Fiberboard and animal glue

It’s hard to give specifics for engineered wood panels (plywood, hardboard, fiberboard) as they are made in various places, from different materials, to varying standards, perhaps with minimal regulation (depending on country of origin).  It’s likely that the store carrying an engineered panel can’t even tell you definitively its specs.  
The industry is also ever evolving – new materials and methods, supply chain issues, changing regulations…this too makes it difficult to make definitive statements about engineered wood panels.
With those caveats, my understanding is that fiberboard panels (wood fibers + synthetic resins + sometimes a small amount of wax) are, on average, about 80% or higher wood content, and thus their surfaces are very absorbent.  In my many years’ experience applying chalk and glue gesso, I think fiberboards are not quite as absorbent as solid wood or untempered hardboard, but plenty porous for gesso to adhere well – particularly if the panel’s surface is properly prepared (roughly sanded to open it up, sanding dust brushed off, then wiped down with alcohol to clean and degrease).

In fact, the absorbency of fiberboard is one of the concerns given by some painters who recommend against it; they feel it’s too porous and hence too vulnerable to moisture, and overtime humidity will cause a panel to fall apart.  The amount of humidity required to make a MDF or HDF panel literally disintegrate would be enough RH to damage any painting (no matter how durable its underlying support), so my own thinking is: (1) use HDF or high density MDF (see below about MDF grades); (2) protect the panel back with a layer of housepaint; (3) keep a painting in moderate conditions.  Do the above, and I believe MDF/HDF are reasonable options.
HDF is a stronger panel becuase it’s denser, but it’s hard to find (and more expensive).  MDF is more readily available; it comes in three grades – Lightweight, Standard, and High Density.  The latter has much more wood fiber and density.  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/
Remember – all of this info is subject to change depending on the specifci product you use, and what’s going on in the industry. ​

“Fiberboard” (which has both a general & specific meaning) is made by chopping wood into a gazillion tiny pieces (lignocellulosic fibers), then binding it back together via heat and pressure, sometimes with added glue, oil, wax or resin. It’s difficult to differentiate among types as processing methods, standards, etc. change; it’s a complex & mutable topic.  As of this writing there are three types with somewhat confusing nomenclature:  
Untempered Hardboard made from wood fibers alone (natural lignin in the wood holds the board together; akin to making paper).  Tempered Hardboard in which a layer of oil or alkyd is applied to the surface of a board to increase its strength. Fiberboard made by combining wood fibers with a synthetic resin and small amount of wax (i.e., additives are within the panel, not just on top).  This includes MDF and HDF (as well as particle board, which is not recommended for artists use)

HARDBOARD – Tempered and Untempered
It’s common to hear Masonite and hardboard used interchangeably; actually Masonite, is a brand name of hardboard no longer produced.  Hardboard is relatively dense, strong, and inexpensive. It’s proven itself fairly reliable since introduced as a painting support in the early 20c. despite a tendency to split at corners (which can be mitigated by chamfering/rounding corners; or applying back braces flush to corner edges).  Thicker, quarter inch hardboard is less apt to flex; thinner, one eighth inch panels are lighter, easier to ship.  A flexed panel can crack gesso/paint layers, so it’s important to keep a panel stable.  Bracing or cradling along with a sturdy and stabilizing frame may be necessary for thinner one eighth inch thick and/or large size hardboard panels.  
Tempered versus Untempered
Some artists believe the oil on a tempered board’s surface prevents gesso from adhering as well, and the oil coating seeps into upper paint layers.  From my and others experience & testing, I believe a chalk and glue gesso does adhere slightly better on an untempered board.  On the other hand, a tempered board is stronger, and most manufacturers add such minimal tempering that gesso likely adheres well enough (helped by proper prep work: rough up the surface, wipe off sanding dust, clean and decrease with alcohol).  The oil surface coating cures and thus, I believe, can not travel into paint layers.  
It can be difficult to determine if hardboard is tempered or untempered.  Information on the manufacturing process isn’t always available.  Most hardboard is made for the building trade, which prefers a tempered board because it’s stronger.  It can, in fact, be quite difficult to locate genuinely untempered hardboard.  

(FYI: To test whether a hardboard panel is tempered or untempered, Eric Thomson recommends this tip from an old-timer at a Masonite factory.  Apply cellophane tape to the board.  If it pulls up with a layer of fiber, it’s untempered.  If it comes up almost clean, it’s tempered. As Thomson relates, you can’t be too careful: “I spent six weeks finding a supplier who could bring untempered hardboard …to me.  I went to the local terminal to pick up my 1500-pound order.  Just before it was loaded on my trailer I saw something on the factory label that didn’t look quite right. So I stopped everything and made the forklift guy go to the office for some Scotch tape, which didn’t improve his mood. Sure enough when I pulled it up off the board, five dockworkers looking over my shoulder, it came up clean and I had to refuse it.  Later, the salesman got a confession from his supplier that it was tempered.”)

A note about Formaldehyde.  Some resins used in fiberboards and plywood glues 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 and most engineered wood products now meet ‘CARB’ (California Air Resources Board’s) stringent emission levels.  

To conclude…. among the various engineered wood panels, my preference is for a high grade, multi-ply plywood, covered in fabric before traditional gesso is applied.  Then, for me, it’s a toss-up between HDF or high density MDF (three eighths inch thick if available) and hardboard (untempered being slighlty preferable) – they each have strengths and weaknesses. 

