MITRA Forum Question Details

I'm not a conservator, just a painter with experience using hardboard.  Here are some thoughts on the topic - hopefully other experts will contribute.

Hardboard panels are made from wood chopped into tiny pieces (lignocellulosic fibers), bound back together under heat and pressure, sometimes with the addition of glue, oil, wax or resin.  It can be difficult to differentiate among types of fiberboards, and processing methods and standards change often.  It's a complex and mutable topic.   Generally there are three types, with the following, somewhat confusing nomenclature:  

1.  Untempered Hardboard made from wood fibers alone (natural lignin in the wood holds the board together; akin to making paper).  

2.  Tempered Hardboard in which a layer of oil or alkyd is applied to the surface of a board to increase its strength. 

3.  Fiberboard made by combining wood fibers with a synthetic resin and small amount of wax (additives are within the panel, not just on top).  MDF and HDF are fiberboards.

Many people refer to hardboard as 'Masonite,' the brand name for a hardboard no longer produced.  Still, it's common to hear 'Masonite' and 'hardboard' used interchangeably. ​

Untempered versus Tempered Hardboard.  It can be difficult to determine if hardboard is tempered or untempered.  Information on manufacturing isn't always available, even to lumberyards (hardboards are often made in other countries).  Because most hardboard is made for the building trade, which prefers a tempered board (because it's stronger) it's difficult to locate genuinely untempered hardboard.  To find it, you'd probably have to do research and be persistent in your questioning.  

I believe grounds (gesso) adhere slightly better on an untempered board.  On the other hand, a tempered board is more durable, and most manufacturers add such minimal tempering that ground adhesion probably isn't much compromised.  

The oil applied atop tempered boards is a polymerizing oil - once it cures, I don't believe it can travel into paint layers.  

Conservators tend to lament the tendency of hardboard to split at the corners. This can be mitigated by chamfering or rounding the corners; or by applying wood braces flush to corner edges on the back.  Thicker, ¼" hardboard is more stable (less apt to flex); ⅛" panels are lighter in weight (which makes large panels easier to ship).  

Fiberboards (MDF, HDF).  While "hardboard" (discussed above) is technically a type of fiberboard, the word "fiberboard" now generally refers to three products: Particleboard, MDF and HDF.

a. Particleboard is a low-quality, low-density board and not recommended as a painting panel.  

b. MDF (medium density fiberboard) is not as dense as hardboard or HDF, yet denser than most plywoods.  MDF comes in three grades: Lightweight, Standard, and High Density MDF; the latter has much more wood fiber and density and thus is the best option. If a store can't tell you what grade of MDF they carry, you may be able to tell by the finish.  A standard grade MDF is softer, more irregular and rough/napped in its finish. Primers sink in more, and cause the surface to 'fur up' (become more napped and textured).  A high-density MDF board has a much smoother, consistent, dense-looking surface appearance.  For more on differentiating the three grades of MDF, see https://mdfskirtingworld.co.uk/blog/the-difference-between-mdf/

If you use High Density MDF and thicker panels (such as 3/8"), and coat them well (ground/paint layers on front, ground/housepaint on back) I think it's a durable option.  Most experts do not feel the resin and small bit of wax within an MDF panel interfere with ground adhesion, since these boards are about 80% or higher wood content, and their surfaces very absorbent. In my experience they're not as absorbent as solid wood or untempered hardboard, but are plenty porous for a ground to adhere well.  

HDF (high density fiberboard) is the hardest, densest, most stable of the fiberboards (although not as dense as tempered/untempered hardboards, discussed above).  It's a good option, but heavy, not commonly stocked, hard to find.  

Formaldehyde.  Some resins used in fiberboards contain urea-formaldehyde.  Low levels of formaldehyde occur naturally in wood, hence no wood-based panel is fully formaldehyde free.  On the other hand, added formaldehyde can cause off-gassing and health problems to both painter and painting.  In recent years there's been an effort to curb formaldehyde levels in MDF and HDF (as well as in many plywood glues) and most engineered wood products now meet 'CARB' (California Air Resources Board's) stringent emission levels.  Whatever engineered wood you choose, be sure it has a CARB seal of approval.

A lot of information, a bit confusing, and heaven knows how much will have changed in the hardboard industry from the time of my research to writing this to your reading this - but, hope it helps.

Koo Schadler

​My experience is with traditional chalk and animal glue gesso, not acrylic gesso.  I did not specifically do an adhesion test.  My belief that an untempered board is more receptive/absorbent (which encourages better adhesion) ​than a tempered board comes from many years of experience applying "true" gesso to various hardboards/fiberboards and getting a sense for their absorbency.   

Additionally, Eric Thomson, at one time a commercial manufacturer of true gesso panels, authored a paper in 2003 for The Society of Tempera Painters Newsletter, titled “Which Hardboard is Best”.  It was based on Thomson's analysis of all hardboards available on the American market at that time, in which he looked at at six characteristics: product integrity, production process, receptivity to true gesso, strength and dimensional stability, chemical stability, and toxicity.  In his study Thomson concluded that untempered hardboard is more receptive to gesso - but I don't know how he did his testing.  

My guess is that if you prepare the board properly (lightly sand to rough it up, dust off the sanding dust, wipe down with alcohol, then apply a preparatory coating [pure animal glue for true gesso; whatever Golden recommends for acylic gesso]) you'd get pretty good adhesion of either an animal glue or acrylic ground to both a tempered or untempered board (albeit maybe a wee bit better adhesion on the untempered...but then you'd be sacrificing some of the strength in a​ tempered board - it's a tradeoff, in my opinion).   For more certainty you may want to do a cross hatch adhesion test yourself.

​I agree, I think a "middle man", as you say, between a support and a ground can be effective.  But which to use under acrylic gesso - whether vinyl or acrylic, & what type - is best answered by a synthetic polymer expert, someone like Greg Watson at Golden.  I would just say that I don't think of fiberboards as oily, even ones that are tempered or have a small percentage of resin/wax within them; I understand what you're getting at, but I think perceiving them as oily isn't quite accurate.   All fiberboard panels are primarily wood-based and, in my experience range from fairly absorbent (tempered hardboard) to very absorbent (untempered hardboard & MDF/HDF), which should be enough to encourage good adhesion.  Hopefully others voices will chime in to corroborate or correct my thoughts.  Koo

Most modern tempered hardboard panels are manufactured in such a manner that they do not require large amounts of oils, etc. Most experts now suggest using tempered hardboard rather than the untempered as suggested by Mayer, etc. in the past.

However, not all hardboards are created equal. It is probably the best to stick with products that you know have been successful. I personally do not like using hardboard for the reasons enunciated on this site so I have no recommendations in terms of brand. Certainly. those sold specifically to artists by companies like Amperstand have been tested for applicability.