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Keep out the cold by caulking and sealing cracks
Oct 23, 2015

With winter on the way, it’s a good time to upgrade the insulation in your house. One of the least expensive, effective and easiest ways to do this is to caulk and seal cracks through which wind and cold air enter your dwelling.

Caulking cracks from the exterior is the recommended method to prevent little eddies of cold air from infiltrating openings in walls around air conditioners, power entrances, windows and doors and many other areas. Caulking from the interior of the house also works, but it does not stop frigid air from seeping inside your walls from the outside, possibly causing moisture accumulation due to condensation.

One product I like is called Draft-Stop by LePage, a transparent caulk that is especially useful for sealing leaks around old windows. It comes in a cartridge and is applied with a hand or pneumatic gun. The advantage over other types of caulking is that Draft-Stop is a removable weatherstripping that can be easily peeled off in spring. I use it every year on a wood window that is still presentable and rot free but shifted over the years, making it difficult to seal with other types of weather stripping. Draft-Stop sells for about $5 a tube and can be applied indoors or outdoors.

Oil-based caulking adheres to most materials and is inexpensive compared to some silicone or butyl products. The main knock on oil-based caulks is that once the oil dries out in a few years, the material will shrink and fall out of cracks. This necessitates re-caulking every four to five years, which is an onerous task because the old caulking must be completely removed before a new product is applied.

Polyvinyl acetate caulking is relatively inexpensive and will adhere to almost any surface. Its con is that it will not stick to a material for a long period of time, especially in areas like kitchens and washrooms that have a lot of moisture. Moreover, polyvinyl and similar resins are considered old-school products that have been surpassed by superior formulations. Unlike oil-based caulking, polyvinyl does not have an irritating smell.

Latex caulk is a good indoor sealant because it can be painted and cleaned up with water. It will last for up to 20 years around doors, windows and other air leaks that are not subject to excessive moisture, which will cause it to shrink. The best way to apply latex is to run strips of masking tape either side of the joint to be filled and then run a wetted fingertip over the bead to flatten it. When the caulk is dry, strip off the masking tape covered with the excess caulking. 

Acrylic caulking can be used indoor or outdoor because it is water-based. It is flexible in cold climates and comes with a 25 year limited warranty. Though it is sold in colours, it can be painted once it has set. It is one of the least expensive indoor/outdoor products, sometimes retailing in packs of five tubes for about $12. I have used this product extensively. My main beef is that the purported “25-year durability” printed on the label is more like 10 years in Manitoba’s harsh climate.

Silicone caulk is a pricey material sold in a multitude of colours because it is non-paintable. Though it can be used outdoors and will purportedly last for up to 50 years on most surfaces, I have only used the caulk as a kitchen and bath sealant because it is mildew resistant, water-tight, has excellent adhesion and low shrinkage. One con is that silicone has a strong vinegar smell that can be irritating to the eyes when first applied. Another is that it must be cleaned up with either methyl hydrate, mineral spirits or, if these don’t work, nastier solvents such as lacquer thinner, acetone or toluene.

Polyurethane caulking is an all-purpose exterior crack filler sold in 300 millilitre cartridges for about $6 each at most big box or lumber stores. The advantages to this product are that it contains no solvents, cures by reaction to moisture in the air and sets to a rubber consistency that gives it elasticity to prevent cracking. It has a life expectancy of about 40 to 50 years, according to manufacturers. The most effective chemicals to clean up polyurethane before it has cured are acetone and methylene chloride. For those who prefer to caulk once in a lifetime, polyurethane is their product of choice.

Polymeric foam (generally known as spray foam) is an excellent joint sealer that will stick to numerous substrates. The low expansion variety is best for sealing around window and door frames because the high expansion product will force the frames to bow inward. However, for large exterior gaps where a house or garage sill plate meets a foundation wall, high expansion foam is a good choice. For big jobs, money can be saved by purchasing a No. 14 or No. 15 application gun that accepts a larger can of foam and will not plug like the plastic straws provided with ordinary cans. (Clean your gun with acetone at least two days after use to prevent the foam from setting inside of it. Also, do not buy cheaper No. 13 guns as they are poorly designed and will cause unending grief.)

For sealing outdoor concrete and masonry, butyl rubber caulk is one of the most highly recommended products. It will also seal gutters, flashing, chimneys and aluminum siding, even in wet conditions. The down side to this caulk is that it is difficult to work with, forming strings and drools that must be cleaned up immediately with paint thinner. Also, because the material expands by about 20 to 30 per cent when it is released from the tube, begin by cutting a small hole in the cartridge’s applicator tube before enlarging it, if necessary. Moreover, butyl tends to shrink as it cures so a second application may be necessary in some spots.  

There are “siliconized” caulks on the market that can be a blend of latex, acrylic and silicone. However, these products do not state the percentage of each sealant they contain, meaning that the consumer has no way of knowing how much silicone, the best of the sealants, is in the mixture. Often, siliconized caulks are an attempt by manufacturers to lure a buyer into purchasing a low-quality product that capitalizes on the good reputation of silicone.

For people intent on buying the highest quality sealants, there are two-part commercial products available that require pre-mixing with a catalyst and colourant in a pail with a 1/2-inch electric drill and paddle. A spatula is used to feed the sealant into a special gun for application. I used an epoxy form of this goop to seal the exterior seams between the logs of my house. Though the caulk was very expensive, tedious to prepare and messy to apply, it has withstood 20 winters without cracking, peeling or otherwise deteriorating. Its normal use is to fill expansion joints on highways.

Good luck sealing your home for winter.