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How To Install Blown Wet Spray Cellulose Insulation




Denny K. from Jersey City, NJ wrote:

Hey Itchy,

I have a addition that needs the walls insulated. I have heard of using a wet spray cellulose. They say it will give me a greater insulating value than fiberglass. Do you know anything about insulating walls with wet spray blown cellulose?

Yes, I have done this type of application many times. Let me warn you - it's messy! The the pros outweigh the cons though. Cellulose is a natural material made of wood products that these days is considered as "green". And guess what? It doesn't itch. When you walls are done you will have a slightly higher r-value. In addition, your walls will be air tight and free of infiltration if installed correctly. 


The process entails using a blowing machine with a 2" to 2 1/2" hose. At the end of the hose a nozzle is attached that sprays moisture on the the wall cavity and mixes with the cellulose. This nozzle is also attached to a garden hose. I will show you how this is done but before you get too antsy to do a wet spray cellulose application, make sure you can locate a rental store that has the nozzle you'll need. 

This application is for new construction or additions only. Make sure you have sealed off windows with plastic. All electrical boxes should be covered with duct tape. Cover any heat vents on the floor that are next to the walls.

The cellulose wet spray will require two people. One to feed the blowing machine and the other to install the insulation. Make sure the cellulose you buy from the building supply company is designed for wet spray. The air mixture from the blowing machine will need to be adjusted to make sure the insulation is moving freely and not getting bogged down. The trick is not having too much moisture or you may have problems down the road. You just want a very light mist as your only trying to activate the glue in the cellulose. Before you get going, spray a little bit on the wall cavity. Next take a handful of the cellulose and squeeze it tightly. If any water drips out it's too wet. You'll need to turn down the water. Once you get the correct consistency you're ready to begin. 

This stuff is dusty. Put on your goggles and dust mask or respirator. Start at the bottom of the wall cavity. Spray the cellulose back and forth from the bottom, filling the wall cavity full and continue to the top. Make sure the cavity is completely full before moving on to the next one. You will be getting the cellulose on the facing of the wall framing and some will be falling on the floor. That's where your helper come in handy. Have the helper scrape the insulation from the face of the wall studs and sweep the floor as you go. Don't try putting the waste insulation back into the blowing machine to recycle it - it will end up too wet. Continue with this process until all wall cavities are completely filled.

Take a look around. The house looks like a dark dungeon or cave. Take time to clean up your mess. Next, the cellulose wet spray blown insulation will need to dry. You should give it at least 3 days, depending on your climate.

If a vapor barrier is required in your neck of the woods you should staple plastic sheeting to the walls, but only after the cellulose has completely dried. 

That's it! Like I said in the beginning, it's messy business but it is well worth it as you now have one of the best insulation applications you can get installed into your walls. 

Related Tips and Advice:

How To Install Blown In Insulation In Walls
How To Insulate Wood Stud Walls
How To Insulate A Concrete Wall
How To Insulate Sound Walls

How To Insulate Knee Walls


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