While there are some differences between caulks and sealants, the terms are used interchangeably, even among contractors and reno­vators. In general, sealants tend to have silicone as a key ingredient and are more elastic than caulk. When cured, they’re less rigid than caulk.

Both products serve a similar general purpose: to fill or seal gaps and cracks. To simplify things, this article will refer to all gap-filling products as sealants.

The siding on your home and the trim around windows and doors move as temperature and humidity levels fluctuate. It’s important that the gaps between building materials are properly filled so the sealant can move without coming apart. Other places where gaps can occur include chimney and skylight flashing, soffit and fascia, plumbing vents, dryer vents, electrical outlets, gutters, downspouts, conduit and piping – just about any component that goes through exterior walls.

Read the instructions

Often sealants fail because the material to which they were applied wasn’t prepared properly or the wrong product was used. Not all sealants are compatible with all materials. As well, the conditions under which these products are applied can affect their integrity. This means you don’t want to grab the first tube of sealant you come across at your building supply store; you want to select the right product for the specific job at hand and install it properly. This is one instance where it’s important to heed the manufacturer’s recommendations.

Sealants for outdoor use typically come in a tube in a variety of colours, as well as neutral and clear, and are applied using a caulk­ing gun. The best-quality sealant will last about 30 to 40 years, but will eventually need to be replaced.

Applying exterior sealants can be messy, but it’s easily within the capability of most DIYers. The first thing you want to do is ensure the gaps you plan to fill are clean and dry; a quick rub with a rag won’t do. Use an exterior cleaner and scrap away any debris, partic­ularly any old sealant. The limit for sealant is about 1/4″ wide and 1/2″ deep. For deeper or wider gaps use a closed-cell polyurethane backer rod. The backer rod prevents the sealant from adhering to the back of the joint, which can restrict the sealant from moving.

Here are six sealants most likely to be used around the home.

Acrylic latex

Probably the most commonly used sealant, partly because it’s the least expensive. It’s fast drying, cleans up with water before it cures, and is paintable. However, it only pro­vides a moderate level of water resistance. Only use it outdoors if it will be painted and only on joints that won’t be subject to a lot of seasonal contraction and expansion. It’s a good choice for non-porous surfaces, including aluminum, glass and ceramic tile.

Latex with silicone

This is latex on steroids. It’s a more flexible and durable sealant than acrylic latex and it’s waterproof. Like its sibling, it’s fast drying, paintable and cleans up with water. If you do plan to use a latex on exterior joints, this is the better choice. Works well on unpainted wood, aluminum, vinyl, metal, brick, drywall, concrete and masonry.

Silicone

Silicone sealants are extremely weather-resistant, super flexible, UV-resistant, bond well to a wide range of materi­als (except bare wood) and last a long time. Premium silicone can stretch as much as 50% of its original width before tearing, which makes it ideal on joints that will move a lot throughout the year. It stays flexible well below 0°F and above 200°F. Silicone sealants also contain antimicrobial properties that inhibit mould and mil­dew. A big drawback to silicone, especially for novice DIYers, is that it’s messy to work with and it doesn’t clean up with water. You have to use acetone or special solvents. Not all brands are paintable (though it comes in a wide variety of colours) and once it cures, silicone is a pain to remove. Repairing essentially means replacing it; fresh silicone won’t adhere to cured silicone. Nonetheless, it’s an excellent choice to use around exterior windows and doors, on trimwork and for siding.

Polyurethane

These are very durable sealants that have a high tensile strength, are flexible, waterproof and paintable. They do take longer to cure than silicone or acrylic sealants. They’re also somewhat more gooey and harder to work with than sili­cone. Ensure the brand you purchase specifically states that it’s UV resistant. Poly sealants have a higher VOC level than other seal­ants. You can clean up uncured poly with paint thinner or acetone. A lot of the sealants labelled for masonry and concrete are poly based. They’re a good choice for use on metal roofs, concrete and masonry control joints, flashing, and exterior trim.

Hybrid (polyurethane and silicone)

These are the newest class of sealants and typically the most expensive. Like poly seal­ants, they’re very durable and adhere well to most surfaces. Like silicone sealants, they deliver superior weather and UV resistance, remain flexible after curing and don’t shrink. They’re somewhat easier to apply than poly or silicone sealants. All of them require mineral spirits for cleanup.

Butyl rubber

It’s sticky, hard to apply, cures slowly and releases noxious solvent odors and VOCs, but it’s just about the best sealant to use on joints that are subject to a lot of expansion and contraction. It’s very durable, has high UV resistance, is waterproof and weather resistant, and has a long (50 years or so) service life. It’s the sealant of choice for use on foundations, roofing, chimney flashing, drain spouts, pipes, gutters and the like.

Foam Sealants

Polyurethane spray foam sealant comes in a can and is extruded in a narrow band through a straw. The foam then expands to fill larger gaps and holes. While it has great sealing and insulation properties, the prod­uct is better used indoors than outdoors. It’s tricky to apply because it’s sticky and dries quickly. UV radiation causes it to yellow and degrade, so it needs to be painted. Once cured it becomes rigid and inflexible and is likely to crack as adjacent materials expand and contract with temperature changes. Sources: Greatstuff.dupont.com, Lepage.ca, Titebond.com, Touch-n-foam.com

Caulking Guns

As not all sealants are the same, neither are caulking guns. Guns come in different sizes to accommodate different sizes of sealant tubes. The least expensive are ratchet guns that push out sealant with each squeeze of the trigger. But you need to pull back on a push rod to keep the seal­ant from continuing to ooze out. They’re fine for infrequent small jobs. Smooth rod guns have a thumb lever that releases tube pressure and prevents the dreaded oozing. They are somewhat more expensive but much more convenient. Both types of guns are available with revolving frames that allow you to rotate the gun barrel to make it easier when sealing around corners. Dripless caulking guns have a spring-loaded metal plate that locks the pressure rod wherever you release the trigger. Manual guns have thrust ratios, the amount of force needed to squeeze the trigger. The ratios range from 3:1 to 34:1, with 1:12 to 1:18 a good all-round choice. Select a higher ratio for sealant with a thicker consistency. If you’re going to be doing a lot of sealing buy a powered (pneumatic, electric or cordless) caulking gun. You’ll work more quickly and do a much better job.