The following is a list of questions and answers posted to the forum regarding MDF, its characteristics and preferred methods of use. Questions are in italics.

I need to glue 2 3/4" sheets of MDF together, face to face, to form the 1-1/2" thick top of my router table. Is yellow wood glue sufficient for this, or do I need contact cement or some other glue for MDF? Also, will the hardwood edging that will be attached to the sides also need to be glued with something else?

• I've very successfully used yellow glue for MDF laminations. I've made table tops (my router table, for instance) and a number of bending jigs using yellow glue, and have never had a glue joint failure.
  
  
• For edging, just gluing it would probably suffice, but I use biscuits for their assistance in alignment and their "clamping assistance" as they swell. Again, no joint failures yet.

I am working on a project which the client has requested PAINTED raised panels. Having never working with MDF, I am wondering if MDF would be suitable for the raised panel sections?? I had originally planed to use poplar, but my thinking is I can avoid gluing up the panels by using MDF. Also, can I expect good results painting the MDF?? What should I expect to pay for a 4x8x3/4" sheet of MDF.

• I built a curio cabinet for a client with MDF that had raised panel doors at the bottom. They painted it gloss white and it looked great. The doors were made the same as real wood doors but the panels can be glued in the rails and stiles without concern for wood movement. When purchasing MDF look for a superior grade that is suitable for routing. Your wood supplier should have several grades with a couple from different suppliers that can be routed/shaped. Don't buy from home depot, they don't carry a superior grade. I pay between $16 to $20 a sheet in the Atlanta area. The only problem with MDF is the incredable amount of dust when routing/shaping, you have to have good dust collection system.
  
  
• MDF is perfect for the purpose. I would recommend plunge type profile bits to give the same effect.Router bits(carbide only, of course) produce very sharp profiles but (depending on how many cuts..) you'll need spare cutters to finish the job. Watch out the dust! I mean it's terrible. Personally, I always try to avoid MDF because of the dust issue. If you've a good dust collection system, it shouldn't be a big problem. In Victoria,BC,Canada they go for around $40 Cdn. per 3/4" sheet.
  
  
• I've been building some things from MDF lately, and I like it! I think it would be great for the painted raised panels. You won't need to worry about sealing an end grain before painting, and as mentioned before, it's dimensionally more stable. Yes, I'll admit, the dust is incredible! I bought my MDF at Home Depot, and it was a pretty good grade, and was just fine for what I was doing (cabinet building and a new computer desk). I paid about $18 a sheet.

I'm working on a workshop cabinet with a top made of MDF. I wanted to put some waterborne polyurethane on it. However, I think I read somewhere that MDF and waterborne finishes don't get along too well and I can't remember the reason why. Is that correct? If so, can I seal the MDF with shellac first and then apply the waterborne finish?

• Its my understanding that shellac will work as a sealer underneath, any other finish product, and only would have compatibility problems on top of certain finish products. So I see no problem using it to seal your MDF, then coat with the waterborne poly.
  
  
• I have used a waterborne lacquer(not poly) on MDF, with no problems. This was years back, and I don't know if your product would do the same. A note on MDF edges. The exposed core of the MDF, does not finish like the face, even when sanded smooth. You might want to add an (wood) edging to the MDF.
  
  
• The last time I checked the water based was more expensive than regular poly. I have a MDF bench and I sloped lots of poly coats on it (it takes lots of coats!) and took it down with progressive grits of sandpaper until it was glassy! Kind of useless for work but then all I do is stack stuff on it. The MDF bench I actually use has nothing on it but lots of holes, glue, stain and other Picasso like renderings! I run over it with a scraper now and again for a re-finish job. I am thinking about turning it over or screwing another piece on top.

I have started making cabinetry and am using 5/8" MDF for the "boxes" but am putting a two inch wide/ three quarter inch thick poplar face frame around the outside edge. I have built my first unit by attaching the face frame with square drive deck screws about 1 1/2 inch long countersunk about 1/8 inch through the poplar into the edge of the MDF - no glue. I then cover the face frame with Nevamar laminate. It seems pretty solid, still I wonder ......

Should I be gluing the face frame to the edge of the MDF? What glue? Regular Titebond?

• MDF has the property of holding screws through the face Much better than through the edge. But it still doesn't hold them as good a solid wood. Therefore I always use glue in addition to any mechanical fasteners when using MDF or particle board. And since I have a biscuit joiner I normally use it whenever possible to avoid plugging screw holes.
  
  
• Glue size the edges of the MDF before the final assembly of the carcase. Spread a liberal amount of the glue you are using on the edge, let it dry about 2 hours and glue and screw or biscuit as usual. The sizing will act as a seal coat, and keep you from having a starved joint. Watch the biscuits in MDF. If they are too near the outside edge, their swelling can telegraph under the laminate.
  
  
• There is a screw on the market for mdf and particle board called the gripper and it has a special lead on the tip of it.

We have all heard a thousand times that a proper glue joint in wood is stronger than the wood istelf. What about MDF? I am using walnut veneered MDF to build some things, but have no idea how much to trust glue joints. Will yellow glue in nice tight dados be good enough for things like frame dividers between drawers, or even for shelves (with dados), or am I asking for trouble?

• Yes, yellow glue will create strong adhesion as you've described. MDF is not a strong as wood, but as long as the shelves are not longer than 30" using 3/4" material, you will be fine. Anything longer than 30", attach a self edge to the shelf of at least 3/4" x 1 1/2".
  
  
• I don't recommend an MDF glue joint WITHOUT some reinforcement (biscuits or dowels). However, since you said you're gluing dados, yellow glue should provide sufficient strength. Using a water based glue in that joint will cause the MDF to swell slightly in the joint which will give some mechanical strength as well.
  
  
• I find you can screw into the face if you predrill, but you can't use a wood screw unless your predrill is the same shape. Use a screw w/ no taper and wide threads. A coarse threaded bugle screw (requires countersinking the head) or, one which I use and have found @HD, the Grabber line. Butt joints don't work and biscuits are little better. I experimented with both. Glued them up then broke them apart - too easily. While the glue held fine, the particles directly below the glue broke away from their cousins . The result looked like your finger would if you wet it and pressed it into sugar. I use dowels. There is supposed to be an MDF made from straw which is lighter, machines better and is less costly.

Paricle board was very prone to sagging and I understand that MDF is more stable but does anyone have any information comparing thickness, length of shelf, and amount of load with the expected deflection (amount of sag), and will this deflection become permanent, like with particle board after a short time?

• I 'd not exceed 30-32 inches span at 12-16 inches of width. If wider shelves are required, add hardwood strips (3/4" square min.) to front and/or back of the shelves.
  
  
• I don't have any real data, but in building bookcases with MDF shelves, I edgeband with 3/4"x1" thick on shelves up to about 30 inches. I use 1-1/4" for shelves that will be 3 foot and try not to make them any longer than that. In my garage the shelves were 46-1/2" and I used 2" edgebanding on the front, and they have held up well. The edgeband is solid stock, not MDF.