Fiberboard insulating sheathing repair suggestions:

This article offers advice on procedures for reparing loose, warped, gouged or stained fiberboard ceiling and wall panels or tiles. We borrow from conservationists and we include some DIY homeowner procedure suggestions for non-historic buildings.

This article series describes and provides photographs that aid in identifying various insulating board sheathing materials used on building walls and roofs, such as Homasote, Celotex, Insulite, and Masonite, Upsonboard, Nu-Wood and other insulating board sheathing products.

Repair or Painting Damaged Fiberboard Panels

Repairs to Loose or Warped Fiberboard Sheets

Loose fiberboard can be re-attached using 4d finishing nails, though if your experience is like mine you'll need to drive longer nails, perhaps 6d on a 45 degree angle through the fiberboard into the stud or ceiling joist for the nail to hold the material in place.

Wilson and Snodgrass suggest that it may be possible to repair de-laminated soft fiberboard by injecting wheat paste between de-laminated layers, using a mixture of 1 tablespoon of wheat starch to 5 tablespoons of distilled water, microwaved 20-30 seconds until the mixture is stiff and translucent.

To make such a repair you may need to remove the panel or to form a press that can be applied to the damaged wall or ceiling surface.

Those authors describe removing a warped panel for repair so that it can be wet slightly, placed flat, and pressed while drying. I do not recommend this repair except for structures and panels of historic value, as in my experience, unless you're an experienced conservationist, trying to remove a 70 year old fiberboard panel from a wall or ceiling leads to ever worse damage to the panel.

Really? For other than historic preservation purposes, in my view it makes more sense to remove and replace damaged fiberboard panels with new ones of the same or similar texture and color. You won't find beveled Nu-Wood panels in new stock as the product has been out of production since about the 1970's or earlier.

If there is extensive damage throughout a non-historic structure, remove the panels entirely and replace them with drywall. That step brings your building closer to modern fire-code requirements, and it provides an opportunity to upgrade exposed wiring, plumbing, insulation and and to inspect the structure for hidden rot or insect damage.

You could instead leave the panels in place and cover them over with drywall: a step involving less mess. But you may find that the window and door trim and receptacles and switches in the room all need to be built-out, making this option expose its own achilles-heel.

Watch out: if you are working on a historic building you should not remove nor modify its materials before consulting with your local historic preservation authority.

Repairs to Dings & Gouges in Nu-Wood®, Homasote®, or other Fiberboard Wall or Ceiling Panels or Tiles

BJ's photograph of Nu-Wood like fiberboard wall paneling above provides more information about the identification of these panels. - B.J. by private email 2017/07/29

The gouge contributed by the movers exposes the characteristic brown soft wood fibers that we'd expect in a fiberboard panel.

The vertical V-groove in thephotograph above is a bit narrower than the panel butt-joint v-groove photo that we provide below. So measuring between the actual butt joints will give the true panel width, probably 48".

Repairs to a deep ding or gouge in fiberboard panels can take either approach.

DIY homeowner approach to interior fiberboard repair on walls and ceilings.

1. Vacuum out or gently dust any very loose materials and dirt or debris from the gouge.
2. Paint the area of damage with a latex or acrylic paint to seal and stabilise the loose fibers. Homasote recommends using latex-based paints and where glues are needed, the company recommends Titebond® #5262 or Elmers® Carpenters Glue
3. Fill the gouge using a latex-based or white vinyl or phenolic non-shrinking caulk or, as recommended by some fiberboard manufacturers like Homasote, you can use a polyurethane sealant.

For deep gouges or wide areas of damaged fiberboard you probably need to use one of the putty-type products listed here and you may need more than one pass, after keeping the initial fill-patchbelow the final surface, to bring the repair out flush with the original surface.

To patch small holes and gouges in fiberboard such as Homasote or NuWood we have successfully used the patching compounds listed below.

For large holes or badly warped panels it's best to cut out or remove and replace the damaged area or the entire panel.

Watch out: these repairs work very well on fiberboard wall and ceiling surface repairs indoors but outdoors I have not found such surface patching durable over the longer term.

