Visible joins in plasterboard after skim

[roughcaster]

RoyC wrote,

A good plasterer won't leave joints showing after he's skimmed awall!!!

I would agree with that Roy .......If a plasterer worked onto sheets that had no tapered edges and used paper tape bedded on, then it would make a bump right away. All of the earlier sheets of p/board years ago had no tapered edges and on every ceiling/wall, there was a joint like those in the pic, every 4 ft..... Another way you can end up with a visible join, is if the gap between the sheets is too big, so you end up with the deeper plaster pushing back out through the fibre tape mesh, especially if using multi finish. With two thin coats of bonding coat on the wallboards and then multi, you cut down the chances of seeing the joints to more or less zero,,,,it's a thin float and set, and I "honestly" never plaster a plasterboard wall/ceiling any other way. I never use multi finish on it's own, and i've said it before.... It takes longer, but worth it,,,, that's my opinion.

Roughcaster.

 

[markwm]

it does not look like bad plastering to me (looking at the image anyhow) , merely a plastered wall with a visible joint.

did the spread use paper joint tape or scrim?

there can be more than one reason why a joint becomes visible particularly when dealing with timber battened walls.

I didn't do the taping. Plasterer did and he uses the self adhesive mesh type tape.

One theory of mine is that, if there's even a slight gap between the boards air gets trapped in there as he skims and causes the join to bubble ever so slightly.

btw, you can't see or even feel these visible joins when it's just dry plaster. It's only after painting that the become more visible.

 

[markwm]

RoyC wrote,

A good plasterer won't leave joints showing after he's skimmed awall!!!

I would agree with that Roy .......If a plasterer worked onto sheets that had no tapered edges and used paper tape bedded on, then it would make a bump right away. All of the earlier sheets of p/board years ago had no tapered edges and on every ceiling/wall, there was a joint like those in the pic, every 4 ft..... Another way you can end up with a visible join, is if the gap between the sheets is too big, so you end up with the deeper plaster pushing back out through the fibre tape mesh, especially if using multi finish. With two thin coats of bonding coat on the wallboards and then multi, you cut down the chances of seeing the joints to more or less zero,,,,it's a thin float and set, and I "honestly" never plaster a plasterboard wall/ceiling any other way. I never use multi finish on it's own, and i've said it before.... It takes longer, but worth it,,,, that's my opinion.

Roughcaster.

So, next time I do any boarding/dry lining....

Should I be using tapered edge boards? And also would it help if I use jointing compound like this http://www.wickes.co.uk/Plaster-Ready-Mixed/Jointing-Compound/invt/220995 to smooth over the joints between the boards before the plasterer skims?

So, board with tapered edge, then tape, then smooth some jointing compound over the joins?

 

[Richard C]

RoyC wrote,

A good plasterer won't leave joints showing after he's skimmed awall!!!

I would agree with that Roy .......If a plasterer worked onto sheets that had no tapered edges and used paper tape bedded on, then it would make a bump right away. All of the earlier sheets of p/board years ago had no tapered edges and on every ceiling/wall, there was a joint like those in the pic, every 4 ft..... Another way you can end up with a visible join, is if the gap between the sheets is too big, so you end up with the deeper plaster pushing back out through the fibre tape mesh, especially if using multi finish. With two thin coats of bonding coat on the wallboards and then multi, you cut down the chances of seeing the joints to more or less zero,,,,it's a thin float and set, and I "honestly" never plaster a plasterboard wall/ceiling any other way. I never use multi finish on it's own, and i've said it before.... It takes longer, but worth it,,,, that's my opinion.

Roughcaster.

So, next time I do any boarding/dry lining....

Should I be using tapered edge boards? And also would it help if I use jointing compound like this http://www.wickes.co.uk/Plaster-Ready-Mixed/Jointing-Compound/invt/220995 to smooth over the joints between the boards before the plasterer skims?

So, board with tapered edge, then tape, then smooth some jointing compound over the joins?

I understand square edge boards may not be available to everyone but it’s not necessary to use tapered edge on a wall that’s being skimmed, you will just create unnecessary prep work.

I’ve had this “shadow line” happen to me a couple of times when I first started but never really understood why; it’s not there after you polish up but seems to “magically appear” after the plaster has thoroughly set & becomes even more visible when overpainted. Could be any one or combination of things; air tapped in/behind the tape, plaster too thin (did he only one or 2 skim coats?), not pre-filling the joint before skimming; it’s almost as if the plaster shrinks back into the joint. I now follow a set procedure with joints & have not had any similar problems for years. I always use a little Bonding & rough fill the joins & screw heads flush, I then tape the joins & PVA over the tape & bonding. When I'm ready to skim, I lightly skim the joint first forcing the plaster well into & flush with the top of the reinforcing tape, I then go on with the usual 1st & 2nd skim coats & finish off.

The plaster seems to shrink back, causing a very minute difference in the level, difficult to feel with a finger but enough to be accentuated under certain light conditions, typically back from a window as in your picture. It’s very annoying on a newly plastered wall but is fairly easy to get rid of; I just applied a light skim of filler & lightly sanded it over using either a ¼ sheet electric sander or just some paper & a block of wood; it’s not ideal but doesn’t warrant re-skimming the whole wall.

 

[roy c]

Like I've posted before we only use tapered edged boards and either fill out the joints with multi then scrim then multi again,or bonding adhesive ,same way prepare all joints before skimming even if left till next day we just roll some unibond on then skim away. Before tapered edge boards and fibre glass scrim tape we would put "Jute " hessian tape, over square edged boards and put the finish on thicker. That was in the days of ciraphite ask rough-caster about that

 

[markwm]

If you fill the joint with a bit of bonding coat and tape and leave to dry. Will this need to be PVA'd before skimming with multi finish?

Also, not entirely sure whether "skrim" refers to tape, or jointing compound.

 

[roy c]

First question....Yes

Second question ...Scrim is Scrim tape..


Unibond just a brand name of PVA that has been around longer than most other brands, and in my opinion still better than the rest....

 

[roughcaster]

The plasterer would/should do that part of the job as part of his prep. "Hessian/Jute Scrim" is probably the fore-runner of all plasterboard jointing/taping.When I first started plastering in the 60's, there were two types of materials plasterers used for board joints/ or board to brickwork,,,,Heavy duty hessian scrim, 3" wide x 100yds, and lightweight bandage scrim, made like bandage material, 2" wide x100 yds long, (I don't know if you can still get that now)..... You still get hessian scrim today, and it's made from the same material as "sacking" is made of, only a more open weave Very handy stuff to carry around. A lot of precast plaster mouldings, ceiling roses etc are reinforced with it..... You would not use it for thin plaster skimming unless you used much thicker coats to bury it. It's better being coated over with bonding first.

Roughcaster.

 

[vik2001]

i had some plasterboard walls plastered today by a reputable plasterer.
Although it all looks superb, I can see traces of scrim tape here and there on one wall. Obvoiusly it will paint over but it indicates to me that in places the skim thickess is hardly anything. Should I worry about it?

its like the skim didnt stick to the scrim tape there. and i can actually see the white scrim tape used ever so slightly (with the pattern of squares etc in it)
when i asked the plasterer he said the boards were uneven, because the stud wall wasnt straight in places(which is true).
im still going to ask the plasterer to sort this out, but does this sound right to anyone, and is there a fix? what problems can it cause having the scrim tape show slightly after a skim...

 

[roughcaster]

Just what we're talking about Vik, a "good plasterer" wouldn't leave a wall with the joints showing through. Some fag papers are thicker than the skim that some people put on a wall. I think this person is a "poor skimmer" rather than a good plasterer.

Roughcaster.