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A Homeowner’s Guide to Caulk

Heating and Cooling, Painting, Interior Published 12/27/2007 by Joe Cuhaj

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Whether it’s sealing around the tub, keeping a winter chill at bay, or hiding unsightly cracks in crown molding, caulking plays an important and often overlooked role in your home. Used to bridge gaps where materials meet, caulking performs the essential function of keeping water and outside air where they belong, which can prevent mold and rot from forming in your walls and save money on energy bills. In addition, caulking can make your house look better and paint jobs last longer. While today’s high-tech caulk is very durable, it won’t last forever. When it begins to fail, repair the joint as soon as possible to prevent damage to your home.

Caulking Considerations

When choosing caulk for a particular job, take into account:

• Materials – Some caulks adhere better to certain materials than others.
• Moisture – In areas that stay wet, such as around a tub or sink, use a caulk that is highly resistant to both water and mildew.
• Temperature – Some caulks can only be applied in warm weather while others aren’t designed to handle extreme changes in temperature.
• Location – When caulking outdoors, choose one that will hold up to the elements and is flexible enough to withstand movement in the joint.
• Paintable – While most caulks can be painted over after they have cured, others cannot.
• Application – Some caulks are easy to apply and can be cleaned up with water while others are messy and require solvents. Several caulks have a strong odor while curing and a few even release noxious fumes.

Types of Caulk

While there are many specialized caulks on the market, the most common ones used by homeowners are:

• Acrylic Latex – Good for general applications such as sealing around windows, doors, and moldings. May be used both inside and out as long as the temperature is 40ºF or higher while curing. Can be painted and also comes in colors. Water and mildew resistant but needs to dry thoroughly before getting wet. Not as flexible as silicone or butyl rubber, but easier to apply and cleans up with soap and water.
• Butyl Rubber – Forms a highly water resistant sealant and is excellent for caulking concrete, brick, or metal surfaces. Can be painted when completely cured. Remains flexible and is a good choice for joints that expand and contract, like gutters and roof flashing. Messy to use and requires solvent for cleanup.
• Silicone – Best for sealing glass, metal, ceramic tile, and other non-porous surfaces. Doesn’t adhere well to porous materials like wood and masonry. While most brands cannot be painted, it’s available in clear and several colors. Remains flexible after drying. Since nothing sticks to cured silicone—including more silicone—it is hard to repair and leaves a film behind that is difficult to remove. Can be applied at almost any temperature. Emits a sharp odor when curing and requires solvent for cleanup.
• Kitchen and Bath – Specifically designed for areas subject to high moisture like around sinks and tubs. Comes in a variety of colors that resist mold and mildew growth. Allow to dry thoroughly before getting wet. Cleans up with soap and water.

Application Tools

Though most caulk is sold in tubes that require a caulking gun, it’s also available in handy squeeze tubes for smaller projects and pressurized cans which can be used for large gaps such as around door frames and windows.

Caulking guns consist of a cradle that holds the tube, a plunger to push the caulk out, and a trigger to control the flow. They range in price from under $2 for bottom of the line models to over $200 for battery powered ones that work at the push of a button. Those in the $10 to $20 price range feature notable improvements such as:

• Dripless – The flow stops when the trigger is released without having to manually disengage the plunger.
• Cutter – Used to trim the tube nozzle to size.
• Seal Punch – Punctures the aluminum seal in caulking tubes.
• High Ratio – More thrust in the plunger results in less hand fatigue.

Applying Caulk

Be sure to use only fresh caulk. When in doubt squeeze a little out and let it dry overnight to see if it hardens properly. Caulking is an acquired skill that takes a bit of practice to master, so practice on scrap until you get the hang of it.

Start by cutting the nozzle at a 45 degree angle equal in width to the gap you plan to fill. Cutting too wide a hole not only wastes caulk but makes the bead more noticeable and harder to smooth out.

Puncture the seal on the tube using the punch on the caulking gun or a nail.

Place the tube in the gun and push the plunger up snug. Squeeze the trigger until caulk starts to come out of the nozzle. Put the nozzle in the gap and pull the gun slowly toward you at a 45 degree angle while pushing the trigger. The bead should contact both sides of the joint and fill the gap.

Use a clean wet finger, damp rag, or special caulk smoothing tool to even out the bead before it skims over.

Wear disposable gloves to keep your hands clean when using silicone and other solvent based caulks.

To make a straight line, use strips of painter’s tape on each side of the gap. After applying the caulk and smoothing it out, peel off the tape.

More Information:

• U.S. Department of Energy Caulking Guide

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• Caulk Saving Trick (video)
• Caulking a Tub