Fillers for Fiberboard Panels, Homasote, Nu-Wood Damage Spots

• Dash Patch for HOMASOTE PANEL REPAIR [PDF] shown just above, recommended & listed as a "joint filler" at the Homasote website at http://www.homasote.com/assets/files/installation/dash_patch.pdf - retrieved 2020/04/14
  
  Dash Patch is a PorRok product: Por-rok products are licensed through Novex Systems Interntional and manufactured/ distributed by CGM, Inc
  
  DASH PATCH is a gypsum based powder which, when mixed with water forms a plastic composition that can be troweled onto most surfaces to provide a smooth base for resilient or hard surfaces. DASH PATCH is designed to have rapid setting, high strength, adhesion and workability. DASH PATCH will not shrink or expand.

• Durham's "Rock Hard" Water Putty [shown above].
  
  Durham's Water Putty is a light tan colored powder that is simply mixed with water to form a patching compound. Don't use more water than necessary to spread a paste that will adhere to the fiberboard;
  
  You may need to either texture the surface as it's nearly dry or smooth the surrounding surface before painting.

• Sikaflex®-1c SL [recommended by Homasote as a "joint filler"] also listed as BASF Master seal.
  
  Sika Sikaflex-1c SL is a single component, self-leveling, premium-grade polyurethane sealant with an accelerated curing capacity. Sikaflex 1cSL can be used in concrete joint 24 hours after the concrete is poured and also in damp concrete applications.

• SONOLASTIC® NP 1™ [recommended by Homasote as a "joint filler"] is also a polyurethane sealant.

Other patching products that may work acceptably on fiberboard walls and ceilings:

• Aquacoat® Clear Wood Grain Filler - not a filler but possibly for use as a sealant?
  
  Aqua Coat Clear Grain Filler is a water-based, easy-to-apply gel designed for filling and leveling the pores of "open-grain" wood structures such as oak, mahogany, and ash. It reduces the number of sealers and top coats required to obtain a glass-like, high-build finish.
• Bona Pacific Water Borne Fille, a trowelable fcompound for filling holes & gouges
• Timbermate® Waterbased Wood Filler
  
  
  Timbermate Woodfiller is an Interior grade 4 in 1 woodputty, grainfiller, edgefiller and crackfiller. When thinned slightly with water can also be used as a sanding sealer. Timbermate does not shrink, sink, crack or fall out and has an indefinite shelf life.
  
  The secret ingredient of Timbermate is tap water therefore containing no Acrylic, Latex or Solvents.
  
  MDF:
  Due to the finishing system used to manufacture MDF it is essential to seal the job with a water based non-acrylic product before applying top coats. Therefore TIMBERMATE meets your needs.
  

Do you Need to Match the Surface Texture of Surrounding Fiberboard?

If the original fiberboard panel surface was textured such as shown in some of the Nu-Wood illustrations and also the classic textured Homasote and other interior-use fiberboard wallboard panels, your patch will look too-smooth unless you texture the surface.

We want to avoid creating a too-smooth island of patch in the middle of a rough-textured panel.

Options for matching the original surface texture include the following:

• Use a scrap of existing fiberboard to press gently into the nearly-dry surface of the patched area to match the surrounding surface texture.
  
  Some experimenting may be needed to sort out just how hard to press the texture-imprinting scrap and you may need to make a reverse-imprint block if the surface indentations rather than raised elements are so-reversed as to be noticeable.
• Use a thin, flexible, flat-bladed drywall knife that is at least a four inches wider than the widest width of the opening that you need to tool.
  
  When making a final pass over the patch surface to smooth your filling compound, hold the drywall blade lightly on the surface so that you allow it to travel up and down over the irregularities of the original surface near the repair-work.
  
  That movement will permit the blade to move up and down or side to side, closely-matching the texture of the surrounding surface.

Above you can see my imperfect but satisfactory attempt to copy the rough texture of T111 plywood siding into what would otherwise have been smooth filler/sealant used at the corner of this building.

I used a small 6-inch drywall knife, dragging it almost at right angles to the surface, holding the blade lightly. As the blade bobbled over the rough T-111 surface the parallel lines in the existing surface copied into the surface of the sealant to make that filler less obvious.

