What have I done wrong here????

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Curmudgeon

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Hi All,

I'm in Western Australia; There was a pine timber ceiling with exposed rafters every 1200 (4ft) with corrugated tin roof over that. There were small timber collar ties at the height of the stainless tension wires I've replaced them with and the pine ceiling was fixed to the 50mm collar ties. I wanted to increase insulation and to expose the raking ceiling to the ridge. So I've bolted the brackets for the Stainless steel tensile wires at the same height as the old collar ties and tensioned up the turnbuckles. I filled the 150mm between the rafters with wool insulation and then used liquid nails and 40mm screws to fix 18mm mdf sheets horizontally across the rafters. Then I've used plenty of liquid nails on the face of the MDF sheets and plasterboard screws to fix 12mm sheets of gyprock straight onto the MDF. I've then used wet and stick paper tape on the joints and built up the joints with jointing compound.
What have I done wrong here????

This is what I get..... horrendous!!

Actually, this is what I get 3rd or fourth time round.... I've tried to grind it all back and redo it over and over with exactly the same result each time.

This doesn't happen immediately... it seems to happen when we get into summer (it gets to 40c here 110f fairly regularly). But I've run out of ideas as to how to resolve this? I'm going to end up putting a timber bead over it. But I want to know what I've done wrong and how to avoid it again in the future. Or even if I can salvage this now?

Help... otherwise I'll be slinging a rope over one of those SS wires!

Thanks all.
 
Try some scrim tape instead of paper tape and use compound over the top and sand it, if it's the only area it's happening it should rule out any movement also there's no signs of any damp in the join?
 
So what's Scrim tape.... I've tried the fibreglass mesh type, that's no good for this type of thing. We don't have many other options here that I know of. And when you say compound... I was using jointing compound. But to my untrained eye, there's so much movement involved it's gonna come back! This is occurring at EVERY joint in the gyprock.... approximately 44m of this!

As for damp.... there's none . These fissures follow the joins in the plasterboard. Those joins obviously don't match the joins in the MDF substrate so there's no avenue for moisture. We don't get much rain and Condensation should be handled under the tin with the anti-con.

Thanks guys.
 
Have you tried what Spunky said? Fibre tape (scrim) instead of the paper tape.

You say it's no good for this sort of thing. What makes you say that?
 
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The mesh type tape cracked even worse, I used it first up and assumed that it was the issue that caused the cracking as someone said that mesh tape shouldn't be used on ceilings (eben if it is a raking one?) ... but I really don't know, I'm certainly no expert!

Bubbles may have a point about weight, but having effectively tied all of the rafters together as a unit by glueing and screwing the mdf sheeting, the whole roof should be stronger. I've reduced the overall rafter span and replaced the collar ties which obviously only work in tension, over the original setup.

The main signs of movement are along the lines of the rafters suggesting lateral movement, rather than across the lines of the rafters that I'd expect if they were overburdened. (though there is movement there too, along the butt joints of the gyprock.

I'm reluctant to dig it all out again and go back to trying scrim tape. Maybe I should use an expanded steel mesh instead, I do that for plastering cracks in brickwork?

Or am I destined to have it cracking for ever?

Thanks all.
 
It could be the heat and I doubt the roof helps like you say it comes every year take the paper off and form an expansion joint in the join and fill it with a flexible the filler then paint over, don't scrim it it tape it or anything, over here we'd use 2 stop beads back to back pop into you're local builders merchants and tell them you need to create a movement joint 2mm thick
 
Im reckoning its the heat as bubbles says, relative expansion rates are going to be massive, Tin roof as opposed to solid plastering. Go for the 'expansion' gap as above.
 
It's no coincidence that tension wire is connected onto the rafter with the crack running down it. Or has it failed along more rafters without the wires?

Another question, does the crack run inline with the edge of the plasterboard?
 
Thanks guys,

It's failed on every gyprock joint, tapered and butt joints. There are only a couple of joints without tension wires, but they've failed too. (though perhaps to a slightly lesser extent, though they are also in a slightly "cooler" location)

Am I right in thinking these failures are pushing out rather than opening a crack up. I'm really non-plussed as to how that can happen when that joint is bonded and screwed to a contiguous sheet of MDF below, everything I've read says MDF is stable as far as expansion and contraction is concerned, but this must be rubbish!

