InspectAPedia®   -   Search InspectApedia

Gypsum lath board cross section © D Friedman at InspectApedia.com Fiberboard Plaster Base Systems
Fiberboard & fiberboard-gypsum panels used as a base for plaster walls & ceilings

Types of fiberboard or fiberboard-gypsum laminate used as a base for plaster walls & ceilings:

In this article series we describe and discuss the identification and history of older interior building surface materials such plaster, plaster board, split wood lath, accordion lath, sawn lath, and expanded metal lath, Beaverboard, and Drywall - materials that were used to form the (usually) non-structural surface of building interior ceilings and walls.

Synonyms for "plaster" include stucco, render, lime plaster, cement plaster, gypsum plaster, and plaster of paris. Lime plaster is also the principal ingredient in whitewash often used on building stone walls both indoors and outside and also sometimes applied to wood surfaces.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

History & Identification of Fiberboard & Fiberboard-Gypsum Plaster Base

Fiberboard-gypsum plaster base sheets in a 1930's home (C) InspectApedia.com TT

Harry E. Sharp (1901) patented the earliest forms of plaster-board we have found. To overcome shortcomings of wood-lath and metal lath Sharp proposed a panel made from "... made from the plastic compound or pulp consisting of a preferably fibrous material ..."

Within a decade or two Celotex, Insulite, Graylite, and other brands of fiberboard or cellulose-based sheathing were widely used both as exterior wall sheathing and as interior wall sheathing or as a base for plastering as we describe in this article. This fiberboard is a cellulose product, not asbestos.

Excerpted from a photo provided by a reader who was renovating a North American home built ca 1930, here we see fiberboard-gypsum panels used as a plaster base.

[Click to enlarge any image]

Fiberboard pre-laminated to gypsum was sold in sheets in several thicknesses for use as a plaster base.

Separately, fiberboard, including Celotex™ was also sold in raw fiberboard form for use as a plaster base, without pre-lamination of the fiberboard or pre-coating of it with gypsum.

These fiberboard sheets were lighter, easier to transport, and less fragile than the fiberboard-gypsum laminate product we show just above. Celotex provided detailed instructions for using their fiberboard as a plaster base. You can see those details just below on this page.

More about Celotex and other fiberboard products used as exterior and interior sheathing as an insulating board is

at FIBERBOARD SHEATHING IDENTIFICATION.

If you are worried about possible asbestos contamination in fiberboard sheathing or in fiberboard-gypsum laminate boards used as sheathing or as a plaster base,

see SHEATHING, FIBERBOARD ASBESTOS CONTENT

Using Celotex™ Fiberboard Sheets as a Plaster Base

Celotex insulating lumber ad Above is a page describing Celotex™ "Insulating Lumber" - used as exterior sheathing and similar products made by other manufacturers used bagasse, waste paper, and a variety of other organic products to which waxes and coatings were added for exterior use.

This same product, but without water resistant coatings or waxes, was used indoors for wall and ceiling sheathing and also as a plaster base.

Insulite™, a cellulose-based (all wood fiber) insulating board or sheathing material that unlike Celotex, was made from wood pulp by-product or tailings fibers.

Both of those products are described in this article.

Both of those products were very widely used for roughly half a century as exterior and interior sheathing that provided insulation as well as a base for other finish surfaces. Fibreboard was produced both as an all-fiber product and as a board product to which plaster was laminated.

...

Details of the materials used to produce fiberboard or plaster-laminated fiberboard sheathing are given separately

at FIBERBOARD SHEATHING INGREDIENTS

[Click to enlarge any image]

Look closely at the photo below and you can see a first layer of fiberboard behind the plaster to which my pen is pointing.

We can speculate about the history of the interior wall finish layers in this building looking at the photo below, moving from left to right:

Wall test cut shows construction © D Friedman at InspectApedia.com
  1. Masonry wall
  2. Wood structure to which interior fiberboard was nailed, in this case probably a window frame - Generally insulating fiberboard was nailed to the wall studs and plastered over.
  3. Fiberboard insulating sheathing used as a plaster base
  4. Plaster base coat
  5. Plaster skim coats -t he plastered surface was skim coated, twice in this case, later probably painted, and possibly even wall-paper-covered later in its life.
  6. Gypsum board - "drywall" Still later, typicallly to cover cracked, damaged plastger, a layer of drywall was installed over the original surface.

Celotex recommended use of their interior fiberboard sheets for use as a base for plaster walls or ceilings, for which installation instructions can be read in the image just below.

I've also excerpted them in more-legible text just below. Thanks to reader [Anon by private email 21/14/15] for this image.

