my Old Workshop

Caulking confusion cleared up

“Just picking up some caulking. Back in a minute!” Twenty minutes later, you’re still browsing through rows of tubes.

There’s hope. That bewildering array is less confusing when you know what surfaces you’re caulking, how much joint movement you expect, whether you want to paint it, whether it’s outside or inside, and what temperature extremes it must endure.

Labels provide exact details for particular brands, but here’s some help to zero in on the right area of the shelf.

You’ll find caulks designed specifically for things like roofing and foundation work, but silicone, latex and acrylic formulations work well for most applications.

Silicone is waterproof and very flexible. It works in wider temperature extremes, can be used indoors and out, won’t shrink, and lasts the longest (one brand claims 50 years). Silicone sticks well to glass, metal, plastic, vinyl and (very smooth) concrete, and some brands are also formulated to bond to some woods. A few brands are paintable. Some smell almost pleasant, but silicone has an annoying way of getting all over your hands if you’re not careful; you need mineral spirits for cleanup.

Latex and siliconized acrylic latex are both water resistant, paintable, will stick to most porous and non-porous materials and they’re recommended mainly for interiors. They’re real easy to apply and they wipe up with a cloth (which makes it easier to smooth a bead with your finger). But acrylic latex is a little less flexible, so it’s not recommended for joints where you expect movement. And latex shrinks, leaving wrinkles or gaps. (Leave a concave bead to counteract this.)

Solvent-based acrylics (you can tell by the nasty smell) have great adhesion and minimal shrinkage, but poor flexibility in low temperatures. You probably don’t want to use this indoors, as the smell can actually contaminate foods.