DIY caulking or hire a professional?

What a DIYer can do, and where to stop

Indoor joints are a good place to start: around windows, baseboards or the bathtub. They're easy to reach and sheltered from the weather. The Government of Quebec actually recommends caulking from the inside first, to control the home's humid air, then from the outside, against rain.

Replacing weatherstripping can also be done without special tools. Same for a few ground-floor windows you can reach from the ground.

The limit is often height. Upstairs windows, gables, roof overhangs and high ventilation outlets call for a ladder or scaffolding. One misstep is enough to get hurt. If the job means climbing a ladder or getting on the roof, leave it to a professional equipped to work safely at heights. Taking that risk isn't a saving.

One last factor: the size of the job. Redoing two windows on a Saturday is reasonable. Redoing every opening in a house, including removing the old joint, takes time, stamina and a steady hand from one window to the next.

The steps to a good joint

A successful joint is mostly decided before application. Here are the steps, based on advice from the Government of Quebec, Natural Resources Canada (NRCan), This Old House and the DOWSIL™ 791 data sheet:

• Remove all of the old caulking, leaving none on the sides
• Clean off peeling paint, dust and residue
• Let it dry completely: a damp surface can lead to mould under the joint
• Insert backer rod in gaps of 6 mm (¼ in.) or more, according to NRCan
• Apply a continuous bead, without stopping halfway
• Smooth the joint before it skins over
• Work from top to bottom, starting with the upper floors and the humid rooms

Hardware-store products and professional products

Not every caulking product suits every use. According to This Old House, silicone bonds poorly to wood and can't be painted, while polyurethane breaks down in the sun if it isn't painted. For the joint between the frame and the wall, the Government of Quebec also suggests a low-expansion foam.

NRCan publishes a table of caulking lifespans. These are theoretical lifespans for the material: they don't account for the quality of the installation, the sun or freeze-thaw cycles. A good product applied poorly doesn't last.

The choice of product also depends on the surface. Wood, brick, stone, aluminum and vinyl don't react the same way. Read the data sheet before you buy: it tells you which materials the product bonds to, whether it can be painted and at what temperature it can be applied.

On our side, we apply DOWSIL™ 791 and DOWSIL™ CWS sealants, with an Adfast gun. For a job with specs, we apply the specified product, or the one the client supplies, on request.

Common mistakes

Most joints that come loose quickly have one thing in common: rushed preparation. Here are mistakes we often see when redoing someone else's work:

• Applying the new joint over the old one, without removing it
• Caulking on a damp or dirty surface
• Filling a wide gap without backer rod
• Choosing silicone where you'll need to paint
• Painting weatherstripping, when the Government of Quebec recommends never doing so
• Blocking a vent or a ventilation outlet
• Caulking the joints of exterior siding, which NRCan advises against

Warranty, RBQ licence and grants

DIY caulking has no installation warranty. With us, DOWSIL™ 791 comes with a lifetime warranty on materials and labour, subject to the terms of the contract.

There's also the question of grants. Hydro-Québec's LogisVert "Roof insulation and caulking" measure can provide up to $1,500, depending on eligibility. It pairs two jobs: caulking alone doesn't qualify. The roof insulation can be done separately, by the contractor of your choice. Once paired, the work is eligible. At SLT Construction, our other division, Région Isolation, does attic insulation.

Hydro-Québec requires a contractor registered with the Registraire des entreprises and holding an RBQ licence in subcategory 7.0, as well as an invoice that details the caulking work. The homeowner makes the application, and no amount is guaranteed. We are a private contractor, neither mandated nor accredited by any program. And programs don't go door to door: be wary of anyone who claims otherwise.

Costs

The price depends on the size of the home, the number of openings, access and the product chosen. DIY costs less in materials, but you have to count the time, the tools and the risk of starting over. The only real number is the one in a detailed written quote, prepared after an on-site assessment.