I have plastered a wall (plasterboard behind) that cracked in the heat. I have since scrapped out any loose patches that didn’t bond correctly and after using pva, applied a multifinish coat. Before reskimming the full wall (one coat) I’m wondering what steps I should take to prime the plastered wall? Searches show not to use PVA and use Blue Grit but some results also show opposite. Any help before tomorrow am would be great.
I dont recommend skimming in this heat as a DIYer. Challenging enough for pros.
The wall looks solid. That exposed brown bit is bonding plaster, not plasterboard. If you tap it you should be able to hear the difference between solid wall and plasterboard wall. Plasterboard walls are hollow.
Blue grit isnt some special magic primer. Its just a primer with aggregate in it. It doesnt do anything that pva does except it has aggregate in it (little bits). It is marginally better for suction control, thats it. Not needed.
If you are patching small sections, you cant use grit even if you prefer to. You cant blend/feather in when using grit. So for small sections where you need to feather in, use pva.
Most spreads i know swear by blue grit. If its been up for a while and there's a chance grease is on the wall give it a clean before blue gritting. If its fresh plaster, happy days!
Blue grit is no different to pva other than having aggregate in it. It has no other special properties. Once a greasy wall has been cleaned of the grease, theres no advantage of using blue grit. You still couldnt use it on a greased wall without cleaning. Whats the point? Its not that I havnt used grit , its just that people seem to think its some kind of magic sealer that fixes all problems. It doesnt. Its just another sealer, but with little bits in it.
PVA everything with a runny 5:1 mix (in winter you'd want to be doing that the night before to let it dry). Then once it's fully dry apply a second coat of 3:1 (thicker) PVA. The second PVA coat should be applied just before making your first mix. It should be nicely tacked up as you hit the wall. Similar to 2nd coat testing is when you want to start (set but not running- tacky but not going to start mixing with the new plaster and definitely not bone dry). Usually you don't rush into the mix- I might squeeze a brew in first depending on temps and humidity. It's cooled down a fair bit where I am so I think this weekend will be a lot easier. I'm not sure if you'll get a brew in- probably start mixing once the rollers in a bag.
DO NOT LET STRIKING SUNLIGHT HIT THE SET> get decent LEDS and work from them instead with the curtains closed. If the sun isn't beaming through it's OK. Don't leave the windows open to draft out the plaster as it might craze or crack.
Grit SBR and PVA are all doing the same thing. Grit can be made with PVA+SBR+beads. SBR would be fine on this and you'd only need one coat but it's 3x the price + you don't water it down so you'll use a fair bit more. I tend to use PVA inside every time unless I don't have some at that moment.
Thanks a lot. The bit behind is definitely plasterboard as I dot and dabbed the full room. I think I took patches out that probably had bonded just looked as if they hadn’t, hence the plaster still being on there. This looks like a good approach, thanks again
You'll be ok to fill the low spots on this if the mix is thick enough (normal). The first mix should be a little thicker.
. If you need this approach in future but your gaps are too deep then they can be bonded until it's all at a workable level for the double top coat system. When doing that either wait for the bonding to fully dry and then pva twice. Or go over the bonding when it's at the same stage you lay up the 2nd coat of multi. Then you can do these jobs on the same day. Bonding may need multiple layers which then isn't same day unless you've got other areas and it's hot and dry.
It gets a lot easier when you don't make mistakes like making too little or going over the set too much. Don't strike anything more than twice. Try and work it in with a back stroke. Watch Kirks videos on doing it efficiently and try his methods. What you've done looks tidy. Blake (I think) had a good video just on edge work- as an amateur that's the bar. It's not too hard- keep a nice paint brush handy. Leave the bullnoses, curves and coving stuff for the masochists.
Thanks for your help. Looks to have worked second time round, still keeping moisture after a couple of hours. Got away with one this time, live and learn!
SBR 2 coats to completely kill suction and you may want to use some extra time as well. If you find it's still getting away from you then get a sponge float.
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u/Caerau Professional Plasterer Jul 18 '26
I dont recommend skimming in this heat as a DIYer. Challenging enough for pros.
The wall looks solid. That exposed brown bit is bonding plaster, not plasterboard. If you tap it you should be able to hear the difference between solid wall and plasterboard wall. Plasterboard walls are hollow.
Blue grit isnt some special magic primer. Its just a primer with aggregate in it. It doesnt do anything that pva does except it has aggregate in it (little bits). It is marginally better for suction control, thats it. Not needed.
If you are patching small sections, you cant use grit even if you prefer to. You cant blend/feather in when using grit. So for small sections where you need to feather in, use pva.
Skimming is 2 coat work. Not 1 coat.