Restoration Guide: Sealants and Caulking for Exterior Walls

Rob Sabo

Editor's Note: This is article 17 of 18 in Chapter 2: Exterior Walls of the Old House Web Restoration Guide. This guide was developed and edited for old homes from original material in the U.S. Housing and Urban Development (HUD) Rehab Guide.


Section 1--Overview

Preservation work on any older structure likely includes replacing caulking and other sealants that have deteriorated over time. Sealants defend a home against moisture penetration and air infiltration, and a properly sealed home provides higher energy savings than a poorly sealed, drafty home.

It's important to note that not all joints should be caulked. Some joints provide an escape path for moisture that has become trapped within the wall. Most sealants in residential homes are tied into a complete weather barrier system that includes:

  • A wall cladding such as wood, vinyl, or other type of siding
  • A housewrap, such as Tyvek or asphalt-saturated felt
  • Ice and weathershield membranes
  • Flashing

Caulking and sealants are used in a wide variety of crucial areas, such as:

  • Between expansion joints
  • In joints of dissimilar materials
  • At windows and doors
  • Along the juncture where siding meets trim
  • Where flashing is required

Section 2: Choosing the Right Type of Caulking

Sealants are not all the same--some are made for certain applications depending on their chemical composition. Factors to consider include:

  • Elasticity
  • Elongation
  • Adhesion
  • Durability
  • Paintability
  • Compatability

Elasticity refers to how well the caulking can return to its original beaded shape once it weathers. Elongation refers to its ability to stretch, while adhesion is the way it bonds to cladding materials.

Each factor is important in how well the caulking holds up over time and interacts with the exterior finishing system. Before buying any sealant, read its labeling for performance characteristics.

2.1: Weatherability

Different types of sealants have different weathering characteristics. When remodeling, inspect the caulking to see if it has hardened, wrinkled, bubbled, or eroded. Old and damaged caulking should be removed and replaced.

2.2: Properly Sealing Joints

Sealants should only adhere to two surfaces, such as two butting ends of lengths of siding. When sealant adheres to three sides, such as the exterior sheathing and two pieces of siding, it can tear and fail since it can't properly expand or contract. Sealant manufacturers recommend use of backer rods between joints or a special bond-breaker tape to prevent this third line of adhesion.

2.3: Installing Caulking

Improper installation is the leading cause of caulking failure--and one of the main reasons why it's important to properly install the caulking during a home renovation. Poor installation can include:

  • Improper priming or cleaning of the siding material
  • Installation with incompatible materials and coatings
  • Installation when the material is too cold, hot or wet

Section 3: Types of Sealants

There are more than 300 different sealant manufacturers in the United States. Choosing the right sealant is essential to properly protect new home restoration work.

The most widely used sealants include:

  • Latex and oil based. These sealants are cheap and easy to use, and are commonly called caulking. They are best suited for interior applications as they don't have high degrees of weatherability.
  • Acrylic latex. This is a more durable form of caulking also best suited for inside a home.
  • Butyl rubber. Commonly used to insulate around windows and between layers of flashing. It has a high level of adhesion, and it resists water and temperature fluctuations.
  • Kraton. This is a solvent-based synthetic rubber sealant that has become widely used as a general-purpose sealant.
  • Silicone. This sealant is used extensively with exterior insulation and finish systems (EIFS are discussed in more detail in article 15 of this chapter). It is the most elastic and durable sealant, but it doesn't hold paint well and it is hard to remove.
  • Polyurethane. Although this sealant has great flexibility and is highly durable, it loses its flexibility with age and does not hold up well under direct sunlight.

Kraton, polyurethane, and silicone sealants have the longest life at 10 to 20 years, but their costs are significantly higher than other sealants.

Section 4: Preparing Existing Surfaces for New Sealant

When applying sealant, it's important that all surfaces are clean and dry to ensure proper adhesion. When applying sealant to pourous surfaces, such as an old foundation, or brick and masonry work, joints should be cleaned with a metal-bristled brush or grinder, and loose particles should be dusted off, vacuumed, or blown out with compressed air.

Section 5. Mechanically Installing Sealant

Sealants most often are applied with a caulking gun from a tube. Bulk-loading guns are available when large amounts of sealants are required. Such guns are either pnuematically driven or powered by electricity or batteries. Powered guns typically help ensure consistent application of the sealant, which leads to better performance. However, it's also easy to over-apply sealant with a powered gun, which may discolor siding materials.

Without proper sealants around crucial junctures, no exterior cladding system can withstand water penetration. Any remodeling job should include a careful examination of the home's exterior sealants to ensure their durability, and aged sealant should be replaced.

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