SBR is an additive that when mixed with cement will stick , and water won't affect it, but it is more expensive than PVA and better with cement.
If it is inside, PVA :sand :cement will work for a slurry .I'm sure others here will tell you if that is not the case .
If you are looking for a key onto the scratch coat it will work.
If you are worried you don't have enough key with the set slurry, you can paint on a coat of pva:cement and coat onto it while tacky
