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Caulking and Other Air-Sealing Materials
Within This Page
- Caulking basics
- How to caulk – Step by step
- Other sealing materials and applications
- Tips on sealing some of the leakiest areas
- Contracting the work
Air-seal any cracks and penetrations on the inside surface of exterior walls, ceilings or floors. Interior sealing will prevent air from escaping into hidden cavities in the walls and roof. The sealing will be protected from the elements on the inside, and it will be easier to periodically check its condition. Any moisture that does reach that wall space, however, should be allowed to escape to the outside; otherwise, moisture problems might result. It is not advisable to seal the outside surface (i.e., the cold side) of an exterior wall. Caulk only those cracks that will allow water entry. If you are painting the house, try not to plug the joints in the siding and use a permeable (latex) paint or stain. The outside of the walls must be left alone to breathe and dispel moisture.
Caulking Basics
Use tubes of caulking compound and a caulking gun for most sealing jobs. Try the grip with a tube in the gun before buying. Some guns may have a trigger spread that may be too large for your hand. The gun should have a shut-off. A thumb release on the gun is convenient since it permits one-hand operation.
If you are doing a complete job, you will need many tubes of caulking – one standard-size tube will make a bead 6 mm (¼ in.) wide and 7.6 m (25 ft.) long
There are several types of caulking compounds available. People often have a bad experience when they first try caulking because they purchase an inexpensive or inappropriate caulking compound. Cheap compounds are difficult to apply and lack durability. Be sure to choose a material well suited to the task. There are many types of caulking, each with specific applications.
How to Caulk – Step by Step
- Identify the areas to be caulked.
- Do not try to caulk in an area where the temperature is below 5°C (40°F); the compound will become stiff and difficult to work with. Read labels carefully for storage and application temperatures.
- Make sure the area to be caulked is clean and free of dirt, loose paint and old caulking. Replace deteriorated wood and re-nail loose boards. If there are particularly large cracks – greater than 6 mm (¼ in.) – use a special filler such as oakum or a foam backer rod before caulking. Push this material into the crack to a depth equal to half of the crack width.
- Cut the nozzle of the tube to a size that will allow the bead of caulk to overlap both sides of the crack. Make the cut square and then break the seal with a wire or long nail pushed down the nozzle.
- Push the caulking gun along at right angles to the crack or joint. The caulk is then forced into the crack to fill the gap completely. Make sure the caulk adheres to both sides of the crack and apply sufficient caulk to allow for movement or shrinkage.
Note: If you plan to caulk around items that are a source of heat (chimney, light fixtures, fan motors, etc.), be sure to use a heat-resistant caulking compound. Silicone or polysulphide sealants usually work well. Special high-temperature silicones are available for flue pipes. - The seal should also be neat. Effective caulking takes practice, so go slowly at first, following instructions on the tube. "Tooling," or finishing the bead, can usually be done with a wetted sponge or finger before the caulk sets, but do not use your mouth to wet your finger!
- Latex and silicone caulk can be cleaned off with water before they set. For other caulks, you can try a standard solvent (e.g., toluene, varsol or brush-cleaning solvent) or check the manufacturer's literature. Be sure to release the pressure lever on the gun to prevent caulk from dripping as you move from place to place.
Other Sealing Materials and Applications
A number of other materials are used to provide an air barrier at different locations in the house. These include specialty gaskets and tapes, as well as sheet materials such as polyethylene, spun-bonded olefin, rigid insulation, drywall, plywood and sheet metal. Installation techniques are critical when using sheet materials as an air barrier. All edges, seams and penetrations in the sheets must be sealed.
Air and Vapour Barriers
It is often possible to install a new air and vapour barrier using sealed drywall as the air barrier and layers of paint or sheet polyethylene as the vapour barrier. Alternatively, sealed sheet polyethylene can be installed on the warm side of the insulation to provide both an air barrier and a vapour barrier. Proper installation is critical (see illustration above).
- Use wide sheets to minimize seams.
- All seams and edges should overlap over a solid backing, such as a stud.
- Run a bead of non-hardening acoustical sealant between the overlapped sheets over the support.
- Staple through the sheets and the bead of sealant. As much as possible, avoid all other staples.
- The finish (e.g., drywall) acts as an anchor, securing the seam. If the polyethylene is recessed in the wall, a batten can be nailed over the seam to provide mechanical support.
- Seal all penetrations. Where possible, they should penetrate at a solid backing such as plywood and be caulked.
