Cracks on second layer of finishing plaster

[paullieo]

Hi all

Please go easy on me, I'm a amateur DIYer at best and only took this on as finding a plasterer to do such a small job has been difficult.

We had a radiator valve leak on an upstairs rad and got to it via the ceiling on the ground floor. Plumber has sorted that now.

After lots of research, I did the following to repair:
- cut plasterboard to size, offered up to ceiling and screwed in to existing joists using coarse thread plasterboard screws, and didn't damage the paper cover thankfully
- PVA'd around the edges
- filled in the larger gaps and PB screws using Toupret interior filler and then PVA'd over the dried filler
- this left about 2-3mm gap for the plaster
- used British Gypsum finishing plaster to do two coats, the first slightly thicker consistency than the second. Did the second coat after the first was firm to touch
- knew I'd never get a perfect finish so was going to sand down before mist-coat and painting

I tried my best to do a nice thin layer each time but given it's my first go, I completely accept it may have gone wrong. Looking to learn why and how to fix it here.



As you can see, the plaster has failed in a few sections by cracking and peeling away. In the second picture you can see the thickness, so slightly more than 1 mm.

Does anyone know what the cause may be? And also how to fix it? I assume take away the failed plaster and maybe use easifill? Then sand and paint as normal?

 

[Wayners]

Too much suction from the background.
You need to seal with PVA and allow to fully dry. Only when fully dry will they PVA do the job.

So.
50/50 PVA
Let that dry overnight to be sure
Another PVA. When sticky plaster.
Use blade to get smooth.
Mix more up and apply when first coat is setting.
If you need to mix up more then again stick that over and smooth.
Damp sponge around edges to blend in and use blade to finish.
No more than 2mm thickness per coat and build up.
Patches like that I put half time in mix to speed up the setting time as I can't wait 45 mins per mix. 15mins is plenty.
Use a straight edge and drag off excess plaster and keep it all flat.

Like I said. Damp sponge the edges to blend in

 

[paullieo]

Thanks. Instructions make sense, so thanks for that.

In terms of repairing, is it best to remove any sections that have cracked? Or take as much of the current plaster off and start again?

The finishing plaster pack instructions had nothing about pva'ing between layers, so disappointed about that.

About waiting time, it's at home so would prefer to have more time tbh!

 

[ree]

OP,
Dont attempt to go over it to try and fix it. It will fail worse. The square of now bad plasterboard should be replaced. If its plaster laths then come back here.
You wont need Pva at any stage for that patch.

Before going back on the ceiling - Can you practice skimming any old sheet of plaster board that you've temporarily stuck to a wall say? Skip dive for some p/b.

Square off a larger, wider area, use pencil lines on the joists, cut thro the pencilled lines with a knife.
Remove the damaged board & fix a new square of p/b. Cut up to the cove dont damage it.
The first skim coat goes on - then, depending on ambient conditions, wait, say, 15 mins then the second coat goes on.
You dont take suction out of p/b - you take suction out of the surrounding edges of plaster.