Gluing hardwood to MDF?

[Jeff Dege]

I'm building a simple workbench. I'd intended to make my top from two layers of 3/4" MDF, using glue and drywall screws to pull them together. I'd been pondering adding 1/4" hardboard on top of that, when I found some edge-glued hardwood panels ay my local home center.

At 24x72", and 3/4" thick, it was probably intended for making tables or shelves, but it seemed ideal as a top layer for my workbench. I'd originally planned on glueing and screwing it to the MDF, just like I had planned to join the MDF, but now I'm wondering. MDF is dimensionally stable. How stable will these hardwood panels be?

Would it be safer to fasten the hardwood layer with screws only, and not with glue? And, perhaps, to make the pass-thru holes in the MDF a bit oversize, to allow for expansion and contraction?

Another question: how functional will the drywall screws be, after the glue sets up? Would it be reasonable to remove the drywall screws that I'd used to pull the MDF panels together, after the glue had set, and then to expand the same holes to drill on the hardwood panel?

And finally, I plan on edging the MDF with 1/2" hardwood. I've never seen anyone mention any concern over expansion with edging of this sort, everyone seems to just slather the glue on. Is this not an issue, because the strips are so narrow?

[Scott Loven]

I would use weight like sand bags to press the two sheets together, you could use a few screws to keep the sheets from sliding around while it drys.

Scott

[Rick Fisher]

Consider using pocket screws. They pull stuff together really well.

I use them for all sorts of stuff which I want tight.

(I dont mean angled screws, I just mean Kreg screws used as normal screws)

[Chris Tsutsui]

MDF is stable. You can edge MDF. It's not like the MDF is going to expand (well it will if it gets wet so don't use too much glue)

If you used drywall screws, i'd keep them in since they will add some strength.

Essentially I would try to make a table that will LOOK solid hardwood, but will be MDF on the core. :)

[Jeff Dege]

Consider using pocket screws. They pull stuff together really well.

I use them for all sorts of stuff which I want tight.

(I dont mean angled screws, I just mean Kreg screws used as normal screws)
From their website, it looks like Kreg's screws are available only as pan-heads. I'd planned on using flat-head screws so I could countersink them with an ordinary countersink bit. Though, in truth, I don't really know why that'd be necessary. It's not like it's going to make any difference to anybody whether the screws on the underside of my bench are countersunk.

They look like the course thread screws might grab MDF better than drywall screws would. I'll keep then in mind. Thanks.

[Jeff Dege]

If you used drywall screws, i'd keep them in since they will add some strength.
Actually, I was considering using 1-1/4" drywall screws to pull the two sheets of MDF together, then taking them out, and using 2" drywall screws through the same holes to fasten the hardwood top. In the end, there will still be screws there.


Essentially I would try to make a table that will LOOK solid hardwood, but will be MDF on the core. :)
That is my intent. What my execution ends up being, is still in question:)

[Jeff Dege]

MDF is stable. You can edge MDF. It's not like the MDF is going to expand (well it will if it gets wet so don't use too much glue)
Yes, but the hardwood could expand. On the edging, with its cross section being as small as it is, I doubt it could create much force. So I'd not be surprised if someone were to tell me that I needn't worry about expansion on the edging, and go ahead and glue it.

On the top, I'm less certain. The MDF may be stable, but how much will a 3/4x24x60" panel of edge-glued hardwood expand? Do I need to accommodate changes, or can I simply glue it down hard?

[Chris Padilla]

I'm building a simple workbench. I'd intended to make my top from two layers of 3/4" MDF, using glue and drywall screws to pull them together. I'd been pondering adding 1/4" hardboard on top of that, when I found some edge-glued hardwood panels ay my local home center.

What is the wood? Do you know?


At 24x72", and 3/4" thick, it was probably intended for making tables or shelves, but it seemed ideal as a top layer for my workbench. I'd originally planned on glueing and screwing it to the MDF, just like I had planned to join the MDF, but now I'm wondering. MDF is dimensionally stable. How stable will these hardwood panels be?

What is the orientation of the glued up wood? Yes, it will expand and contract across the grain but how much is dependent upon the species and dependent upon how it was cut (flat vs. rift vs. quarter).


Would it be safer to fasten the hardwood layer with screws only, and not with glue? And, perhaps, to make the pass-thru holes in the MDF a bit oversize, to allow for expansion and contraction?

You could glue the hardwood top along the middle only and then screw either side down from underneath through the MDF through oval/elongated screw holes. This would certainly allow the expansion.


Another question: how functional will the drywall screws be, after the glue sets up? Would it be reasonable to remove the drywall screws that I'd used to pull the MDF panels together, after the glue had set, and then to expand the same holes to drill on the hardwood panel?

You may also remove the drywall screws with no ill effect. This might be a good idea if you plan to drill dog holes into the top. You certanly don't want to hit the drywall screws--especially if you don't know where they all are. Look at the screws as clamps...clamps are always temporary.


And finally, I plan on edging the MDF with 1/2" hardwood. I've never seen anyone mention any concern over expansion with edging of this sort, everyone seems to just slather the glue on. Is this not an issue, because the strips are so narrow?

