Basic plastering

[ClockPie]

Just curious for next time

Did my first ever skim over a new plasterboard stud wall I built using Gysum finishing plaster. Anyway, long story short, pretty damn good if I say so myself (thin skim).

Most of my house is 1930s grey-ash-blocks, with 10-15mm plaster on top. With the odd bit that will fall off due to age.

The stuff I used is for 2-3mm only, and I guess as simple as it gets.

When repairing a patch (<1m2) - of 10+mm deep missing plaster back to block, just enquiring on the basic method of approach?

British Gypsum Thistle Hardwall Plaster for main thick fill?
then
British Gypsum Thistle Multi Finish Plaster for top coat?

Spray blocks with water first?
Make the thick coat "flush", or recessed ready for top coat?
When is top coat applied?

Just looking for basic method at this point. I've survived OK till now but would be good to improve

 

[23vc]

If it's low suction (ie. conc. block) then use bonding (purple bag) - wet down first
if it's high suction (thermalites or bricks) then I PVA it as it controls it easier - then use bonding
Hardwall's fine too though, for higher suction - I only use hardwall for full walls float and set, use bonding for any patching
once you've got it on, cut back the edges by a couple of mill so the skim finishes flush. The art is in the blending in so it doens't show / doesn't need much rubbing down

 

[ClockPie]

Thanks
How long till the "top skim"? Just wait till the base plaster is hard and ready to be polished?

 

[23vc]

you don't polish the backing coat, you just rule it off smooth/float it (got a poly float?) or scratch it lightly for a key
you can go over pretty much straight away if you know what you're doing and how to avoid issues with the skim, but I'd say leave it a couple of hours, skim will then go on nicely
OR, leave it a day or more, but then PVA it to control the suction

 

[ClockPie]

Thank you. (Just have metal float and hawk)

 

[23vc]

unless you're doing big areas, not worth buying the poly float just for little bits of patching, just cut it off level. Save it for when you start rendering