What kind of plywood should I buy fo a desktop?

January 9, 2008 4:15 PM

What plywood is guaranteed to be straight and rigid? i.e., suitable for use in furniture construction?

I have never built anything before, but getting into the idea of carpentry and wanting to build this very-easy-to-make desk:
cheap desk

My problem is I don't understand all the wood choices at my local Lowe's... there seems to be so many different types of plywood and particleboard and mdf... some of the plywood is clearly warped and bowed... some of it appears to be relatively straight and rigid.

Since I want this to be a desktop I, obviously, want something that will not bow or sag.

How do I choose a plywood that will give me a flat, straight surface and will continue to do so after years of bearing weight?

posted by robotdog to home & garden (14 comments total)

I recently built myself a desktop for use with some Ikea Vika legs. I use the term "built" very loosely, because what I actually did was buy a nice piece of MDF, vut it down, and attach it with the hardware provided.

The MDF is exceptionally straight and great at holding the weight of my laptop, hard drives, monitors and a lamp. I would, however, recommend sealing or otherwise finishing MDF if you use it; little strands of it tend to work loose and can feel like splinters on your palms or whatever parts of you touch the desk for long periods.

I submit refinishing ideas like Dan's for your perusal. By the way, an un-drilled, hollow-core interior door on filing cabinets makes and awesome inexpensive desk. Good luck!
posted by littlerobothead at 4:27 PM on January 9

NO plywood is guaranteed to be straight, but some is certainly better than others. In most cases it's best to design your furniture with reinforcing elements to add strength and stability; the best plywood won't make up for bad structural design, but good design can make pretty crappy materials work out okay.

The pics in that link show basic 3/4" birch plywood. The big-box stores sell a cheap grade of this stuff for around $40 a sheet. The face veneers are painfully thin, and the cores vary from acceptable to awful depending on where they bought a particular bundle.

To get better, you'll be seeking out a specialty wholesaler or retailer and buying cabinet-grade plywood at half-again or twice the price. The best choice is Baltic birch. which has heavy face veneers and is solid birch all the way through, but is especially expensive right now for some global economic reason I haven't really looked into.
posted by jon1270 at 4:28 PM on January 9

You want A grade plywood. You can get it in 1/4, 1/2, 5/8 and 3/4, and probably a few more sizes. The top layer is some kind of veneer (birch, maple or oak most commonly). It's defect free on at least one side, and there are no pockets in the middle since they usually fill them. A grade sheets are made specifically for making furniture and cabinets.
posted by sanka at 4:28 PM on January 9

Well the article you link to calls for Birch plywood. This is not the regular plywood used in rough construction. You'll have to suck it up at Lowes and specifically ask for this, they'll show you where it is.

Since I want this to be a desktop I, obviously, want something that will not bow or sag.

You also want something that is "finished", on at least one side, like the Birch plywood called for. Two is even better. "Finished" will be pretty smooth to the touch, no rough stuff.
posted by poppo at 4:30 PM on January 9

I also suggest skipping plywood and going with doors if you're okay with the basic rectangular shape. Doors will be much less likely to bow. If you simply attach legs to the bottom of a sheet of plywood, it WILL bow over time if you put any significant weight on it.

Doors come in solid core and hollow core. Solid core will be much sturdier but also more expensive. The core is made up of a cheap particle board, so if you cut them at all, you'll want to put the cut edge at the back. The strength is really in the edges, so you really don't want to make too many cuts. Hollow core doors can't be cut, they'll just fall apart.

The doors also come in wood veneer or paint-grade, which is just like mdf. They'll both be nice and smooth. Wood veneer will me more expensive.

If you want to go with plywood like the "cheap desk", I would buy the thickest and most expensive sheet you can find. Like everyone else said, you'll probably find birch, baltic birch, or maple... You might also find cherry. I would suggest 3/4" at least, 1" if they have it. It will cost more, but it'll be worth it. You definitely want Grade-A or "cabinet grade" or "furniture grade".

You'll want to look at both sides, because sometimes a cheaper veneer is used on one side and a more expensive veneer on the other. The cheap veneer might have holes that are filled with putty or little knots, but as long as the 'good' side looks nice you'll be fine.

Finally, try to keep the weight where the legs are, or put legs where you think you'll have weight, especially if you go with the plywood. That will help to minimize bowing.

Good luck!
posted by ssimon82 at 5:02 PM on January 9 [1 favorite]

OSB is good, AdvanTec is even better---but it's still engineered structural timber. It will all be great if you run a simple 2x4 stringer along the edge of the underneath all around the table.

