How to select & apply exterior caulk & weather stripping to weatherproof your cabin.

By Fran Sigurdsson

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Cabins are all about inviting the outdoors in. And by “outdoors,” think light, views, and natural wood and stone. NOT wind, cold air and moisture.

99818155Even a well-insulated retreat can have gaps that let in these uninvited guests. Cracks don’t have to be big, either, to cause drafts and high heating bills. They can also lead to mold and rot.

Now’s the time to check for and seal any trouble spots that may have developed over the winter.

Sealing comes in two basic forms: caulk (aka sealant) and weather stripping. The difference? Caulk is a flexible compound that comes in a tube. It’s used to fill cracks in any construction material.

It also seals gaps between two different materials, like window frames and siding.

Weather stripping is a strip of vinyl or metal fitted around moveable doors and windows. It’s easy to apply from inside the cabin, and it supplements caulk for a belt-and-suspenders approach.

Caulk choices

Family may be the glue that holds a cabin together, but it takes caulk, too. Caulk has come a long way since the oil-based putty of yesteryear. Today, caulk is made from silicone, acrylic, polyurethane, latex, synthetic rubber and hybrid mixes.

The myriad types of caulk are differentiated by the surface(s) you’re caulking, whether you plan to paint the area, and user-friendliness. Each type has its recommended uses, strengths and weaknesses. For instance, water-based latex is easy to apply and clean up, but it can shrink as water evaporates; it’s best for interior jobs. See more caulk choices in the sidebar to the right.

Confused? Visit manufacturer’s websites and read product labels for more information. Look for an ASTM rating of C920, which means suitable for exterior use, and consider the length of the warranty.

A Better Caulk Gun

Anyone can caulk, but it takes practice to do it well. Most caulks come in a disposable cartridge and are applied with a caulk gun. (Toothpaste-size squeeze tubes are also available for small jobs.) A good quality caulk gun can help your projects go well, advises Mike Gorman, vice president of marketing at DAP Products.

The old style of applicator gun is a ratchet-rod-type device. These have a serrated push rod that “ratchets” (moves in set increments) down the caulk cartridge. But they can require effort to push (caulks vary in viscosity or thickness), and it’s hard to control and stop the flow.

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Newer smooth rod dripless guns let you adjust the pressure. A spring-loaded metal plate makes it easier to push; when you release the trigger, the flow stops.

Whatever model you choose, look for one that won’t bend or break if you drop it from the ladder, adds Gorman. Make sure surfaces are clean and dry, or even the best caulk won’t stick. If the crack is deeper than a half inch, insert a filler material such as backer rod before you caulk.

Caulk should only bridge a crack, not adhere to the bottom of it, or the caulk can’t stretch. Hold the gun at a 45° angle to push a bead of caulk. Then use your index finger or a finishing tool like the Newborn Brothers Caulk Buddy to smooth the bead.

Foam sealants

Foam sealants in spray cans are a good alternative to gunable caulk for gaps ¼ inch to 3 inches wide. The foam expands to fill cavities, and it can be used around windows and chimneys, ducts, vents, and outdoor faucets. A straw extension lets you access small gaps or hard to reach areas. There are two kinds: latex and polyurethane. As with caulk, both have pros and cons.

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  • Water-based latex sealant is minimally expanding, so it’s less likely to warp vinyl window frames. It’s also easy to clean up.
    Cons: It doesn’t adhere as well as polyurethane. Also, it can absorb water which may lead to wood rot.
  • Polyurethane sealant has a higher expansion rate and is water-resistant. It cures firm, and can be trimmed/sanded with a knife and painted.
    Cons: It’s not UV-resistant, so it will turn orange if you don’t paint or cover it with sheet metal. You need a solvent for cleanup.

Weather stripping

Adding weather strips to windows and doors reduces air leaks, making a cabin more comfortable and energy efficient. While it may not last as long as caulk, weather stripping technology also has progressed. So in addition to the felt Grandpa may have tacked to the door jamb, you’ll find lots of options. These include adhesive-backed foam or tape, tubular gaskets, door sweeps and V-strips.

Weather stripping may be made from vinyl, metal, open- or closed-cell foam, rubber – or a combination thereof. Desired location and appearance, durability, depth/width of the gap, and cost are all factors to consider. (Just like anything else, expect to pay more for quality.)

