This solvent-based primer undercoat promotes paint adhesion to wooden surfaces and flexes with the substrate, helping to prevent and alleviate flaking and cracking. Sandtex Trade Flexible Primer Undercoat is a high-performance product developed for professional use. This premium wood primer and undercoat delivers a tough foundation for exterior gloss and eggshell paint, promoting the adhesion of exterior paint to wooden surfaces. Offering 10 years’ proven durability, our advanced, flexible formulation flexes with the substrate, providing superior resistance to flaking, cracking, and peeling.