DAP Alex Flex Moulding & Trim Sealant, 300 mL — Paintable, Class 12.5

Crown gaps open first. A moulding and trim sealant has to stretch with a joint that moves every heating season, because the seam between crown and ceiling is where a standard caulk splits and shows a white hairline against the paint. DAP Alex Flex is built for exactly that seam: an advanced acrylic polymer rated to plus or minus 12.5 percent joint movement, which is the ASTM C920 Class 12.5 line most latex caulks never reach. It skins in 15 minutes and takes paint at 30, so trim can be run, sealed and finished in one pass, and it will not shine through or discolour the coat that goes over it. It bonds wood, MDF, PVC, composite trim, drywall, vinyl, aluminium, brick and stone, which covers everything a trim carpenter touches in a day. Cured, the seal is waterproof, weatherproof and mould-resistant, and DAP backs it for 60 years. On crown, casing, baseboard and any joint that will be painted and then watched, this is the one that holds its line.