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Caulk a small cosmetic baseboard gap

Clean a sound, dry seam above baseboard, apply a small bead, tool it neatly, and allow time before painting.

Match the illustrated design first. Top-of-baseboard cosmetic gap only | Sound, dry joint | Keep floor movement gaps open
3D GUIDE · 74 SECONDSNIKI NARRATION

Open the MP4 video · Written steps below

Representative educational illustration with working and waiting time compressed. Read the exact model scope, safety checks and complete written procedure before starting.

Match your repair

A small, stable, dry joint at the TOP of securely attached interior baseboard where it meets a painted wall, using DAP ALEX FLEX. Known-safe coatings/materials only. No floor expansion gap, loose trim, butt-joint repair, water damage or structural movement.

Safety and stop conditions

  • No lead/asbestos disturbance; unknown old coatings/materials stop before removal or scraping.
  • Do not caulk floor expansion joints, loose trim, wet surfaces or recurring cracks.
  • Use finishing tool rather than bare finger; gloves, eye protection and ventilation.
  • Product limit is 1/2 inch wide by 1/2 inch deep, with backer rod for deeper joints; this tutorial intentionally covers a much smaller cosmetic seam and does not teach large-gap filling.

Tools and materials

  • DAP ALEX FLEX paintable molding and trim sealant, cartridge or squeeze tube
  • Caulk gun if using cartridge; safe nozzle cutter
  • Damp finishing tool and cloth/sponge; optional painter’s tape
  • Protective gloves, eye protection and ventilation

Before you start

  • The trim must be secure and the joint dry and stable. Caulk does not fasten baseboard or correct wall movement.
  • A gap under trim may be a necessary floor expansion gap and is outside this guide.

Repair steps

  1. Check the joint

    Use this for a small, stable gap above securely attached baseboard. Stop for loose trim, dampness, recurring movement, or suspect old coatings. Do not fill a floor’s required expansion gap.

  2. Clean and dry

    On known-safe surfaces, remove old caulk from the section being repaired without damaging the paint. Clean away dirt and residue, then let the joint dry completely. Protect the floor and provide fresh air while working.

  3. Prepare a small bead

    Wear gloves and eye protection. Cut the nozzle at a forty-five-degree angle, starting with a small opening suited to the gap. Load the cartridge into the caulk gun if needed.

  4. Fill the gap steadily

    Run a controlled bead of paintable molding-and-trim sealant along the joint. Maintain steady pressure so it contacts both surfaces. Release the gun’s pressure when you stop to limit drips.

  5. Tool while wet

    Smooth the fresh bead with a damp finishing tool before it skins over. Wipe away excess with a damp sponge. If you used masking tape, remove it while the sealant is still wet.

  6. Let it dry before painting

    Follow the label before painting. ALEX FLEX needs at least thirty minutes, longer in cool or humid conditions. If the gap reopens, investigate movement or attachment rather than repeatedly covering it.

Check the result

  • Inspect for a continuous neat seam bonded to both wall and baseboard.
  • Check again after the finish dries. A reopening seam requires diagnosis.

Common questions

Can I caulk the gap between the floor and baseboard?

This tutorial covers only the upper wall-to-baseboard seam. Do not fill a floor manufacturer’s required expansion space.

Does thirty minutes mean fully cured?

No. For ALEX FLEX that is the minimum paint-ready time in suitable conditions; cool or humid conditions take longer. The technical sheet lists a typical 24-hour full dry-through time.

Why does the gap keep opening?

Recurring movement, loose attachment or moisture needs investigation. Another cosmetic bead may only hide the cause temporarily.

Manufacturer and safety references