Finishing MDF

[Mike Cruz]

I am building a bench for my chop saw. To the left of the CS it is 12 feet long, 2 feet deep, and 1 1/2 inches thick (two layers of MDF). To the right of the CS, will be a 4 foot long version of the same thing.

I built a similar work bench (to the 12 foot long one) but used birch ply. The reason I switched to MDF for this bench was that the birch ply wasn't perfectly straight and even though my supports for the birch ply bench were quite close to level, it ended up with a little bit of waviness to it. I finished off the edges of the birch ply bench with 3/4 X 1 1/2 inch maple...glued and screwed (I didn't care about the aesthetics...just wanted it to last).

SO, the question is twofold:


A) Does anyone see a problem with edging the MDF with the same maple strips?;

B) I was thinking of polying the MDF bench. Does MDF react adversely to poly?

This CS bench is based on the one we had at my last job (dream shop...somewhere about 8,000 sq ft, two unisaws, 20 inch planer, 18 inch sander...again, a dream). And with all the things we did in that shop, very little was ever done with MDF, and none of it was ever finished.

PS, yes I had my shop fan on with the windows open, and yes I wore a mask. That MDF is pretty nasty stuff, that much I know.

[glenn bradley]

My workbench is 4 layers of MDF with BLO and wax for a finish. I've been pounding on it for awhile now. Poly can scratch up (if you care), the BLO needs very little attention. Oh, I glued 1-1/2" thick fir directly to the edges of the MDF for trim, no problems.

[Todd Burch]

I would biscuit on the maple edging. Poly over MDF is fine. Yes, it will scratch, but the MDF is pretty soft (in the scheme of things).

If you wanted to get fancy, you could put 1/4 ply over the MDF.

If you wanted more durable, you could use melamine for the top sheet - stuff slides on it very well.

You could also put plastic laminate on the top sheet of mdf. More durable than melamine, but it costs more too. Don't use vertical grade (also called cabinet liner).

Todd

[David Christopher]

Mike, I made a router table out of MDF and I put sanding sealer on it, sanded it lightly and waxed it and it worked great

[Andrew Rogove]

I've used multiple coats of paste wax on MDF and it protects as well as reduces friction. Never tried poly though.

[Mac McQuinn]

I built a Stain glass work bench for my wife several years ago and finished it with a water-base poly varnish. It's held up very well although I discovered the MDF will grow quite a bit with a water-based product. I built a cabinet for underneath and left 1/16" clearance to slide it in easily once finished although discovered it was a very tight fit once the finish was applied and dried:eek: I trimmed the top of bench out w/ Douglas fir and 10 years later, it's still tight.

I also just finished a Re-loading bench for basement and used MDO in a torsion-box construction as the top & legs. I used Tried & True's Original Wood Finish, Polymerized Linseed oil & Beeswax as a coating and it came out pretty nice but is a little blotchy from MDO not accepting it equally throughout. I love the smell and old look it gives the bench though. Plus it's non-toxic which for me is a good thing.

Mac

[Zach England]

I did this once with poly. it worked ok, but took a lot of coats. I did another with boiled lindseed oil and wax on top. The finish was better and so far has beer more durable. It will also take a lot of coats, but less time between them. I just put the boiled lindseed oil on until the mdf stopped sucking it up, then wiped off the excess and put on the paste wax.

[Chris Kennedy]

I put BLO on my MDF top -- haven't bothered to wax it. The BLO is a good finish and easy, but work fast. MDF absorbs it fast. Also, BLO on wood dries slowly -- on MDF it dries almost immediately.

I put pine edging on my MDF table, and just fastened it with brads. So far, so good.

Cheers,

Chris

[Bill Huber]

If it was me, which its not, but I wish I had the room for that.....

I would make the bench with the MDF and then add 1/4 hard board on top, then make the edging even with the hardboard. When it gets all scratched up you just go buy some more hardboard and replace it. Its cheap, works well and has a nice finish on it.

My main work bench is done this way and it is really nice, when it gets messed up I just get some more hardboard and I have a new bench all over again.

[Mike Cruz]

Thanks for all the advice, guys. You gave me a bunch of choices .

Bill, how (if you do) do you attach the 1/4 " hard board?

Mac, that is what I was afraid of with water based finishes...swelling. I just didn't know if the same would happen with poly. Boy I think you guys in Minn would be able to hear me screaming if I got this thing all leveled out with my chop saw, put the poly on, and :eek: the MDF swelled up over the maple edging...thus being higher than the chop saw!

David, sanding sealer sounds like a neat idea, too. But does that actually harden the surface of the MDF? I'm thinking about when I lift up a 12 foot board of, well, whatever and plop it on the bench. I can only imagine that the MDF will give before the board will.

Glenn, no, hehe, I don't care if the poly gets scratched up. I CARE when projects do, but not my bench. Thanks for the warning, though.

As for those of you that have mentioned BLO, I have never used it, and am hesitant to "try" something new on something that I hope to have around for quite some time. Because of cost, heft, and my distain for RE-doing things, I think I will have to hold off on that approach...not that it may not be the best solution...just not in my comfort zone on this one.

[Larry Frank]

I built a workbench with MDF on the top and finished it with shellac. I like how quick it dries and the finish looks good. From the replies, it appears that almost any finish will work on the MDF. Some of them may be more scratch resistant but for a shop table top, all will get scratched to some degree.

[Bill Huber]

Thanks for all the advice, guys. You gave me a bunch of choices .

Bill, how (if you do) do you attach the 1/4 " hard board?



I didn't, I have a strip of quarter round on the back that it slides under and then just lays there. The last time I replace it I did have a problem with it not laying down in front but I put a scrap 2x4 under the middle and weighted it down on the edge overnight and the next day took the 2x4 out and it laid right down.

