Restoration Guide: Windows and Doors Weatherstripping

Editor's Note: This is article 11 of 12 in Chapter 4: The Windows and Doors Guide of Old House Web Restoration Guide. This guide was developed and edited for old homes from original materials in the U.S. Housing and Urban Development Rehab Guide.

11. CAULKING, SEALANTS, AND WEATHERSTRIPPING

Section 1--Sealants and Caulks

Caulks and sealants are designed to accommodate movement and keep moisture and air from penetrating joints in your home. Not all joints should be caulked, however, because some are designed to let air or moisture trapped within walls escape. Sealants are used outside. Caulks are used indoors and are generally less flexible yet easier to apply than sealants.

If you've ever had to choose a sealant, you know how difficult it can be to sort out the different claims made by manufacturers and interpret the confusing terminology. As you go through the process, remember that no single product works for every use. Closely follow the technical guidance and instructions from manufacturers. When selecting caulk, choose a product that will adhere best to the surfaces you're treating, and choose the product that offers the characteristics that are most important for your project, such as durability or ease of application. You should also consider the degree of movement that the caulk must accommodate. Small joints are the toughest to seal because the tiniest movement represents a large percentage of expansion.

New sealants feature greater flexibility, last longer, are less expensive, and are easier to install than products of earlier generations. But no product is ideal in every aspect. Here's a look at the common types of sealants:

• Latex and oil-based sealants are used indoors as caulk. They are less flexible and usually don't last as long as other sealants, but they are easier to work with. They should not be used in any areas exposed to prolonged moisture.
• Acrylic latex, also known as rubberized latex, is more flexible and durable than water- or oil-based latex caulk and can be used indoors and outdoors.
• Butyl rubber is used in insulated window units because it resists water and temperature extremes. It's tough to install and only moderately flexible.
• Silicone, one of the most flexible sealants, is hard to remove, not suitable for porous materials, and it should not be painted.
• Polyurethanes last a long time and accommodate movement well, but their flexibility deteriorates over time, and they're hard to apply and clean up.

Before you apply sealants, follow the manufacturers' directions for preparing the surfaces and applying primers. Sealants can accommodate movement in only two directions, so if they're attached to a third surface, they come loose from whichever surface provides the least adhesion. To prevent that from happening, a bond breaker or backer material, which doesn't stick to the sealant, is placed on one side of the opening between two joints. The bond breaker, which must be durable and compatible with the sealant, also supports the sealant profile.

1.1: Installing Sealants

No sealant will work if it's not installed right. Application methods vary widely, so consult the manufacturer's directions. Sealants come in four types:

• Preformed
• Tube
• Cartridge
• Bulk

In general, sealants that perform best are also the hardest to install. To seal exterior sides of windows and doors, you'll need a high-performing sealant in large quantities and some sort of mechanical device to apply it. A variety of devices are available-- from a simple hand-operated gun to large power-assisted equipment. New tools and materials make installation easier, and you can find materials for almost any condition. Just be careful to choose the right sealant. The wrong sealant can damage or discolor joints.

Section 2--Weatherstripping

Weatherstripping provides a barrier against air, water, and noise between moving parts, such as door panels and window sashes. Here are the three main types of weatherstripping:

2.1: Inter-locking Assembly

This type lasts longest and is made of metals that resist corrosion, such as aluminum or bronze. Two materials join to make a tight fit when the door or window is closed. If they're painted or bent, inter-locking assemblies prevent the door or window from opening properly, as many an owner of an old house knows.

2.2: Compression Seal

Most new windows and doors use compression seals, such as tube, flipper, or leaf seals. Tube seals work well and last a long time, but they work only for installations that have minor variations in width. Flipper and leaf seals aren't as effective as tube seals, but they accommodate more width.

Compression seals are made with materials that have "memory," such as:

• Silicone
• EPDM rubber
• Neoprene
• Open and closed cell foam
• Vinyl
• Wool
• Spring metal

Silicone and EPDM rubber are flexible even in the cold. Neoprene is less expensive, but not as flexible in the cold. All three materials work well for shutting out noise. A magnetic strip with a flexible gasket is another type of compression seal, which, when used with metal doors, provides a tight seal.

2.3: Sliding Seal

Sliding seals resist friction and include sweep-sills and brush-sills. They are made from polypropylene or nylon and are most effective when face mounted.

Usually the same weatherstripping materials are used all around the perimeter, except for door sills. The threshold must hold up well against wear and tear of moving parts and traffic. They are usually made of strong materials with inserts that work as tube seals.

Section 3--Installing Weatherstripping

Before you apply any weatherstripping, make sure the window or door works well and repair it if necessary. Applying weatherstripping takes time--lots of it. For the most cost-effective remodeling results, choose the best materials when hiring a professional to apply them. If you're doing the job yourself and have little experience with weatherstripping, you'll find the less costly materials are easier to apply.

3.1: Interlocking Weatherstripping

This type of weatherstripping, often used in old houses, requires replacement when it wears out. It's a good choice because it's durable and lets windows and doors open and close without resistance. However, it doesn't provide a full contact seal, and the installation requires skill. It's not a task for an amateur do-it-yourselfer.

3.2: Compression or Sliding Weatherstripping

These types of weatherstripping are called resilient because they can accommodate irregular surfaces. You'll find many different brands with varying degrees of effectiveness. Follow the manufacturer's recommendations for sizing when considering compression weatherstripping. The ANSI standard provides helpful guidance. Compression weatherstripping is durable, provides a tight seal, and doesn't require much skill to install. New sliding seals last longer than earlier products and also provide a tight seal. However, resilient weatherstripping might prevent tight closure of doors and windows, impair the function of hardware, and degrade in the cold or under exposure to UV rays.

3.3: Door Thresholds

The type of weatherstripping you choose depends on the configuration of the threshold. New thresholds are made from durable materials that improve thermal performance. But you need some skill to replace an entire threshold, and unique designs might be tough to repair down the road.