The first step in any successful project is making sure you know what you are setting out to accomplish. For block walls, there’s not much to consider other than your targeted R value, which will determine your spray thickness. For a simple thermal break and air sealing, an inch should suffice. If you are temperature controlling a living space, we’d recommend two or three inches. For projects that will be inspected and have to pass code, we defer to what your local municipality requires. Closed cell Foam it Green has a very high R value at approx. 7 per inch.


Your total required number of spray foam kits is determined by your total board feet need. A board-foot is one squared foot at one inch thick. Let’s assume you are spraying your walls to a thickness of two inches. Total up the surface area (length X height) of the walls you will be spraying, and multiply it by 2” to get your total board feet. Take your total board-feet need of the walls, and then add about 10% or so for waste. Divide your total board-feet need by 600 (the board-feet a Foam it Green 602 kit can cover), round it up to the next whole kit, and place your order!


It’s difficult if not impossible to get foam off of surfaces it hits. So, be sure to take the time to cover anything you do not want foam stuck to including floors, windows, equipment in the area, and even you once you start spraying! Along with the recommended PPE, the sprayer should have no exposed skin or hair during application. How do you get foam out of a beard? In a word, scissors. The components throughout the tanks need to be between 65-85F degrees to expel material at the right rate. As always, make sure your target spray surfaces measure between 65F-85F. 75F is ideal for material and surface temperature.


Target a wet foam application thickness of 1/3” as that will expand to one inch cured. Whether to use the extra green fan spray tip or not is a matter of personal preference. Usually, it’s best to “box out” the wall cavity by spraying where the corners of the studs meet the substrate. From there, work either vertically if using the fan spray tip or side to side when using just the black mixing nozzle alone. You won’t be able to get the foam perfectly flat, but how it looks isn’t as critical as just making sure you aren’t missing any spots. If you are spraying more than one inch in total, do not attempt to achieve that thickness in a single pass. Instead, spray one third of an inch, let it rise in 30 seconds and cure in 5 minutes, and then do it again for a second inch.


Injecting a block wall with slow rise foam is not recommended for two reasons. First, with all of the pieces that connect the back to the front inside the blocks, it is difficult to make sure you are feeding the foam everywhere it needs to go. You can end up with pockets of dead air and no insulation. Second, those same pieces of the blocks freely conduct the temperature from one side of the block to the other, so while the foam will do a great job insulating where you put it, these areas will not be well insulated.

If you frame up a wall set apart from the blocks, the foam can expand behind the studs and create a nice thermal break, but it will not move the studs. If you prefer to use furring strips attached directly to the block wall, you can spray between them like a normal wall cavity and then install your desired wall covering. It is ok to have empty space in the wall before installing drywall or sheetrock. In fact, unless your code dictates it, there is no need for a vapor barrier over the foam either. The vast majority of vapor permeance happens through air movement, not direct diffusion. So, since the foam is stopping that air movement, from a building science perspective, you are good to go. Again, if your local inspector says you need one, then you need to put one in.

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