Tips on Sealing Some of the Leakiest Areas
Electrical Outlets
If you notice a draft through an outside wall electrical outlet, it must be sealed. (Some inside wall outlets can also provide leakage paths, so check them as well.) Turn off the power to the outlet by turning off the circuit breaker or removing the fuse. Check to make sure the power is disconnected by turning on a lamp. There are special foam pads, approved by CSA International, that fit between the cover plate and receptacles. You will obtain a better seal if you caulk the gasket before installation. Place child safety plugs in seldom-used outlets. Some foam pads come with a gasket that fits on the safety plug.
If you are installing an electrical outlet during a renovation, get a good seal by placing it in a special plastic box that is available from many hardware or electrical supply stores. Caulk the penetration for the wire, and seal the new air and vapour barrier to the edge of the box.
Trim Areas (Baseboards, Mouldings, and Window and Door Casings)
Seal areas of air leakage around all trim. In some cases, this can be done easily by sealing all the joints with a flexible caulk that is clear, paintable or of a matching colour. A more effective solution for leaky or poorly fitted trim is to carefully remove the trim and seal behind it. Insulate wide cracks with a foam backer rod and seal them with caulking, polyurethane foam or other suitable material.
If baseboards are removed, you might also be able to caulk between the wall finish and the bottom wall plates and between the plates and the floor.
Glass Panes
There should be a tight seal between glass and its wood frame. Check the glazing carefully and be certain that all the seals are intact, with no cracks or missing sections. If required, repair them with putty or glazing compound. Putty usually costs less but tends to dry out and crack faster, unless you put linseed oil on the wood first. A glazing compound, on the other hand, lasts longer and stays semi-soft and usable longer. Remove the old putty and apply the new materials with a putty knife. Be sure to press it firmly into the space for a good seal.
Fireplaces
A crackling fire makes a room cosy, but what happens when the fireplace is not in use? If the damper is left open, warm air from the room shoots up the chimney. When the fireplace is not in use, close the damper. Take a flashlight and make sure the damper fits tightly. If it doesn't, fix it yourself or have it repaired.
Even with the damper closed, a great deal of heat still escapes up the chimney. Commercially available glass doors for fireplaces are usually not very tight or effective. Ideally, you should also install an outside combustion air duct to the fireplace to improve operation, efficiency and safety. Ask at your local building-supply outlet or wood-burning appliance dealer if a kit is available.
You can also seal off an unused fireplace. Close it up by putting an airtight plug of some sort in the chimney or across the fireplace opening. This can be made from board material that is cloth-covered and provides a good seal at the edges (see diagram above).
Check for air leaks where the chimney meets the wall. (Remove the trim if necessary.) Caulk this joint with a flexible caulk.
Chimneys
There may be a large gap where a masonry chimney rises through the attic. This space can be partially sealed by stuffing it tightly with pieces of mineral wool batt. Do not use any material that is, or may become, flammable. For greater effectiveness, cut pieces of sheet metal to fit around the chimney. Seal all the joints with a flexible, heat-resistant sealant (see diagram above ).
If there is a factory-built metal chimney rising through the attic, do not insulate closer than 50 mm (2 in.), as this can create hot spots in the chimney lining and can present a fire hazard. Instead, install a collar of metal or other fire-resistant material around the chimney and caulk to prevent air leakage into the attic.
Attic Hatches
Seal the attic hatch exactly as you would seal a door to the outside. Caulk around the frame and between the casing and the ceiling plaster board. Apply weatherstripping along the edges of either the casing or the access panel itself.
Finally, install hooks with eye bolts or some sort of latch mechanism to hold the hatch firmly against the weatherstripping. The hatch itself should be insulated.
Windows That Are Never Opened
If you don't need a window for ventilation or as a possible emergency escape route, seal it by caulking rather than weatherstripping. Caulking is likely to be quicker, cheaper and more effective. Install a special strippable caulk that can be removed when you want to operate the window again.
Mail and Milk Chutes
Seal the chute if it is no longer in use. If you use it regularly, seal around the frame and replace the weatherstripping. If the chute cover is on a spring, make sure it closes properly. A drop of oil can sometimes work wonders or, if necessary, replace the spring. Alternatively, you can buy a new cover. Consider closing your mail chute permanently and replacing it with an outside mailbox.
Contracting the Work
Homeowners can usually do an effective air-sealing job if they have the time and patience and are conscientious about air sealing in areas that can be difficult and uncomfortable to work in, such as the attic. However, professional air-sealers can usually do a much better job because of their experience in locating and sealing leaks. Contractors may be experienced in using a depressurizing fan door (sometimes called a "blower door") with smoke pencils and with specialty caulking and sealants. Many air-sealing companies can also assess ventilation and combustion air requirements and test backdrafting.
Typically, professional whole-house air sealing can cost from $500 to $2,000 depending on the size and complexity of the house and work required. The contract should specify each area to be sealed and the materials to be used.