Caulking in winter: can it be done in Quebec?

The product: what the label says

Every caulking product has a minimum application temperature. It's printed on the cartridge or in the manufacturer's data sheet. It's the first number to read before you buy.

Consumer products often need mild weather. This Old House, a magazine for DIYers, advises waiting for at least 45 °F, or about 7 °C, and a 24-hour stretch without rain. For a hardware-store product, that's a careful rule. If the forecast is below your product's minimum, put off the outdoor work: a joint applied in the cold doesn't bond well.

Architectural-grade silicone sealants, on the other hand, are made to work outdoors. The data sheet for DOWSIL™ 791, one of the sealants we apply, says it can be applied in any weather and cures at room temperature on contact with moisture in the air. That's why we caulk all year, inside and out, with DOWSIL™ 791 and DOWSIL™ CWS.

There is one nuance, though. Since this silicone cures thanks to moisture in the air, it cures more slowly when the air is cold and dry. The joint stays fragile during that time. So we avoid rubbing it, covering it or putting it under strain. We won't give you an exact time: it depends on the product, the thickness of the joint and the weather. The manufacturer's data sheet remains the reference.

The real enemy: frost and moisture

Dow's data sheet is clear: 791 is not applied on a frosty or wet surface. In winter, that's where everything is decided. A frame can look dry and still carry a thin layer of frost in the morning. It can also be damp after a storm or a thaw.

This Old House also reminds us to let the surface dry completely. Otherwise, mould can form under the joint.

Before applying, we prepare each joint:

• We remove all of the old caulking
• We clean off peeling paint, dust and residue, as the Government of Quebec recommends
• We make sure the surface is dry and free of frost
• We apply the new sealant, then smooth it

Indoors: a natural winter project

According to the Government of Quebec, air leaks can account for 25% of a home's heat loss. Winter is a good time to find them. The government's page describes the candle test: you hold a flame near a frame or an outlet and watch whether it flickers.

The Government of Quebec also recommends caulking from the inside first, to control the home's humid air, then from the outside, against rain. You work from top to bottom, starting with the upper floors and the humid rooms. Indoor work doesn't depend on the weather: it can be done in the middle of January without any problem.

During indoor work, we work cleanly, room by room. You have nothing to clean up after we leave. We also tell you ahead of time which rooms we'll be working in, so you can plan around it.

Why not put it all off until spring?

Waiting has a cost. As long as the joint is open, warm air escapes, and with it the home's moisture. The Government of Quebec explains that these warm-air leaks can cause hidden condensation in the walls, damage the insulation and lead to mould and rot in the framing.

Water matters too. A cracked joint lets in rain and melting snow. When that water freezes in the crack, it makes it bigger. By spring, the damage is often greater than it was in the fall.

So if a joint is clearly open, it can be redone right away, with a product made for the cold. Finishing touch-ups, on the other hand, can sometimes wait for milder weather.

What we look at during a winter assessment

Winter shows things that summer hides. During a visit, we pay attention to a few specific signs. You can do the same walk-around yourself before calling us, and note what you see:

• Frost or ice on the inside edge of frames
• Drafts around windows, doors and outlets
• Joints that are peeling, cracked or hardened
• Flattened or torn weatherstripping
• The condition of the wood in frames and sills
• Access to high openings, depending on snow and ice

When to postpone the work

Even with a product made for the cold, some days aren't suitable. We postpone when the surface can't be dried, or when it isn't safe. In that case, we suggest another date, and we can do the indoor work in the meantime.

• Freezing rain, wet snow or a thaw that leaves frames soaked
• Frost that won't go away on the surfaces to be sealed
• Rotten wood that needs repair before caulking
• Ice on high access points: a ladder on ice is a risk we don't take, and we advise you not to take it either