Why We Love Pu Expanding Foam (And You Should, Too!)

What is pu foam sealant?

pu foam sealants are a type of spray polyurethane foam (one component foam) that has insulating, air sealing, and adhesive properties. pu foam sealants are available at home improvement stores and come in small cans (typically 12-24 oz.). These products are intended for use in a “bead type” application for air sealing or as an adhesive. Their small volume, ease of use, and portability make them well-suited for smaller projects tackled by the Do-It Yourself. They are typically dispensed using a straw or small dispensing gun. These “canned” foam products have specific safety information on the label that should be carefully followed.

Where can I apply pu foam sealant?

pu foam sealants are useful for small DIY projects such as sealing holes, gaps and cracks around your home where air leakage could occur. Some possible areas to consider sealing around include:

· Window and door gaps

· Baseboards and vents

· Sill plates, pipe and duct penetrations

· Sink plumbing, floor/wall junctions, around electrical boxes (not inside)

Can I use pu foam sealant outside?

Yes, you can. Exterior uses could include the following:

Where the siding meets the foundation

Gas and electrical penetrations

Garage ceiling and wall joints

Around outdoor faucets and exterior vents

Landscaping applications such as stone wall repair, pond/waterfall fillers and repair, as well as to secure landscape blocks

Are there specific tips for using pu foam sealant?

The best advice is to follow the manufacturer’s instructions for application. That said, one reasonably standard tip for exterior applications is that it can be helpful to paint the cured foam surface to be treated with black paint (appropriate for outdoor use and the surface selected) to help prevent UV degradation and discoloration of the foam.

Are all pu foam sealants basically the same?

No, not necessarily. There are different grades of pu foam sealants for different uses. Refer to the product label for information on appropriate product uses. For more information, see “Typical Uses for pu foam sealant.”

Does the pu foam sealant help control moisture in my home?

Gaps and cracks in the home can allow uncontrolled movement of moisture-laden air in and out of the building. Loss of interior moisture control can make the interior air excessively dry or moist, which can cause occupant discomfort, poor indoor air quality, higher heating and cooling costs to control moisture, and in some cases, hidden deterioration of the building and possibly mold and mildew growth. Air sealing these gaps and cracks with pu foam sealant can help control interior moisture levels (other measures, like having the walls insulated with SPF can help a great deal more).

Can I use pu foam sealant for projects other than its stated use?

Use pu foam sealants for the uses described by the manufacturer on the product label. Please note that pu foam sealants are not intended for use by children. Check with the product manufacturer if you have questions about its intended use.

How do I prepare the area where I’ll be applying the pu foam sealant?

Read and follow all instructions on the product label. This includes following the product manufacturer’s instructions about ventilating the room in which the project will be done. It also includes wearing personal protective equipment (generally, safety goggles or safety glasses, and gloves), and work clothing, such as a long-sleeved shirt to minimize contact with skin. Product manufacturers recommend that the product not be used by children and that children not come into contact with the product. 

Can I use too much? Is it possible to seal the house too tightly?

Given the small volumes of foam used when filling cracks and gaps in your home as a DIYer, it’s unlikely you will seal your house too tightly. However, you may want to consider discussing your project with an architect, building design engineer, weatherization professional, or your local building code officials if you have questions. Proper ventilation in a home or building is very important. You may also wish to consider having a heating and cooling technician check large appliances (e.g., water heater, dryer) after air sealing to make sure they are venting properly.

Can I leave the cured sealant exposed?

Generally, it is considered acceptable to leave cured or “hardened” pu foam sealant beads exposed when it is used to seal small gaps and cracks. Manufacturers may recommend painting the material if it is exposed to UV light.

Do I need to trim the foam? When can I trim it?

pu foam sealants generally do not need trimming because the product is applied in a narrow “bead.” However, if you wish to trim the applied product, it is good practice to wait until the foam has cured or hardened before attempting to trim it. Consult the product label and instructions for trimming information and cure times.

How should I dispose of the trimmings from pu foam sealant?

Cured foam trimmings may be disposed of as you would other household waste. Be sure to thoroughly clean up the work area after the job is completed.

What is in the can?

The can is filled with a group of chemicals referred to as polymeric methylene diphenyl diisocyanate (MDI) and a resin blend that may contain a mixture of polyols, catalyst (primarily amines), hydrofluorocarbon or hydrocarbon propellant, surfactants and flame retardants. See the manufacturer’s label for specific product contents since they may vary slightly depending on the type of sealant. When these chemicals are combined during manufacture, a reaction occurs to create a prepolymer in the can that subsequently reacts with moisture in the air when it is dispensed—this is what creates the pu foam sealant. Before the foam has sufficiently hardened, there may be potential for exposure to these chemicals. Therefore, it’s important to follow the safety precautions and wear the protective equipment (e.g., safety glasses/goggles, gloves and full- coverage clothing) as described on the product label.

Do I need protective gear while applying pu foam sealant, also known as “spray foam in a can”?

Yes, it is important to wear protective gear, often referred to as “personal protective equipment” (PPE) when applying pu foam sealant (sometimes referred to as “one component foam” or “foam in a can.”) Wear the gloves, clothing and eye protection recommended by the product manufacturer on the label. This often includes safety glasses or goggles, full-coverage clothing such as long sleeves, and gloves.

What should I do if the foam accidentally contacts my skin or eyes during application?

Immediately remove it from the skin without spreading it before it hardens. Refer to the product label for first aid instructions. Keeping the instructions on the product label available and readable at the project site helps in the event that first aid guidance is needed.

How do I know the foam has cured or “hardened” so that my family can reenter the project area?

Generally, people can reenter the area when the pu foam sealant has hardened to the point where it is considered “tack free” (no longer wet or sticky on the surface). The amount of time it takes for the foam to cure or harden varies depending on the product-specific formulation, temperature, humidity, the amount of foam being sprayed, and other variables. Typically, pu foam sealants cure quickly at moderate temperatures and humidity. The foam surface cures first, and then gradually cures inside of the foam body. The thicker the foam is applied, the longer it takes to cure throughout. Spraying a mist of water on the substrate or/and between layers of foam can speed up the curing process. Typically, it can take between 5 and 60 minutes for the foam to become tack-free. Full cure may be reached in a time range of about 8 to 24 hours, depending on the product and site conditions. Consult the product label and instructions regarding cure times.

Does the cured sealant pose a fire hazard?

Insulating foam are designed to meet building and fire code regulations when properly installed. Installed cured product is combustible and will typically begin to thermally degrade at temperatures above 240oF/116oC so you should carefully read the instructions on the product label and follow them with respect to avoiding installations in areas exposed to high heat, such as around fireplaces, heaters, radiators, heat lamps, recessed lighting, bare copper wires, or inside electrical boxes. In addition, the product cans should not be stored in high heat areas or near heat. Cured foam will burn when exposed to a direct flame. Finally, it is important to not do any welding/torch cutting or use a heating appliance that produces a flame near cured foam that is not protected by an ignition barrier (e.g., drywall).

What do I do with partially used or empty pu foam sealant cans?

Empty cans may be disposed of as non-hazardous household waste or recycled. For full or partially used cans of pu foam sealant, follow the product label instructions regarding storage and disposal. The ingredients in the can are pressurized, so upright storage of the can at room temperature consistent with the manufacturer’s recommendations is important (avoid freezing or hot temperatures). Remember that the temperatures in a parked vehicle in the summer can rapidly reach very hot temperatures, so plan your purchase and transportation of the pu foam sealant accordingly.

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This is Jojo Shi from Juyou Building Materials Co., Ltd. in China, which are professional manufacturer of different kinds of pu foam sealant

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