What is caulking, and why does it matter?

Caulking, weatherstripping, sealant: the right words

People often mix up these three words. But they don't mean the same thing.

Sealant, or caulk, is the product. It comes in a cartridge and is applied with a gun. There are several families: silicone, polyurethane, latex, butyl and others. Each one has its uses.

Caulking is the work. A bead of sealant goes into a joint between two parts that don't move in relation to each other. For example, between a window frame and the wall, or between a door and the brick.

Weatherstripping is for the parts that open. ENERGY STAR sums up the rule well: caulk for fixed components, weatherstripping for moving parts such as doors and operable windows. The two work together. A well-caulked frame with worn weatherstripping still lets air through.

For sash windows, the Government of Quebec suggests V-strip or tubular weatherstripping. And one tip people often forget: never paint weatherstripping, or it loses its flexibility.

Why it matters

According to the Government of Quebec, air leaks alone can cause 25% of a home's heat loss. Natural Resources Canada agrees: it puts air leakage control first among the renovation work to do in a home.

Energy is not the only reason. When warm, moist indoor air escapes through an open joint, it carries moisture into the walls. The Government of Quebec explains that this moisture can cause hidden condensation, damage the insulation and lead to mould and rot in the framing.

On the outside, the joint also keeps rain from getting behind the siding or around the frames. A cracked joint is a way in for water, and sometimes for insects.

Where to caulk in a house

Leaks often hide where two materials meet. The Government of Quebec points out that doors and windows themselves are not always the problem: it is often the installation, and the joint between the frame and the wall, that lets air through.

For its measure that pairs roof insulation with caulking, Hydro-Québec lists the components to caulk. It gives a good idea of the spots to watch:

• windows and patio doors
• exterior doors
• attic access hatches
• range hoods and bathroom fans
• electrical outlets
• fireplaces

Inside or outside: the recommended order

The two sides don't play the same role. The interior joint stops moist indoor air before it gets into the wall. The exterior joint stops the rain.

The Government of Quebec recommends caulking the inside first, then the outside. Work from top to bottom, starting with the upper floors and humid rooms such as the bathroom and kitchen. Before applying a new joint, clean the surface well: peeling paint, dust and old caulking.

Natural Resources Canada adds a practical tip: a window you never open can be caulked instead of weatherstripped.

A word on joint width. According to NRCan, once a gap reaches 6 mm, you first install a backer rod, a compressible foam rod. The sealant sits on it and keeps an even thickness. Without it, the product sinks into the gap and the joint performs poorly.

On our job sites, the order is always the same: we remove all of the old sealant, clean and prepare the surface, install a backer rod if needed, then the sealant, and we tool the joint before cleaning up.

What caulking doesn't fix

A new joint closes an opening. It doesn't repair what is behind it.

If the wood of a frame is rotten, it must be repaired first. Sealant applied to soft or wet wood won't hold. If a window is at the end of its life, with broken glass or a warped frame, caulking will help a little, but it won't make it new again. The Government of Quebec also explains when it is worth replacing a window.

During the assessment, we tell you plainly what caulking can fix, and what calls for a different kind of work.

A house, a condo or a commercial building

The principles are the same everywhere. What changes is the scale and the access.

For a house, we caulk windows, doors, siding joints and wall penetrations, and we replace worn weatherstripping on request. For a condo or commercial building, we caulk entire façades and coordinate the job with management. We also work as subcontractors for general contractors, using the product specified in the specs.

We apply professional DOWSIL™ sealants, including 791 and CWS. Joints done with DOWSIL™ 791 carry a lifetime warranty on materials and labour, under the conditions written in the contract. We caulk year-round, in Greater Montreal, Lanaudière, the Quebec City region, the Beauce, the Eastern Townships, the Outaouais and the Saguenay.