Restoration-conservationist approach to fiberboard repair

• Make a flour and water paste, mix up fibers from a scrap of extra fiberboard of the same or similar brand and model,
• fill the gouge with a patch of fiberboard material and paste or a cut and trimmed patch to fit,
• press until dry, polish the surface,
• paint to match surrounding surface.

Expertise, plenty of time and labor, and trouble mean this is probably not appropriate for a non-historic building.

Once the panel surface has been repaired you'll need to re-paint the panel, wall, or ceiling if you don't want to look at an obvious, white patch job that doesn't match its surroundings.

See FIBERBOARD PANEL PAINTING below.

Watch out: Because a few fiberboard products such as some Nu-wood (Conwed) ceiling tiles contained asbestos, see a discussion of possible asbestos at plants producing these cellulose-based ceiling tiles produced

at ASBESTOS CEILING TILE FAQs

Watch out: about fire safety.

I like these old fiberboard walls, but I am compelled to add the caution that for improved fire-resistance to meet modern codes you may ultimately decide to laminate a layer of drywall over them - something to discuss with your local building inspector.

While treatments were done to some products to improve fire resistance their fire rating, particularly after many decades of service and possible deterioration, might be in question.

How to Paint Fiberboard Panels

Re-painting existing, already-painted fiberboard panel or tile ceilings or walls requires using an interior paint that is compatible with the paint that's already on the surface.

If the existing fiberboard surface is stained from previous leaks, and assuming you were smart enough to fix the leaks before trying to paint, you may need to seal the stained area with a lacquer primer-sealer to prevent the stain from bleeding-through the new paint job.

This is particularly necessary on fiberboard panel paint jobs since solvents in some paints (as well as some water leaks) can dissolve tannins and other components in the panel to form a brown or black stain that may simply bleed through a new coating of a water-based latex or acrylic paint.

Watch out: using an incompatible paint on an already-painted surface can cause the new or old or both layers of paint to fail by peeling, bubbling, or falling right off of the surface. Details are

at INCOMPATIBLE PAINTS [separate web article at InspectApedia].

Painting previously-un-painted fiberboard panels, comes up when a fiberboard-covered interior room is being converted from storage to living space or "modernized" or when you're sick of looking at stained Beaverboard.

If you must paint previously un-coated fiberboard, the job may not be as easy as you think: a bleed-through problem may infect your paint job unless you first coat the fiberboard with a lacquer primer/sealer, just as I discussed above.

Above: a painted-over Nu-Wood ceiling discussed below in a Q&A

about NUWOOD ASBESTOS CONTENT

Watch out: as we warn throughout these articles, don't start slapping paint onto un-painted surfaces of a historic building before you've consulted your conservation authority.

Note: presently in the U.S. a separate company, Nu-Wood Synthetical Architectural Millwork, Syracuse, NY, produces polyurethane-based faux stone and brick panels and columns used indoors and outdoors. These products are not those described in the article above.

Watch out: if you're worried about asbestos in fiberboard panels or sheathing products,

see SHEATHING, FIBERBOARD ASBESTOS CONTENT

Fiberboard Conservation, Repair, Painting Research

Photo: Homasote 440 Sound Board insulating board, a cellulose / paper product cited below.

• "Conwed Corporation, An Inventory of Its Records at the Minnesota Historical Society Manuscripts Collection", Minnesota Historical Society, retrieved 2015/12/04, original source: http://www2.mnhs.org/library/findaids/00477.xml
• HOMASOTE 440 SoundBarrier® INSTALLATION INSTRUCTIONS [PDF] Homasote, 932 Lower Ferry Road, West Trenton, New Jersey 08628 USA, 800-257-9491 609-883-3300 Fax: 609-883-3497 609-530-1584 Sales Extension 1500 Website: www.homasote.com Email: sales@homasote.com Technical Support: Extension 1332 Email: techhelp@homasote.com
  
  Excerpt: Homasote 440 SoundBarrier® is a special-density, structural board made from 100 percent environmental Homasote® cellulose fiber, a homogeneous composition manufactured with uniformly distributed protection against termites, rot and fungi and resistance to moisture. It also insulates, with twice the R-value of wood.
  
