Celotex insulating sheathing identification guide:

Here we help identify and give information about the manufacture, ingredients & use of Celotex® insulating fiberboard building sheathing products used as exterior wall sheathing and as interior wall & ceiling surfaces.

In this article series we provide fiberboard product names and we describe the components, properties, and applications of various fiberboard, hardboard, and insulating board or sound deadening board products.

We also answer questions such as do Celotex or Homasote or other fiberboard and insulating board products contain asbestos? fiberboard water resistance, fiberboard recycling.

How to Identify Celotex® Insulating Board / Celotex Insulating Lumber, Fiberboard Products

Our photographs show Celotex® insulating board with an older Celotex fiberboard building sheathing board at above/left and a more recent Celotex insulating board product shown at the top of this page.

Also see this closeup of an OLDER Celotex INSULATING SHEATHING BOARD [image file] product.

Components & Properties of Celotex Insulating Lumber

Celotex described their Celotex Insulating Lumber as an exterior sheathing product intended for use as a base beneath plaster or beneath a stucco building exterior as well as for roof insulation.

Celotex insulating lumber was sold in 7/16" thicknesses (and possibly other thicknesses), in 4 foot width boards at lengths from 8 ft. to 12 ft. and weighing about 60 pounds per square (100 sq.ft.).

Celotex Corporation produced the first fiberboard made from bagasse in 1920. (Jester 2014).

Celotex insulating lumber (today we call it insulating board or insulating sheathing) was sawed "like ordinary lumber" and nailed directly to the building framing to support stucco, brick veneer,m or other finishes.

Celotex Insulating Lumber was a cellulose fiber board made from bagasse or sugar cane fiber using a felting process, and produced in Celotex's New Orleans LA plant.

These fibers "each of which contains thousands of sealed air cells", were fabricated into "building lumber" using a patented press and bonding process.

Several patents listed in the mid 1920's addressed the production of insulating, structural, and sound-absorbing board products for walls, roofs, and ceilings produced by Celotex.

See CANEBOARD PANELS for details.

In wood frame construction Celotex insulating lumber was used as a structural sheathing to replace horizontal or diagonal 3/4" thick board sheathing while adding insulating and sound-deadening properties. The company described the insulating value of this new product as

"... equal, as insulation, to 3 1/3 inches of solid wood, 12 inches of solid plaster, 12 inches of solid brick, or 24 inches of solid concrete".

We estimate, based on the wood comparison, that the R-value of this 7/16" thick board was about R-3. According to Celotex this insulating lumber product was waterproof, could be painted, and could be used itself as an exterior finish as well, though we have not seen any surviving examples of that application.

Celotex's insulating lumber was also advertised for use as an interior finish, left natural, stained, painted, or stenciled.

Celotex recommended its use also as a base for plaster walls or ceilings, for which some installation instructions can be read in the image just below. Thanks to reader [Anon by private email 21/14/15] for this image.

A number of these instructions suggest that over-wetting or prolonged wetting of these boards might lead to swelling, weakening, buckling, bulging, or other issues in the finished plaster job.

see FIBERBOARD PLASTER BASE SYSTEMS - instructions for applying plaster to Celotex boards - for details.

From our own field inspections, we believe that Celotex insulating lumber or similar products were indeed also often left exposed as an interior finish most commonly in summer camps, cottages, and in commercial or farm buildings.

According to one source the material was also used to construct insulated shipping boxes. [8] By 1925 Celotex had published "Celotex insulating Lumber Specifications and Details for Standard Building Board" and also offered "Your Home" a plan book of twenty-five ideal small homes.

A review of the patents and product description for Celotex insulating lumber products shows that asbestos was not among the product's ingredients.

Celotex Cemesto Board Structural Panels - 1/8" Asbestos Cement Board Laminate

Cemesto-Board,1 1/2 to 2-inch thick 4' x 8' or 12' panels comprised of asbestos-cement panels adhered to a vegetable-fibre core (Celotex sugar cane), first introduced by Celotex in 1937, is described in detail at

CELOTEX CemestO BOARD HOMES

Celotex Regular Insulation Sheathing Continues in Production as Blue Ridge™ Fiberboard & SturdyBrace® Sheathing

In 1955 there were at least fourteen different insulation fiberboards examined by the US FPL. Today Celotex continues as a major producer of the product. [15]

As of 2012 Celotex continued to produce a wide range of insulation products including PIR polyisocyanurate foam boards in various designs and for various applications. The company continues to produce Regular Insulation Sheathing as a 1/2-inch thick insulating board with an R-value of 1.2. Celotex Regular Insulation Sheathing is described in contemporary product literature as:

Produced from cellulosic interlaced fiber bond with natural binders. Manufactured from Sugar cane by-product called bagasse, recovered wood chips and consumer newsprint. Available in 4' width in standard lengths of 8' and 9'.

