Advice on ceiling repair, cracking butt joints (plaster board).

Advice on ceiling repair, cracking butt joints (plaster board).

Could somebody please give advice on repairing cracking along a plasterboard ceiling butt joint. The joint is about 1000mm long located across a hallway. Originally the joint had a protruding lip from a plasterboard sheet sagging.
I have installed cross members between the ceiling joist both sides of the butt joint and screwed along each side of the joint into the cross members every 150mm. This has reduced the protruding lip.
I have also scaped and sanded both sides of the joint till reasonably flush, in doing so part of the original paper tape has been scuffed and emerging through the original plaster coasts.
My questions are,
Have the steps taking so far been adequate ?
What steps are needed to complete the repair?
Can I tape and plaster over original tape?
Do I need to replace paper tape?
Do I need to sand a groove to place the new tape into?
Do I need to sand an indent or rebate along the joint so new coats of plaster don’t create a hump or ridge?
How wide and deep should I sand an indent?
How many coats of plaster are needed?
Is general-purpose plaster filler all right to use for all or any coats?
What tools are required or recommended?
Is sanding between coats required?
How do I get a smooth finish to reduce sanding back?
All advice is welcome
Jerry

I have just repaired a similar cracked joint in my sisters house and have one in my own to do shortly.

With a but join the best method is to pull the tape out and replace it. Paper take is not always that easy to get out so be prepared to do a bit of scraping. A small amount of water with a wet sponge will help and using a suitable tool. I like to use a triangular raking tool that you can buy in a paint shop. For recessed joins that have cracked taping over is ok but butt joins are normally over filled to start with hence the need to get rid of the old tape.

Scrape out slightly wider than the tape so that the new tape can be imbedded below the surrounding surface.

You have done the right thing in providing support for the join. You will need to trowel out at least 300mm either side of the tape to get the join level, perhaps even more in some cases. Replace the tape as you would normally tape a join but make sure it is very well imbedded and that there are no dry spots under it. For the first coat don't try and fill out any wider than the tape. 2nd coat fill over the tape with an 8" joint knife without trying to feather the edges let the joint knife find the level. Then apply another coat 300mm wide either side of the tape with a 300mm joint knife(these can be bought reasonably cheap, but dont get plastic). then a 4th top coat over the entire area. This should give you a flat join.

If you go to a local building site where plasterers are working they may give you enough basecoat to tape in and 2nd coat etc. The final coat should be top coat. Or else by a 5kg bag of cornice adhesive and use that (base coat is not sold in 5kg the smallest is 10 kg that I know of). You can buy 3kg or 6kg top coat and 20m roll of paper tape, whatever you do don't use fibreglass tape.

Being in a hallway, particularly if it is an open plan house, you may find it will crack again, being a weak spot in a large expanse of ceiling. There are several ways of fixing the problem if it does crack again. Perhaps the most effective but most unpalatable is to put in an expansion joint, they dont look much better than the crack! The other method is to cut out an expansion slot in the board 20mm wide then over the top of this put in a small 100mm deep bulk head or "beam", this creates a break in the ceiling wich allows expansion. This does not need to be over the crack to be beneficial. Just reapair the crack again and place the bulkhead where it would look best.


Cheers Rod

quick question Rod

would back-blocking help - assuming Jerry can get above the sheets - over this expanse?

I have installed cross members between the ceiling joist both sides of the butt joint and screwed along each side of the joint into the cross members every 150mm. This has reduced the protruding lip.

This is as good as back blocking, hence no mention of it in my post.

Cheers Rod

as usual reading late at night with droopy eyes - missed that little sentence - yep, that would do it