Joint sealants don't always get the attention they need. Failing to prep right or budget correctly for a caulking job can lead to problems like moisture damage, hazardous mildew and mold, and wasted energy from inefficient heating and cooling.
To avoid these issues later, plan your caulking ahead. Choose your sealants carefully from the wide variety available—they're all designed for specific applications. When it comes to application time, clean the area first, and work quickly so you don't end up smudging your lines as they dry.
This solid prep will all help you get a functional, durable seal. Here's an overview of the process.
1. Pick the Right Caulking Product
Popular for its ease of application and ability to adhere to most materials, latex caulk can be painted to match its surroundings. It's also is easy to clean up, thanks to its water solubility.
It won't expand, but it can shrink over time, which can cause it to crack or peel. Budget permitting, you might want to reach for siliconized latex instead.
This is an improved version of latex caulk. The addition of silicone to the compound gives it added elasticity and flexibility. It's available in an interior and an exterior grade—the exterior can be used inside but the interior can't be used outside.
This compound works best on concrete, concrete block, brick, stone, gutters, flashings, and chimneys. Butyl caulk is special because of its ability to be used under extremely wet conditions, making it a great product for jobs underground and on the roof.
Butyl caulk, however, is stringy and messy during application, which makes it difficult to work with. It requires paint thinner, both to smooth out the bead and clean it up.
Although butyl caulk can be painted, it takes a long time to dry enough for a second coat.
Silicone caulk is especially well suited to sealing dissimilar materials such as metal, glass, tile, and other smooth, non-porous surfaces. It is not, however, meant to be used on masonry or stone, and it doesn't do well on redwood or cedar.
Like butyl caulk, it's difficult to work with, but only suffers minimal shrinking. It also requires a solvent such as alcohol for cleanup.
Most silicone caulks are not paintable, but there are specially formulated "paintable" silicone caulking products specifically designed for that purpose.
Polyurethane caulk has the ability to adhere to many dissimilar materials such as concrete, wood, glass, plastic, and metal. This makes it a great sealant for materials that expand or contract at different rates. Moreover, it has very high tensile strength and boasts resistance to most chemicals.
This caulking can also be a bit difficult to handle, as its consistency is like putty and it's a bit sticky, but it can be stretched by more than 300%. To finish it and clean it up, you'll need a mineral spirit solvent.
2. Prepare the Caulking Tube
Make sure the caulk is warm enough to use effectively. Cold caulk can harden and become difficult to squeeze out of its tube. Additionally, it can be hard to apply it accurately once it is out. To keep the caulk warm and easy to work with, soak the tube in hot water for about 20 minutes before using it.
3. Prepare the Surfaces
A bead of caulking is just an extra layer, often applied on smooth surfaces like ceramic tiles. It needs direct contact with the surfaces being sealed to form an effective bond and provide durable protection.
Any dust, dirt, foreign particles, scum, greasy film, or any other substance between the caulk and the surface will cause a problem in the long run. The caulk will adhere to this intermediary, which will eventually cause the sealant to unstick, creating fissures for intruders like bacteria and fungus, or just allowing moisture to pass through.
So before applying caulk onto any surfaces, get some rags, cleaning agents, and solvents, and thoroughly wash and dry the area. A good solution to fight things like shower scum is a mixture of vinegar and baking soda, to which you can also add lemon juice if you'd like.
Pro Tip: If you're sealing the inside corner joints around a bathtub or a shower stall, or when you have a long straight run to cover, consider applying painter's tape along the sides of the line you're caulking, leaving only a 3/16 inch gap to apply the sealant. That way when you smooth the caulking, the excess will spread onto the tape, which you can just remove to create a nice clean line.
4. Cut a Small, Angled Hole in the Nozzle
When you place the caulk tube into your caulking gun, cut the tip of the tube with a utility knife at a 45-degree angle. Make the hole slightly smaller than the size of the bead you want to apply. The width of the bead will be about 30 percent wider than the diameter of the hole you cut.
Try it out on a piece of scrap material and compare the size of the bead of caulk you just produced to the gap you plan to fill. If it's too small, make a slightly larger hole to get the right size. Always start these cuts on the smaller size, since you can only make increasingly wide openings.
5. Do a Practice Run
Before applying the sealant, double check that all surfaces are perfectly clean. If this is your first time applying caulk, practice the techniques on scrap material until you're confident that you can replicate them on your actual project.
Hold your caulk gun at about 30-degree angle to the work surface. Squeeze the trigger gradually, moving the tip of the caulk tube along the gap you're to sealing off. Proceeding slowly and evenly will produce an even bead you won't have to correct later, as touch-ups are more difficult.
6. Apply Evenly
For the best results, hold the tip steady and move the gun smoothly to make an even bead. If you change the angle of application during the process, you could easily crush, smear or otherwise damage the bead.
The caulking should touch both sides of any recess and fill the groove completely, as a full-contact on all surfaces is crucial for maximum adherence. For a depth greater than a quarter-inch, fill the gap first with a packing dowel or string to form a base.
If you're applying a long bead, you can break it up into shorter sections, but be careful when overlapping, because it can get messy and difficult to smooth. Always have the proper solvent handy, along with plenty of rags or paper towels for cleaning up.
7. Finish Strong
For the smoothest results, you'll probably need to use a caulking tool. Butyl, silicone, and polyurethane caulk should be smoothed with a proper caulking scraper, but if you don't have one, you can use a curved, disposable instrument like a plastic spoon.
Water-based caulk can be tooled with a finger moistened in water or dipped in dish detergent. Just make sure to wet your tool with solvent to prevent the caulk from sticking to it, and have your cleanup supplies ready.
One word of warning about butyl caulk—It dries quite fast, so you should stop tooling it when its surface becomes sticky. DO NOT insist on tooling it after it becomes slightly hard. Accuracy and speed will serve you better.
If you're planning on painting over your caulking, you should first let it dry for three days.