Designed for use as an insulating sheathing for frame walls under exterior finishes such as lap and panel sidings, stucco, masonry veneer and shake shingle products.[2]

Celotex Blue Ridge™ Fiberboard, also referred to in its product literature as SturdyBrace® is a wood fiber product that is described by the company as:

SturdyBrace® meets national codes for structural integrity. The insulating exterior wall sheathing is competitively priced. You may bid with confidence year round. SturdyBrace® improves the structural integrity of homes and light commercial buildings and eliminates the need for corner bracing.

SturdyBrace® meets codes for wind shear and seismic conditions. Check with code officials in your area.

Trapped moisture in exterior walls is caused by condensation and water leaks. This moisture can lead to mold growth and other water related problems. SturdyBrace® “breathes” permitting the moisture to escape into the outside air.

Mold experts recommend use of wall sheathing with a minimum ASTM permeability rating of 5. SturdyBrace® rates more than 20.0 perms while OSB and plywood have permeability ratings of 2 and less than one respectively.

SturdyBrace® is an earth-friendly fiberboard made of recovered wood fibers interlaced and bonded with asphaltic binders for strength.

It is easy to install and cuts with a knife, saving you time and money. SturdyBrace® is available coated on one or six sides. SturdyBrace® saves energy costs at a low cost per R-value. Our wall sheathing provides R-value of 1.3 per 1/2”, more than doubling the R-Values of OSB and gypsum sheathing.

*Building codes may require use of weather resistant barrier. [2]

Watch out:

Blue Ridge Fiberboard products must not be used in close proximity to chimneys, heater units, fireplaces, steam pipes or other surfaces which could provide long term exposure to excessive heat (maximum 212*F) without adequate thermal protection. [2] - guidespec

See CELOTEX HISTORY & PRODUCTS

Celotex Strong-Wall Fiberboard Sheathing

Photos of this 1960's Celotex Strong-Wall fiberboard insulating sheaathing is provided courtesy of InspectApedia.com reader Elton White.

[Click to enlarge any image]

Comment: CeloteX Strong-Wall BOCA-12A - 1960s insulating sheathing

2021/02/01 Elton W White said:

I'm remolding a house in Baton Rouge, LA that was built in early 1960s. It has black 7/16" sheeting on exterior of framing under an exterior siding such as brick. It's nailed directly to the exterior studs and labeled as CeloteX Strong-Wall BOCA-12A.

I've read about CeloteX products on this site, but have found nothing directly addressing this product. Does anyone have additional info and would you like additional pictures beyond the attached.

Thanks Elton@katzwhite.com

Moderator reply:

Thank you so much for the Celotex Strong-Wall photo, Elton.

Your sheathing is brown,not black, but indeed some "black" or dark-coated fiberboard sheathing products uses an asphalt-base coating for water resistance, as well as a treatment called the Celotex Ferox Process to help resist termites & rot.

I've posted older photos of the Celotex product line, including sheathing products, here and at the companion

page CELOTEX HISTORY & PRODUCTS

but not the exact one in your photo so its a welcome addition that I'll include above along with what information I can add.

You may enjoy seeing this historical document describing Celotex products - these are 5 years or more earlier than the Strong-Wall shown in your photos.

Celotex "Strong Wall-board" was described as early as 1930 (Blondin 1930) but has not appeared widely in online resources.

• CELOTEX STRUCTURAL INSULATION AND OTHER BUILDING PRODUCTS [PDF] (1954) from Sweets 1955 Construction Guide.
  
  Here is similar, HIGH RESOLUTION [PDF] copy of the same document.

Celotex products described in this older document include (this is not the whole list)

• Celotex Celo-Rok weatherproof (Core-Treated) sheathing
• Celotex Cemesto structural insulating panels - a laminate of cement-asbestos board over a cane fiber core - also see
• Celotex structural / insulating sheathing boards, asphalt coated and Ferox Process treated fibres resist termites & dry-rot
• Celotex sheathing backer board
• Celotex insulating interior finishes

Research on Celotex Strong-Wall Products

• Armin, Elmendorf. FIBER PLANK [PDF] U.S. Patent 2,377,484, issued June 5, 1945. Filed by Celotec Corp.
  Excerpt:
  
  This invention relating to cement-fiber boards has as an object the provision of such a board block or other insulating mass having relative rigidity so that it may be used particularly in building construction in various manners, not only to insulate against the transmission of sound, heat and cold, but also as a supporting base for desired finishes as in wall construction.
  
  The principal object of the invention hereof is the provision of a cement-fiber board as above which is a distinct improvement over such boards as they have been heretofore proposed in that such cement-fiber boards made in accordance with the inventions hereof are decidedly superior 'in strength and stiffness when compared with boards of this type as heretofore proposed, and in addition has other improved and distinguishing characteristics as compared with cementfiber boards heretofore proposed.
• Joseph, Blondin. Aircraft supporting and controlling surface [PDF] U.S. Patent 1,775,386, issued September 9, 1930.
  Excerpt:
  This skeleton is encased in a covering 20 of light and strong wall-board, such as Celotex, which is glued and screwed, or otherwise fastened, throughout all zones or surfaces of contact, ...
  
