A skilled homeowner draws a bead on caulk

The Inspector's Eye

First try with sealant may be clumsy, but practice makes perfect

October 14, 2001|By Dean Uhler

Possibly the most valuable skill a homeowner can have is the ability to caulk. More specifically, the ability to caulk properly. Shower surrounds and shower doors rely on caulk to keep water inside. At the exterior of a house, caulk helps keep water and drafts out.

Even on low-maintenance house exteriors, there is often high-maintenance wood trim, mostly at window and door exteriors, and especially at bay windows. Wood trim is generally not rot-resistant, so it must be protected from moisture.

Water that seeps into the end grain of wood trim - where the wood was cut across the grain, such as at corners and butt joints- will saturate the wood and lead to rot. A good caulk joint keeps water out.

But caulk can lose flexibility and adhesion with exposure to the elements and then split or loosen as changes in temperature and humidity cause the wood to expand and contract. For that reason, joints in wood exterior trim can require touch-up caulking annually to avoid water intrusion and rot.

Here are some basic pointers on caulk.

Caulk types. Silicone caulk, polyurethane and polysulfide caulks are long-lasting, premium caulks. Regular silicone caulk is not paintable, so read the package before buying if you plan to caulk and paint wood trim, for example. Latex and acrylic latex caulk are typical painters' caulks - low-cost and paintable, but less flexible and durable than the premium caulks. For tubs and showers, caulk must contain mildew retardants.

Surface preparation. A clean joint is essential. Remove old caulk, using a heat gun if needed to loosen old, hardened caulk. If caulking wood that will be painted, prime the wood before caulking. Clean surfaces thoroughly. Detergent and water can be used; just before caulking wipe the area with alcohol to remove any residue.

Backer rod. If the gap being caulked is more than a quarter-inch, the caulk joint will be much more reliable if you first insert backer rod.

Backer rod, also called caulk backing, is a foam "rope" that is pressed into the gap so that its surface is no deeper than the gap is wide. This reduces the depth of the gap, so the caulk joint will not be too deep.

A caulk joint that is relatively shallow, and which does not adhere to any solid surface other than the two sides of the gap, has maximum flexibility and durability.

Applying caulk. Cut the tip of the tube of caulk at a 45-degree angle, puncture the foil at the base of the tip and start caulking. There is an art to applying a presentable bead of caulk. You will improve with practice.

If you're very good, you can apply a neat bead by gunning caulk ahead of the tip as you move it forward, matching your pace to the flow of caulk. For everyone else, avoid applying too much caulk, then smooth it with your finger.

Keep a bucket of water and damp sponge handy to clean and wet the smoothing finger and to clean up mistakes.

Inspector's Eye

Dean Uhler has been a home inspector for more than 12 years and is president of Baltimore-based Boswell Building Surveys Inc. Uhler is a member of the American Society of Home Inspectors (ASHI) and is the treasurer of the Greater Baltimore Chapter of ASHI.

Questions, with name, address and daytime telephone number, about homes and home inspections can be faxed to 410-783-2517, e-mailed to real.estate@baltsun.com or mailed to Inspector's Eye, Second Floor, 501 N. Calvert St., Baltimore, Md. 21278-0001.

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