How do I deal with high suction backgrounds?
Management of high suction backgrounds would be dependent on the substrate and the material being used.
This would be required if the plasterboards were old and had been installed for some time. This would need a weak solution of Thistle GypPrime at a 5:1 or 6:1 ratio. Do not wet the plasterboards just dampen the face.
Brick and block
For bricks and blockwork, test the suction by splashing water on the background and observe how quickly the water is absorbed into the substrate. If high suction and using Thistle HardWall apply Thistle GypPrime at a dilution of 4:1. If using Thistle BondingCoat apply Thistle GypPrime at a dilution of 3:1 for and apply 3-4mm of material to aid with suction control which should be then built up to the required depth immediately.