• Hahn, Frank R. Building construction and building element [PDF] U.S. Patent 2,164,322, issued July 4, 1939.
  Excerpt:
  The next step is to apply an insulation material to the surface of the wall. This insulation material may be of any composition material such as Celotex, Insulite, or Beaver Board or the like.
• Lathrop, Elbert C. "The Celotex and Cane-Sugar Industries1Bagasse or Sugar a By Product?." Industrial & Engineering Chemistry 22, no. 5 (1930): 449-460.
• Lindahl, Robert L. "Building construction." U.S. Patent 2,317,926, issued April 27, 1943.
• Munroe, Treadway B., and Elbert C. Lathrop. "Fiber storage and preservation." U.S. Patent 1,920,129, issued July 25, 1933. Assigned to Celotex Corp.
• Researching the product name "Strong-Wall" or StrongWall" is a bit confounded as there are also steel and other products sporting the Strong-Wall™ name, so having the photo you provided is helpful. For example Simpson Strong Tie describes their
  
  Simpson SSWT - Steel Strong Wall for Timber Frame Racking Resistance [PDF] product series that combines steel components with Celotex GA3000 on the outside face.
• Samuel, Krajci. "Unit for roofs and walls." U.S. Patent 2,400,357, issued May 14, 1946. Filed by Celotex Corp.

Working together makes us smarter. Thank you again for taking the time to post and contribute.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-02-01 by (mod)

Thank you so much for the Celotex Strong-Wall photo, Elton. I've included your photo and a bit of discussion in the article above on this page.

Working together makes us smarter. Thank you again for taking the time to post and contribute.

On 2021-02-01 by Elton W White

I'm remolding a house in Baton Rouge, LA that was built in early 1960s. It has black 7/16" sheeting on exterior of framing under an exterior siding such as brick. It's nailed directly to the exterior studs and labeled as CeloteX Strong-Wall BOCA-12A. I've read about CeloteX products on this site, but have found nothing directly addressing this product. Does anyone have additional info and would you like additional pictures beyond the attached.
Thanks Elton@katzwhite.com
[Photos shown above on this page - Ed.]

On 2020-06-24 - by (mod) -

Yes you can but keep in mind that you may need to build out trim and receptacle wall plates Etc

On 2020-06-24 by Anonymous

Can you install sheet rock over this

On 2020-03-04 - by (mod) -

Peter

I would open the walls,
remove the wet or disintegrating fiberboard,
Let the remaining fiberboard trapped between siding and studs dry
Repair or replace wiring
Insulate with closed cell foam

On 2020-03-03 by Peter Spano

My question is this my house got flooded with 26,000 gallons of water from the inside out upstairs floor to the bottom for the insulation board got soaking wet almost through the whole house is just totally deteriorated 25 years old my Home

I need to replace that for the water came from the inside out is it verifiable that fiber board for 25 years old with the room to get water hit it from the upstairs down continuously for three days I cannot seem to dry it out and when it does dry out it turns to dust

On 2019-07-14 - by (mod) -

There are some cellulose or paper tape gray insulating board products. However it's also possible that if the board was put there as a fire barrier it contains asbestos. I'm sure you will understand that we can't accurately identify material by text alone. A photo would be helpful. Meanwhile treat the material as presumed to contain asbestos, or have a sample tested. The test cost is not significant. Typically around $40.

On 2019-07-14 by Chuck

I'm currently working on a condo in Phoenix AZ that was built in the early to mid 70's the second floor sub floor looks to be some kind of fiber board ,grey board or a soft board the sheets are 2'x 8'x 1/1/2'' T&G. I have never seen this before and need some help in trying to identify this product unfortunately i have no photo yet and any help will be greatly appreciated
Thank you!

Question: Celotex wallboard wetting before use in plastering

I know per your articles that Celotex interior fiberboard usually does not contain asbestos but the directions on the back of mine talk about spraying it the day before installing it. My question is what might that spray do to the product?

I'm enclosing a picture of my product label. I find no other product marking however and want to be assured that it is not something containing asbestos.
Any thoughts would be appreciated. - Anon. by private email 2015/12/14

Reply:

Thanks for the question and also for the image - it was one I've not seen and it contains helpful details.

In the article above in the Celotex section I've posted your image of the Celotex instruction label discussing wetting the wallboard before use in plastering

OPINION: The spray was intended to boost the adhesion of plaster when this board was used as a substitute for (earlier) wood lath. These products were somewhat water resistant, some including waxes specifically for that purpose.

Wetting wallboard 24 hours before installing it as a plaster base would have increased its moisture content a bit; I doubt it'd have become too soft to apply or the manufacturer wouldn't have advised spraying both sides.

In this context I wouldn't expect other problems (such as mold growth) from this step as the board was to be installed to studs or ceiling joists promptly.

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Continue reading at CELOTEX HISTORY & PRODUCTS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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  • CELOTEX DRYWALL ASBESTOS
  • CELOTEX HISTORY & PRODUCTS
  • CELOTEX: IDENTIFY Celotex® Insulating Board and Fiberboard Products
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