Why is plaster expanding when drying?

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QueenofMaps

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Hello,

I'm brand new to this forum and hardly know anything about plastering so any help appreciated.

We have sunk some cables into a wall to plaster over and smooth off. The depth of the channel is less than 2cm. We mixed up some Polycell Plaster Repair and half filled the channel roughly. This dried completely.

A few weeks later we got round to filling in the rest of the channel and smoothed it off. The next morning however the plaster had expanded so that the channel now bulged slightly with damp plaster.

Why has this happened? I thought plaster shrunk not expanded. Could old plaster cause this?

Thanks
 
Hi welcome to the forum

are you sure it has not just slumped?

I have never used the stuff and its very different to real plaster :-)

should be easy enough to sand back and fill again :-)

Danny
 
I suppose it could be. Its only about 1cm thick though. Would this amount still slump?
 
Did you go over the plaster with your trowel at 90 degrees to the chase or did you go across the chase, i.e. was your trowel edge at 90 degrees or parallel to the chase?
 
Isnt that polycell stuff an acrylic polymer base? could be why? Im just thinking gap filling properties as its aimed at DIY.
 
I doubt many plasterers use polycell plaster repair you want to go on a decorators forum that's the sort of thing they use.
 
i would guess its done what bonding does when u fill out a dusty chase. where it doesnt pull into the brick/block, it comes away lightly as the suction is too high. has it cracked around the edges??
 
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