[Zach England]

I built a workbench with MDF on the top and finished it with shellac. I like how quick it dries and the finish looks good. From the replies, it appears that almost any finish will work on the MDF. Some of them may be more scratch resistant but for a shop table top, all will get scratched to some degree.

I know this from having built a lot of speaker cabinets: Almost any OIL-BASED finish will work--it is just a question of how much you want to apply. MDF is like a sponge.

[Tom Esh]

Poly on MDF makes for a fairly nice, durable surface IMO. I would however suggest first sealing it with shellac. Bare MDF will drink up loads of finish on the first application and to that end shellac is both cheaper and dries faster.

[Mike Cruz]

Thanks, again for the replies. I am leaning toward poly or maybe a thin laminate or melamine. I will check out my HD and Lowes to see what they have. I would suppose that contact cement (spray on) would do the trick. My shop (for the moment) is not heated or air conditioned. It is a stand alone building. So I am afraid of just "laying" something on top of the bench. Depending on $ (poly vs laminate/melamine) the cheaper will probably win out, since both seem to be suitable solutions. I must say, though, I am a bit concerned about the laminate/melamine being too slippery...you don't want your stock to move during a cut. :rolleyes:

[Charlie North]

Will you share a picture of this Bill?




I didn't, I have a strip of quarter round on the back that it slides under and then just lays there. The last time I replace it I did have a problem with it not laying down in front but I put a scrap 2x4 under the middle and weighted it down on the edge overnight and the next day took the 2x4 out and it laid right down.

[Todd Burch]

FWIW, I used maple ply on my CS wing cabinets. Edged with 2" wide x 1.5" thick full bullnose mahogany, finished in poly. Over the last ~10 years, the worst wear is on the outermost edging where I slide boards across with loading or unloading from the station.

And it looks good too!

I use melamine on my tablesaw outfeed table, and after ~10 years, it is very ready to be replaced with a new sheet, more-so from stains and router depth overruns than scratches or gouges.

Todd

[Tom Esh]

...I must say, though, I am a bit concerned about the laminate/melamine being too slippery...you don't want your stock to move during a cut. :rolleyes:

Actually a surface that's too "grippy" can be a real hinderance when sliding a workpiece into position. Better to apply some adhesive-backed sandpaper to the saw's fence or use clamps.

[Mike Cruz]

Yeah, I had a feeling someone would take that the wrong way...I didn't mean that I want the surface to "rough", just not slick. I don't know if all/most Dewalt CS's do this, but when I squeeze the trigger/handle, the saw jumps a bit abruptly. So, when working with smaller pieces, the jumping of the saw can actually move the wood a hair...the slicker the surface, the more it can move. My point is that I don't want it to be as easy to slide material on this bench as it is to slide material across my TS...friction there is bad. But thanks for all the input.

Oh, yeah, I just got back from HD and didn't particularly like any of the stuff they had for covering the bench. They had an 1/8 inch sheet of stuff that looked like MDF covered with a thin coat (like it was painted on) of melamine. I was afraid that that coat would last. I'll keep looking, but poly may win out in the end...although I really like the idea of a top piece.

For those that said to watch out for how much the MDF will soak up poly, how many coats do you think this will take? 5? or more?

Thanks

[Larry Fox]

I built a workbemch with an MDF top and it has held up for several years now with a finish of just sawdust and random gunk that I drip on it while finishing.

I have a melamine as an outfeed table and it has held up well. About ready for replacement because I cut veneer on it and am running out of non-sliced spots.

[Todd Burch]

... I don't know if all/most Dewalt CS's do this, but when I squeeze the trigger/handle, the saw jumps a bit abruptly. So, when working with smaller pieces, the jumping of the saw can actually move the wood a hair...the slicker the surface, the more it can move.

You know, that Dewalt CS has holes in them thar feet to bolt 'er down... :eek: How small a piece are you running through that thing? If I can't safely hold a piece, it doesn't get put in that saw.


For those that said to watch out for how much the MDF will soak up poly, how many coats do you think this will take? 5? or more?

Thanks

Nope. 3 will be plenty. Poly is pretty high solids. MDF's surface is (for lack of a better term) case hardened. Now, the edges will soak up a ton.

Todd

[Mike Cruz]

The edges will have maple on them, so that shouldn't be a problem. And 3 coats is no biggie either.

As for small pieces, yeah, I can get a bit daring. I know, I know, not that I should, but I do.

And when I saw that the saw jumps, I don't mean that it physically moves its position, but it can make the material move. But yes, I will be mounting the saw. Otherwise, I would have to realign the fence every time. Thanks for the input.

[Scott Schwake]

For those that said to watch out for how much the MDF will soak up poly, how many coats do you think this will take? 5? or more?

I recently finished a 4'x8' MDF assembly table with oil-based poly, took just over a quart to put on 3 coats, most of it was used with the first coat.

[Bill Orbine]

I did my radial arm saw with 8 foot by 12 inches deep by 1" thick MDF wings on both side of the saw. Used it for more than 12 years with very little dings and bangs and NO finish applied. Not even wax.. nothing. It stood up very well considering the many 4/4, 5/4, 8/4, 12/4 lumber I put that saw to work on. And I did my table saw extension in MDF and I put poly finish on it (less than a year ago).... only because I use this table as a glue up bench and the dried droppings are easy to remove. The finish looks kinda beat up now (now I'm thinking refinish). Yet the radial arm saw is still looking sharp. No hardwood edgings. Nothing. Just a 3/8" roundover on the edges. Just avoid the light MDF as that stuff is too soft, fragile and very spongy.