Does yellow PVA swell MDF?

[Michael Adelong]

Entire post in title...

Thanks,
Mikchael

[tod evans]

not that i`ve noticed....02 tod

[Howard Rosenberg]

The same gluing processes apply as when you're gluing solid wood.

Use enough glue to properly bond the MDF pieces to each other:
- don't use too much - you'll waste time on cleaning up needless squeeze-out
- don't use too little - you'll starve the joint

HTH
Howard

BTW - MDF swelling on contact with fluid is an old-wive's-tale repeated as fact by well-meaning people on the internet who saw it somewhere and continue to repeat it as fact.

It takes LOTS of contact with fluid over a prolonged period of time to change dimensions.

P.S. - if you have more MDF/glue questions, please feel free to e-mail me

[Michael Adelong]

Thank you gentlemen.

Specifically, I am making a torsion box assembly table out of 1/2" MDF. Instead of making the grid out of many short individual pieces, I attempted to make 5 long runners, and 7 short runners - all 3" tall. I then cut 1/2" dados 1-"1/2 deep in them so that I could assemble them in an interlocking fashion. Dados up on the long runners, down on the short runners. The pieces fit perfectly together dry, but I could not assemble them after putting glue on them.

I'm on take 2 now. This time, I put a shim in the dado stack. The joints have a bit of wiggle in them now. I glued up a joint in some scrap last night, and it seems pretty rigid. I'm wondering if the little bit of play between te 2 parts is a result of glue filing in the gap, or the MDF swelling it closed (the gap created by the shim).

Michael

[Lee DeRaud]

Specifically, I am making a torsion box assembly table out of 1/2" MDF. Instead of making the grid out of many short individual pieces, I attempted to make 5 long runners, and 7 short runners - all 3" tall. I then cut 1/2" dados 1-"1/2 deep in them so that I could assemble them in an interlocking fashion. Dados up on the long runners, down on the short runners. The pieces fit perfectly together dry, but I could not assemble them after putting glue on them.Huh. I've had problems with "closed" joints (like Pergo tongue-and-groove) not wanting to close up because the glue can't get out and is exerting hydraulic pressure against the pieces. But usually in an "open" joint like you describe, the glue lubricates the joint and makes the thing go together easier.

[Greg Koch]

For us slow ones...what's "PVA" and "MDF"?

Thanks

[Lee DeRaud]

For us slow ones...what's "PVA" and "MDF"? PVA = polyvinyl acetate(?, maybe 'acrylic')...AKA "wood glue":D (or at least the usual white or yellow like Elmer's or Titebond).
MDF = medium-density fiberboard.

Now...will somebody tell me the difference between MDF and "particle board"? I swear I see the same thing sold under both names.

[Frank Chaffee]

PVA = Polyvinyl Acrylate

[Charles McKinley]

Hi Lee,

MDF is made of very fine fibers almost like cardboard and is very smooth. It is usually a darker brown color than particle board.

Particle board is made up of larger bits of saw dust and is much rougher on the surface.

HTH (hope this helps)

Gregg,
I believe there is a thread with most of the abbreviations explained.

[Earl Kelly]

Michael, yes MDF does swell when using any glue containing moisture. Even solid wood will, but, the solid wood will shrink back down and MDF will not. If you've ever looked at a table top and seen impressions where the joints are, that's a telltale sign they sanded before the moisture from the glue had a chance to dry. If you're gluing MDF, especially edges, do it quickly before the glue has a chance to start affecting the fit. Anytime I do MDF veneer doors, and glue edges, I allow extra time for the glue to dry, and still the edges are raised ever so slightly. Anyone can test this with a good fitting dado, glue the edge, wait for a minute or two and then see if it will still go into the dado as before.

[Mike Monroe]

I've seen dark brown MDF (at Menards) and light tan MDF (at Lowes). The dark brown stuff was smoother and looked tougher than the light tan stuff. Never noticed any swelling due to PVA glue.

When gluing up the edge of MDF I like to smear/ work glue into edge and let it dry. Doing this some what seals up the edge and gives a better surface for the final glue up to "bite" into.