Glue for MDF Mouldings

Millwork installers share tips on how to glue MDF moulding joints. September 5, 2006

I'm used to working with moldings made of real wood, and I never have a problem with bonding miters. I usually use Pro-Bond fast acting wood glue. Recently working on a private job, I was using cheaper moldings made from MDF, and found that my wood glue was not sticking even after leaving the moldings packing-taped up overnight. Why am I having this problem?

Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor N:
We use TiteBond II with MDF and have no problems. Sets up fairly quick.

From contributor W:
The end/edge of MDF is very porous. Use a liberal amount of glue. If that does not work, ask your local Titebond dealer to order you some moulding glue. Most places don't carry it. It is the best thing since sliced bread. It is thick like pudding so it won't drip, and sets in 5 minutes. Absolutely awesome for doing trim work, wood, or MDF.

From contributor R:
Titebond molding glue is the best.

From contributor B:
We solve porous end grain (similar to your situation) sticking problems with Titebond 2 as mentioned above. However, we first size the joint with a very light coating of Titebond 2. After it dries (typically about 15 minutes), we proceed with the regular glue-up with the same Titebond 2 glue. If your sizing glue coating gets too thick, scrape it after it dries with a standard cabinet scraper.

From contributor S:
We do the same as contributor B. We also do the same with porous woods like cedar, redwood and mahogany. If you just glue normally and put it together, excess glue will squeeze out and the remainder will get sucked up into wood and leave a dry joint.

From contributor G:
We use 2P10 thick glue from Fastcap (cynoacrylate glue), with the accelerator. Usually takes about 10 to 15 seconds to set. Sometimes the joint fails because the glue gets absorbed. Then we sand the end slightly to even out the joint (usually about 1 minute), and do it again, which takes another 10 seconds.

Superglues are unforgiving because any real mistake will cause you to scrap the molding, and you only have a few seconds to set the joint properly. That said, it's been years since we used any yellow glue on MDF molding. Superglue is so much faster than anything out there.

From contributor C:
I use LDF crown molding almost exclusively and love it. The best glue for your outside corners and returns is the Steinel HiPurformer hot melt glue. If you apply a thick bead of it, you only need to hold it together for 30 seconds before it bonds. The gun is about $99 and the cartridges are about $7.50 each. It's worth every penny.