I'm trying to undercoat plaster a brick wall that is now inside a conservatory. I'm using browning which I am mixing fairly wet, also wetting the wall. There is some cracking of the plaster as it cures but more worrying is small patches that sound "hollow" as if they haven't bonded to the bricks.
Is this likely and do these areas need to come off and be re-done?
Any idea how I prevent this from happening?
Thanks, Jon
What was on the wall before you began to plaster it? Browning plaster isn't really a bonding base coat. A bonding coat is best for your first layer.
The is best keyed before you begin. This can be done with chisel and hammer to scrape some of the mortar out and allow your bonding plaster to grip better between brick courses.
The best technique to use to cover the wall is the daub and stick method. You mix up some bonding plaster and make daubs of it on the walls. Then you take plaster board and stick it to the bonding plaster before it dries. Big sheets of plaster board take about eight or nine daubs of plaster to get them to stick properly.
I would use bonding coat. (Actually, I've never come across a situation where browning was preferred.)
Bonding coat sticks just fine without doing that. You should wet the brickwork with dilute PVA first. If it all gets sucked straight into the brickwork, wait for it to dry and repeat. Ideally, apply bonding coat when PVA is nearly dry but still slightly tacky.
That's "a" technique, but not normally the best. It may be the best achiveable for someone who can't lay down a flat scratch coat. However, you should use proper plasterboard adhesive, which is a rapid setting cement mix with adhesive and fibres to give it good bonding and strength in tension, which plaster or cement alone don't have.
The base is drawing moisture out of the plaster too fast.
It's always a good idea to prime the wall with a weak PVA solution first and leave to dry.
Think you should have used bonding coat rather than browning.
I've always wondered that.
Ok, thanks guys, I'll try the PVA trick and I'll try bonding. I used Browning because the excellent article that often gets posted here about plastering says:-
"With a brick wall the best (IMO) roughing coat is Carlite Browning."
I must admit, the guy in the builders merchant did say "are you sure you want browning, nobody has used that for years" :-)
Well, if the stuff they had in stock was old, this would make matters worse.
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