The Celotex instructions for use of this fiberboard as a plaster lath base include some interesting details for Celotex applied as a plaster base. These plastering instructions were provided by the Celotex Company in Chicago and were affixed to Celotex fiberboards from the New Orleans Plant [and perhaps others].

Quoting Celotex in italics, we include additional explanation or speculation in the [bracketed comments]

Instructions for using Celotex as a plaster base substiting for lath or gyp board (C) InspectApedia.com TP

Below: a photo of cellulose or wood-based fiberboard that was not covered by plaster. You may still find this material in building interiors, often in an otherwise un-finished attic.

The fiberboard sheathing in the photo below was nailed to enclose the under-side of the overhanging portion of a raised ranch home in New York, constructed ca 1960.

Fiberboard sheathing like Homasote (C) Daniel Friedman

[Instructions] To the Plasterer [for plastering over Celotex fiberboard sheets]

[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.]

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.

Cross-Section Photos of Plaster Lamainated to Insulating Fiberboard Interior Wall Sheathing

Below is a reader-contributed photo showing original fiberboard or "brownboard" interior wall sheathing used as a "lath" base for a rough-coat (white) and finish coat of plaster.

Fiberboard insulating wallboard from a 1944 Minnesota home (C) InspectApedia

Our photo below shows a round cross section test plug we cut from a finished interior wall in an older home. Oldest materials are on the right side of the plug. From left to right we see

Gypsum lath board cross section © D Friedman at InspectApedia.com

More about these surfaces is at FIBERBOARD SHEATHING.

If you are unsure about identifying fiberboard sheathing products

see FIBERBOARD SHEATHING IDENTIFICATION

Graylite - Insulite, Wood-Pulp FiberBoard Plaster Base

Insulite plasterboard from patent app.Insulite was a cellulose-based (all wood fiber) insulating board or sheathing material that, unlike Celotex, was made from wood pulp byproduct or tailings fibers.

Insulite was patented by Carl G. Muench who founded the Ontario Paper Company, and who started manufacturing Insulite, billed as "the first rigid insulating board", in International Falls, Minnesota in 1915. (Jester 2014)

We cite some of Muench's early patents below. His 1916 patent 1,187.476 describes equipment to produce fiberboard panels, filed 13 August 1914 and granted June 13 1916, referred to the construction of a felting machine to use basically left-over tailings or scrap from pulp mills, saw mills, and the like.

[Click to enlarge any image]

The Insulite board was treated to "... resist moisture, vermin and rodents" and also was sold as a "sound deadener"[10] and in some applications the product was installed in the air space between gypsum board partitions to improve sound isolation between building areas.

Insulite was described as having stronger structural properties than Celotex, the latter being superior for insulation and sound insulation while Insulite offered greater strength for other applications. Insulite was

... composed of large sliver-like particles often 1/16" to 1/32" in width and say one half an inch long. These sliver like fibers give great porosity to the mass but they render the binding together of the particles more difficult. [10]

Insulite as a plaster board contained rabbeted grooves or "joints" in its surface to which plaster or other material could be applied. Insulite's name for this product was Lok-Joint Lath. (The same engineers later developed "Bildrite Sheathing" that was used to replace horizontal wood bracing in wood frame construction.) The product cost was as low as 5 cents per sq.ft.

In "Insulite Co. vs. Reserve Supply Co", a 1932 lawsuit, relevant patents and ingredients are described, including a composition of plaster of paris, cement, or other like substance, combined with hair, wood fiber, sawdust, wool, wood shavings, excelsior, straw, or similar substances. (Asbestos was not cited in the product description. )[11]

Treadway B. Munroe, from Forest Glen, Maryland, was a prolific inventor who patented a variety of cellulosic board products assigned to companies including Dahlberg (St. Paul MN and Celotex, Chicago IL).

One of his early patents U.S. No. 1,333,628, described a plaster-board of fibrous material intended to provide a less costly base for plaster walls and ceilings.

Insulite board advertisementThis was the earliest citation of "Insulite" that we could find. It improved on the original "insulite" construction by including additional long fibers for strength combined with more short fibers to serve as filler for the mass, developing a board that was light weight, had adequate strength, and included entrained air for improved insulation.

This invention, instead of impregnating the insulating board with a waterproofing compound, simply coated its surface. The result was a product [intended and claimed to be] well suited for use as plasterboard.

Sound absorbing board for walls and ceilings", Patent No. 1,554,180, issued to W.S. Trader, September 15,1925, first disclosed a wallboard constructed from "Celotex", a felted mass of strong bagasse fibers, so compacted as to be capable of use as an artificial lumber in that it can be sawed and nailed, and has sufficient strength in many cases to be substituted for lumber.

