This is the fourth post on rice hulls for insulation. The first was back in 2016, a couple of years after I learned about insulating with hulls. That post was an attempt to confirm their efficacy and understand the uncommon logistics involved with buying, transporting and getting them into a structure. Two recent posts set the stage for this post that describes the actual use of the hulls for the wall and ceiling cavities.
Reminder: click on any picture to enlarge it for better viewing.
Buying the Rice Hulls and the Diatomaceous Earth
It appeared that Riceland Foods, Inc was willing to sell direct (instead of referring to a dealer) only because of the size of our order. Their hulls come in two configurations -- large bales or 50 lb bags -- with the latter seldom sold to end-users, especially consumers, in truckload quantities. Consequently, our order triggered a special run that needed to be picked up almost immediately after ordering. I had been proactively in contact with a freight broker who promptly caught a ride for the shipment and was able to schedule it to arrive on Friday so that we could offload it over the weekend.
Buying food grade diatomaceous earth (DE) was made easy by a local farm and home store that handled it in 40 lb bags for mixing with livestock feeds. The DE as an insecticide will not only kill rice weevils but any other insects with exoskeletons (hard shells), apparently for as long as the building exists.
Receiving the Rice Hulls
With a crew of 11 and three pickups, 768 bags of hulls were moved from the semi-trailer to our building site in less than 7 hours. |
It was a bit of a problem storing the hulls and still having access to the exterior walls for insulating and additional drywalling. They occupied over half of the space in the garage and most of the non-bedroom, non-bathroom floor space on the first floor. However, intentional sequencing for blowing the hulls quickly eliminated the bags that were most in the way.
Blowing the Hulls
We positioned the blower in a central
Friend, Bob, loading the blower hopper with hulls at the rate of about one bag every five minutes. t |
less than 5 min per bag which we thought originally would be too fast for one person working alone to manage. However, after a little practice with two at the blower, we found that one person could in fact keep up. The guy(s) working at the blower were already wearing N95 or equivalent masks due to COVID-19 although the amount of dust was minimal. At the business end of the hose, the dust was so problematic that, in addition to an N95 tight-fitting mask, I wore swimming goggles, long sleeves, tight collar and gloves.
With rice hulls, as opposed to fiberglass or cellulose, the hose clogged more readily, presumably due to their greater density. We found two maneuvers that eliminated clogging. One was to fine-tune the flow rate by trial-and-error and the other was to make sure that the hose was kept as straight as possible and, when bent, with curves as sweeping as possible. And, in addition to these efforts, I needed to be careful that the end of the hose did not bottom out and become blocked by the hulls already in the wall or ceiling. The good news was that the flow rate was not diminished when the hose was elevated to reach the ceiling of the second story.
Second Thoughts About Diatomaceous Earth (DE)
After a day and a half of blowing rice hulls, we began to wonder whether the dust created by blowing was due to the DE rather than the hulls themselves. By that time we had finished insulating behind the first course of drywall on the first floor and the interior of the building was already pretty dusty. It was hard to say whether it was hull dust or DE dust or a combination.
days after the first session). The search yielded enough information to warrant a bit of caution. The major concerns are pulmonary effects and eye irritation. The former was a non-issue for us in that the warnings apply to workers who experience long-term exposure such as those mining and processing DE and we were already wearing N95 masks which, according to the online sources, was adequate for DE dust. The latter concern, eye irritation, was real for me after being at the business end of the hose but not a concern for those working at the hopper. It motivated me to search for goggles that sealed against the face better than the ones I was using and to consider alternatives to mixing the DE with the hulls before blowing.
In order to decide whether to continue mixing DE with the hulls, we blew a few bags of hulls without the DE to see how dusty they would be compared to rice hulls with DE. As I had hoped, the amount of dust with or without DE seemed to be a wash. Since I would be the one at the dusty end of the blower hose and would rather not miss the opportunity to have walls and ceiling laced with a deadly but environmentally-friendly insecticide, I decided to continue with the DE. By the time the second stage of drywalling was over and we were ready to resume insulating, I had bought tight-fitting swim googles that eliminated most of the eye irritation that I experienced after the first session. However, the amount of dust at the business end of the hose, even with masking and goggles, made the job extremely unpleasant to say the least.
Wall Insulation
Yours truly at the business end of the hose |
We filled the wall cavities brimming full so that there would be no doubt that the junction between walls and ceilings would be filled uninterruptedly when later the insulation would be blown into the space above the first 4' course of ceiling panels. By the time the walls were filled, not quite half of the original 768 bags of hulls had been consumed.
Getting the Ceiling Ready for Insulation
First floor ceiling showing the temporary strips supporting the weight of the rice hulls until they can be replaced by definitive trim boards. |
Installing the Ceiling Drywall
First floor ceiling bays being filled with rice hulls as seen through the second floor wall. |
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