OSB meaning "oriented strand board", "mdf" meaning "multi directional fiber". OSB has structural rigidity, where "mdf" does not. "MDF" often actually has the consistency of hard styrofoam.

I've got all the stuff to make this table at my store, and it would cost you a total of ~$18 with OSB or ~$30 with a door.

The issue you ARE going to find with a door is getting a solid core door without any panels or glass. I've got a waiting list a mile long for people looking for this same door for the same purpose.

I actually built this table for my check out desk, all out of scrap pieces of both OSB and 2x4's. Took me the better part of half a day's labor, but its tested capacity is about 1000 lbs and it was cheeeep.

For the edges, consider getting "Construction L's", which are NOT the same things you edge drywall with, rather they're sold where you would find steel 2x4's, and generally cost about $1.20 for an 8 foot section.

One last suggestion, even as a work bench, it's worth stopping by a flooring store to pick up a scrap of vinyl flooring to cover the top. Squirt on some liquid nails, lay it down, then cover the edges with the construction L's I was talking about. Solid, attractive, drillable, and won't rape you with splinters. MeFi mail me for more info or questions.

Oh, a note: Do NOT get particleboard. It's stupidly expensive, heavy, brittle, and will swell if a moist fart occours near it.
posted by TomMelee at 7:09 PM on January 9

And of course if you really want to go "all out" you could get some marine grade plywood - maybe some 3/4" teak?
posted by blaneyphoto at 7:12 PM on January 9

I like this stuff: Appleply.

Alternatively, the flake patterns of OSB can be rather appealing if you don't mind a visually busy surface. And if you don't mind finishing the holy hell out of it.
posted by aramaic at 7:14 PM on January 9

Actually, MDF stands for Medium Density Fiberboard.

You could minimize bowing by screwing 2x4s that run the length and breadth of the top into the bottom of your plywood top at 90 degree angles every foot or two. Look up "torsion box" for an idea of what I'm getting at. It'll be stronger than it is pretty.
posted by jewzilla at 7:20 PM on January 9

Usually I'm quite impressed with the quality of advice given in AskMe, but I have to say there are some rather peculiar responses here. Doors? MDF? OSB? Bowing? 2X4's every foot?The plan that you linked to is quite simple and quite effective. All you need is a decent 3/4 inch plywood as described, supported by the legs as described.

Plywood is engineered to specific international standards and as long as you buy a suitable grade (A,B,C, or D in decreasing quality) you can be pretty well assured of its quality. If I were to build that, I would use G2S (Good 2 Sides) A or B grade. It depends how high a quality of end product that you want.
posted by Neiltupper at 9:38 PM on January 9

I am an architect, we use a product called finply (also known as appleply / other things) all the time for cabinets / tables. It has a very nice finish that comes in many colors and can be cleaned. We have a table made out of it in our office that holds up nicely, just one sheet on some legs. Make sure you get a thick piece!

http://www.fincolorply.com/koskiform.htm

OSB / MDF are cheap but wont last for too long and will warp / fall apart if exposed to too much moisture / spillage. They are also porous and hard to clean.
posted by outsider at 10:11 PM on January 9

Seconding Appleply, particularly because there isn't too much holding up the spans shown in the "cheap desk" article. You can get Appleply in 3/4" sheets - it's not all that cheap - but even for 3/4" plywood it's very stiff and it looks wonderful if you finish it halfway decently.
posted by jet_silver at 10:16 PM on January 9

Agree with Neiltupper... some damn peculiar advice in this thread.

You want 3/4 inch "finish grade" or "cabinet grade" hardwood plywood. That hardwood can be oak, birch, or what have you (what's available may vary a lot depending on where you're shopping, and where you live.) They key is hardwood... not pine, or fir, or any other softwood. Marine-grade, for example, is most always Douglas fir, or Larch if you're on the left coast... not what you're looking for. Besides, you're not building a boat.

You wanna get real fancy, go for A1 (A grade on 1 side) which should have a very nicely figured grain, and may be available in premium hardwoods (cherry, walnut, etc.) You'll pay through the nose for it, though. ;)
posted by deCadmus at 10:22 PM on January 9 [1 favorite]

jon1270, at least where I get it, the quality of Baltic birch has nosedived in the past few years. The supplier tells me that a lot of it comes from China now and it used to be Russian, but I really don't know. The thickness varies quite a bit across the length of the sheet, there are many more surface blemishes, and the three-quarter inch is overall thinner (about 0.687" where it used to be around 0.720"), and the edges are even less straight and square than they used to be.
posted by Killick at 8:13 AM on January 10