Design & DIY

Applying new caulking

Exterior caulking keeps out water, critters, and drafts. From time to time, do a walk-around inspection at the cottage and replace any caulking that’s missing or damaged

Out with the old: Old caulking is the enemy of new caulking: Cracked, hard, and fossilized remains have to go. My favourite caulking remover is Re-Mov (about $12 for a 236 ml bottle; check for retailers), a pleasant-smelling liquid that softens the bonds between many types of caulking and surrounding surfaces. Squirt some on, then work in from the edges of the bond with a putty knife. Expect to repeat this several times before all the old caulking is off. Caulking is tough—especially old caulking. It’s a miracle that anything loosens it at all.

Choosing the new: You get what you pay for. Inexpensive formulations such as latex or butyl cost half as much as more durable options, but they last less than half as long. Where are the savings if $1.99-a-tube caulking won’t last until the next election, while the $8 stuff lasts until 2050?

Silicone caulking is an expensive, time-tested choice that’s widely available and stays elastic forever. Trouble is, silicone doesn’t always remain stuck to surfaces and can’t be painted. Polyurethane caulking stays flexible, never lets go, and is completely paintable. LePage 
PL Polyurethane is one brand that’s easy to find at hardware stores.

Application Information: You’d think exterior caulking would block a narrow gap better than a wide one. Not always. In a tight space, seasonal movement is relatively much greater: For instance, a gap between a window and wood siding may be only 1 mm after warm spring rains but can easily expand to 3 mm during dry, cold times of the year. No caulking can stretch 
to three times its original width without failing. But if that gap were 
4 mm in warm, wet weather to start with, it would still expand the same 2 mm distance when it’s cold and dry. Any decent caulking can stretch that far; it’s only 50 per cent. The best time to caulk is when the joint is widest, or you can sometimes widen tight joint gaps with an oscillating multi-tool.

More tips:

  • Beware of gaps that are too deep. Caulking beads that are deeper than their width use unnecessarily large amounts of caulking, and are more prone to movement-induced failure. Stuff foam backer rod, available at hardware stores, into deep gaps before applying caulking.
  • For fast, neat results, apply masking tape along each side of a joint. Smooth the caulking bead with your finger and immediately peel off the tape.