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Caulking: Pro Tips

Whether you're caulking a siding, a bathtub or exterior doors, it's important to fill gaps completely and lay a neat caulk line. A pro shares his tips for getting great results.

By the DIY experts of The Family Handyman Magazine

Lessons learned from miles of caulking

I’ve emptied at least 5,000 tubes of caulk in my career—that’s a bead about 20 miles long! I’ve filled in gaps so flawlessly that the caulk was virtually imperceptible, but there’s been plenty of times that I’ve globbed things up pretty good.

To help you get a top-notch caulking job with a lot less frustration, I’m going to share a few tips I’ve learned along the way.

Choose the right caulk for the job

The selection in the caulk aisle at home centers is mind-boggling, but actually choosing the right one is pretty simple. Most of the caulk on store shelves is basically one of four types: elastomeric, polyurethane, latex or silicone. Here’s how I make the right choice:

  1. Siding, windows and doors: Polyurethane is my hands-down favorite. It’s paintable. It doesn’t shrink. It stays flexible. It adheres better than silicone, and it doesn’t attract dust and dirt the way silicone does.
  2. Roofing: I like an elastomeric or rubberized product. This stuff won’t dry out in extreme conditions, and it sticks to everything.
  3. Interior trim: If I’m sealing gaps and nail holes in trim that’s going to be painted, I always use latex. It cleans up easily and dries fast. It’s also easy to tool—and cheap.
  4. Kitchen and bath: This is where silicone products shine. Silicone tools well. It can be purchased with antimicrobial additives, and can be easily removed and replaced when it gets grungy.
The After-Mess

Some tubes have air in them and “burp” at the worst possible moment. Some continue to run after you set them aside. The bottom line: There’s going to be cleanup. Use mineral spirits to clean up elastomeric and polyurethane. Latex cleans up great with just a wet rag. Silicone is another story. It seems to get on everything. My only tip for cleaning up silicone is that when it does get all over your gloves (and it will), just consider the waterproofing it provides as a bonus.

My favorite gun

Choose the right color

When you’re caulking gaps between prefinished siding and trim, use the color of the siding. When working with stained or natural wood, choose a color a little darker than the wood. A darker color will blend in with the knots and other imperfections.

Push, don't pull

Clean out old caulk

Clean out old caulk

Foam backer rod.

Foam backer rod.

Prepare a Solid Base for Caulk

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, 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.)

For a gap wider than about 1/4 in., insert a special foam backer rod to fill the bulk of the gap. If you fill the entire gap with caulk, it'll soon harden and crack. To retain flexibility, your ribbon of caulk shouldn't be more than 1/8 in. to 3/16 in. thick . Home centers and hardware stores carry foam backer rods in several sizes.

Ride the smooth side

Cut tips off straight

Tooling tips

Don't use your wrists

Salvage a wet tube

Meet in the middle

Pull the plug

Caulking stone and masonry

Choose a caulk color that'll blend with concrete or other masonry so you can leave the caulk unpainted. Use backer rod for big gaps, and neatly tape off the stone – caulk mistakes on masonry and stone can be impossible to scrape off. If the caulk gun is bouncing all over the jagged stone, smooth the caulk with a rounded putty knife. Pull off the masking tape immediately after you've tooled the joint.

Where Not to Caulk

Don't caulk joints that aren't affected by water and won't mar the appearance of the final paint job. Two examples are horizontal joints under lap siding (Photo 5) and the tops of drip caps over windows and doors where flashing carries water to the exterior. Joints protected by roof overhangs don't need caulk either.

In general, don't use exterior caulk as a way to make your home more airtight for better energy efficiency. Moisture generated inside must have ways to get out. If you seal your home in an airtight skin, you'll trap that moisture in the walls, especially in cold weather, and it'll soak the wood, cause rot and lift the exterior paint.

Still, a good caulking job will make your home more airtight. So afterward, check your gas- or oil-burning appliances to make sure they continue to vent waste gases properly.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

    • Caulk gun
    • Putty knife
    • Rags
    • Utility knife

You'll also need gloves and a caulk-tooling kit

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

    • Silicone caulk
    • Polyurethane caulk
    • Elastomeric caulk
    • Latex caulk
    • Mineral spirits
    • Water
    • Duct tape
    • Masking tape
    • Drywall screw

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