Glue problems

[Benevolance]

Hi folks,

Long time listener, first time caller. My wife and I decided to build our own arcade cabinet, and we've been following a lot of the great advice on the forum and in the wiki. The site is great, and all of you have contributed some tremendous cabinets. It's inspiring.

We ran into a problem with our cabinet assembly. Based on some previous projects, we decided to fasten our cabinet together using LePage wood glue, sans screws. We're using 3/4" MDF board. We glued the pieces, clamped firmly, and left over night. When we wheeled the cabinet out to work on the next day, several of the boards we glued had pulled away. The glue itself was solid, but it pulled off a thin layer of the fibre board from the piece it was affixed to. We were able to re-glue, re-clamp, etc. But we've had this problem a couple times now.

Our solution has been to drill and screw the boards in place after the fact. Another solution - impractical for us - would be to never move the cabinet, since the movement is what jostled the boards loose. But I'm wondering if other people have had this problem with MDF and wood glue?

[Chadwick]

If you're not on a tight budget, run to your nearest big box and get a small air compressor that comes with an 18 gauge brad nailer.  Buy that and some 1-1/4" brads.  That should solve your problem.

Other ways would include a router and some decent routing skills.

Yet another option would be adding gussets in the corners or using a bunch of those steel "L" brackets you can get at any hardware store..

What you are experiencing is not uncharacteristic for MDF.  When that glue dries, it forms a bond that is stronger than the MDF and the MDF will fail first.

[Jdurg]

I got my air compressor with nail gun and staple gun for $89.  I don't know how I built ANYTHING without it.  There's no way my poker table would be even partway done if I didn't have it.

[ChadTower]

If it's coming off with parts of the fibreboard still attached then the glue isn't penetrating very far.  Could the glue be old or diluted?

[Benevolance]

I was wondering if humidity might play a factor? It was a brand new bottle of wood glue, bought for this project. I would hope that Home Depot isn't selling old glue! 

Chadwick, does a brad nailer offer significant advantage over using screws? It's moot at this point, since we've now used a combination of screws and glue on the cabinet and it's satisfactorily sturdy. But this won't be our only arcade cabinet; my wife has admitted that it's been a lot of fun building. Anything that makes the next cabinet easier is welcome.

[Chadwick]

Working with MDF is different than working with wood.  MDF is very compressed and it tends to not hold fasteners as well as say, plywood will.  If you use screws, you need to use coarse thread screws so they will "dig in" to the MDF.  If you use a fine thread screw, it will not hold well because the threads just fill up with the MDF dust that you are creating as you drive the screw in and you are left with little to no "grab" into the MDF.  You should also pre-drill your holes which 1) extracts the dust that would otherwise pack into the screw thread, and 2) allows you to drive the screw in more easily and prevents you from cracking the head right off the screw before it is even halfway in.  If you have ever tried to drive many screws into MDF without pre-drilling your holes, I'm sure you cracked off a few screw heads or ruined a few screwdriving bits in the process.  This is due to the density of the MDF. 

Screws also have a high propensity to "blow out" your MDF if you try to screw into the edge; again, this is due to the density of the wood.  Think of water displacement... fill a glass and drop an ice cube into it and water will spill over the edge.  Same concept with MDF.  It is so dense that the area your screw is occupying HAS to be displaced somewhere else. 

Thirdly, screws are way more labor-intensive to cover/fill when finishing than brads and the tiny hole they leave behind.  Brads (sometimes called "pins") are very small in diameter...18 gauge usually.  With a compressor set to around 100psi you can easily countersink a brad into MDF.  Brads do not displace the MDF the way screws do, rather, the brads just "super compress" (for lack of a better term) the material ahead of their path as they enter the MDF.  No pre-drilling needed, no dust extracted, no broken screw heads, no broken driver bits, no blisters, no sore wrists, no blown-out edges, no muss, no fuss.

Either way, you should always, always, always use glue to get a strong bond.  Without glue, you could easily pull apart two pieces of MDF, regardless of fastener used.

MDF just plain sucks to work with.  The dust is very fine, gets everywhere and all over everything, it is toxic, and it smells like sh**.  MDF is also extremely brutal on carbide and HSS tools and dulls them at a much faster rate than non-composite woods do.  The ONLY reason to use MDF in my opinion, is if you plan on painting your work.  If you are going to laminate/stain/whatever instead of painting, use plywood every time.

[ChadTower]

^^^

That and where it takes a bit of time to predrill and screw, it takes less than a second to shoot a brad.

[sstorkel]

Brads (sometimes called "pins") are very small in diameter...18 gauge usually.

Brads are 18 gauge. Pins are smaller, usually 23 gauge. I have guns for both, but rarely use either.

The ONLY reason to use MDF in my opinion, is if you plan on painting your work.  If you are going to laminate/stain/whatever instead of painting, use plywood every time.

The only reason to use MDF is if you need to route complex profiles in the edges of your pieces. If you just want to paint your cabinet, use MDO (Medium Density Overlay) instead of MDF.

[Benevolance]

Either way, you should always, always, always use glue to get a strong bond.

Well, that sort of brings me back to my original problem, which was that the glue wasn't penetrating very deeply into the mdf. 

I think that I'll pick up some better tools for the next project. I've almost completed assembling this cabinet, using only a router and a drill. It was a good first go, but there were more than a few things that could have gone better.

I noticed MDO mentioned in the Wiki, but a search of the local lumber yards produced no results.

[ChadTower]

I noticed MDO mentioned in the Wiki, but a search of the local lumber yards produced no results.

Yep.  MDO isn't available in a lot of places unless you special order it. 

[TAG]

Yep.  MDO isn't available in a lot of places unless you special order it. 

I'm using MDO on my cab but got very lucky with the purchase.  I had called various local lumber stores, and they all confimed that they'd have to special order it.  A few weeks later, on a whim, I stopped by 84 Lumber and asked about MDO again.  The clerk indicated that they normally had to order it, but that they had just had a guy change his mind about some MDO he ordered, so they had several sheets sitting in the back.  It was normally $55 or $60 a sheet, but he gave it to me for $30 just to get rid if it.  Since that wasn't much more than MDF, I snapped it up. 

Totally worth it so far!

I guess the moral of this post is that it never hurts to ask twice!

[sstorkel]

Well, that sort of brings me back to my original problem, which was that the glue wasn't penetrating very deeply into the mdf. 

If your joints are popping apart without damaging the wood, then your glue is the problem. If the MDF is breaking, the glue isn't your problem. You can build a cabinet without any screws, nails, brads, or pins. You might need to add some glue blocks or angle brackets to your design, however, especially if you plan to do much moving of the cabinet before it is complete.

Of course, there's always the possibility that your cuts aren't straight and you're not getting good mechanical contact between the pieces being glued. Wood glue won't fill gaps with any strength. Not sure how you're clamping your pieces, but if you do it incorrectly it can also lead to problems. Clamp too tight and you squeeze away all the glue. Clamp too loosely and you end up with gaps the glue can't fill. You need to do it just right if you want good results.

[Benevolance]

Clamp too tight and you squeeze away all the glue.

That may have been the problem. I was clamping those suckers on tight as I could get.

[BobtheAddict]

Not sure this would help but have you thought about mounting the pieces together via a groove? If you have a table saw, you can use a dado blade to cut a groove to mount / glue to.

[ChadTower]

Not sure this would help but have you thought about mounting the pieces together via a groove? If you have a table saw, you can use a dado blade to cut a groove to mount / glue to.

Router may be easier if he has one.  Cutting dados in large panels is hard on a small tablesaw.