  See also instructions for all Homasote products at http://www.homasote.com/installation
• HOMASOTE 440 SoundBarrier® ARCHITECTURAL SPECIFICATIONS [PDF] includes installation recommendations but not much about repair, retrieved 2020/04/14
  Excerpt:
  
  Replace panels that cannot be repaired.
• Jester, Thomas C., ed. Twentieth-century building materials: History and conservation. Getty Publications, 2014.
• Oregon Caves NM: HISTORIC STRUCTURES REPORT (Part V), [PDF] U.S. National Park Service, discussing preservation of Nu-Wood panels, retrieved 2017/07/30, original source: https://www.nps.gov/parkhistory/online_books/orca-hsr/hsr5.htm
• SHEATHING, FIBERBOARD - Fiberboard insulating sheathing used on or in buildings
• Wilson, Richa, Kathleen Snodgrass, "Early 20th-Century Building Materials: Fiberboard and Plywood", [PDF] (2007) United States Department of Agriculture, Forest Service, Technology & Development Program, 073-2308-MTDC, retrieved 2017/07/29, original source: https://www.fs.fed.us/t-d/pubs/htmlpubs/htm07732308/
  
  This article makes helpful distinctions between fiberboard, low-density fiberboard, medium density fiberboard, and hardboard.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-10-20 by (mod)

@Jocelyn Berman,

That sounds reasonable.

On 2021-10-20 by Jocelyn Berman

Thanks for the response. The sill plate is only damaged in a few areas; 3' section length by one wall, and 8' section at a corner (4' on each side) near the a/c compressor. As a precaution, I am going to remove the 1st two bottom courses of cedar shakes and remove the fiberboard insulation to check the entire sill perimeter, just to make sure there are no other needed sill repairs, a week before we are ready to install the new siding. I already dug down 6" from the sillplate exposing the slab and using salvaged 2" thick paving stones and gravel from the old patio, around the house perimeter, leaving 4" of exposed slab, so there will no longer be soil build-up. Thanks again for the advice.

On 2021-10-13 by (mod)

@Jocelyn Berman,

I wish we could be more helpful and apologize, but most of your questions can't be answered usefully just based on a text note. For example "what kind of board is on the exterior?"

But in general, for the problems you describe, the best solution is to remove siding and rotted framing, supporting the building wall as necessary, then build up a masonry foundation to a foot above grade or more; then repair the framing, bringing it down to a pressure-treated sill plate atop the new foundation.

As you plan to re-side the whole building with vinyl it does not , in my OPINON, make economic sense to try to match the original fiberboard sheathing and cedar shingles or shakes; any temporary weatherproof enclosure would suffice.

On 2021-10-13 by Jocelyn Berman

I just bought a Hi-Ranch built in 1974 on a slab with cedar shakes and 1/2" rigid board under the shakes. The board is dark grayish/brownish and appears fine pieces or like sawdust, where has disintergrated and broken off into small pieces around 6-10" as my handyman broke off 6' length and 16" high, from the sill plate up about two shake courses due to soil build up over slab and moisture/seepage into the board and sill plate. No paper between the shakes and board, so moisture discoloring the board is evident where shakes are missing from walls and seepage from soil build up over slab. When re-grading the soil to remove soil over slab, we could see the moisture/seepage from the soil had rotted out some of the board and damaged the cedar shakes touching the soil. We started to remove 2 courses of shakes in the section we found sill rot, and removed the damaged board as well, and now need to decide; 1. what product to use to replace the board and seal the joint to the remainging board, so we can replace the cedar shakes temporarily. The inside of the house has paper covered batt insulation in the walls between the studs, between the attic joists, and foil batts in exterior wall in the bathroom. We plan to re-side the entire house, in vinyl siding. If it's too late to do in November, we will do it in the spring. My next questions are 2. besides what type of board is on the exterior, 3. is the board acting as a structural element attached to the studs, and should I leave it all; just replaceing 16" from the sill up around the perimeter, replacing the disintergrated board due to the soil encroachment. 4. Lastly, if the board is not a structural element, should it all be removed when we remove the shakes and just install foil insulation board covered by vinyl siding. Thanks for any advice.

