Masonite hardboard © Daniel Friedman at InspectApedia.comMasonite™ & Similar Hardboard Ingredients
History & Ingredients; no asbestos

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What are the ingredients in Masonite™ & does or did it contain asbestos?


This article series describes and provides photographs that aid in identifying various types of hardboard as well as softer fiberboard sheathing and insulating board & fiberboard sheathing materials used on building walls and roofs, such as Homasote, Celotex, Insulite, and Masonite insulating board sheathing products.

Our page top photo shows the back side of an early hardboard interior-use product labeled "GENUINE MASONITE DE LUXE QUARTRBOARD".

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Is there Asbestos Content in Hardboard Masonite™

Painting on Masonite type hardboard - asbestos contamination unlikely (C) MJReader Question: is this painting on hardboard shedding dangerous asbestos into my home?

2019/01/03 Anonymous asked:

This painting was painted in black (painted) weave thin fibre board

Does this seem to be asbestos

The edge is frayed so I covered the back with cardboard and sellotaped edges

Really value your thoughts

Can I leave this in the house? - Anonymous by private email

Reply: No. Recommendations for risk reduction & painting preservation of works on Masonite™ type hardboard

In my opinion the risk of asbestos contamination or asbestos health hazards from the painting in your photos in the conditions shown is probably zero because Masonite™ type hardboard generally does not contain asbestos.

However, because the painting edges are damaged as visible on the back, I do have some recommendations to reduce risk and to preserve the work.

Damaged masonite hardboard painting backer board needs conservation (C) MJ

1. No asbestos: it is not likely that your hardboard "Masonite" type board that was painted-over in oil or acrylic contains asbestos - hardboard is a wood or cellulose product.

As we note at HDF HIGH DENSITY FIBERBOARD, synonyms or equal product names besides Masonite™ include Hernit, Karlit, Quartrboard, TreeTex, Torex, and "pressboard".

In the photo of the back surface of your HDF or Masonite™ like product, notice the characteristic window-screen like imprint on the back surface of the hardboard material, its brown colour, and its hardness or density in comparison with much softer (and usually much thicker) MDF or LDF fiberboard products that we describe at FIBERBOARD SHEATHING.

Below I give the original patent information describing the ingredients in Masonite hardboard. In the UK where your painting is located, I expect the formulation to be about the same.

Where there have been reports of asbestos contamination in related products it was a cross-contamination issue found in some softer fiberboard sheathing (that is not hardboard) and of course in cement-based asbestos-cement board or millboard - a completely different, non-cellulose, product.

2. Damaged painting hardboard support: Although the probability of a detectable release of asbestos fibres probably zero for your painting on fiberboard, because the board edges shown on the painting back surface are damaged, the wood-material shedding risk is not zero and the painting hardboard support deserves preservation.

- the front surface of the board is completely over-painted

- the edges of the board are surrounded by framing

- the back surface of the board appears damaged and could be shedding material, for which some action is needed

3. Recommendation for preservation: [If this is a valuable artwork you should also check with an art conservator before doing anything to the painting]]

To encapsulate the board back to stop any measurable shedding of the hardboard fibers, and also to preserve the board and painting, including reducing the chances of moisture absorption through the board backer that can sometimes lead to brown bleed-through to the painting surface, you might spray the back with a clear lacquer sealant.

That will also further prevent even the smallest potential shedding of material.

Watch out: in reading the articles I recommend below, be sure you distinguish between hard fiberboard such as the Masonite™ type hardboard on which your painting was executed, and the considerably softer (and possibly asbestos-contaminated) medium or low density fiberboard products such as fiberboard building sheathing that is the main focus of the articles below.

More information about the ingredients in hardboard such as Masonite™ are given below on this page.

Information useful to your question and for preservation of your painting are at

Reader reply:

I have covered the back.

The board edges where damaged are actually painted in cream paint it’s not the colour of the board your seeing but the paint colour over the damage

Thanks a lot for your detailed reply

History of Masonite™ Hardboard & Ingredients of Masonite™-like Hardboard or Fiberboard

As you will read in these patent disclosures by William H. Mason, the inventor of Masonite hardboard, asbestos was not an ingredient in Masonite hardboard products.

A 1932 patent does describe the use of asbestos in the equipment used to produce masonite hardboard. For that reason it is very slightly possible that one might detect a rare asbestos fiber in Masonite™ if the hardboard producing equipment such as an asbestos coated roller was damaged.

In sum, the probability of detectable asbestos in Masonite™ is effectively zero.


Continue reading at ASBESTOS TESTING LAB LIST or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see FIBERBOARD SHEATHING IDENTIFICATION- how to identify various brands of cellulose-based insulating board or fiberboard sheathing

Or see this

Article Series Contents

Suggested citation for this web page

HARDBOARD Masonite™-like INGREDIENTS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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