Ceiling Joint Cracking

[stevew]

I have just finished a join in the ceiling and top coated with CSR joint compound,skim coated three coats.
The job turned out perfect ,So I went ahead and sealed and undercoated and two coats of ceiling white..looks fantastic.
However ,we have had a cold spell here and have had the gas heater on each night.This morning when I arose I noticed that the ceiling joint has a crack running along the joint.Appears the hot air from the heater must expand the joint and when it cools overnight it cracks.
Have I used the wrong skimming coat.??
Is there some brand of skim coat that will allow for some expansion and contraction.??
Any clues as to how I can repair the crack correctly ,as it appears that I have done it wrongly the first time.
Cheers.
Steve

[rod@plasterbrok]

Hi Stevew,

There are several things that are the most likely cause for cracking in ceiling joins.

If you use fibre glass tape instead of paper.
If did not back block the joins.
Movement in the building.
The wrong type of plaster for the ceiling joist spacing.

The best method of fixing it is to use WET AND STICK paper tape, (NOTE: this is the only application I recomend wet and stick paper tape).

It sticks like a postage stamp. Using either base coat or top coat trowel out either side of the tape the width of an 8" Joint Knife.

Then another coat with a 10" trowell through the center over the tape, then the full width of the 10" either side.

The final coat is the same as the 2nd coat but use a 12" joint knife.

This is difficult to explain, much easier to show, but here goes. When doing the 2nd and final coat, the run through the center 1st, will form an edge on either side as the center of the join is raised because of the tape. Use the edge to indicate how much fill is needed, to get a flat join. (see taping butt joins on my web site).

Fixing this joint is like doing a butt joint.

Cheers Rod Dyson

[Pedal Harder]

Rod/Others,

Not sure if this should be a new thread though it is related - I have hung my ceiling but not yet stopped up/joined etc. I mistakenly ran 5400 long ceiling sheets parallel to the metal battens, not at right angles......a builder I know dropped past & said whoops that's gonna crack all the time....

What is your opinion on this - is it true, and what do you recommend I do to stop this happening (am really not keen to pull down the sheets - they are on a raked ceiling and are glued + screwed...). The battens are however within 100mm odd either side of the recessed joins.

Use wet & stick or add more back blocks or???

Cheers

[echnidna]

Is the roof cavity accessible?

[Pedal Harder]

Yes - if I remove colourbond sheets (not a real problem and am prepared to do so....)

Cheers

[rod@plasterbrok]

Its not a good thing to have an unsupported join like that. When you say "more back blocks", are you saying that the joins have been back blocked?

If they have been back blocked well and are only 100mm away from the batten they will be ok.

If not you will need to put back blocks on down the length of the join.

Cheers

Rod Dyson

[Wombat2]

I have a similar problem but at least it is only across the width of a passage but right where it enters the lounge room so all can see it. There is evidence that it has been repaired several times and I have done it once when I painted but it has opened up again. A friend from interstate was visiting who was a plasterer in a former life and said to get an expansion joint and install it and left :confused: Anyone know what he would be talking about?

[rod@plasterbrok]

By the sound of it it is a butt joint that has been taped with fibre glass tape.

Did you repair it by re-taping with paper tape?

Cracks in plasterboard CAN NOT BE REPAIRED WITHOUT TAPE.

If you have taped it with PAPER TAPE and it is still cracking, that would indicate some weakness in the framing. In that case an expasion joint would be the only way to repair it. The only thing is an expasion joint in your ceiling won't look that nice. Particularly if it does't line up with a specific part of the ceiling, where it might look like it is meant to be there.

An expansion joint is part number p35 from Rondo. Simlar products are made by others but every on will recognize the Rondo part number.

An expansion joint is basicly 2 stopping angles, joined together with a rubber strip. To install it, cut a chase through where the crack is, 15mm wide. The expansion joint fits into the chase. Then stoped up either side, (like an external corner). It leaves about a 5mm gap that has a black rubber insert, that allows for movement. You won't have a crack but you will see the 5mm gap.

Typically expansion joints are used in stair wells of 2 storey houses between floors.

Another point, expansion joints need to be trowelled very wide, to avoid leaving a bump in the wall or ceiling. They sit down approx 2mm, so you need to trowel this out quite wide to blend it in. The difficulty you most likely have, is that the crack, is most likely on a butt join that will already be over filled. Adding to the problem of filling out the expansion joint.

An idea in this case, is to remove the tape from the join and get into it with some serious sand paper to cut back the filling to the surface of the board. Then install the expansion joint.

Before all that though I would try repairing using wet and stick paper tape as described above.

Hope this helps

Rod Dyson

[John99]

Did you use base coat compound for the first two coats in the join? and tape, you can use easy tape.
If you just used CSR joint compound it will crack you must use base coat for the first 2 coats then CSR joint compound as a topping coat :rolleyes:

cheers

[rod@plasterbrok]

Hmmm. Easy tape is not a good thing for ceiling joints EVER nor for internal corners.

People DO NOT USE EASY TAPE ON CEILINGS EVER. IT CRACKS!!!!!!!

If you do you are taking a punt! Some wont crack but some will.

When you see as many plastering jobs as we do, you would also see how many recalls there are where Easy Tape was used on ceilings.

We had one only 3 weeks ago where a contractor used easy tape contrary to our guidelines. 2 joins had very fine cracks that had to be repaired at the contractors expense.

Another reason all manufacturers warranties a void if easy tape is used on ceilings. If the job cracks because of OTHER REASONS you will still be liable if you use easy tape. It is just not worth the risk.

Cheers Rod Dyson