As we say in Oz... "bugger"
 
I thought Aussies said " strike a light, fair dinkem you great gallaaa. Chuck another shrimp on the ute you bute!" Toby, where's bouncer? Go ask Miss Mangle!


Sorry I got carried away.
 
what ever is causing the movement is causing it, if you cant solve the movement problem out then i would suggest trying the following
1. cut out all your cracks and put in a 3mm expansion bead in all of them
2. then after priming the ceiling put a flexible base coat over the lot (Parex Maite) with TV10 mesh embedded into the base coat
3. top off with a plaster finish or a sand smooth acryic top coat which also has fibres in it

the beads should cope with the movement the flexible basecoat should cope with the beads moving

i think these guys may have something suitable in your neck of the woods mate

Choose a Texture | Render Systems Australia
 
If excessive heat is causing the problem and you want a final solution you could use a foil back board to overboard the existing the foil reflects the heat, boards are cheap and it wont take a couple hours. Then tape and joint it with proper drywall tape that is installed over a thin layer of ames and feathered back before sanding.
wet n stik is bonded to a board and if the board ever moves so will anything on top of the tape. ames underneath it allows some flexing.
The picture shows the tape delaminating from the board which could be the wet n stik glue heating up and delaminating or the ames could be a bit dry when you bedded tape in (maybe because of the heat)

Or you got a water leak down Yabbey creek
 
Hey render bollox.. whats the link to that resin floor stuff you do, Can it go over liquid screed. I will give ur details to the customer. Its not a big area but i think the house maybe goin in one of those fancy mags or tv programmes
 
@ Curmudgeon.

Nothing to do with this thread, but what is it like for work where you are. I have heard that Perth is short of skilled workers and the money is very good. Any truth in this?
 
Render Systems said:
what ever is causing the movement is causing it, if you cant solve the movement problem out then i would suggest trying the following
1. cut out all your cracks and put in a 3mm expansion bead in all of them
2. then after priming the ceiling put a flexible base coat over the lot (Parex Maite) with TV10 mesh embedded into the base coat
3. top off with a plaster finish or a sand smooth acryic top coat which also has fibres in it

the beads should cope with the movement the flexible basecoat should cope with the beads moving

i think these guys may have something suitable in your neck of the woods mate

Choose a Texture | Render Systems Australia
Click to expand...
Are you having a ******* geeraffe?
 
If you've any more to do I reckon you need to use a suspended system with wires taking the weight. This will stop any warping caused by that tin roof from transferring to the boards :RpS_thumbup:

Maybe something similar to this:

Link Removed
 
I think Bubbles has got it, the way you have constructed the ceiling it is part of the roof so any thermal movement caused by summer heat will be transferred to the ceiling hence the failure, a suspended ceiling would have been better.
 
Thanks for all of your advice guys.... intrigued that we still talk about "artex" sort of textured flexible coatings.

Dannymac, Re: your off topic question about Perth.... Your pretty right in what you've heard, we've got very strong employment and depending on your line, some pretty good money floating about.

BUT..... you don't want to be coming across with a whole lot of money in your pocket, as it'll be worth jack. Our exchange rate on the OZ$ is very strong and a weak pound means your getting nearly half what we used to for sterling pre 2007. It's a great lifestyle here, but stuff here is now very expensive to go with those wages, your basic shopping trolley will cost a lot more here than you're used to there.

All in all you'd need to do some good research to make sure your work sector is one of the busy sectors, because some are flat-lining due to the exchange rate. If your in mining or a good tradesman you'd be laughing though and driving around in a new V8 Commodore Ute before you know it!

Despite that we're off to France ....!
 
hi it just the movement there is a filler that is resin baced that we use in hospitals that will flex with the walls and celings apply it when its at its hottest and this will solve your problem you can get the grout / filler from any good tile supplyers hope this helps
bob
 
I lived in Perth in the early 80s great place loved every minute cant believe how expensive it is now especialy property.
 
Thanks Bob,

We've got a week of over 40 degrees coming up, so now would be the time to try your resin filler. Would you be suggesting this just as an expansion jointing idea with regular compound to flush the joint smooth over the top or will this resin flush smooth itself and be a paintable finish?

Cheers
 
I have been seriously thinking of setting up EIFS company over in Aus as its not very well established over there and is great for keeping the heat out of buildings... my mates over there and he recons it would go down well... whats your thoughts
 
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