June 2003 Edition

Caulking Basics

We are painting our house this summer and need help with selecting the right type of caulk. There are so many different types on the market. Which type should we use?
Caulking is just as important as painting. Using the wrong material will cost you time and money in the long run. Despite the vast, confusing array of caulks on the home center shelf, you need only two types for your home’s exterior acrylic and polyurethane. Both types stick solidly to wood and most other building materials, accept paint well and retain their flexibility for years.
Acrylic
Use acrylic (sometimes called acrylic latex) as an all-purpose caulk. It’s water-based, so you can smooth it and clean it off your hands and tools easily. Once spread, it skins over within minutes, so you can paint it almost immediately with an acrylic latex paint. Buy the highest-quality premium acrylic caulk available. Price is a good indicator the more expensive the better. Better acrylics typically cost $2 to $4 per standard 10-oz tube. Silicone acrylic is more flexible, a good feature. However, if you buy it, make sure the label states that it’s paintable.
Polyurethane
Polyurethane performs better than acrylic in all ways, but it’s stickier and a lot harder to apply. You have to use mineral spirits or paint thinner for cleanup. Use it when you caulk concrete, stucco or other masonry and when you want extra-strong adhesion, for example, in areas especially vulnerable to water. It costs $4 to $5 per tube.
Follow these three step caulking basics
Step 1: Prepare a solid base
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Dig out old, loose caulk with a putty knife or sharp-pointed tool. Caulk hardens and cracks as it ages, usually breaking away from the wood and leaving it exposed to moisture. Clean loose caulk from cracks and gaps but leave the caulk that still adheres well. (Poke at it with your putty knife. If it readily breaks away, dig it out.) Then work primer back into the gaps. (Normally you’d do this during the paint scraping and priming stages, but if you missed spots, get them now.) Because primer adheres better to bare wood, it’s the best base for caulk. This isn’t the case with concrete, brick and other masonry surfaces. With these materials, use polyurethane caulk, which is sometimes called "self-priming" because it adheres so well.
Step 2: Lay a ribbon of caulk
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Rest the tip of the tube on the joint and squeeze on a ribbon that just covers the gap. Technique pays off here. Pull the tip of the tube along the joint, concentrating on covering the gap with a layer rather than completely filling it with a thick bead. The idea is to bridge the gap with caulk, not to fill it. A thick bead will crack and pull away from the wood when it hardens. A ribbon will stretch with the normal expansion and contraction of the wood. For smoother caulking, cut the tip of the tube at a 45- to 60-degree angle so the hole is slightly smaller than the size of the gap you want to caulk. It’s much easier to squeeze out additional caulk than to clean up the mess caused by too much.
Step 3: "Tool" the caulk to ensure good adhesion and to smooth it
Dampen your finger (with water for acrylic, thinner for polyurethane) and run it along the joint, pressing the caulk against the sides and flattening and smoothing the surface, a process called tooling. The key to a durable caulk joint is to get good adhesion on each side of the joint. Your finger will leave the joint slightly concave but don’t press the caulk tightly into corners trying to make them sharp. Acrylics and polyurethanes shrink 20 to 30 percent when they dry, so you can expect the concavity to increase.
Keep a wet cloth on hand to clean acrylic caulk from your hands and to wipe away excess. Work about 2 ft. of joint at a time, stopping to smooth each section. Otherwise, acrylic caulk will begin to skin over and won’t smooth easily.
Where To Caulk
Caulk3
Caulk all exterior joints that are vulnerable to water. Moisture is your home’s worst enemy so caulk around doors, windows, decks and other penetrations where water or wind-driven rain could get into the walls and rot the framing. Caulk also protects wood siding and trim. Water soaking in through joints can cause paint to peel and siding to rot. Finally, caulk gaps and cracks to improve your home’s appearance.
Buying A Decent Caulking Gun
Professional caulking guns begin at about $25, but even as little as six or seven bucks buys you a decent one. The quality is all in the action. Better guns (even priced as low as $6) have smoother-operating, no-slip ratcheting mechanisms, easier-to-squeeze handles, and better pressure control, so you can deliver just the right amount of caulk where you need it. Look for one that’s also "dripless," which means that it releases pressure when you relax your grip so you don’t have that 2-in. bead of slop-over dribbling onto your shirt and shoes.

Source: The Family Handyman, September 1999


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Prudential Georgia Realty

2168 Scenic Highway

Snellville, Georgia 30078

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