it appears to be the backing coat.
The universal mortar appears to be for wet areas in conjunction with their water proofing / tanking products.
phone their tec helpline to be sure.
it’s pricey stuff whatever.
Just in case it is of any help to others I spoke to Wykamol and they said just mix SBR and water 1:1 and add some cement to make a slurry. Paint it on as a key for the renovating plaster coat.
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