How to Fill a Concrete Block With Spray Foam

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Concrete Block
Concrete Block (Image: Jupiterimages/Photos.com/Getty Images)

Installing foam in concrete block is a great way to insulate a house where there is no room to install insulation on the exterior or interior of the concrete block. Another benefit to filling the block with foam is removes another area for insects and rodents to live or make entry to the house. The spray foam kits required for insulating concrete block are available at some large home improvement stores and many different online sites.

Things You'll Need

  • Spray foam kit
  • Work lights
  • 2 inch drill bit
  • Right angle drill
  • Safety glasses
  • Gloves
  • Disposable coveralls
  • Dust mask
  • Plywood platform

Set up the work lights in the attic to light the area where the top of the concrete wall meets the roof rafters. Concrete block is made with two holes as seen in the picture. Each hole in the concrete block will need to be accessible so that the gun attached to spray foam kit can access each cavity.

Put on the coveralls, safety glasses, gloves, and dust mask to protect yourself from the insulation in the attic. Depending on how steep the slope of the roof, laying down might be required so have the plywood platform handy. Using the 2-inch drill bit make holes in the center of each section of each concrete block. Sweep or vacuum all the wood shavings from the drilled holes.

Determine the amount of foam required to fill the cavities. Typical concrete blocks are 6 inches wide or 8 inches wide on residential construction. Spray foam kits are sold by the board foot (12 inch-by-12-inch-by-1-inch thick). Each 6-inch block requires 2.5 board feet and each 8-inch block requires 3 board feet to fill. Count the number of blocks to be filled and multiply by the corresponding number to figure out what size spray foam kit is required.

Read the instructions included in the spray foam kit along with the Material Safety Data Sheets to make sure the kit is properly set up and ready to spray. Set up kit and pressurize lines for spraying.

Put the tip of the gun into each hole and begin to fill slowly so the foam can find its way to the bottom of the cavity. Fill each cavity approximately half way to allow room for expansion. Once all the holes have been filled half way (or 10 to 15 minutes have elapsed) you can fill the remainder of the cavities.

Once the foam has fully cured (the amount of time will be located in the instructions of spray foam kit) cut off the excess and discard.

Tips & Warnings

  • Spray foam kits are expensive so depending on the size of the project (number of block to be filled) it might be more cost effective to have an injection foam company install the foam after all the prep work has been completed.

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