The hardwood edging is pretty narrow such that its expansion is very, very small. Slather the glue on...but use a roller and spread it all nice and uniform on both pieces. No reason to use more glue than you need. However, what happens to the freedom you just gave that hardwood top now that you are going to edge-band the whole top? :)

[Jeff Dege]

What is the wood? Do you know?
Aspen. Not the toughest, but I'm figuring it will be more resilient than bare MDF.


What is the orientation of the glued up wood? Yes, it will expand and contract across the grain but how much is dependent upon the species and dependent upon how it was cut (flat vs. rift vs. quarter).
The grain runs lengthwise, of course. I can't tell you how it was cut.



You could glue the hardwood top along the middle only and then screw either side down from underneath through the MDF through oval/elongated screw holes. This would certainly allow the expansion.
Or glue down the front edge, and let it expand to the rear. That'd keep the front dog holes lined up. Or I could just screw it, which would mean that I could replace it at need.

The hardwood edging is pretty narrow such that its expansion is very, very small. Slather the glue on...but use a roller and spread it all nice and uniform on both pieces. No reason to use more glue than you need. However, what happens to the freedom you just gave that hardwood top now that you are going to edge-band the whole top? :)
I'd only planned to edge-band the MDF - the hardwood panel will span the edge-banding.

[Chris Tsutsui]

Bare MDF is actually pretty durable as a work bench top. though if you had problems with how it will "look". Then here was was I was picturing when you said hardwood top, and MDF core, with hardwood around the MDF.

This would make it look solid i think...

Experts, please let me know if there are issues with this type of construction. :o

[Chris Padilla]

The grain runs lengthwise, of course. I can't tell you how it was cut.

Look at the end-grain. :)

[Jeff Dege]

Look at the end-grain. :)
I will, when I get home.

How well do you think aspen will hold up, as a bench top? It's a hardwood, but it's by no means one of the harder hardwoods. I've been wondering whether to pick up an Ikea countertop. They're available in beech, which I would think might hold up better than aspen, but I don't really know.

[Chris Padilla]

I've no direct experience with aspen but I think it is likely to be fine. If the price is right, go for it. Beech would work out well, too. Southern Yellow Pine is popularized by Chris Schwraz (he wrote a Workbench book). Where do you live, Jeff? SYP could be cheap and easy to get and it seems to make a great workbench top.

[Jeff Dege]

I've no direct experience with aspen but I think it is likely to be fine. If the price is right, go for it. Beech would work out well, too. Southern Yellow Pine is popularized by Chris Schwraz (he wrote a Workbench book). Where do you live, Jeff? SYP could be cheap and easy to get and it seems to make a great workbench top.
I'm in Minnesota, and SYP is available, but it's not a discount wood, here.

What I'm thinking is that if I attach the aspen to the MDF with screws, and without gluing, if in a year or two I decide it isn't working, I should be able to pull it off and put on something else. If I were to switch to an Ikea countertop then, I'd need to replace my vise faces to adapt to the increased thickness, but I figured I'd need to replace my vise faces every now and again, anyway.

So I'm beginning to like the idea of just using screws, for more reasons than avoiding possible problems with expansion.

[Jeff Dege]

Experts, please let me know if there are issues with this type of construction. :o
I'd be very interested in knowing if edging with endgrain, they way you are, wouldn't cause problems.

[Dan Forman]

Aspen is very soft, I wouldn't use it for a top. I wouldn't try to put a wood top over MDF due to movement concerns- it could bow or cup in addition to expanding across it's width. My bench top is 1/2 MDF over a solid core door. It's held up fine over a couple of years. If you want, you could add another 1/2" sheet over the two sheets you glue together, and just pin it or screw it to the others, and replace when needed. I gave mine a couple coats of minwax wipe-on poly, just to keep errant drops of glue from sticking to it.

I plan on making a solid wood bench as soon as my wood dealer gets in some more 8/4 ash. If you want a wood top, best thing to do is laminate your own, but I wouldn't mix with MDF.

Dan

[Jeff Dege]

Aspen is very soft, I wouldn't use it for a top.
So I've been discovering. Still, it's a nice piece of panel, and it was cheap. I'll use it for something.


I wouldn't try to put a wood top over MDF due to movement concerns- it could bow or cup in addition to expanding across it's width.
Which is why I was asking.


My bench top is 1/2 MDF over a solid core door. It's held up fine over a couple of years.
Odd. The MDF I've had in the basement for the last couple of weeks already has dings and crushed edges and corners, and it's just been carried into the basement.

[Dan Forman]

I think they make different grades, I got mine at a plywood/hardwood dealer, not one of the Borgs, so that might make a difference, but can't say for sure. It's not indestructible, but is holding up pretty well, and you can always replace the 1/2" layer if it gets to beat up.

Dan

[Rich Engelhardt]

Hello,

I dont mean angled screws, I just mean Kreg screws used as normal screws
Let me second the use of Kreg screws.
When I fastened my (MDF) Rockler #1 router table top to a piece of plywood, I asked here what adhesive to use.
I was advised to just use Kreg screws alone - with no adhesive - whcih I did.
They really hold tight. Much tighter than I imagine drywall screws would.