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Insulating With Spray Cellulose

- Continued A wall-spray job begins by prepping the house. The combination of moisture and cellulose can leave quite a mess, so all windows and electrical outlets are covered with polyethylene and electrical boxes are protected with tape (Figure 4).

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Figure 4. As protection from overspray, windows are covered with poly (above), and electrical boxes are taped over (left).

Add water. The key to a good spray job is achieving a proper blend of air, fiber, and water. We've seen and heard about installations in which the product was sprayed so wet that the water literally started to seep out of the bottom of the cavity just as it would from a saturated sponge. That is unacceptable. Normally, the liquid-to-fiber ratio should be .3 to .4 pounds of water per pound of fiber, or about a gallon of water per bag of insulation. In simple terms, this means that the applied material should be damp but not wet. A basic test we often use is to grab a handful of wall-spray cellulose right after it is sprayed and squeeze it. If any water can be squeezed out, the mix is too wet. Scrubbing and scraping. The spraying itself goes pretty quickly. It takes about 30 to 45 seconds to fill an 8-foot wall cavity, and a three- or four-person crew can spray a 3,000- to 4,000-square-foot house in a day. Spraying well takes some experience. If you spray at too oblique an angle or don't get close enough, gaps may appear between the cellulose and the framing. This happens most often in the last three to five inches below a plate or sill, resulting in a horizontal defect we call a "smile" (Figure 5).

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Figure 5. "Smiles" are horizontal gaps that result from poor technique when spraying below window sills, plates, or blocking. To correct the problem, the worker is compressing the insulation by hand before re-spraying the affected area.

When a cavity is sprayed, it is filled past the face of the studs. This fills the cavity completely but also creates another step. We use a tool called a scrubber — a rotating brush that rides on the face of the studs — to cut or shave the cellulose flush with the face of the studs (Figure 6). Our usual crew consists of one worker to spray, one or two to move material and keep the hopper filled, and one to run the scrubber and keep the job clean.

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Figure 6. The area at left in this photo has already been scrubbed, leaving the faces of the studs flush with the surface of the cellulose. The scrubbed-off material accumulating on the floor will later be collected, combined with fresh material, and reapplied elsewhere.

The scrubber works well on open expanses of wall, but it can't get all the way into inside corners, so there's always some hand work as well. To clean out corners and other obstructed areas, we use a wide-bladed paint scraper with a threaded socket on the handle. This accepts an extension handle like those used with paint rollers, making it possible to reach the angle between wall and ceiling (Figure 7). To allow the blade to slide easily over the framing rather than digging in, we often cover the metal edge with a strip of duct tape.

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Figure 7. Damp, freshly sprayed cellulose comes off easily, but the material sticks firmly when dry. Corners and other areas too tight for the scrubber to handle are cleaned with a paint scraper fitted with a pole extension.