Use construction adhesive with a contact activator and a stack of clamps to hold baseboards flush for a true no gap finish.

Start by preparing the wall and the back of the baseboard so both are clean, dry, and free of dust; sand any paint gloss and wipe with a damp cloth. Measure and cut the baseboards precisely and test fit each piece dry so gaps at corners and floor are known before any adhesive goes on. Apply a high-strength polymer construction adhesive in a continuous bead along the back, concentrating near the top edge where gaps form, then spray the adhesive activator on the wall or back of the board according to the product instructions to accelerate grab and reduce slippage. Press the board into place and immediately use caulking poles, spring clamps, or temporary shims to hold the top flush against the wall while the adhesive skins over, checking with a straightedge to keep it straight. For longer runs or heavy mouldings add a few discreet finish nails low on the back edge near the floor and counter sink them so they are nearly invisible; this prevents bowing while adhesive cures. Finally fill any tiny countersink marks or joints with paintable flexible caulk or wood filler, sand smooth once cured, and prime and paint while ensuring the bottom edge remains tight to the floor.

Common problems start with poor surface prep which causes the adhesive to fail, so always clean and degloss both surfaces and allow full cure times listed by the adhesive maker. Another frequent issue is the board bowing away from the wall before the adhesive grabs, which you prevent by using an activator, applying pressure immediately, and using clamps or removable cleats to hold the board until the adhesive sets. Third, visible fastener heads or overfilled areas can ruin the no gap look, so when you do use a few nails place them at the very bottom edge, counter sink them slightly below the surface, use a flexible paintable filler or caulk to hide tiny depressions, then sand and paint lightly so the repair blends seamlessly.

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