MDF & glue ?

[Bulkley]

What is the best glue for MDF? I've had MDF glue joints come apart. Not many, but it has happened.

[LarryG]

All I've ever used is ordinary yellow carpenter's glue (specifically, original Titebond) so I really can't say for sure whether it's "best." I do know that I've never had a joint come apart using it.

Remember what I wrote to you in your other thread about applying sizing first. Any glue joint, with any material, can fail if the joined surfaces are starved for glue.

[Bulkley]

You might be right. I tend to be a bit stingy with glue because it can be difficult removing excess.

[mschrank]

I recently attempted making an add-on fence out of MDF. It was designed as three pieces forming a small "h" when viewed from the end, and would straddle the stock fence.

I used dado joints and regular yellow Titebond. Long story short: after the glue cured and I tried sliding it over the stock fence, the gap was too narrow. Out of frustration I "violently dropped" it onto the concrete floor.

The corner got banged up, but the joints held. I got curious and tried everything I could to break the joints, but couldn't. It's now in several pieces, but none of the joints are broken.

So, my limited experience says to use dados and yellow glue. Clamp overnight, have a bomb proof joint in the morning (and maybe measure thrice ).

[LarryG]

I think every woodworker, at least until he acquires a BUNCH of experience, struggles with how much glue to use. I know I do. There are so many variables ... the type and depth of the joinery, how snugly the pieces fit together, the density of the wood fibers. Like you, when I get a lot of excess squeeze-out, I get a little frustrated. But if I don't get enough -- or worse, none at all -- I get worried. So I tend to err on the side of too much. Sometimes it ends up being WAY too much. Just all part of the game, though.

[Bulkley]

I've had excess glue create patches in wood that would not stain or finish properly. A few of those makes one really wary of using too much.

Mike, was your tight fence caused by bad measuring, or does glue cause MDF to swell?

[Scottydont]

I have used Titebond II on MDF and never had any problems.

[Otter]

tightbonde II here, and it works just fine

[monte]

I've used Original Titebond and Titebond II both with no problems.

[mattc183]

Tite bond and a damp rag to wipe off squeeze out.

mattc

[RayintheUK]

With MDF, always apply glue using a brush - rollers may be OK, but they can skid, giving an uneven application. Smooth out the glue like you're painting with it, but only use a very thin coat, as long as all the mating surfaces are covered completely.

On the edge of MDF, you can expect some additional soak-up into the fibres that will not occur on the face. Try to resist overloading the edges to compensate - put on a thin coat as usual, then check again just before clamping. Top up if/as required. My practice is to apply glue to all edges first, then into the dados/rabbets, then check edges again.

Regarding dados and rabbets, I run a small glue bead along the corner(s), then run the brush along so that the glue is spread up the side(s) of the joint first. I then spread any remaining glue into the rest of the joint, adding if required.

I have found that this method achieves excellent adhesion and reduces squeeze-out to an absolute minimum. With MDF, I use a barely damp cloth to remove any traces of excess glue if I can sand afterwards. If I can't sand after assembly, I always use masking tape on the internal faces.

With natural timber, whether I mop up when wet or scrape when dry depends entirely upon the wood in use. Beware of using a very wet cloth or sponge on real wood, as it will allow the aliphatic resins present in the glue to penetrate the grain even more. This will resist later sanding and may prevent finishes, stain, etc. from being applied. At the very least, you'll see it in the finished product. Mask real wood wherever you can - it's worth the trouble. HTH

Ray.

[Bulkley]

Masking the work before gluing. Now that's a good idea. Never thought of that. Thanks.

[LarryG]

Oh yeah, masking is a HUGE help. I'm sure I spend more money on blue painter's tape than I do on the glue itself.

[don_hart]

I use standard white PVA glue (Elmers)for glue joints in MDF, I apply The glue staright from my glue bottle and spread it with a foam brush. I make sure I get a good coverage on all surfaces and with MDF I am not too worried about excess squeeze out. I clean the squeeze up with a soft toothbrush and some warm water then I wipe it down with a paper towel. I have never had a glue joint in MDF come apart with MDF properly glued it is like you no longer have two pieces of MDF but a single peice. If I had to guess I would say the times you had a glue joint come apart was when you were a little stingy with the glue.

[tmaceroli]

I've used Titebond with no issues. I always spread the glue out with an acid brush, to make sure I get a uniform film on the whole joint. Clamp pressure can also affect the joint. If you put too much pressure on the joint, it will squeeze all the glue out.

Usually glue is a more of a problem on end grain, for open mortise joints, and on the inside corners of a joint. The previous poster who recommended masking was on the money. That will take care of the latter. But end-grain exposed joints are another matter. It's very difficult to get the glue out of end grain. To avoid problems, pre-stain your end grain and put a few coats of shellac on before you asemble. Of course, take care not to get finish on the parts of the joint to get glued...