Sealant Selection Considerations
Design professionals specify sealants on practically all aspects of a building – and anywhere two components of a structure meet, contractors place sealants. Common applications include expansion joints and control joints in vertical and horizontal applications, perimeters of framed openings, and flashing joints.
With so many applications and so many product options, contractors need to be certain that they install the correct product to deliver long-term quality.
Use sealants when movement is expected
Sealants are different than caulks. The Sealant, Waterproofing & Restoration Institute (SWRI) describes sealants as “elastomeric materials used in exterior and interior wall construction to prevent the passage of liquids and gases between two components where differential movement between those components is anticipated.” In comparison, caulk is used to simply fill a void when no movement is expected.The ability to remain on the surface when there is movement is why sealants are used to protect structures by providing waterproofing, noise control, firestopping, and glazing.
How manufactures classify their products
Contractors can easily match the proper sealant to their application if they understand the product classification system. Most manufacturers sell products that comply to the standard contained in ASTM C 920, Standard for Specification for Elastomeric Joint Sealants. This document outlines “the properties of a cured single - or multicomponent cold-applied elastomeric joint sealant for sealing, caulking, or glazing operations on buildings, plazas, and decks for vehicular or pedestrian use, and types of construction other than highway and airfield pavements and bridges.” To be in compliance, manufactures must classify each product as to: (1) Type; (2) Grade; (3) Class; and (4) Use.
Manufacturers include this information on their spec sheets or packaging with a common label that looks like this: “Type M, Grade NS, Class 25, Use T”.
This system allows contractors to quickly determine what product will work best for the application at hand.
1. Product Type refers to how the sealants arrives at the jobsite. There are two types of material composition products: those that are premixed (Type S), and those that require mixing at the jobsite (Type M).
Multi-component products cure faster than their single-component counterparts, which is often advantageous for joints subject to traffic or similar exposures.
- Type S (single-component) products arrive in prepackaged cartridges, sausages, or pails. They are ready to use and require no mixing. Type S are frequently more expensive than their multi-component counterparts, but they often save time on the job.
- Type M (Multi-component) products are those furnished in two or more parts for mixing at the jobsite.
- Two-Part products consist of a base and a catalyst.
- Three-Part products consist of a base, a catalyst, and a separate color component.
Multi-component products cure faster than their single-component counterparts, which is often advantageous for joints subject to traffic or similar exposures.
2. Grade refers to the product’s application characteristic, referring to how it fills the joints or openings into which it’s placed.
- Grade P (pourable) products have sufficient flow to fill joints in horizontal surfaces. They self-level during placement, providing a smooth surface prior to curing. Contractors use sealants with this grade designation for horizontal expansion joints on pavements and slabs.
- Grade NS products are formulated to be suitable when installed in vertical joints and inclined surfaces. They are also commonly referred to as “Non-Sag” or “Gun Grade” as they remain in place after installation without deforming when temperatures are between 40˚ and 122˚F.
3. Class refers to how well a sealant remains in-place and adheres to the substrate into which it’s installed. Another term for this designation is movement capability. This rating is determined in a laboratory. ASTM C719 allows manufactures to designate their sealant in one of five classes. Most commonly used sealants meet either Class 12 ½ or Class 25. The higher the class designation, the more durable the sealant was during lab testing. It’s important to note that this classification may not reflect field performance.
4. Use refers to the application and/or substrates into or onto which the manufacturer expects the contractor to place the sealant. Manufacturers must meet certain standards to classify a sealant within a use category.
T - Traffic area (these sealants are harder and more durable)
NT - Non-traffic area
M - Mortar
G - Glass
O - Other substrates
T - Traffic area (these sealants are harder and more durable)
NT - Non-traffic area
M - Mortar
G - Glass
O - Other substrates
Product Selection Guides
Many manufacturers offer sealants that share multiple product classifications and can be used in different applications. To help contractors match the sealant to the application, they provide product selection guides.
Contact your local White Cap representative for a guide.
