How to Caulk Woodwork

Knowing how to caulk only requires following a few simple steps. Well detailed caulking can help give painted woodwork a professional looking finish.

Applying a bead of caulk is the best way to fill the joints that form between separate layers of materials. Typical areas where these joints exist include the following:

  • door and window casing to wall
  • baseboard to wall
  • crown molding to wall and ceiling
  • cabinet edges to wall
  • door and window casing to door and window jamb
  • door panel moldings to door panels, stiles, and rails
  • inside corners at baseboards and crown moldings
  • stacked moldings – wood to wood

These gaps are especially noticeable on painted woodwork finished with off-whites and pastels. The joints show as dark lines against a light backdrop. On the other hand, stained woodwork is typically caulked only at the joints that form with the wallboard.

For previously painted woodwork, most of the joints should have already been filled. If existing caulk is damaged and protruding, it can be cut away with a utility knife and removed so a new bead of caulk can be applied. For unfilled joints, you should apply a bead of painters caulk over the entire length of the gap.

For new wood trim, all the joints will need to be caulked. New woodwork should have at least one coat of primer before any caulk is applied.

Types of Caulk
There are two types of caulk that are commonly used for interior painting applications. The first type is acrylic caulk with silicon. It adheres well and maintains good flexibility. Once the caulk is fully cured, it can be painted over with all types of paints. Acrylic caulk should only be used for gaps up to ¼ inches.

The second type of caulk is elastomeric caulk. It has the ability to bridge wider gaps than that of acrylic caulk. As with any caulking compound, elastomeric caulk is subject to shrinkage. Wide gaps greater than ¼ inches usually require more than one application.

Preparing the caulk tube
Knowing how to caulk begins with preparing the tube of caulk for use. For gaps less than ¼ inches, it is best to cut a small hole in the plastic spout. A hole about 1/8 inches in diameter is a good size so as to keep excess caulk to a minimum. With a utility knife, make a cut near the tip of the plastic spout at a 45 degree angle. For gaps greater than ¼ inches you may choose to cut a slightly larger hole.

Fish a thin piece of wire through the hole to puncture the foil seal at the base of the spout. Some caulking guns have a small attachment for this purpose. Place the tube of caulk into the caulking gun with the 45 degree cut facing downward. Before you begin caulking, pull the trigger of the caulk gun a couple times to bring the caulk to the tip.

How to Caulk
Place the plastic tip of the caulking tube at one end of the joint with the cut end situated flat on the joint. Lightly depress the trigger while pulling the caulk gun in a continuous fluid motion toward the other end of the joint. Learning how to caulk well comes with a little practice. The goal is to lay down an even bead of caulk.

Once the bead of caulk is in place and before it has a chance to form a skin and set up, wipe away any excess material and evenly distribute the caulk bead with your finger and a damp knit rag. Knit rags are a good choice for working with caulk because they are made from lightweight material that does not shed. A putty knife or a 5 in 1 painter’s tool can be used to properly clean the excess caulk from the corners of the joints.

Gaps Greater Than 3/8 inches
Foam backer rod is a product designed to be used in conjunction with caulk for wider and deeper joints. Backer rod comes in a variety of diameters. The size should correspond to the width of the gap. Place the backer rod over the length of the joint. Lay a bead of elastomeric caulk over the backer rod. After the first coat of caulk has dried, a second coat may be necessary. When preparing the caulk tube, cut a hole in the plastic spout at least ¼ inches depending on the width of the gap.

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Professional Painting, Inc. is a full service painting company serving the San Francisco Bay Area since 1988.