Plaster splitting

[Tiger]

I don't know if this has happened to any of you but a couple of my plastering jobs have resulted in splits developing. These have happened at the point where I've used the tape which covers joins in plasterboard. It has happened not in all jobs but about half of them. I'm stunned as to why it's happened in some places and not in others as I use a fairly consistent approach to jobs.

Does anyone know why this happens and how to prevent it as I now need to re-do the ****** thing again?

[miked]

Gidday Tiger, I have had this happen to me a few times, but only when I have used the "cloth type" joint tape (with the little holes in it). The last few walls I've done, I have used the paper tape and there have been no problems at all.

I know this isn't the fix you wanted, but it may help you for next time. Hopefully there is someone more qualified, can post a remedy for you.

Cheers

Mike

[Skew ChiDAMN!!]

Did you use the premixed Gyprock (as used by tradies) or mix your own from dry?

If the former, you didn't use Finishing plaster did you? That's really only for final dressing, not for fill, and I've noticed it tends to act as you describe if used as a filler.

If the latter, you may've mixed it a bit wet. The more water, the narrower the gap it'll fill without cracking as it dries. Ie. greater shrinkage.

Don't take the above as gospel, I ain't no plasterer, but I've worked alongside a few with their apprentices and seen (and heard!) my share of... "mistakes." That sorta thing tends to stick in my head. :rolleyes:

[Pulse]

Tiger, did you backblock the joists? (glue off cuts to the back of the sheets). This is recommended for some joints eg ceilings in garages and large unbroken runs of plasterboard. The Gyprock application manual has details of when to backblock to avoid this splitting. I assume it is due to movement in the framing or building settlement.

Cheers
Pulse

[echnidna]

Has the base coat properly dried and cured before you put the topping on.?

[Tiger]

Have had to exercise the old memory muscle to remember exactly what I did.

Didn't use backblocking as these were only small jobs. Mixed my own plaster filler using cornice cement. It seems to have happened with the paper joins on the internal corners more than anywhere else, is there something you need to do to the paper before using it? From memory I applied some mud, then set the paper on top of it and then covered it with more mud.

What sort of consistency are we after when we use cornice cement?

[echnidna]

If its mainly confined to corners put a piece of sheetmetal angle (plasterers angle) behind the sheets in future

There is a self adhesive tape used by panters to cover minor splits, (sorry I've forgotten the name) theoretically you can paint over it and its supposed to be invisible. I found it wasnt but by using a light scrape of finish coat over the tape it becomes invisible. I have used it to fix the cracks that happen with fibrous plaster successfully. This method should fix your splits unless they are caused by frame movement.

[Tiger]

If its mainly confined to corners put a piece of sheetmetal angle (plasterers angle) behind the sheets in future

Bob, is this a standard item that can be bought from a hardware supplier or do you need to go to a plaster supplier?

[echnidna]

Its only 26 g galv sheet folded, some hardweares carry it but you should get it from all plasters supplies (see also my edited previous message)

[Tiger]

There is a self adhesive tape used by panters to cover minor splits, (sorry I've forgotten the name) theoretically you can paint over it and its supposed to be invisible. I found it wasnt but by using a light scrape of finish coat over the tape it becomes invisible. I have used it to fix the cracks that happen with fibrous plaster successfully. This method should fix your splits unless they are caused by frame movement.[/QUOTE]

This would be handy, does this mean that I won't have to do the entire job again? Is this available from hardware stores or is only from paint suppliers?

[echnidna]

I've forgotten whether I got it from a paint shop or hardware shop.
But its worth hunting around for coz it could save major works.

Suspect a fine smooth masking tape might do it too (like the cheap home hardware stuff)

[Tiger]

Thanks, Bob I'll try and get some this weekend.

[BrisBen]

No matter how good you set it - the joins will still crack if the house/structure moves

[ausdesign]

If there is a definite 'crack' in the joint its structural movement. It doesn't matter if you've used paper tape or gauze tape.
If it's a 'hollowing' along the joint its possibly due to too thick a bed of jointing cement instead of 'building' up the joint.

[Nick Moore]

Hi assume you're using modern to modern plasterboard?

if not..

I heard an old plasterer on ABC radio handyman show.. recently

Was describing plaster cracks reappearing on amateur old house repairs..

His point was that modern plasters / patch material being stronger than old plaster cause the cracks. ..flex at difft rates to base sheeting.

For old house plaster have to mix base filler using old fashioned type formula (like brickies mortar style)

Also have to really vee out crack to give wide sface area to bond to..
(Think he said you also had to keep wet with spraypak water bottle.?)

The old style mix Is a more flexible base you can then overcover with modern spakfilla etc ok.

As I said above relates to old plaster patching..Renovation type repairs.

I use good quality no more gaps acrylic filler for longer runs on eg cornices ..seems to go well in Tassie cooler climate.

[Nick Moore]

Hi assume you're using modern to modern plasterboard?

if not..

I heard an old plasterer on ABC radio handyman show.. recently

Was describing plaster cracks reappearing on amateur old house repairs..

His point was that modern plasters / patch material being stronger than old plaster cause the cracks. ..flex at difft rates to base sheeting.

For old house plaster have to mix base filler using old fashioned type formula (like brickies mortar style)

Also have to really vee out crack to give wide sface area to bond to..
(Think he said you also had to keep wet with spraypak water bottle.?)

The old style mix Is a more flexible base you can then overcover with modern spakfilla etc ok.

As I said above relates to old plaster patching..Renovation type repairs.

Definitely flexing points need wood backing blocks or light plasterers angle .
Modern houses are flimsy in build these days compared to old wooden houses. Like the all hwood frames here in Tassie old houses..

[Andrew in Tas]

Hi Tiger,

you said you used cornice cement for the joints. Cornice cement is an adhesive that is used for fixing cornice or for fixing plasterboard to masonary. You need to use basecoat and then the premixed topping coat. If the job is only small you could use the premixed total jointing compound.