Product Sector Guidance: Joint Sealants

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close up image of woman caulking a window

Choosing Joint Sealants that Minimize Health Hazards

A sealant goes in between two different substrates (wood, glass, metal, brick, etc.) and joins them together.  Their job is to fill a gap—often at a place where two building elements need to be joined together—and form a barrier. They help prevent structural damage from materials entering joints, help prevent mold development, and function as an air and water barrier. They also must, depending on the materials being joined and the location of the structure, have some degree of elasticity to allow for the impact of heating and cooling and seismic movement. 

What about caulk? Caulks are considered a joint sealant, but there is a distinction. Sealants are considered high performing materials with a high level of elasticity that allows for shrinking , expansion,  and high weatherability while maintaining its job as a continuous barrier between substrates. Caulks have much less elasticity. They create a paintable surface by filling a space where there are gaps or penetrations. Caulks include acrylic and latex sealants, are water-based, and contain fewer hazardous chemicals than other heavier duty sealants. They still  prevent moisture and air passage, but they last for a shorter period of time before needing re-application.

Sealants that react onsite are the most hazardous and should be avoided whenever possible. Polyurethane products contain hazardous isocyanates, which are described as a leading cause of workplace asthma. It is also common for sealants to contain endocrine-disrupting plasticizers called phthalates. Additionally, beware of products claiming to contain antimicrobial agents and fungicides. As with most products, it is recommended to choose products that are low VOC and that carry a third party certification such as GREENGUARD Gold.  Products with less than 50 g/L are considered low VOC, though products under 25 g/L of VOCs are preferred. 

Information in this section is based on the work of the Healthy Building Network (HBN). Visit the Product Guidance section from HBN (healthybuilding.net) for more information.

Healthier Joint Sealants

Look for these labels:

 

 

 

 

Joint Sealant Type

Application

Chemicals of Concern

Health Hazards

Guidance

Pre-compressed polyurethane foam tape

Good for sealing gaps around walls, windows and doors- and where final joint will be visible 

Mostly safe, but in the rare case, flame retardant TCPP may be added

Endocrine disruption; asthma trigger; developmental harm

Check with manufacturer that product does not contain halogenated flame retardants

Acrylic and latex caulk

Best for interior applications and those requiring painting, also works for exterior and to seal windows and doors 

Most ingredient content is safe, but may include additives such as ethylene glycol and Stoddard solvent

Birth defects, developmental harm, cancer, gene mutations

Ask the manufacturer to disclose plasticizers and make sure the product is phthalate-free. Look for very low VOC products, <25 g/L

Siliconized latex caulk

Several interior and exterior applications such as sealing windows and doors 

May contain ethylene glycol

Birth defects, endocrine disruption

Look for very low VOC products (<25 g/L) and phthalate free products

Acoustical sealant

Meant to seal seams and small cracks to reduce sound transmission, adheres to most building materials

Mostly safe but may contain ethylene glycol

Birth defects, endocrine disruption

Ask the manufacturer to disclose plasticizers and make sure the product is phthalate-free. Prefer products with very low VOC content, 

≤ 25 g/L.

Butyl sealant

Caulk with high water resistance used in exterior applications such as on flashing, gutters, and chimneys. Also seals joints around windows and doors. 

Stoddard solvent, ethyl benzene

Cancer, gene damage

Because the application is typically exterior, the health risk is lower for occupants

Single-component silicone sealant

Several interior and exterior applications; adheres to glass, concrete, and wood. Used for structural glazing, in bathroom and kitchens, and around windows and doors.

Installation process releases acetic acid,   methyl ethyl ketoxime, or methanol

Asthmagen, birth defects, cancer, developmental harm

Avoid formulations with organotin catalysts like dibutyltin dilaurate, a reproductive toxicant. Prefer those with titanium-based catalysts.

Single-component polyurethane foam sealant

Several interior and exterior applications, able to fill small gaps, used around windows and doors

Isocyanates, halogenated flame retardants

Asthma, cancer, endocrine disruption, reproductive harm, developmental harm

Avoid the use of this material in interior applications. If necessary, ventilate the area thoroughly during installation and curing time.  

Hybrid polymer Sealant

 

Modified polymer sealant

 

STPE sealants (hybrid of silicone and polyurethane)

Interior and exterior gaps including siding and around windows and doors

Organotin catalysts (fungicide),  phthalates, methanol

Reproductive harm, endocrine disruption,  developmental harm

Prefer products with full ingredient disclosure and use non-phthalate plasticizers (ex. propylene glycol)

Mildew resistant/ sanitary silicone sealant

Kitchen and bath, high moisture areas

Antimicrobials, acetic acid, arsenic

Bacterial resistance,  asthma, birth defects, cancer, endocrine disruption, reproductive harm, gene damage

It is preferable to avoid products with fungicides. Look for products free of arsenic-based fungicide, or opt for a solvent-free silicone caulk

Single component polyurethane sealant


 

General purpose sealants used in both interior and exterior applications including on concrete, masonry, expansion joints, and window and door perimeters

Isocyanates, phthalates, organotin catalysts (fungicide), xylene, ethylbenzene

Asthma, developmental harm, reproductive harm, carcinogen

Avoid the use of this material, especially in interior applications. If absolutely necessary, ventilate the area thoroughly during installation and curing time.  

Two-component polyurethane sealant

General purpose sealants used in both interior and exterior applications including on concrete, masonry, expansion joints, and window and door perimeters

Isocyanates, phthalates, dibutyltin dilaurate, xylene

Asthma, endocrine disruption, reproductive harm, developmental harm, birth defects

Avoid the use of this material, especially in interior applications. If absolutely necessary, ventilate the area thoroughly during installation and drying time.  

 

Information for the following table is from Healthy Building Network’s Guidance for Specifying Healthier Insulation and Air-Sealing Materials.

 

Sealant Application

Good

Better

Best

Small gaps

Silicone sealant or phthalate free, modified-polymer sealant. Sealants must meet the requirements of SCAQMD Rule 1168

Acrylic latex or siliconized acrylic sealant. Sealants must meet the requirements of South Coast Air Quality Management District (SCAQMD) Rule 1168.12 

Acrylic latex or siliconized acrylic sealant with VOC content of ≤ 25 g/L+

Large gaps 

 

Non-isocyanate spray foam sealant with an HPD with all contents characterized, screened, and identified at 1000 ppm or lower threshold. (At the time of this research, none of these products were commercially available with an HPD. Customer demand is needed to make this available.)

Preformed foam sealant tape or drywall and acrylic latex or siliconized acrylic sealant with VOC content of ≤ 25 g/L

Fire-rated (flame spread)

Acrylic latex sealant, siliconized acrylic sealant, or intumescent acrylic latex firestop sealant. Sealants must meet the requirements of SCAQMD Rule 1168.

Acrylic latex or siliconized acrylic sealant or intumescent acrylic latex firestop sealant with VOC content of ≤ 25 g/L

Noncombustible sodium silicate caulk

Air ducts

Wet-applied mastic sealant, free of halogenated flame retardants and alkylphenol ethoxylates (APEs). (At the time of this research, it was unclear if products free of these chemicals of concern were available. Customer demand is needed for this content information to be made available.)

Foil-backed butyl tape  

Foil-backed butyl tape with VOC content of ≤ 1g/L