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I am repairing my sagging gyprock plasterboard ceiling sheets.
Can I use the old method that I used back in the 70's with fibrous plaster sheets, where a fibre material was dipped in wet plaster mix and draped over the rafters and onto the sheet.
I have forgotten what the fibre material was called. Can I still buy it?
What plaster product do I need for this process.?
You can, but it probably won't work as well.
Gyprock is plaster sandwiched between paper layers, so the 'patch' won't adhere as securely as it would if it could contact the cleaned, old plaster.
I've never tried it myself but I suspect that, while it'll work alright for a while, in the long run the joint'll fail as the paper delaminates.
As for the fibres, doing heritage work we've used everything from horse-hair through strands of sisal up to strips cut from fly-screens. I don't think it matters what is used so long as it's strong, durable and the plaster can 'grip into it.'
The fibre material was called "hemp",if I remember correctly the process was called "scrimming".
Jim
I have repaired a couple of ceilings this way, both the old style plaster sheets and newer paper faced gyprock where we were wanting to avoid needing to flush, sand and repaint the whole ceiling. We used Fiberglass rovings and cornice cement (both were available through the local Gyprock outlet). Worked quite well and after 10 or so years haven't seen any troubles with either ceilings.
With the plaster method you will need to hold the sheets up & flat until the plaster dries.
Have you looked at gyprock stud adhesive? Would be a lot easier using stud adhesive & screws to hold sheet up while adhesive dries. From what I have seen this is standard methods used by many people.
Scrimming is the old school method for fibrous plaster and not really relevant to plasterboard
You are much better off using an adhesive and screws BUT do not screw in the same place as you glue as the screws will pop over time
Is it sagging between joists, or pulling off the joists ?
If it is coming off, why not just add screws to reattach. If it is between joists, then why? Too thin, ie not rated for ceiling, or joists too far apart.
Not sure there is a decent way to fix other than remove and replace.
(it could be like part of my ceiling, sagging because it was flooded by an overflowing bath above :(
Ps, new sheets would normally be attached with screws around the perimeter and stud adhesive between, but the adhesive is only used afaik because it is quicker. It's not allowed in some situations like fire rating requirements)