Caulks are intended to seal small gaps and holes (less than 1/4" wide; 5 mm); just make sure that you choose the best caulk: caulks vary in quality and price and should be chosen taking into account the type and location of the gaps, their possible exposure to the weather and high temperatures, or issues like friction and pressure.
Caulks come in different prices and vary in their quality; you should look for caulks that remain flexible for many years, and avoid low-quality products.
There are several types of caulks:
- silicone caulks;
- urethane caulks;
- elastomeric latex sealant caulks;
- latex caulks;
- siliconized or silicone/latex caulks;
- acrylic caulks and...
- butyl rubber caulks.
Silicone and urethane caulks perform best overall, with elastomeric caulks coming next. Most silicone caulks aren't paintable, contrary to urethane and other caulking products. 100% pure silicone can be very messy to apply and to clean, but it is more adhesive and flexible, and less prone to shrinkage.
Latex caulks are easy to apply and to clean, contrary to silicone and urethane caulks. Butyl rubber caulks are a poor choice.
When choosing a caulk, consider criteria like temperature and fire-resistance grade, strength, color, or friction and pressure resistance. The color can be an important feature for inside space and conspicuous exterior areas.
Caulks & foam caulks
While air sealing caulks are used in small openings (up to 1/4 inch; 5 mm), foams are typically used in medium-sized ones. But some new foams can be used as ordinary caulks, for small gaps...
Caulks vary in strength and properties and energy improvements depend a lot on it. Pay attention to their grade: interior, exterior, high-temperature, fire-resistant, water-resistant, mildewcide (this last type of caulk is often advantageous, but should be avoided close to dishwashers...). Labels should tell you whether the product is suitable for what you want to seal, and its type...
If the caulk is intended for gaps bordered by different materials (wood, cement, glass, aluminum, steel…) its adhesive properties are critical.
If the caulked joint is going to be visible, pay attention to its color or choose a paintable caulk (most silicone caulks can’t be paintable).
When not to apply caulks
Foams are better than caulks for cracks and holes above 1/4 inch/ 5 mm wide.
Caulking materials can be applied where two surfaces meet (such as in window and door trims) but not on surfaces subject to movement (use weatherstripping products in the movable parts of windows and doors).
When dealing with joints and materials that are sensitive to temperature variations (metal, plastic, glass…), gaskets can be a more suitable option. Only very flexible caulks will respond properly to temperature variations.
Caulks are not recommended for many sealing jobs in the attic (foams are a better option); they do not stick well to dirty and dusty surfaces.
Some caulks can help prevent moisture and water damage. Silicone caulks are ideal for bathrooms and kitchens, and around faucets, water pipes, drains, or for ceiling and plumbing fixtures...
Cans and Tubes
For small caulking projects consider cans and injection/squeeze-tubes; for larger ones, consider disposable air sealing caulk cartridges.
When you start a can, you must use it quickly; in complex jobs, cans can be awkward to use and difficult to control.
Read carefully the instructions on the caulking cartridge, and pay close attention to preparation. Preparation can be as important as the application of the material.
Removing old caulk or paint residues can be critical; porous materials like masonry or wood may need scrapping, brushing and dusting; non-porous materials (metals...) require cleaning with an adequate solvent.
Cleaning the dirt and grease with water is often sufficient, but oiled surfaces may require proper solvents...
On critical joints, the caulk should remain flexible and strong; you may use a backer rod between the joints to get it: the caulk will not stick to the backer rod, allowing flexibility; the roundness shape of the rod creates a thinner bead and extra-flexibility...
Dry surfaces and Warm temperatures
Make sure the area to be caulked is dry; avoid applying the product at low temperatures (below 45°F/8°C); warm temperatures provide a better adherence.
If caulking with a gun, keep it at a consistent angle. The right angle is the one that forces the caulk into the crack as it comes out (45º is the best angle for getting deep). Do not apply too much caulk; release the trigger before pulling the gun away, or use a caulking gun with an automatic release.
Avoid stops and starts; do it in a straight continuous stream, as much as possible; to avoid bubbles, the caulk should be sent and fill the bottom of the gap. Make sure the caulk sticks to both sides of the crack without oozing out. If the caulk shrinks, reapply it; apply a smooth bead and carefully seal the entire crack.
GE has excellent silicone caulks, probably the best. But they haven't other types of caulks, or foams. Dap and Dupont have a larger offer, that include some good silicone caulks. As to Dow Chemical, their classic line Great Stuff includes some of the best foams in the market.