Caulking

When to Use Caulk

Caulk is most commonly used to fill small holes, cracks, and gaps (usually no larger than a quarter of an inch deep or wide) throughout a building where air can leak in or out.

Filling gaps between drywall and baseboards or drywall and window or door trim also makes the trim look neater. It creates a smooth transition, so the trim looks like part of the wall. Once painted, it is easier to keep clean as well. Caulking baseboards where they meet the floor cuts down on air exchange between conditioned living space and exterior or unconditioned spaces (such as basements and crawl spaces).

There are more specialized types of caulk as well.

Types of Caulk

Before you start, check the tube to make sure you have the right color and kind of caulk for the work. Check to find the temperature range in which it is best to apply and cure the type and brand of caulk you are using. For most interior work, you want to use an acrylic/latex blend that is paintable; some 100% silicone caulks are now paintable also. White caulk should be used on white trim. Clear caulk should be used on bare wood trim; it goes on looking white and, after curing, looks clear and shiny.

Mortar caulk may be used to fill cracks and make small repairs (less than about 3/8-inch thick or deep) on cinder block, brick, stone, concrete, and many other forms of masonry. Fire-rated or “intumescent” caulk is used where it could be exposed to heat and to prevent the spread of fire from one compartment to another wherever cables, wires, or other services pass through firewalls and/or floors.

How To Open A Tube of Caulk

 Every caulk gun is different. Some have a hole in the stock of the gun for cutting off the tip, but these often mangle the cut. For more control of the hole size and angle, cut off the tip with a utility knife or sharp scissors.

You want to err on the side of cutting a smaller hole in the tip, rather than a larger one, because you can always recut the hole to make it bigger; not the reverse! You don't want a huge goopy mess of caulk to come out every time you press the gun’s trigger; you want a thin, controllable bead. Also, making this cut at a 45 degree angle will allow you to get the angled tip into corners.

Once you've cut the tip off the tube, some brands of caulk have an inside membrane where the tip meets the top of the tube. Some caulk guns have a thick wire that can be swiveled out to jam down the tube; otherwise, puncture the membrane with your own wire or a 3” nail.

How to Apply Caulk

Windows and doors leading outside are a major source of air infiltration in any building. The framing around either goes right to the outside. In old buildings, there is generally no insulation inside door and window frames. Even very small cracks will let air flow right through.

Examine the trim carefully, especially the parts that you can't easily see, such as above a door or window, or below a window. This is where painters often won't caulk and where there are sometimes large cracks letting in cold air. Even a small crack can let in a lot of air.

Clean the area you'll be caulking well; you don't want the caulk to stick to the dirt rather than the surface. Ideally, use a vacuum. Do any water-based cleaning ahead of time and allow to dry or the caulk won't stick. You can wipe with alcohol instead, which dries quickly. In larger or deeper gaps, you can stuff backer rod (a flexible open- or closed-cell foam “rod” that comes in various diameters and can be cut to length) to fill the bulk of the space.

Put the tip of the caulk tube in the crack and pull on the gun trigger. Drag the tip along the crack you want to fill, applying a bead of caulk in the crack you want to fill. Now run your finger over the caulk bead to press it into the crack and make it is smooth. Check carefully to see that there are no small holes. If there are, add more caulk.

Whenever you need to stop or pause in applying the caulk, let go of the trigger and take the pressure off the caulk tube. Depending on the caulk gun, do this by pushing the "off" switch on the handle or pulling back on the plunger. If you don't do this, the pressure will continue to push the caulk out and dribble it down onto your feet and that nice oriental rug you're standing on. Then you step in it and walk the mess around the house!

So long as the caulk is an acrylic/latex blend (not 100% silicone), it is water soluble, so if you make a mess, you can clean up with a wet rag. If it is 100% silicone, you have to use mineral spirits. If you get caulk on your clothes, it’s easiest to wash it out fast, before it dries.