Bench building question

May I assume that "solid core doors" are some variant of MDF on the inside ?

T.I.A.

You may assume :), but for the most part solid core doors are just that, solid wood glued up like a butcher block, but likely in random length pieces.
They make excellent bench tops, IMHO.

There are several sorts of "solid core" doors.
Some are solid wood, such as Sam suggests, some are particle board as you assume, and some have gypsum plaster cores (fire doors). All are comparatively heavy, generally nice and flat (though not always), and useful as work surfaces--especially those with plywood skins. But because the skins are plywood, they're rather fragile as a work surface. I've used solid core doors as drafting boards (wonderful), and as work tables (not so wonderful). If I were to build a workbench using a door blank, I think I'd cover it with MDF or hardboard or both. Check with your door supplier for the composition of the core--or if you've found one and aren't sure, just cut into one end of it. Regardless of the core, there will be a piece of solid wood at all the edges, to facilitate attaching hardware.

The vast majority of solid core doors are particle board, fibrous material or solid wood. I have not seen a core of MDF, although it is possible. I would think the moisture issues would cause problems. they have a farily water resistant particle board material so it isn't as much of an issue.

I think they make pretty good temporary bench tops if you get the right one and it is flat.

Be careful of some of the older fire rated doors, they can contain asbestos. If you don't disturb it there wont be an issue but there are probably holes in it with this material exposed.

Good luck.

Phil

Solid core flush doors historically were filled with a roughly glued up array of ends and pieces of the rails and stiles, but the quality wasn't good because the skins are only 1/8 inch and as the door dried the look of the blocks would telegraph. In otherwords look across an older door and see all the little blocks. The newer particle board cores are not like the particle board you'd buy at the lumber yard. The particles are larger and the edges are not finished. Only the surfaces are sanded.

The switch to particle board was pretty much the rule in the 70's.

About the only time there were demands for wood cores was when some
old school architect required it.

In any case, the doors are designed to perform as . . . well, as doors. In the vertical plane. As Bill says, the solid wood cores are junk wood, assembled without regard to grain or strength when the door is used in the horizontal plane. If you do use one as a workbench, I highly recommend adding some kind of ribbing as support or you will likely experience some sagging. Especially if you have a humid environment. If I had a solid core door (wood or particle board), I might consider using it as a utility surface, one I don't care about abusing, but unless you already have the door, the cost of setting up a decent workbench using one is pretty close to just building a bench top from scratch.

Thanks for all the replies, I`ll stick with laminated 2x4`s for bench top construction.