Help!! - Plaster Devorative Ceiling Troubles

[Cobber]

Hi everyone,
Can anyone tell me how the old decorative plaster ceilings are held up suspended on the ceiling.

My builder tells me mine are held up by the cornice only but should have some hessian backing behind it in the roof? He reckons they are staring to sag in the middle.

I am putting a 2nd storey extension above there and I am afraid they will be damaged! He said he put in a screw but because its so thick it didnt work. Is there anyway I can hold these ceilings up somehow?

Cheers

Cobber

[gnu52]

Hello Cobber,
I assume you have fiberous plaster that is probably double nailed every 450 mm or so. This can usually be saved, but it is always a suck it and see job.
We are trying the same thing in a current renovation. We will, as we have done previously, try to lift the ceiling & reattach it to the battens. Firstly we locate the batten & ping a chalk line on the room side so we know where to place the screws, then blow as much dust as possible off the cavity side of the ceiling before glueing up. Then we either screw wooden cleats to the underside to lift & hold the plaster or use a alloy plank, rubber strips up, & acrow props to lift & hold until dry.
Then remove the cleats & plaster the holes. I try to run some long gyprock screws in as well but really the glue is doing the work.
Light cracks in the ceiling can usually be covered by finish coat and as textured a paint as you like. Avoid fluro lights because they highlight any unevenness in plaster.
Good luck, Bill

[durwood]

I had to repair one of these ceilings years ago in the inlaws old house.

I was told to clean off the plaster in the ceiling as well as the battens so I gave then a good dust down.

I then used a wide plank and some 4 x 2 timber and some wedges (acrow props would be better) to push the ceiling back up to the battens and armed with some plaster of paris and some hemp I dipped the hemp in the plaster and draped it over the battens and onto the plaster between and let it set. Its still there, saved patching up the ceiling if I had screwed or nailed.

[rod@plasterbrok]

Cobber is certainly on the right track, although I would use screws in every case. The dust on both the sheets and joist will cause the glue to fail down the track a bit.

Fibrous plaster sheets were often nailed and scimmed. Srimming was done by using hemp dipped in plaster and placed over the battens/joists and stuck to the back of the sheet. The clouts they used often come loose over many years and the scrim can let go if it was not done properly. We come across ceilings that are scrimed only. A scrimming mix needs to be very wet to get a good bond. Most of the time that scrim has failed we be due to fact the mix was not wet enough when the job was done, or the mix was starting to set a bit.

Good advise Gnu with regard to propping the ceiling. If you don't the screws will often just pull through. I would put a double scew in every 300mm along the joist/batten even more if needed, and not worry about the glue. The dust factor alone would bother me with the glue.

Also the back of fibrous plaster is just neat plaster. Unlike plasterboard where the glue is sticking to the cardboard liner, plaster itself does not glue well over the long term. Mechanical fixing is required or scrimming with plaster and hemp/fibreglass strand.

Plasterglass is still around today and is mechanically fixed with screws or it is scrimmed exactly the same way as it was years ago. Glue does not absorb into the plaster surface and create a bond as plaster to plaster does.

Cheers

Rod Dyson

[rod@plasterbrok]

Yes durwood that is the best way if you have access into the ceiling space and can get rid of all the dust.

I still like screws as well, although if the scrimming is done right it will hold.

[Cobber]

Thanks everyone. It does look dusty above the plasterboard so Im not sure if I fancy getting rid of the dust...who knows whats in it...I hear you can get alot of lead in it.

Anyway it appears that there is no hemp and they are just screwed in and the middle part is out.

I cant really understand the advice about proppin g it up? Do you mean get some wood and attach say some ply wood to it...have someone push it up and hold in the plaster and then screw the screws in it?

Im going in the morning to take photos of it and will post them tomorrow.

Basically the roof of my house is off to do the upper floor extension. I asked the builders to take it easy on the ceiling because one of the battens was loose and they had aa look and told me today about the sagging in the middle (looking from the top) and the fact they werent well suspended. Im scared they will all fall off with the nail gun and all.

Its one thing after another with the reno at the moment....

Cobber

[gnu52]

Cobber, Sorry I had a seniors moment there when I said the glue does the work, I was thinking of gyprock & not fibrous plaster.
Rod, The ceilings in the house we are currently working on were nailed up and then a slurry apparently poured in against the battens but no hessian or fibre was set over the batten. Was this the practice at the time or just badly done?
I have also had a win in the past on a ceiling without access by drilling a line of holes & using an a silicone tube to push cornice cement into place after blowing out each hole with an air gun. Then lifted the ceiling & screwed it off. On a test piece the cornice cement seemed to bond to the cypress batten.
Appreciate your comments on this as a few of these old ceilings are coming my way now, mostly without access. ie lower floor. Thanks, Bill

[rod@plasterbrok]

Hi Gnu, The job was badly done!

