I’ve noticed that too and it seems a bit odd. The boards I have which are wet process are made in 20mm boards so the 40mm is two 20s bonded together.
We didn’t do a parging layer but we did make sure the walls were very flat so the fixings hold the wood fibre tight to the existing plaster. We filled any small holes with finishing plaster and big holes with base coat.
Our plasterer is doing the finish coat so I think she will decide what we use. I would guess a lot of finishing plasters are suitable.
These bits have been filled yes. There was quite some patching to do after removing the cornice. Will probably do a second coat before getting the boards on.
I’ve been mixing up nosterfield sand and quicklime 4:1. It’s fairly easy to mix if you’re careful about the heat in generates. Goggles and gloves are a must.
I think that would make for a good parge coat.
I’ve read that some of the NHLs set harder than initially thought so worth bearing in mind. They’re tested at 28 days which is when cement reaches its peak hardness but the NHL gets harder over the years as it carbonates.
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Are you saying you used gypsum plaster to fill the holes and flatten the wall? Was that for practical reasons or do I missunderstand? Sorry, just a bit confusing as bonding coat and finishing plaster are gypsum based.
Isn’t that defeating the objective of using the woodfibre boards and lime finish?
Sorry for the confusion. When I say finishing plaster I mean a top coat lime plaster with a very fine aggregate.
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