Preventing a crack in a plasterboard ceiling.

[Dave Plowman (News]

As part of a re-furb in the cloakroom - new lighting and different plumbing, I'll have to replace the plasterboard ceiling. Approximately

1.4 x 1.2 meters. Joists along the major axis.

About half way along those, the ceiling changes to a slope - part of the original roof design. So the joint in the pb at the bend at right angles to the joists. And the old was cracked there - despite not being that old.

What was a sloping roof above is now a roof terrace, and IIRC the joists for that not connected to this ceiling ones.

What would be the best way to avoid the new cracking? Suppose I could fit noggins to support the ends. I don't intend having it skimmed, as that would require trades brought in. (The old was skimmed but cracked anyway.)

[Tricky Dicky]

Noggins will certainly help. As you do not intend to skim, presumably you are going to use drywall filler on all the joints in that case joint tape will prevent cracking. Apply a thin coat of filler either side of the joint press the joint tape into the filler with scraper then overfill the joint and tape. Allow to set then apply final coat of filler feathering it out for at least 150mm each side of the joint.

Richard

[alan_m]

+1 Paper tape and plasterboard joint filler

I've been using this on some ceilings over-boarded with plasterboard and then (paper) taped

Note the powder takes a lot more water than you first think, mix well and leave for a few minutes before deciding that the mix is correct. It appers that ready mix jointing compound in a tub ALWAYS requires extra water and thoroughly re-mixing to knock out the air in order to get the best results.

Probably going to the extreme with specialised tape.

The Vancover Carpenters Youtube drywall "mudding" (covering joins) videos are quite good. There are a lot of them.

[Andy Burns]

I prefer the fibreglass mesh tape.

[RJH]

(Even) I had some success replacing the boards to a water damaged wall and ceiling. I used pre-mixed, and didn't need to dilute it, and a key tool seemed to be the special 'spreader' - thin, wide and bendy.

[alan_m]

Many youtube videos indicate for corners paper is always used. For patching flat walls etc. (where no movement is expected) mesh can be used.

Before I embarked on re-boarding a couple of ceilings I watched a LOT of youtube videos on "drywall" and jointing including quite a few on the mesh vs paper

Just search Youtube for mesh vs paper Example: (on of many on a similar theme)

[RJH]

I used paper for the corners and flat panels - worked fine. The V seemed to give a nice bed for the filler.

[Andy Burns]

you're right, I was forgetting Dave's join is at an angle. for that I use a paper tape with metal strip, similar to this.

[alan_m]

A photo may help but stopping one side of a join moving with respect to the other side with noggins or a strip of wood would help prevent cracking.

Also pre-filling any largish void in the join before taping helps.

Was there any tape beneath the skim plaster?

Plasterboard (USA drywall) jointing compound is very easy to sand but try to get a decent finish when applying compound and avoid a LOT of dust later.

Based on my experiences....

screws should not penetrate through the paper. The bits above in a power tool stop the screw going too far in. Otherwise drive the screw most of the way in with a power tool and then use a manual screwdriver to finally tighten the screw so it's just below the surface of the board.

To fill any screw holes apply the compound in one direction and immediately wipe of any excess in another direction. It usually takes 2 or 3 applications to fully hide a screw head if not skimming. Let the compound dry between applications.

A proper jointing knife helps a lot

blades have a lot more flexible than a blade perhaps used for stripping wallpaper etc. The flexible blade helps with feathering edges. Note these high carbon steel blades can rust easily so after use and cleaning dry immediately with a cloth or kitchen towel.

[harry]

Scrim over the joint. Retrofit on existing plaster by grinding away the plaster on either side of the joint, Apply the scrim with Polyfilla of similar.

[Jimk]

"Quick set mud" "air dry mud" ?

Muricans.

I'll stick w fibreglass mesh.

[alan_m]

Wrong

Good idea - just because you object to Canadian terminology you stick to something that is difficult to use in corners and probably will not work to prevent cracks.

[Jimk]

And you use air dry or quick set mud?

Fibreglass mesh has always worked for me with UK plasters, why change on basis of an inappropriate amateur yt video & someone who doesn't understand the difference?

[Tricky Dicky]

Richard

[Jimk]

Never wished I'd had it....

[alan_m]

It's not plaster and the OP expressed a wish not to plaster.

You don't have to skim plasterboard.

[Jimk]

Again what "mud" you using? Gyproc? So Gypsum based? Like plaster?.....

I'd still use mesh, once it's in & set how's it ever going to 'twist & shear' & allow cracks more than a bit of paper??

[alan_m]

British Gypsum also recommend paper for corner joints and other joints. They state that their mesh tape is doesn't provide the same level of crack resistance as their their paper tape.

[alan_m]

Ive already posted that information.

[Jimk]

Gorra link?

They sell both IIRC, I've always been ok with fibreglass mesh tapes, I can kind of fold it over a trowel for long enough to get it stuck in place in corners.

Which "mud" do you use ? (3rd time of asking, is it a guilty secret?)