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joint caulks & sealants

Caulks and sealants are both meant to fill cracks or gaps between materials and prevent the flow of air and water. Caulks cure more rigidly and are meant for situations where expansion or movement is expected to be very minimal. Sealant however is meant for situations where the gap or crack to be filled may be larger or is expected to experience differential movement between the materials. Sealant joint widths most commonly range between 3/8″ and 3/4″ but can be an inch or more or even down to 1/4″ in some situations. A ‘gunnable’ sealant is a sticky liquid that is injected into the joint with a sealant gun and cures within the joint and becomes rubberlike.

Type S sealants are single component and require no jobsite mixing. Type M sealants are multi-component and must be mixed on the jobsite.


In general, Type M sealants will cure faster than type S and have a better variety of color choice. Dye packs can be added during mixture. Grade P Sealants (self-leveling) are pourable and are most commonly used in horizontal joints. But a Non-Sag (NS) formula can be utilized for vertical joints.

Class defines the elongation capability of sealant. A Class 25 sealant can tolerate up to 25% expansion and contraction under normal circumstances and temperatures. A Class 100/50 sealant can handle 100 percent expansion and 50 percent expansion.


‘Use’ defines the material application scenario. A ‘Use T’ Sealant is rated for the physical abuse of pedestrian or vehicle traffic. A ‘Use I’ Sealant will be utilized when the joint will be exposed to submerged water or other acceptable liquid. Use M (Mortar), Use G (Glass), Use A (Aluminum), and Use O (other) are available for application on specific materials.

Sealant installed in cold weather will have to stretch less during it’s life cycle but will have to compress more in summer. Sealant installed in hot weather will have to stretch more and compress less during it’s life cycle. Mild weather is preferable when joint sealants are installed outdoors. If excessively hot or cold temperatures exist during installation, joints should be proportioned to minimize overstretching and overcompression. Gunnable joint sealants must be installed by trained craftsmen.


Each joint must be prepared by assuring all substrate’s are clean and dry, in some instances a primer may even be used to increase adhesion.


Sometimes backer rod is utilized as a space filler and to minimize caulk waste. It is typically a cylindrical strip of highly compressible foam that is slightly larger in diameter of the width of the joint.

After placement, it is common for the joint to be ‘finished’ with a mechanical tool, similar to the way mortar is tooled, which compresses the sealant firmly against the sides of the joint and into the voids on either side of the backer rod. Tooling also provides a surface profile that is desirable.


‘Gunnable’ joint sealants are commonly grouped into 3 categories:

Low-Range Sealants (Caulk) – Have limited elongation abilities up to only +/- 5% of the width of the joint. Primarily oil based or acrylic and used to fill cracks in non-moving joints in preperation for paint. These caulks cure through evaporating water (or organic solvent) and can shrink quite a bit during this process. 


Medium Range Sealants – Made of materials like butyl rubber, neoprene, or acrylic, can safely elongate in the range of +/- 5-10% of joint width. Primarily used for exterior building walls in nonworking joints (both mechanically fastened and sealed). Some shrinking may occur with mid-range sealants. 

High-Range Sealants – Can handle elongations of up to 50-100% of joint width. Materials may be polysulfides, polyurethane, polymercaptans, or silicone. Polysulfides are typically site mixed of two-part components which initiates a chemical curing process. Polyurethanes may be also two-part component mixed or cure by reaction with water vapor existing in the air. Silicones cure by reaction with moisture vapor in the air and are considered the longest lasting and best performing of the 3. None of these types of sealants shrink during curing because they don’t rely on evaporation into the air or a solvent to effect the cure. Also all three adhere very aggressively to the surfaces on which they are applied. They are resilient rubber like and durable for up to 20 years if properly formulated and installed.  Polysulfides were used for quite some time for exterior working joints until polyurethanes and silicones become more advanced, cost efficient, and effective. Polyurethanes and silicones account for 90% or more of the high-range sealant construction market. 

Solid Sealant materials are also commonly used in lieu of or in addition to the above sealant materials to seal joints. Below are some types and applications of Solid Sealant Materials:


Gaskets – Strips of cured rubberlike material made in different sections and sizes for different purposes. They are typically compressed into a joint or inserted loose and expanded with a ‘lockstrip’.


Preformed Cellular Tape Sealant – Spongy polyurethane strip impregnated with mastic. It will come delivered in an air tight wrapper compressed to 1/5 or 1/6 of it’s original size. When it is unwrapped it expands to fill the joint and cures by a reaction with air vapor to form a watertight joint. 


Preformed Solid Tape Sealant – These are only used in lapped joint situation like mounting glass in a metal frame or lapping two metal panels. It is commonly thick and sticky ribbons of polybutene or polyisobutylene that adhere the joint to seal and cushion it. This type of solid sealant material is extremely sticky and can only be applied to by installing on one of the joint materials first and pushing the other onto it. 

Caulking and Sealants can be a a scope of work that is done by all sorts of trades depending on the project schedule and type of material that the caulk is touching. For example, casework/millwork, ceramic tile, and terrazzo contractor’s will typically handle all caulking within and at the perimeter of their work. Also Mechanical, Electrical, Plumbing, and fire sprinkler contractors will be responsible for their own caulking. Below is a spreadsheet denoting some of the more common trade associations with different types of caulking work:

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