Our Thistle GypPrime bonding agent should be used to pre-treat surfaces where suction is extremely high. With some very porous surfaces, wetting alone may be insufficient as the water is almost immediately absorbed. If there is any doubt about the suitability of a background for direct plastering, a trial panel should be plastered and tested for adhesion once dry. If adhesion is inadequate, the appropriate bonding agent (e.g. Thistle GypPrime) must be applied to the background prior to plastering. When suction is high but not extreme, suction control may still be advisable (again with Thistle GypPrime), but is not usually necessary.
Suction and background recommendations for individual Thistle plaster products can be found in our plaster selector guide produced in a handy reference chart format. Please refer to WHITE BOOK Chapter 07 Section 02 Page 03 and Page 04 for further details.