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Whatever kind you choose, weather stripping should fit snugly and meet tightly at the corners. It should also be thick enough to press tightly between door and jamb or window sash and frame, but not so thick as to make it hard to close.

  • Adhesive-backed foam tape comes in rolls, is inexpensive (can be under a dollar per foot), and is easy to install. It’s best for where the sides of a door or the bottom of a window sash close against the frame. Alas, the tape loses its grip over time and may pull away from the door or window frame, leaving a sticky residue behind. Foam also loses the ability to spring back and cushion the gap. It may last up to five years, depending on the brand.
  • Felt is still on the market, though it’s not as effective or durable as other types. It comes in rolls of either plain felt, or reinforced with a flexible metal strip. Staple or nail plain felt around a door frame; reinforced felt can be used around both windows and doors. It usually lasts up to two years before you need to replace it.
  • Tubular gaskets are effective for large and/or irregular gaps you’ll find around an old cabin door. They are hollow and compressible. When the door presses against the gasket, it forms a tight seal. Less expensive ones are peel-and-stick; better gaskets have a flange that can be tacked or stapled in place. These may last five years or more.
  • V-Strips (aka tension seal) are springy strips of vinyl or metal folded lengthwise into a V-shape. (Face the opening outward towards the elements.) They are designed to bridge the gap between door and jamb, or the sides of a window sash and frame, but can be hard to install. Vinyl ones are self-adhesive and last a bit longer than tape; copper or bronze ones are more costly, but look better and can last for years.
  • Door sweeps are mounted to the bottom of a door. A flexible vinyl or rubber flap seals the gap between door and threshold. Steel or fiberglass doors usually require a slide-in or snap-on sweep. L-shaped sweeps for wood doors screw onto the interior side of the door. Wraparound U-shaped sweeps fit under a door.

Breaking down four caulk options

Pure silicone

Pure silicone withstands extreme weather and adheres to glass and metal, but not to wood – with some exceptions. It is thick and can be hard to gun; for cleanup, use a solvent like mineral spirits or paint thinner.

Butyl rubber

Butyl rubber is stretchy and the most water-resistant, so it’s ideal for gutters, roofing, flashings, and around skylights. But it’s stringy and can be hard to work with; it requires solvent cleanup. Also, be aware that this product is combustible.

Polyurethane

Polyurethane is durable and adheres to practically everything. That makes it a good choice for sealing joints, since building materials expand and contract at different rates. But it can be hard to apply,
and requires solvent cleanup.

Newer hybrid formulas that combine properties of different types give you even more options. For example, siliconized acrylic latex has improved flexibility and water-resistance for exterior use, combined with easy cleanup.

And today’s modified silicone (MS) polymers combine the best qualities of silicone, polyurethane and water-based caulks for great adhesion, movement/flexibility (you might see “elastomeric” on the label), paint-ability, durability and resistance to weather.

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Spring Checkup

In spring, a cabin owner’s thoughts turn to the great outdoors. But your first hike should be around the cabin. “A visual inspection is the first critical step,” says Mike Gorman, vice president of marketing
at DAP Products, a leading caulk manufacturer. The biggest gaps are usually around door and window frames. Check gutters and the roof for leaks and/or damaged flashing and tiles. Also examine:

  • where the deck meets exterior walls
  • around air ducts and vents
  • openings for plumbing and wiring
  • exterior light fixtures
  • around skylights and the chimney
  • where siding meets windows, doors and eaves.

The cabin’s already caulked, you say? That old stuff your dad applied might not be pulling its weight. Caulk lasts anywhere from two years to 50, depending on the type. Over time, it deteriorates due to weathering and the cabin’s structural movement.

Deterioration may be uneven, depending on exposure. For example, caulk on one side of a cabin may blister or discolor, while the same product on the opposite side is fine. Incorrect application – not choosing the right caulk for the location or following the instructions – can also lead to problems. Whatever the cause, if you see that caulk isn’t making the full bond from one side of the joint to the other, remove it, clean and re-caulk.

Fran Sigurdsson likes to talk the caulk at her lake house in New York’s Adirondacks. She is happy to leave the actual caulking to her hubby, Hal.