We’ve talked a lot about densities and density checks, today we’re going to discuss how to do an actual density check.

First we need to know what the density of the blow in product is. We’ve been using the 2.3 pounds per cubic foot of wall area, so we’ll continue using that density.

To do a density check we must first decide when to do the first one. It is STRONGLY recommended to the first check after the first 5-6 cavities are done on each job. This way we will know if we have the settings of the machine set correctly and if the installer is maintaining the correct density according to the manufacturer’s guidelines from the beginning.

After the first one, it’s suggested to do a density check after the next 800 to 1,000 sq ft of wall space with no less than 3 density checks per house no matter how small it is. Once the installer does several of these, they will find it will only take a few minutes to complete a density check. Well worth the time to make sure they are on track. If they aren’t consistent, then, as we’ve talked before, there will be settling if too little is installed and will have to have more product installed to bring it up to the guildlines.

If too much is installed, the cavity will typically have to be emptied of all product and redone.

A density check is a simple, and quick, process. Let’s say we are insulating a 2×4 wall cavity. We must remove 1728 cubic inches, or 1 cubic foot of insulation from the wall and weigh it. If the walls are framed on 16” centers, then we need to determine how much a cubic foot of product to take out.

A 2×4 is actually only 3.5” deep, not 4”.And 1.5” wide, not 2”. So we need to take that into consideration. If you use the common 2×4”, the density will not compute correctly.

Because we need 1,728 cubic inches (equaling 1 cubic foot) we need to take the inside measurement of the stud cavity from the inside of one stud, to the inside of the next stud, or 14.1/2”. Our depth, from above, is 3.1/2 inches. To get one cubic foot, we’ll measure up, or down the cavity 34 1/8” to get our cubic foot. 14.1/2” x 3.1/2” x 34 1/8” = 1,728 cubic inches, or 1 cubic foot of material.

Once the measurements are marked on the Insulguard fabric, cut the piece of the fabric out, 14 ½” x 34 1/8”. Then take all of the fiberglass out of the open part of the cavity. Don’t leave any extra and don’t take out too much.

Then weigh the entire cubic foot of product. According to the manufacturers guidelines, this amount of product should way almost 2.3 pounds if installed correctly. If it’s to heavy, you’ll need to adjust the amount of product you are installing to put less in the cavity or you will have an irate drywall contractor and loose $$. If it’s to light, add product to the cavities that need extra material or you will have settling.

Once the density check is done, cut a piece of Insulguard fabric that is somewhat larger than the piece you cut out earlier and staple it over the empty part of the cavity and then reblow if full.

Then mark the area you just finished with a can of brightly colored spray paint so everyone can see where your density checks are. Then mark them on your work order as well. Take pictures if you can.

Let everyone know how proud you are to be a certified blow in wall cavity contractor.