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How to Use Spray Polyurethane Foam

spray polyurethane foam

Spray Polyurethane foam is a great way to seal cracks, small crevices or holes in your home. You can get small aerosol cans of spray foam sealant at most hardware stores. They are designed for the homeowner in mind and are easy to apply. For larger jobs, there are two component, low-pressure spray polyurethane kits. However, these kits are more complicated to use and require more care and exactness in the application process.

The process is based on four guiding principles:

  • Wear protective gear
  • Warm the tanks 
  • Shake the tanks 
  • Clean/change the nozzle regularly

Wearing Protective Gear

Spray polyurethane foam is considered safe after proper installation and curing time but during installation, it can be hazardous. The chemicals used to create the foam are dangerous if you ingest, breathe, or touch it. Proper protective gear is essential. Before it is cured, spray polyurethane foam is very sticky so it is important to cover yourself completely with protective clothing (gloves and hooded coveralls). Eye protection and an air purifying respirator are also essential. Some retailers have protection kits available for purchase. 

You want to cover the furniture, carpets, floors, etc. in order to protect them from any over spraying. Make sure to shut down your HVAC system and seal any air intakes to avoid getting particles in your system. You also want to make sure that you have adequate ventilation by opening all of the windows and using a fan for fresh air.

Warming the Tanks

For proper spray function, the tanks of both chemicals need to be heated. You can use a domestic heater or place them in a warm airing cupboard overnight. The temperature of the enclosure you use to heat up the cylinders has to be at least 86 Fahrenheit. 

An alternative would be to warm up the tanks in a bathtub filled with warm water. In this case, the water should be around 100 degrees Fahrenheit. This is the recommended temperature and it should not be any hotter.

You also want to make sure that you heat up both tanks at the same time in order to have a uniform viscosity. Hitting the right temperature in both cylinders ensures good foam quality and that you will get the maximum amount of foam out of the kit. If during the installation process, the temperature of the tanks drops below 75 degrees Fahrenheit, you want to stop right away and re-heat the tanks.

Shaking the Tanks

By shaking the tanks, you ensure that the chemicals within are evenly mixed. If you’ve bought bigger tanks, rocking them back and forth for about a minute should do the job. Without this process, you will get less foam for your money.

Cleaning/Changing the Nozzles

Nozzle management is crucial to your spraying project. Polyurethane foam begins to cure and harden when its two components are mixed. This happens within the nozzle as well. To counteract this, the nozzle should be changed every 5 minutes if you are spraying continuously and if you stop spraying for 30 seconds or more.

Used nozzles can be either thrown away or cleaned with acetone. Changing nozzles is very important because even a short break to move a ladder will leave room for the foam to settle and create blockages which can damage the hose or the gun itself. This type of damage is irreversible, while nozzles are easily replaceable. If you choose to clean the nozzles, they should be submerged in a tub of acetone immediately. 


It takes practice to get the spraying technique down. It can be difficult to get an even layer of foam with the correct depth needed. Think of spraying foam as you would of spraying paint. The principle is the same – you start off with a thin layer and then build on that, if necessary. The main difference between spraying foam and spraying paint, however, is that foam expands, so one 1/8” layer will expand to about 1”.  Also, make sure to check the internal temperature of the foam. If it is still hot and another layer is added, it could create a poor quality foam.

After Use

Once you’re finished, the best way to store any leftover material is by closing all of the tank valves and leaving the kit assembled with a nozzle attached to the gun. The foam within the nozzle will harden and seal the gun, making it waterproof. The kit can be stored for up to 2 weeks in this state. Longer than that and it will need to be cleaned. The nozzle itself is unusable after the foam hardens since acetone will not be able to moisten and remove the excess. The kit should only be cleaned with approved cleaning oil. Dispose of material and empty containers properly according to federal, state, and local waste disposal guidelines.

Is This a DIY Project You’d Like to Try?

Foam insulation is a very versatile insulator. You can save money if you are willing to spend the time and energy to do the job yourself. Unfortunately, spray polyurethane foam is made with hazardous chemicals and can cause all kinds of problems if not handled properly. So unless it’s a small job that can be accomplished with an aerosol can, you might be better off hiring a professional with specialized training and equipment. If you decide to give it a try, make sure to read the manufacturer’s paperwork for complete, detailed instructions specific to your spray polyurethane foam and follow them exactly. Contact us for more details or any questions you may have.





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