glueing two sheets of MDF

[footprintsinconc]

hello,

just about finishing the assembly of my workbench ( i know i still have pictures to post), but right now i need to glue two sheet of mdf togather to make the top.

should i just use normal wood glue (titebond II) or use gorilla glue. if i use the gorilla glue, it is an expansive glue, wont that warp the top because it will want to expand? secondly, doesnt it need water to activate, so if i moisten the mdf with water, it will swell up and the top cant be thicker than 1.5" (2 sheets of 3/4" mdf).

thanks in advance for all the advice!

regards,

[cabinetman]

IMO your best bet is to use TBII. Get good coverage and slide the sheets on each other to help spread out the glue. Make sure you use cauls or dispersed weight on the top sheet to get even pressure across the entire area of the top sheet..

[RodKirby]

TBII - spread with a small "veneer" (hard rubber), roller.

The top is 3/8" on 5/8"

[final_t]

I just used Gorrila Glue, and spread it pretty thin - was doing 2' x 4' sheets, just clamped the edges and left it overnight. IIRC, no foam out.

[DonHo]

I've had good luck with tite bond II as well but for limanations like workbench tops ( where one side won't show) I just use drywall screws ( from the underside ). If you plan any cut outs like for router table tops etc either leave the screws out of that area or just remove them before you do the cut out.

DonHo

[bradley_osu]

I used TB II for mine and predrilled countersunk screws on the underside to provide even clamping and to keep the sheets in line during glue-up and it worked like a charm.

[cabinetman]

I've had good luck with tite bond II as well but for limanations like workbench tops ( where one side won't show) I just use drywall screws ( from the underside ). If you plan any cut outs like for router table tops etc either leave the screws out of that area or just remove them before you do the cut out.

DonHo

One problem with using screws is that if the two pieces have any gap where the screws go from one to the other, it's possible for some breakout from the first piece to get in between the sheets and prevent them from pulling together. To solve that, line up both sheets prior to the final assembly with screws, and pilot hole the first sheet to the second wherever you are to put screws. Then separate the sheets and use a countersink bit, slightly countersink both holes where the sheets touch. That way when screwing together, there will be no breakout.

[footprintsinconc]

thanks!

tbII it is! as for the screws, i will think about those screws just becasue i want to drill in bench dogs, so i will have to figure out a pattern before i glue the boards togather.

thanks once again.

regards,

[Tamarack]

I laminated a shop cart top with TB11 and screws from underneath, once the glue was dry I removed all the screws, never have to worry about hitting a screw in the future.
Paul

[Tom Miller]

...once the glue was dry I removed all the screws....

You can't beat screws for some good clamping force in this "large-area" situation, and with Paul's excellent suggestion, you don't have to worry about them later. Doing it this way also means you can use whatever screws you want (including pan head), and you wouldn't have to countersink for heads, or anything fancy.

But, don't underestimate the point that cabinetman brings up. It may seem like a lot of extra work to drill pilot holes, and then countersink them. But nothing could suck more than having two glued together sheets of mdf that aren't good for anything. Remember to oversize the pilot holes in the first sheet of mdf, too, so the screw threads only bite into the bottom sheet. (You probably knew that already, but just in case....)

Regards,
Tom

[footprintsinconc]

thanks + one question: coarse or fine thread screws?

thanks tamarack for the idea of removing them. and as cabinetman and then tom reinforced, i'll drill the pilot holes and remove the stub so that the sheets can be pulled togather tightly.

ONE QUESTION: coarse or fine thread screws for clamping? i know the fine coarse will hold better, but just wanted to make sure before i do something.

tom, thanks for the reminder of oversizing the holes. it seems like i have thought out the process of doing something, but then when i go to do it, i miss a step here and there and then remember it as soon as i am done. so the reminder will now stick.

thanks everyone for the helpfull suggestions. i had promised some pictures, but since i have been very lazy, i will hopefully post some after this weekend. hopefully this will force me to finish my table this weekend.

regards,

[LarryG]

ONE QUESTION: coarse or fine thread screws for clamping?

For MDF, plywood, and softwoods, use coarse threads. For hardwoods, use fine threads. In my shop I probably use five coarse thread screws for every one fine thread.

Understand, however, that "softwoods" and "hardwoods" are generic terms and have to be tempered by the specific species with which you're dealing. For example, poplar is technically a hardwood but it works more like a softwood so for it, you'd get better results with coarse thread screws.

[footprintsinconc]

thanks larry. when i used kregs screws the first time i was using mdf. the kit came with coarse screws. so of them held tight, while others would just continue to spin. then i tried fine and got the same result. i got the same results when i was assembling my work bench, so it just confused me.

my thinking was: since mdf is highly dense, i thought (just like hardwood) the fine threads would be better.

i will give the coarse threads a try again. - thanks

[RodKirby]

thanks larry. when i used kregs screws the first time i was using mdf. the kit came with coarse screws. so of them held tight, while others would just continue to spin. then i tried fine and got the same result. i got the same results when i was assembling my work bench, so it just confused me.

my thinking was: since mdf is highly dense, i thought (just like hardwood) the fine threads would be better.

i will give the coarse threads a try again. - thanks

Sounds like you are "overtightening" to me.

If you are driving in with a drill, don't go all the way - do the last 2 turns by hand - one hand

[footprintsinconc]

will keep that in mind, thanks rod