# Forum Home Renovation Plastering  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

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## Rod Dyson

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

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## 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

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## echnidna

Is the roof cavity accessible?

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## Pedal Harder

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

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## Rod Dyson

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

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## 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?

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## Rod Dyson

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

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## 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

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## Rod Dyson

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

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## rod1949

You bloody beauty, the Wet n Stick sounds just what Ive been looking for.  I've done all my horizontal wall joints with the stick-on mesh tape (as supplied by the Gyprock Sales bloke) and they have all cracked. The plasterboard joints are at 1350mm high (2.7 ceiling). The steel framed noggins are at 1200mm. Due to my impatience and with the benefit of hindsight I now wish I re-nogged at 1350 or backblocked, as there is no real support at the 1350 joint.  I had thought of and discussed with the Wife as to installing a wallpaper strip freeze (being a bit like Wet n Stick paper tape) or a timber chair rail but the height would made it well different.  I had limited my search for a wet/sticky paper tape to the Gyprock sales centres, thinking if such a thing was available then they would have it but they dont. So Ive just rung an independent mob The Ceiling Supermarket and they have it, so Ill get a roll or two and give it a go in amongst the other 101 things Ive got to do in being a true owner builder.   Thanks Rod the plasterman for mentioning the wet n stick.

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## ScottMa

I've had some problems over winter too with joints cracking - one ceiling, plus a couple where there have been vertical joins (near doors) and no tapering of the plaster. 
I tried Bunnings to see if there was some sort of elasticised paint that could allow expansion, but they had none. 
The alternative they suggested was a spray-on elastic coating. Can't remember the exact name now, but the same crowd makes a graffiti removing spray. Yellow can, red writing... I've applied it, but haven't painted over yet. 
Oops, am admitting to cheating!  :Smilie:  Has anyone else tried this stuff?

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## rod1949

> ... is to use WET AND STICK paper tape... 
> Cheers Rod Dyson

  Hi Rod,
Please correct me if I'm wrong but I have not read anything of your's in the past that specifically states the Wet and Stick paper tape. Is it a new product? 
Thanks
Rod1949

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## Rod Dyson

You will find refererence to it on my website under tapes.  Repairing cracked plasterboard joins is the ONLY application that I reccomend its use. Therefore I don't mention it often.   
The product has been arround for about 13 years and is not widely used by contractors. 
The problem with it for general use is that bubbles frequently occur where there are any gaps in the board or nail hole dimples etc.  Unless all these things are prefilled it is hopeless.  But on a perfectly flat surface such as a painted ceiling it is perfect.  It sticks like a postage stamp and gives you the flatest possible method of repairing an existing crack. 
Cheers Rod

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## sundancewfs

So... if you have a cracked ceiling joint, don't use mesh tape, use wet-n-stick paper tape. How should you go about preparing the surface of the crack/surrounds? Do you need to strip back to plasterboard? do you need to remove any existing tape? Can you use normal paper tape and circumvent the problems of bubbles in wet-n-stick?

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## Rod Dyson

Never use mesh tape! It simply wont do the job. The only prep work I do is to run a scraper over the crack to make sure there are no protruding flakes of paint etc. I don't remove any of the existing tape. Depending on the painted surface I will scuff up the area along the join first with the point of a trimming knife. I would never try to trowell straight over a glossy surface. Top coat and cornice adhesive adheres fairly well to flat painted surfaces if not too thick. 
You can use normal paper tape without any problems I prefer the wet and stick for this application simply because it will stick flatter to the surface than paper tape with a thin layer of plaster underneath. Also normal paper tape will swell a bit more than the wet and stick paper tape. This just makes flattening the join out that little bit easier. Particularly if the join is already overfilled like many plasterers leave them.  
Put this way if I went to a job to repair and I only had fibreglass tape, I would not use it under any circumstance and go and buy wet and stick. Yet if I got to the job and had normal paper tape I would use that instead. 
BTW most non plasterers would more likely get bubbles in normal paper tape. Never worry about them just use a sharp trimming knife to cut out the affected area and patch. They will normally show up after you do a second coat. 
Cheers Rod

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