is not necessary directly beneath the loft conversion area,
it isn't worth messing about just using foil-faced plasterboard around the
ceiling perimeters. Might as well use foil-faced plasterboard throughout
and done with it.

I also intend to install an additional layer of 3/8" foil-faced plasterboard
onto the existing ceilings (foil-face up this time). This is primarily to
recover the old ceilings that aren't in very good condition.
--
Mike
-Please remove 'safetycatch' from email address before firing off your
reply-

On Wed, 13 Feb 2008 14:04:22 -0000, "Bob Mannix"
head down on the keyboard, banged out this
message:

... xx"Phil L" wrote in message
... m...
... xx The Natural Philosopher wrote:
... xx Phil L wrote:
... xx
... xx
... xx But you are defeating the object.
... xx The foil is a barrier against moisture coming from *above*!
... xx
... xx It most certainly IS NOT!
... xx
... xx It most certainly IS.
... xx
... xx I don't recall ever seeing anyone plastering the foil side of a foilbacked
... xx PB ceiling, YMMV
... xx
... xxWell, you wouldn't. The foil goes on top (NP never suggested otherwise) and
... xxis NOT to form a barrier from moisture from above (as NP said) it's to
... xxprevent moisture going up into the cold space above and condensing. Putting
... xxpolythene sheeting up first and then ordinary plasterboard just as good of
... xxcourse!

I have just decorated a bathroom where foil backed plaster board was
used above,
Vinyl matt had been painted on the ceiling which rolled off as soon as
rhe roller touched it.
The plaster was damp all over the room .... very naughty :-)

Mike P

In article ,
"Phil L" writes:

But you are defeating the object.
The foil is a barrier against moisture coming from *above*! - if you have it
foil side down, the opposite side (the roof facing side) of the foilboard
could be soaked and will perish.

The foil was never intended as a moisture barrier at all.
It's a low emissivity coating to reduce radiative heat loss.
At the time it was introduced, it was sufficient thermal
insulation by itself. Of course, it falls way short nowadays
and is pretty redundant.

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