​The Birth of Venus was originally painted on canvas.   It was painted a few years after Primavera, which is on wood. Canvas was a relatively new option in the 15th century; it was less expensive & lighter in weight than wood; preferred at that time primarily for secular paintings for private villas.  As noted in “Botticelli, Life and Work” by Ronald Lightbown, The Birth of Venus “is painted on two canvases, which were carefully and skillfully stitched together and strengthened by a thick cross-stitching that joins them in a round rib, some one-sixteenth of an inch in diameter.  The two canvases were then nailed along the edge to a plank…”   I don’t know what “plank” specifically refers to, and I can’t find the conservation report for The Birth of Venus – perhaps a conservator has access to it and can comment?
Somewhere (I can’t find it) I have a photograph of a 15th c. painting removed from not only its wood support but also from its chalk and glue ground!  It was painstakingly done as described here:   https://en.wikipedia.org/wiki/Transfer_of_panel_paintings    From what I understand this is not a favored conservation practice anymore; a conservator would know more about current practices for removing paintings/grounds from wood-based panels.
As for engineered wood panels – At the time of this writing, I know of just two companies that make engineered wood panels specifically for artists: Ampersand and Art Boards Panels.  These companies describe their panels as made from higher quality materials and more durable than panels from a lumberyard.  I don’t know if there are independent studies to confirm these claims – which isn’t to say they aren’t true, I just don’t know.  
Of course the engineered wood panels sold at a lumberyard are not specifically manufactured for artists use.  Higher grade/more expensive plywoods/fiberboards use more durable glues than lower grades; still, as you note, they are not “fine art” glues.   Still, plywoods are made to withstand extreme weather & changes in moisture and temperature – conditions which a painting is unlikely to encounter (or, if a painting did encounter, would be problematic regardless of the support!).  And while hardboards have great density, plywoods are in fact stronger and less flexible. I appreciate your preference for hardboard panels, they are a good option – still, I believe a high grade plywood is also a reasonably good option.  All choices (hardboard, fiberboard, plywood, aluminum) have benefits and drawbacks.
As a tempera painter who wants maximum absorbency in a ground, I use nearly exclusively traditional chalk and glue grounds (or, very occasionally, a very high PVC  synthetic polymer ground, such as Natural Pigments Tempera Ground) – so I’m not experienced with Lascaux gesso and can’t speak to your application.  My one comment is that I’d first sand a wood-based support with a rough (80 to 120 grit) sandpaper – this creates much better tooth than a Scotch-Brite pad.  Brush off the sanding dust, then use a shop cloth to wipe the surface with alcohol (the goal being to clean/degrease the surface – no need for the Scotch-Brite at this point).  A minor adjustment to your method, but I think it would improve adhesion.   

Hi Damir,
Agreed, I’ve seen sheets of plywood in rough shape (warped/split plys) that were left exposed to weather and/or are poorly made.  I’ve also seen hardboard with swelled areas & splitting at the edges.  All wood products (wood fibers & glue) can degrade if improperly stored.
My husband used to make table easels out of 3/4″, cabinet grade, birch plywood.  Fifteen years ago he predictably got flawless sheets.  In the past five years, even when he insisted upon and paid for the most expensive grades, he’d find voids, chips, splits (at the time, from China – the lumberyard said it was the best they could get, but it wasn’t very good!).  Given supply chain & quality control issues, it can be very hard (perhaps impossible, depending on where you live) to get a truly high-grade plywood made from glues tested to withstand many decades of harsh conditions. Nonetheless, such plywoods do exist (at least, they used to!).  So, if you can find one, I think they’re as good an option as hardboard (which also may not be produced to the highest standards).  
If the conclusion is that engineered wood panels are too poorly made and/or unpredictable now, how about solid wood?  An old growth/fine-grained, radially cut, properly aged, hardwood panel is a good choice, but good luck finding one!  Sigh…

I don’t mean to say they’re aren’t real differences between wood-based panels; only that I don’t see, among the options (solid wood, plywood, hardboard, fiberboard), that one is clearly, significantly superior to the others in all its characteristics (as long as, whichever you choose, is the highest grade).  So I stand by a high grade plywood (face coated with fabric) as a good choice; it has characteristics both superior & inferior to a dense, high-grade hardboard.  

If conservators want to weigh in on this, it’d be good to hear from them.

As to the veracity of Ampersand and ArtBoard Gesso’s claims that they’re panels are better…I agree with you, they’re likely not different from a high grade lumberyard panel.  (Interestingly, each company says theirs is the best option, yet Ampersands uses hardboard & ArtBoard uses MDF/HDF – go figure).   For more info:

https://ampersandart.com/full/introduction-to-ampersand-hardbord
https://www.art-boards.com/Nat%20Fib-SolidCoreConstruction.html
On both sites I find what I consider some misleading or incorrect information.  I find many artists very trusting of art supply companies whereas, in reality, many manufacturers overhype their products.  I often see manufacturers & marketers who are neither experienced artists and/or scientists; frankly, they often don’t seem to know much about materials and methods.  The few suppliers (many of whom contribute to MITRA) that actually research & test, work with experienced painters, have deeply educational websites, etc. – they’re more the exception then the rule (and hence deeply valued).  

​Amidst this jumble, I just try to use the best materials and methods I’m capable of – then let go of how long the work lasts.  I’ve had well-made paintings burn in housefires, fall apart through water damage – nothing lasts forever…