How to Caulk Baseboard Moldings

Oak Wood Parquet Installation
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Seal baseboards with caulk to keep out cold winter air.

The main motivation for caulking baseboards is usually cosmetic, but it can be more. Baseboards cover the gap between the wall covering and the floor, and caulk is sometimes needed to seal out cold air that comes through that gap. Whether you're caulking to improve room insulation or to make the walls look better, you should use a product that contains silicone. Pure acrylic products tend to dry out and crack with age. In most cases, siliconized acrylic is the product to choose. It's paintable, and it's easy to clean up with water.

Gather Your Equipment

Paper towel wiping hands.
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If you use your finger for tooling, have plenty of rags or paper towels on hand to keep it clean.

The most obvious supply you need for caulking is a tube of caulk. One hundred percent silicone caulk is waterproof and provides the best seal of all caulks. However, once you apply it, it's difficult to remove, so use it only if you're definitely not going to paint. If you're planning to paint, or if you haven't decided yet, opt for paintable silicone caulk instead.

You'll also need a caulk gun. Most models, not including very inexpensive ones, work equally well, but those with notched plungers require less effort to operate. If you have one of these, you can release pressure on the caulk by simply rotating the plunger. That's an important bonus that makes it easier to avoid spills.

After you apply caulk, you'll need to tool it, which means to smooth the bead to form a concave surface. You can buy an inexpensive plastic tooling implement at any paint store, but when applying water-soluble caulk, your finger works better, and it's easier to use. You should have rags on hand to keep your fingers clean, and also a bucket of water to keep the rags clean. Pure silicone doesn't dissolve, so when applying this product, you won't need water, but you will need more rags or paper towels. Many professional painters consider the plastic tooling implement the least messy option for tooling when applying pure silicone.

Tips for Applying Caulk

Man sealing a bath or basin with silicone
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Get a clean bead by pulling the gun toward you rather than pushing it into the fresh caulk.

Caulking is almost a minimalist art form: the less energy you exert while doing it, the better the job will be. Before caulking baseboards, it's important to check for gaps wider than about 1/4 inch. It's difficult to fill wide gaps without having the caulk sag and break up, so tap in a few more nails to close the gaps. A few more tips can help you get great results:

  • Prepare the tube of caulk by cutting the tip at a 45-degree angle with a utility knife. The farther down the tip you make this cut, the wider the bead will be. For most applications, it's best to make the cut about 1/2 inch from the tip. Insert a 3-inch screw or nail to puncture the seal on the tube and you're ready to go. Some caulk guns have a puncture tool—a piece of stiff wire—riveted right to the body of the gun.
  • To get an even, clean bead with no excess, remember to always draw the gun toward you and away from the fresh material you just deposited. Keep the tapered tip of the tube in contact with the surface and apply a steady, even pressure on the trigger as you move the gun. Release pressure on the caulk by rotating the plunger or pressing the release lever as soon as you finish each bead.
  • The perfect bead just fills the gap with little or no overage and with no bubbles or breaks. If you notice a break, finish the bead you're doing, then go back and apply a bit more caulk to fill it.
  • After completing a bead, tool it by running your finger or a tooling implement along the surface in a smooth, uninterrupted motion. Think Zen calligraphy here. A single swipe, properly executed, produces better results than multiple passes. Excess caulk will build up on your finger, so keep a rag handy to wipe it off.

Always remember to release the pressure on the caulk before setting the tube down. Even after you've released pressure, the tube will probably still drip a little, so the safe thing to do is to wrap the tip with a rag or paper towel.