That same patent mentions "Insulite", a building board made from wood pulp tailings and which likewise has a porous fibrous body portion and which is possessed of considerable strength so that the same can be nailed, etc.

Celotex was preferred as an insulating material because its internal cells produce a sound-deadening insulating effect.

Graylite interior-use insulating board produced by Insulite™ is described on p. 7 in Peck (1942) as follows:

The insulating board made from wood fibers, produced by a cold-grinding process, felted into a rigid board. The fibers were chemically treated and intimately mixed with finely divided asphalt before felting to increase the strength, water resistance, and resistance to rot and termites.

One surface of the boards had the appearance of closely woven fabric, designated "linen texture." There were two thicknesses, 1 in. and 1 1/3 in. The Insulate Co., "Graylite".

Other Insulite Product Names

We found references to Insulite mastic as early as 1913. By 1940 we find the additional sheathing product names associated with Insulite, a Minneapolis MN company.

Reader Question: is it ok to plaster over "beaver board" ?

Gypsum lath board cross section © D Friedman at InspectApedia.com

Can I plaster over beaver board ? - Richard

Reply:

Richard, as our photo shows, people have indeed installed plaster over wood-fiber insulating boards, such as in the concrete building in our photo.

In my review of the bases on which plaster was installed I have confirmed that soft wood fiber board was widely used as a plaster lath system.

In addition to fiberboard as a plaster base, proposed as early as 1900 in the U.S., people also used wood lath, metal lath, and gypsum board lath, and also fiberboard to which gypsum or plaster was laminated to provide a plaster base coat.

These systems are described at FIBERBOARD PLASTER BASE SYSTEMS.

I'd be concerned that the beaverboard may not in all circumstances form a good base for plaster finished walls or ceilings installed in a wood-framed structure for these reasons

  1. If beaverboard was installed over widely-spaced or under-sized framing in an older, "light-weight" structure, that beaverboard is likely to be too flexible- leading to plaster cracking
  2. If your beaverboard has already been painted, or if it's a wax-coated product you may also have bond strength problems; normally the plaster base coat depends on mechanical adhesion.
  3. For some types of fiberboard (you may be using the term "beaver board" loosely, you may find severe bleed-through and brown staining of the finish plaster surface, though that's more likely if your "beaverboard" is an exterior product that was coated with asphalt or waxes.
  4. If the fiberboard is not flat then your job will be horrible.
  5. See the Celotex plastering instructions given above in this article

    Watch out: DO NOT USE LIME PLASTER when plastering over Celotex™ or similar products.

I'd consider installing a laminate of drywall over the beaverboard instead. If you want a plaster finish install a base of gypsum board ("Rock lath"), or expanded metal lath to make a most-durable job.

See FIBERBOARD SHEATHING IDENTIFICATION to get help identifying just what product you have installed.

There you will find descriptions allowing you to IDENTIFY BEAVERBOARD / BUFFALO BOARD as well as other products.

Also see

Weaver: Beaver Board and Upson Board: Beaver Board and Upson Board: History and Conservation of Early Wallboard, Shelby Weaver, APT Bulletin, Vol. 28, No. 2/3 (1997), pp. 71-78, Association for Preservation Technology International (APT), available online at JSTOR.

Research & Patents: Composition & History of Fiber-based Plasterboard, Insulite, Graylite, Fiberlite

Insulite wall panel machine, Ellis Patent 220-8511 July 16 1940 at InspectApedia.comIllustration: Method of Making Wall Panels, Ellis' 1940 patent of a fiberboard production machine assigned to the Insulte Company U.S. Patent 2,208,511 cited below.

Sharp's plasterboard partition or wall patent US 68942 in 1900 (C) InspectApedia.com reprint from USPTOIllustration: Sharp's 1901 patent for a partition or wall using wood pulp based fibrous plaster board.


...

Continue reading at PLASTER TYPES & METHODS in BUILDINGS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

Suggested citation for this web page

FIBERBOARD PLASTER BASE SYSTEMS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING INTERIORS

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Note: appearance of your Comment below may be delayed: if your comment contains an image, photograph, web link, or text that looks to the software as if it might be a web link, your posting will appear after it has been approved by a moderator. Apologies for the delay.

Only one image can be added per comment but you can post as many comments, and therefore images, as you like.
You will not receive a notification
when a response to your question has been posted.
Please bookmark this page to make it easy for you to check back for our response.
Our Comment Box is provided by Countable Web Productions countable.ca

Comment Form is loading comments...

Citations & References

In addition to any citations in the article above, a full list is available on request.



ADVERTISEMENT