Exterior Caulking near you

Caulking belongs wherever two parts of the outside of the house meet and water could slip between them. It is the first line of defence, not the only one: the siding, flashing and membranes behind it still have to shed whatever gets past.

Exterior sealants are sold by chemistry, and the label says what each one bonds to, how much joint movement it tolerates and whether it can be painted. The notes below are general; the right choice depends on both surfaces of the joint and on the manufacturer's instructions.

A new bead is only as good as the joint beneath it. The old caulking is cut and scraped out completely, and the joint is cleaned of dust, paint flakes and residue so the new sealant bonds to sound material; leftover silicone needs particular care, since most sealants won't stick to it. Rotted wood found behind a bead is repaired before anything is sealed over it.

Joint size matters too. For the space around a window frame, Natural Resources Canada's Keeping the Heat In says gaps of 6 mm (¼ in.) or less can be insulated and caulked, while wider gaps call for a backer rod with sealant, or a low-expansion foam. The backer rod, a flexible foam cord pressed into the joint, sets the depth of the bead and keeps it bonded to the two sides only, so it can stretch as the joint moves. The bead is then tooled smooth so it presses into both surfaces and sheds water.

Sealants cure by drying or by a chemical reaction, and both depend on the weather. Every product has a temperature range for application, a limit on surface moisture and a waiting time before it can take rain, all printed on the label, and those limits vary from one product to the next. Follow the label rather than a rule of thumb.

In practice, that makes exterior caulking mostly a job for milder, drier weather. Surfaces must be dry and free of frost, which rules out dewy mornings even when the afternoon is warm, and a wall baking in direct sun can make a bead skin over too quickly or sag. Because joints open in the cold and close in the heat, a contractor may plan around the forecast or work the shaded sides of the house first. If a joint leaks in winter, ask about a temporary fix until conditions allow proper work.

Look over the joints you can reach from the ground each spring and fall, and use binoculars for the high ones rather than a ladder.

Outside caulking is mainly about water: it keeps rain and meltwater out of the joints so the wall stays dry. Air sealing is mostly done from the inside, at the air barrier, where it stops warm, moist indoor air from leaking into the walls and attic. A common building-science principle is to make the inside the tightest layer, since a wall sealed hard on the outside but leaky on the inside can trap moisture. For drafts and heat loss, see the insulation and air sealing pages.

Exterior caulking also shouldn't block openings meant to let water out. Weep holes along the bottom of brick veneer, drainage gaps at the base of some window frames and the bottom edges of lap siding all let water escape, and sealing them traps it in the wall. A careful installer knows which joints to close and which to leave open.

Health Canada lists caulking and sealants, along with putty and paint, among the materials in older buildings that may contain asbestos. It advises avoiding disturbing materials that may contain asbestos, having a professional test them before renovating and, if asbestos is found, hiring a qualified removal specialist. The hard original caulking and window putty on an older house are worth testing before anyone cuts, scrapes or grinds them out.

The trim around those joints may also carry old paint that contains lead, and Health Canada advises against sanding, heat guns and torches on lead-based paint because they create toxic dust and fumes. Before recaulking an older home, ask the contractor how they will test, contain and dispose of the old material.