On 2021-09-02 by (mod)

Re-posting without improper link

so according to this it says fiberboard ceiling boards and panels contained asbestos


Moderator reply:

Rose that's a law firm looking for litigation business, not an authoritative information source on asbestos use in building products.

In general, fiberboard is a plant product: made from cane or bagasse or wood fibers - those are not asbestos.

There were some reports of cross-contamination of some fiberboard products made by companies at the same time and same location as where those same manufacturers produced or used asbestos in other products.

Use the on page search-box to find ASBESTOS in FIBERBOARD and you'll find

SHEATHING, FIBERBOARD ASBESTOS CONTENT https://inspectapedia.com/structure/Fiberboard-Sheathing-Asbestos.php

that actually cites supporting scholarly reserch

On 2021-08-23 by (mod)

@samie,

You posted this question and we replied at

https://inspectapedia.com/interiors/Fiberboard-Ceilings-Walls.php

On 2021-08-22 by samie

would asbestos be in a 1950s mobile home ceiling.the ceiling is not tiles,it is a panel or board material

On 2021-06-04 by (mod)

@Greg,

Using a ceiling tile like the one in your photo, provided the tile itself is new enough that you're not worried about fooling with asbestos material, is a clever move if you don't have scraps of fiberboard panel to repair the damage in your earlier photo.

Use a very sharp box knife ("drywall knife" like the fancy Stanley Box Cutter shown below) and a steel straight edge to cut out the damaged area;

Work carefully, don't get trash in your eyes and don't cut off a finger. Getting blood all over the ceiling is a mess (speaking from experience).

I make my existing-ceiling cuts on a 45 degree angle with the larger-dimension "up" towards the ceiling.

I trim my replacement piece of fiberboard (or ceiling tile) to be just about 1/8" smaller in length and width, and of course cut its bevel the opposite to that in the ceiling opening.

By angling the replacement square up into the ceiling and if necessary pulling it down with a couple of coarse-threaded sheet metal screws, I glue the replacement in place using a paintable acyrlic sealant.

When the repair is flush I leave it alone for the sealant to cure.

As your original ceiling was smooth, you may want to use some drywall compound to skim-coat the area of repair before re-painting the ceiling.

Let me know how this works for you.

Below: Stanley box cutter knife useful for cutting LDF and MDF fiberboard panels

On 2021-06-04 by Greg Cunningham

The ceiling is board and batten, and is fixed, I was just going to use the ceiling tile as additional material to fill in the hole (image attached).

With the hardware stores closed in Canada, it's hard to know what to get.

On 2021-06-04 by Greg Cunningham

Hey Daniel,

I have a cottage which has a hole in the ceiling caused by a water leak and stepping through by mistake from the attic. It seems like the fiberboard is cardboard, is there risk to using a water based filler as it would just be absorbed by cardboard and not bond?

I found another ceiling tile, and was going to cut a hole the same size as the (ceiling 6" hold saw"), put sticky tape in the attic to hold it in place, then caulk around and finally fill in. What do you think?

On 2020-09-13 by (mod)

Any building supplier,
But first take a look at the fiber board repair suggestions above on this page. Are you sure that won't work for you?

On 2020-09-12 by Diana Berne

Our home is just about to close escrow but we need to fix a huge concave hole in the fiberboard. Where do I find this material?
Thanks

On 2020-07-20 by Tony

In 1970 I was a carpenter apprentice and learning names of the tools we used

In the case of what we call a utility knife today was called a Cellotex knife

The explanation given by the old carpenters was that the knife was developed to cut Cellotex

50 years later I still call it a Cellotex knife

On 2019-02-02 by (mod)

Ned

Our best advice for patching a crack or ding in a Beaverboard ceiling panel, better organized and more complete than if I make it up off the cuff here, is in the text of the article above on this page.

Clean, seal, paint.

On 2019-02-02 by Anonymous

@Ned adams,

On 2018-02-28 by Ned adams

How to patch crack in beaver board ceiling circa 1948

 

...

Continue reading at FIBERBOARD SHEATHING IDENTIFICATION - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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