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Cellotex is a brand name for asphalt impregnated fiberboard sheathing. The faces are black (asphalt) and the interior is brown. It is quite soft. It is non-structural. Used as sheathing, every 5th sheet and all corners had to be plywood to provide minimum racking resistance.

I think one of the biggest headaches with fiberboard sheathing is that it tends to warp and bow, especially if it gets wet. The exterior walls end up being wavy.

There is a different but similar product used on roofs. Generally it is a light gray or white (not asphalt impregnated), and is higher density than the fiberboard sheathing. The stuff used on roofs is used for insulation, building crickets, and cant strips.
Technically according to Celotex's Rep that spoke at our college material science classes about the product a number of years ago, they claim that with the proper nailing(staple) pattern it is considered structural when using thier sturdy brace product and does meet minimum ASTM standards for rack resistant wallboard. Because the company had donated many lifts of the product to our labs at the time for use and testing, I will never forget the backlash that the students gave him when he made these claims. We hated the stuff. He is correct though in thier certifications.

It is a sugar cane base product. The interesting thing about Celotex is that during the Katrina aftermath when we were paying 15 bucks for a sheet of 7/16" OSB it was still 6 to 7 bucks. People who normally wouldnt use it, started to just because of cost. These past few years as OSB supplyy capacity has caught up with demand and has dropped as low as 4.75 a sheet Celotex remained at 6-7 bucks. THis led to a huge drop off in demand and eventual sale and losure of several of the new plants that they had just opened. They were bought out by another company called Blue Ridge.


Just stick to OSB sheathing... ;)
 

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ThermoPly is sheathing as well as a weather barrier, it does NOT have an R-value,therefore you would need some sort of insulation board. the stuff is about 1/8" thick. i would never use it ,especially when OSB is only 7 bucks a sheet.
 

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I started out working for a contractor that went from building quality condos to putting up Ryan Homes packages. They all used Thermoply. The stuff is strong, I'll give it that. It needed no braces for rack. If we had a wall panel that wasn't square, even by a tiny bit the Thermoply had to get taken off. Even if the wall was only out of plumb an eigth inch. The major issue I have is that the siding installed over it will get wavy depending on how the sun hits it and is caused by how the wall panels were allowed to sit uncovered, water and snow would lay on them and bow the ply between studs and once installed and sided over these bows would cause the siding to wave. When I left that contractor Ryan Homes was just starting to work on a solution. The sad thing is those Ryan Homes wouldn't be bad if they payed there subs better, there was no time to fix factory screw ups like out of square panels, and spent a little more for better lumber and materials, Towards the end of my time putting them together the studs started looking more like bulsa wood.
Now I do alot of repairs, maintenance and remodels on some that I originally helped put up, For the most part 15 years later they are still holding up. Their deck contractor left alot to be desired though...
One thing that surprised me was how well drywall inside corners have held up without cracking using metal clips on one side of the inside corners in lieu of a stud.
 

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when i see these ''non'' solid wood sheathings ill usually bid going over them with osb
to assure a nailable base
LOL.
In the seventies a <cough>builder<cough> here had the homes framed with 2x4 stud walls left open with foam backed aluminum siding as the only covering.
Every time I get one of these jobs it's, tearoff,bat insulation and OSB unless someone had blown insulation put in. Then it's tearoff with tarps on the ground to catch all the insulation.

Customers are usually shocked when they see what they thought was a decent home.
 

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ThermoPly- strong, weather resistant

ThermoPly is used instead of OSB and does not need a housewrap. You can get it with a poly coating or with a foil coating. You do have to fur out windows because it is only about 3/16" thick but it is easy to work with- it can be cut with a razor knife.
 

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There is another advantage to Thermo Ply that has not been mentioned in this thread. It has to do with mold liability.

1/2" Celotex, 1/2" osb, & 1/2" Thermax all have the same problem in this regard. Most mold issues result from masonry being too tight to the sheathing face. The typical space between the sheating face, & brick is too tight to provide decent ventilation for moisture removal. With the added 3/8" space resulting from 1/8" Thermo ply use, you can go to a full 4 5/8" (insted of 4 1/4") brick ladder, & hence improve mold mitigation. Mold lawsuits are the main reason for Thermo Ply being used by big builders, not cost. It is a time proven product. The insulation value is in it's reflective quality, not in it's R value.

However, I used 1/2" Thermax on my first home in '78, & again in '88, & wouldn't hesitate to use it again.
Joe
 

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I don't have much to say about Thermoply AS SHEATHING, but I have another use for it.
- About 30 years ago in RI I redid a small wing on a the house of a friend who was in dire need for the space and needed it cheap. It was a cathedral ceiling with 2x8 rafters, and we wanted to maximize the insulation value. We installed foil-faced insulation with the foil up, but slashed a lot of holes in the foil with with a utility knife (didn't want the vapor barrier THERE). Then, we ran strapping running up the rafters to create a space between the foil and the cdx roof sheathing. Used 1-1/2" roofing nails so that the extra length would help hold the foil away from the sheathing, to maintain the air space that would enable the radiant barrier to do its best work, while at the same time providing a vent-space between the ridge-&-eave vents. A poly vapor barrier went on the inside, and the system worked AWESOME. Warmer in the winter than any other roof with only 8" of fiberglass, and nice and cool in the summer, even with fairly dark shingles.
- But it was a minor pain in the butt farting around with the insulation before the sheathing was on, and I fantasized about welding a self-clearing leather-hole-punch onto the front of a hammer and attacking a pile of thermoply, then installing the perforated thermoply, strapping, and sheathing before the insulation. Though come to think of it now in my old age, after the first 5 or 6 sheets, I'd get a laborer to do the perforating. Or modify a nail gun with a punch, somehow. Or find some drill bits that wouldn't get all clogged and jammed?
 
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