Glue for MDF

[wtnhighlander]

Upcoming project requires me to create some custom moldings. Using built-up layers of MDF for stability and paintability. Any recommendations on what glue to use between layers?

I plan to supplement the glue with brads, and use auto body filler for the brad holes, etc...

 

[gee-dub]

I have used PVA on MDF drawer unit carcasses for the shop.  Been in hard use since about 2005 without issue. 

If the strain of a drawer unit opened and closed many times a day for years did not cause problems I would imagine PVA (TB-I in this case although TB-III seems to stay a bit more flexible) would serve you well.

[lewisc]

Titebond 2 is my usual - just glued up some MDF sheets (similar to the WW mitre bench but with MDF and not plywood) to make a benchtop and even if I took the screws out, I expect it would never come apart on the glueline.

[BillyJack]

Just regular titebond...

[Chestnut]

I use MDF to make mods for bent lam and regular wood glue works well. I've also used a fair amount of hardwood faced MDF and joinery on that worked great with regular wood glue.

 

[drzaius]

I just use TB II, which is what I normally have on hand. What kind of MDF are you planning on using? My experience with the types I have used are:

- The ultralight is awful stuff & has few redeeming qualities. The only time I'd consider using it is if light weight was essential. The stuff between the faces is much softer & even when painted will easily yield to wear & impacts, fuzzing up & disintegrating. It also seems to absorb moisture most readily. It also delaminates extremely easily. Don't even think about nailing or screwing into the edge, even with pre-drilling.

- Standard MDF is better, but moisture resistance is still not good. There are different brands & quality can vary widely. The worst will probably be found at the home centers. I think Plum Creek is good stuff, but I can't remember the other brands I've used.

- Water resistant, Medex is the brand I'm familiar with, is far and away the best I've used. It's a little heavier than the standard stuff, the core is harder & stronger, and doesn't delaminate nearly as badly. And of coarse, it's quite water resistant. I tested a 1" thick piece by soaking the end of it in water. I was only going to do it overnight, but forgot about it for a week. The wet end swelled up about 1/16"  and water had wicked up just a little above the water line. Integrity was still good & when dried out, it shrunk back almost to the original size.

The face of all MDF paints very well, but he edges, or core, needs proper priming. Ultralight is the worst, Medex the best. Glue size makes an excellent primer/sealer for the edges.

[wtnhighlander]

@drzaius, I plan to use the "Premium" 3/4" MDF from my local home center. I think the ultra-light stuff is what they make factory moldings from, and yes, it is terrible. Not that the sheet goods from the big-box are great, but it is obviously denser. I do plan to seal (as needed)  and prime all surfaces before application, then paint in place. Using Kilz(TM) original primer.

You know it's good, because it smells horrible! 

Thanks for all the replies. I read somewhere that wood glue was not so great for MDF, but it seems you all have proved that wrong.

[Ronn W]

+ one on Tiebond glue with t he added thought that if you are gluing the edge of a piece of MDF, I would spread a alyer of glue on and allow it to get almost but not quite dry before  applying the final glue and assembling.  I have found that this will prevent the second glue application from just being sucked into the edge of the mdf rhater than staying in the joint where you want it.  Same trick works for me on solid wood end grain.

[Tpt life]

WTN, hey R. No glue is good for MDF...if you think it will behave like wood. MDF can delaminate for lack of a better word. Guys were bad mouthing glues early on because they were popping MDF into homes while it was under loads that flexed the MDF. The glue was a hard bit that would not flex the same and caused that delam. If your expectation is realistic, as others have said...most anything will do. 

[Tom King]

I built this coffered ceiling with nothing but MDF, and Powergrab.  The crown molding is MDF too.  Shooting any kind of nail into it leaves a crater, which is a pain to do anything with.

[wtnhighlander]

@Tpt life, don't worry, this MDF is just some custom-shaped trim. No structural load.

@Tom King, you used the Power Grap to apply the MDF to the ceiling? What sort of surface is behind it?

[Tom King]

Each coffer box is a separate, complete unit.  They were assembled before lifting to the ceiling with a couple of sheetrock lifts.  The angled edges of the raised panels are separate pieces.  Each box was mounted to plywood, protruding past the edges of the boxes, and the plywood, around the edges of the boxes, was screwed to the ceiling joists. There is a 3/4" layer of foam under the ceiling joists that the screws go through into the joists. 

 It's a 10' ceiling in that room.  If I ever do that again, the fillers in between the boxes will be in grooves in the sides of the boxes, instead of just butt joints, like that one.  It was extra work to get all the but joints tight together with the heavy boxes on top of the wobbly sheetrock lifts.

The boxes were nailed together, and then all the pieces stuck in with Powergrab.  Powergrab doesn't hold it to the ceiling, but just all the parts together in the coffers. 

The coffers are about 4' x 5'. It still looks good after being up for 13 years now.

[wtnhighlander]

Something I tried, and can recommend to anyone cutting a bunch of MDF: Buy an inexpensive carbide circular saw blade. Even  6" blade elevates enough in th TS to cut sheet goods, the thin kerf cuts waste considerably, and at $10 or so, it is disposable. Saves your good blades from the horror of MDF.

[pkinneb]

4 hours ago, wtnhighlander said:

Something I tried, and can recommend to anyone cutting a bunch of MDF: Buy an inexpensive carbide circular saw blade. Even  6" blade elevates enough in th TS to cut sheet goods, the thin kerf cuts waste considerably, and at $10 or so, it is disposable. Saves your good blades from the horror of MDF.

Well now is a fine time to tell me

I just ran through about 6 sheets of the stuff and I was thinking  today I probably should have bought a cheap blade...oh well that ship has sailed for this project.