Just a word of warning on the cornice cement and timber. It will stick very well at first but due to the dissimilar surfaces, when they heat up and cool down they expand and contract at a different rate. This causes the bond that was there to crack and fail. This is why sticking cornice around cupboards with a MDF bulkhead, using cornice cement doesn't work.

[rod@plasterbrok]

Just for a bit more general info on old ceilings, I went out and had a look at Cobber's job today and here is what I found.

The original ceiling had not been scrimmed or nailed, yet it had been there since 1927. (cobber may confirm that date). Therefore the sheets had sagged away from the joist about 50mm. Initially, from looking at it from the ground it appered that the sheets could be propped and screwed or scrimed off.

However once we had a look from the top and saw how much sag there was, I was a bit concerned that the sheet may not take being pushed back into place with cracking too much. So I gave one a try. I hadn't pushed it up more than 10mm and could tell imediatley that it wasnt going to work.

The reason for this was, the sheet was very brittle and was poorly made lacking fibre. It was almost raw plaster. Had the sheet been made with lots of fibre, the sheet would have been more flexible, (baggy), and could have been pushed up leaving face "crazing" (many small surface cracks.

Crazing can be fixed with a skim coat of top coat and sanded. The cracks won't reapear at the sheet is still well supported with the hemp.

In cobbers case, the lack of fibre in the sheet meant the the cracks would be right through the sheet. I would say the sheet would have shattered almost like glass when pushed up. Also screws would not hold in a sheet in this condition. Meaning even if the the sheet could be pushed up scrimming would have been the only answer.

I guess the moral here is that the cap won't fit all heads.

How a repair is undertaken or if it can be repaired will depend on many factors, unfortunatly even in the old days tradies took short cuts.

The answer for cobber is that the ceilings cannot be salvaged and will need to be replaced.

Sorry cobber!!

Cheers

[Cobber]

Thanks for coming out to have a look today Rod. It was much appreciated and saved me some time trying to save it.

Typical of my luck that they cant be replaced. I can find exact replicas and Im sure it will look ok when its done again (although my wallet will also look different...smaller no doubt).

If I wasnt putting on an upper storey who knows they may have lasted a lot longer.....a warning to those who plan on exteding upwards I guess...although if it was more fibrous and was actually installed properly it wouldnt be a big problem. ii was suprised to see how brittle it was compared to the walls.

The guys who put the plaster in must have been in a rush to get to the pub or plain forgot to scrim it!

Thanks again.

Cobber

[Cobber]

Hi Rod,

Do you think I could hang the plaster up pn the ceiling myself with a plaster lifter and a couple of helpers? I would also need to out the decorative panels up and straps as well.

Can any old DIY person do this or will it be too much trouble especially considering I'll be keeping the walls?

cheers

Cobber

[rod@plasterbrok]

Its certainly not beyond you cobber.

check out tips on hanging and handeling plasterboard on our web site they should help.

The pannel lifter really makes the job easy. When you wind it up it locks in position and you can release it slightly to make minor alignment adjustments before screwing the sheet off.

You place the sheet on the lifter in a vertical positon while it is low, wind it up to about head height the tilt it over flat, and wind it up the rest of the way.

You won't need anyone holding the sheets up on the ceiling the lifter does this for you. Also you can just get up on a step ladder to screw the sheet. Get all the screws in then release the lifter. Easy as!!

Just hang all the sheets then mark out where the pannel goes and cut that section out. Insert the pannel and screw it up.

If you see the section on patching a large hole on our site it will tell you how to "cleat" the corners of the pannel. Treat the pannel just like the sheet in that example. Use the lifter to hold the pannel in place as well.

Stop up the plaster joins as normal, as you won't be able to align the joins over where the straps go because the plasterboard is not as wide as the old fibro sheets used. You won't have to stop up the join of the sheets and the pannel as they will be covered by the straps.

Those corner strips will need to be cut, to the height of the new cornice, with a pannel saw. They have that lath running through them any attempt to use a chissle will cause them to break up. You will find it awkward, and will need to cut through the wall sheet a bit along the cornice line to get the saw in. This won't matter as the small cut will get filled up with the cornice.

Cheers

[Cobber]

Thanks Rod.

I spoke to the builder this morning...he reckons it will be tough getting the plaster even as he thinks the joists arent straight so he recommended putting metal battons on and using a laser level to get them straight and then adding the plaster.

Is this the way to go do you think? How much will it lower the ceiling heights (I dont want to if I can help it)

cheers

Cobber

[rod@plasterbrok]

Use a 16mm metal batten, it wont lower it by much.

There is a clip part number 304 that goes with the batten that you will be able to adjust the height up and down.

I would check the level once the plaster is removed and see how bad it is before committing to using battens.

With the ceiling height you have, a few mm here or there, won't be noticable from the floor. the cornice line will be most important to get straight.

Cheers

Rod

[Cobber]

Thanks Rod.