# Forum Home Renovation Painting  Plastering over existing ceiling?

## merfsta123

HI there,    
I'm new to this forum. 
Have just moved here from O.S. Was wondering if there are any special condiserations for platering over an existing ceiling. Do I need to use longer screws? Will the adhesive be effective on the existing plaster ceiling?
Any other thing I should do before putting the new sheets up? 
Thanks...

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## seriph1

1st of all a big welcome to the forum  -  2nd of all, welcome to hell if you get this little job wrong   :Biggrin:  :Biggrin:  :Biggrin:  :Biggrin:  :Biggrin:  
  -  need more info: what is the existing ceiling made from? Lathe? regular plasterboard/Gyprock/Drywall (uncertain where you're from so don't know how to describe it), or cement-mixed-with-horse hair or -Hessian type? 
If you're uncertain, let me know the age of the home and it will give a guide  -  also, why are you recovering the ceiling? Is it damaged beyond repair? 
Longer screws will of course be required as will accurately siting the ceiling joists.  
In addition, copious amounts of glue will be needed I believe, to reduce the likelihood of the ceiling sagging or worse....but even then, you will have to prepare the surface to ensure decent adhesion ... not much good ensuring the glue is well bonded to already sub-standard paintwork that may fall away. 
This is a fairly straightforward though tough job to do.... easy in that you get sheets of stuff and stick them on the ceiling  -  tough in that you have to lift them over your head and hold them in place while you screw them ... and of course theyre heavy and difficult to manoeuvre. there are lifters you can buy/hire that make it far easier, but when I did the ceiling in our 1920 Coburg home, I made up a pair of "T" pieces out of stud material  -  these enabled the plaster to be basically positioned well enough so I could fix them. 
The issues you face even after doing all this the "correct" way is that you effectively double the weight of your ceiling therefore you may find it sags anyway, but I guess you can add supports in the roof space if that seems likely. 
If you think I may be trying to convince you to seriously consider having the existing ceiling repaired, you'd be right  :Smilie:  
Personally, these days I wouldn't do a ceiling over an older one. I would either repair or replace, even though the latter is BLOODY MESSY! it is ultimately worth it for a lasting result. 
Please tell me more about the home and what you want to do with it ..... always keen to hear this stuff.

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## Rod Dyson

Hmm Sorry Steve, I don't quite share your tales of woe over going over and existing ceiling. Sure there are circumstances where you would not attempt it.  But generally it can be done without too much fuss. 
The sheet lifter advice is good.   
If the ceiling is reasonably straight you can go straight over the top of it no worries. If it is all over the place you will need to batten over the existing ceiling and pack the battens our straight.  There are many ways of doing this and just how you tackle it depends on the nature of the existing ceiling. 
Assuming the existing ceiling is not too bad the process is as follows. 
Find the existing framing members and chalk a line across the room at the center of each framing member.  The new sheets will go opposite to the direction of the framing. 
I do use glue although its effectivness is very limited.  You will need to screw the sheets along each framing member at *400mm* centers.  I put 2 screws beside each other.  This way you reduce the chance of getting popped screw heads later on. 
It is the screws that do the job holding up the sheet not the glue.  You could quite easily use no glue at all with screws at 400mm centers. 
If you have areas of the existing ceiling that are sagging simply screw them up first or you can cut out a very bad section and pack the framing level. 
Leaving the old ceiling in place helps with sound proofing and insulating so if it can be done there is no reason not to. 
Cheers Rod

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## seriph1

glad an expert responded to this  -  I am still in therapy from that job   :Biggrin:

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## merfsta123

Seriph and Rod.... thanx so much for your advice. 
NOw, should I use longer screws that 100mm? Also, should I not bother w the glue at all and just go w the screws? 
Also, I've already patched up some uneveness on the xisting ceiling...
Are there any other issues I should be wary of??
Thanx again 
Pete

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## Bloss

100mm screws??  :Confused:  
I'd rely on Rod's confirmation advice, but think that'd be a little long- if the framing is softwood maybe 50-65mm maximum, probably overkill if doing double screwing as Rod suggests, if into HW then 35-42mm maximum.

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## peter_sm

I did or loungeroom ceiling exactly as Rod explained with the steel battens. I screwd the new steel battens over the old plaster after finding where the original framing members were. Then the new plaster was simple from there. I used longer  screws to fix the steel battens through the old plaster and to the old members. Then just 32mm screws to hold the new plaster up.

