Part 2 - Understanding DIY Spray Foam

1. Kit foam theory: Kit foam is like epoxy glue, 2 chemicals that are liquids when separate make a glue when you mix them. The glue is wet for only a short time and then it starts to cure or harden. Kit foam is the same, 2 chemicals A and B that are liquids, when you mix them they make foam that starts to cure as soon as you mix them. Like epoxy, proper and proportional mixing is important to make a good product. Unlike epoxy, kit foam is mixed when the 2 chemicals are pushed through a gun. Remember, as soon as the 2 chemicals touch they start to harden.

2. Kit foam is NOT "plug and play", if it is not done correctly it is messy and a waste of money. READ THE INSTRUCTIONS before you start, this is not one of those products you can figure out on your own.

3. Foam gives off heat as it cures; if it applied in thick layers (over 2") all at once it can build up too much heat and make bad foam. Resist the urge to apply the foam in layers thicker than 2" at a time and avoid making big piles of foam. The risk with kit foam is very low but professional foam can get so hot it will ignite if it is sprayed into a large pile.

4. Mixer theory: The 2 chemicals must mix equally and well to make good foam. As soon as the chemicals enter the mixer they start to cure so ideally you want to push the foam through the mixer as fast as you can. Kit foam, therefore, is great for spraying continuous areas or filling large voids BUT is not great for detailed air sealing. If the chemicals run slowly through the mixer the mixer starts to fill with cured foam and clog up. If the mixer is too old (a mixer can be too old in as little as 30 seconds) you will get improper mix and bad foam.

5. Temperature: Proper mixing and curing is temperature dependent. The canisters need to be 70-80 F (21-27 C) and the surface you will be spraying on needs to be at least 50 F (10 C) while you are spraying it and for at least 24 hours after spraying it . The surface must also be dry, free of water, frost, or ice. If spraying in cold conditions you may want to wrap your canisters in blankets during use and store them in heated space for 24 hours before use.

6. Pressure: The propellent for the foam is a limited to just what is in the tank so the pressure tends to decrease over time. In most applications this is not a major problem but you may find that the first foam you sprayed just doesn't "act" the same as later foam. You can sometimes compensate for this by changing mixers more often when the pressure is low and the mix is not as thorough.

7. What does good foam look like? Good foam is uniform in color, generally pale yellow (some companies dye the foam but it adds nothing to the quality). It looks like frosting when it first comes out and it will hold its initial shape although it should grow for a few seconds before it starts to cure to a hard finish. Kit foam takes 5 minutes or so to form a skin and ½ hour to be rigid. If you cut into good foam the bubbles (or cells) will be tiny and tightly packed.

8. What does bad foam look like? It can look different depending on how bad the mix was. Sometimes it will come out looking like frosting but instead of growing it starts to collapse and slide apart like goo, this will stay a liquid and slide off the wall. Foam that cures but is not uniform in color, if you can see swirls in it, it is bad foam. Foam that is gummy is bad and foam that is overly crispy or flaky (friable) is bad also. If you cut into the foam and you see long or large bubbles the foam is lower quality.

Return to the DIY Spray Foam Insulation page from the Understanding DIY Foam Insulation page

Next --> Part 3 - Applying DIY Spray Foam Insulation