An alkali resistant high solids un-pigmented penetrating bonding sealer using modified acrylic resins for sealing powdery or friable surfaces enabling superior adhesion of water-based top-coats (where conventional bonding liquid is insufficient in binding power), or over previous paint that is very powdery or excessively chalky. Recommended for use on porous roof tiles (particularly clay tiles) that have been exposed to u.v. radiation for a long period of time leading to breakdown of the roof tile substrate to ensure proper adhesion of final coat. Suitable as a primer for Rhinolite. N.B. All surfaces must be completely free from moisture before applying Surface Conditioner.