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## Rod Dyson

You need about 25mm of bite into timber and about 15mm into metal.  So the length of the screw will depend on the thickness of layers of plaster. 
You can go without glue if you want but make sure you screw as I have described. 
Cheers Rod

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## merfsta123

Thanx Rod, Really appreciate your help 
Pete

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## merfsta123

I've read a few things about backblocking the ceiling joins but not quite sure what this entails???? 
How do I do this? What is the easiest way to get a good result? 
Any advice would be fantastic ...thanx again

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## Rod Dyson

If you are going over the top of the existing ceiling you will not need back blocks.  However it would not hurt to put daubs of glue along the join between the joist.  This would do the same thing as back blocking in this case. 
Generally back blocking is strips of plaster cut about 200mm wide that fit in between the joist.  Using back blocking cement, (or any other setting plaster), smear the back block with plaster and lay it half on the back of the join between the joist as you are putting up the sheets.  This forms a bond between the joins over the top of the board. Back blocking cement is specially retarded setting plaster to allow you more working time, (up to 2 hours before setting), 
Back blocking does not replace taping as a reinforcement of the join. It should be done in conjunction with taping with paper tape. 
Cheers Rod

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## merfsta123

Thanx Rod, 
Appreciate the advice again.

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## jacy_m

> If the ceiling is reasonably straight you can go straight over the top of it no worries. If it is all over the place you will need to batten over the existing ceiling and pack the battens our straight.  There are many ways of doing this and just how you tackle it depends on the nature of the existing ceiling.

  I am having a internal wall removed and need to redo my ceiling. Whilst getting the hanging beam installed for the wall removal, I am having an extra hanging beam put in the roof to take the weight of the 2nd ceiling (the existing one already sags) and some in roof storage.  
The builder says I will need to batten first to level it all out then gyprock... Is this something a newbie could consider doing? Do you have any more info on how it is to be packed straight? I think the existing ceiling is old masonite with wooden jointing strips.  
I'm a little concerned that having never done a wall before, starting on a ceiling might be too hard? 
thanks

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## Rod Dyson

It really depends. It is really easy for me!! but it might not be easy for you. 
Having said that, if you prefer to leave the old ceiling in place, (which is not a bad idea as it helps with insulating and sound reduction), you need to screw the battens to the existing joists.  
You will need 50mm screws to screw the 16mm metal batten up.  The most important part is around the perimeter, I would flick a chalk line around the perimeter to guide you. You can screw all the battens up and then pack them out to your line at the perimeter by backing off the screw and inserting the right amout of packing then nip the screw up again.   
Then you can use a straight edge to do the same in the center or the room working out from you perimeter. 
Or you can take the old ceiling down and fix the battens with a leveling clip. basically the same proccess.  Although I could expand on some methods using leveling clips  I dont have the time right now. I have just finished doing a night shift, (to beat the heat), putting up suspended ceilings. 
Cheers Rod

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## jacy_m

> you need to screw the battens to the existing joists.

  This may sound like a ridiculous question but do I put up the batterns parallel or perpendicular to the existing joists? The reason I ask is that my joists are not a standard width and vary from 450-700 spacing (and everywhere in between). I would have to check what the min and max is for that room.  
I know what you mean about the heat. I had to give up preparing another ceiling for painting until a weekend morning. The room faces west and cops the sun all afternoon. 
thanks for your help

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## seriph1

perpendicular is the go  -  nothing to fix them to if parallel ... unless you just added them to the existing joists

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## Batpig

Dear Merfsta, 
If you are still tuned in, I might just add a few items to what's already been said: 
1) Further to the point made about laying the new sheets at right angles to the existing supports, download this relatively-short manual from CSR Gyprock in order to get more of a feel on how to lay sheets out: http://www.gyprock.com.au/downloads/...Guide_5704.pdf 
2) It is especially worth mentioning that you should try to use sheets that are long enough to run the full distance across the room in question, so that you don't end up with any "Butt" joints (because they are harder to do than "Recessed" joints...) 
3) Once your Cornices come down, you might be able to pinpoint the location of the supports through the little gap that might be left between the edge of the existing sheets, and the wall. Other giveaways are straight rows of either small dimples, or small lumps - both of which are probably hiding fasteners into the supports. As an extra resort, an electronic Stud Sensor (my $50 Zircon Pro-SL from Bunnings seems quite accurate) might come in very handy for detecting the supports. 
4) Try to work out where the existing Recessed joints are. With just the right amount of sideways light (either from certain windows only, or at night from the ceiling light), you should be able to identify their location). Then - since your new sheets will be running in the same direction as the old ones (because both will be using the same set of supports...) - try to "offset" your new Recessed joints from the existing ones by at least the distance between two adjacent supports. You could achieve this by perhaps starting your layout with a full sheet from the opposite side of the room to where the original Plasterers started, or just cutting your first sheet in half, or something. This "offsetting" will enable the existing ceiling to fully work as "Backblocking" for the new ceiling. 
Good Luck with it. I may yet end up having to do the same thing as you at my place... :Redface:  
Best Wishes,
Batpig.

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