Plaster types

[Andy Burns]

Is there a difference between bonding and undercoat plasters, or is it just down to different manufacturers names for the same thing?

[Tricky Dicky]

Yes. The British gypsum site has some useful advice on selecting appropriate plasters and their application.

Richard

[Andrew Gabriel]

The two main types are bonding and browning. Personally, I always use bonding coat - sticks extremely well. It's plaster, plus light weight fillers (like mica), plus a glue.

There are other possibilities too, such as lime and cement render scratch coats. Lime handles more movement by tending to form many microcracks, whereas cement will handle moisture and can be made waterproof in varying degrees from moisture repelling through to fully tanked.

Lime takes weeks to set, cement takes days (although weeks to reach final strength), and plaster takes hours.

[John Rumm]

It depends... one is really a subset of the other.

Bonding and Browning are different, but they are both undercoat plasters. The bonding version includes an adhesive as well.

[Andy Burns]

Thanks, the confusion comes from the sheds selling big bags of "Thistle Bonding" and "Thistle Browning" while also selling smaller bags of "Thistle Undercoat", I guess the latter is aimed at DIYers, but is it Bonding, Browning or something different?

I'll go with the big bag of Bonding ...

[John Rumm]

Yes ;-)

Usually a safe bet IME.

[polygonum]

Is there ever a case where browning is better than bonding? Or does it just work out a bit less expensive?

[Andrew Gabriel]

It's supposed to be better for some types of brick or blockwork (I forget which chartacteristics that's based on). I've never used it - always use bonding coat.

One other point, neither are suitable if there's any chance of damp. They both behave like a sponge, and gypsom is just sufficiently soluable that it will eventually fail if kept damp.

[John Rumm]

One is preferred for high suction backrounds - can't remember now which. (the BritGyp site will no doubt tell you). I think the browning is also a bit cheaper.