MDF Delamination

[Joe Pelonio]

Is the top layer of MDF actually laminated or veneered?

I have a guy that wanted 1/2" thick MDF 10" letters for his business, he will paint and install. I am cutting them with 1/4" MDF and then gluing and clamping them together since my laser won't do 1/2" and so far so good except for one thing. It appears that the mdf is made like plywood, or veneer, which surprised me. On two of the letters so far (Times New Roman Bold) the end of the serif is slightly apart after cutting, enough that I can bend back and reglue.

[George M. Perzel]

Hi Joe;
Noticed the same thing. Drive a screw into the edge of a piece of 3/4 MDF and it comes apart in layers. I don't think it's just the top/bottom layer. I haven't laser cut much of it but do like the way it cuts and the kerf is very fine.
George

[Dave Jones]

That's odd. I haven't used MDF with the laser, but used to build walls in a museum using it and the cross sections never looked like layers to me back then.

[Lee DeRaud]

I've seen some cheaper MDF (and most particle board) where the surface layers are denser than the center. Having seen how it's made, I'd guess it's compression from the final rolling step. It's usually more obvious in the thicker stuff (1/2" and 3/4") than in the 1/8" and 1/4" I usually laser, but yeah, at its worst it looks like separate layers.

[Mike Null]

I use it to make jigs for various engraving jobs and have never run into the layer situation. From a mfg. standpoint I can't think of a reason that it would be layered.

[Doug Jones from Oregon]

Joe, if you can find it, (Hardwood Industries in So. Sea) source MDF that is considered "double refined". Plum Creek M2 is the brand that comes to mind.

MDF is just sawdust that is glued together with high pressure. It is the pressure and the heat generated that gives the finish on the top and bottom of the mdf sheet, not a final layer of material.

I'm curious, what is the wattage of your laser that you can cut through .25", and is that a single pass?

Doug

[Joe Pelonio]

It's 45 watts, and cuts 1/4" single pass at speed 4 100% power. This MDF was actually free, my neighbor (woodworking shop) has a lot of extra as his good wood is delivered with this around it for protection. Since I'm gluing together letters anyway I just put a little under the lifted bits before clamping.

[Mike Null]

Joe:

There's a material called particle board that gets confused for MDF. They're not the same and particle board is coarser and not nearly as good quality.

There's also a higher density MDF which is too heavy to use for any application I have.

[Larry James]

Joe,

I remember watching a tour of a factory that made MDF on TV - may have been on "This Old House." A thick liquid mixture was poured on to a conveyer and passed through a roller. The process was repeated several times building up the MFD to the required thickness. This may account for the separation. Not sure, but I think the reason for layers was to remove air and voids???

Larry

[Joe Pelonio]

Joe,

I remember watching a tour of a factory that made MDF on TV - may have been on "This Old House." A thick liquid mixture was poured on to a conveyer and passed through a roller. The process was repeated several times building up the MFD to the required thickness. This may account for the separation. Not sure, but I think the reason for layers was to remove air and voids???

Larry
That may be the answer. BTW, this is definitely MDF rather than particle board.

[Joe Pelonio]

After finishing the MDF job when I cleaned the mirrors and lenses there was actually a nice brown film on them which I have not seen before even with wood. Just a note to tell you that if you cut MDF you need to clean them more frequently and after.

[Dave Jones]

Some lumber yards around here call chipboard and particle board the same thing, and it is the very coarse stuff that has shavings in it (some can be 2 inches long or even more in the really coarse versions).

Other lumber yards here sell them as 3 seperate types of material, with "particle board" being the coarse stuff with shavings in it, "chipboard" being a fairly dense set of chips with no shavings, and then "MDF" which is so fine it has almost a uniform color.

Some of the chipboard has layers where the surface is denser and the center is coarser. All of the chipboard is much coarser than MDF. It typically has rough edges and small voids in the cross section when cut. MDF doesn't. If you cut and sand MDF it should look the same on the cross section as it does on the top surface.

Here is what I call particle board, and some local lumber yards interchangeably call chipboard or particle board:

http://www.redtengu.com/images/raw/particleboard.jpg

The one below is a pic of what some places here call chipboard (these are the places that consider chipboard and particle board to be different). This version has the coarse center and finer top and bottom, but some are more uniform throughout. They all have that speckled pattern on the faces.

http://www.redtengu.com/images/raw/chipboard.jpg

The one below is MDF. The particles are so fine they are almost a uniform color, and cross sections are solid. No voids.

http://www.redtengu.com/images/raw/mdf.jpg

[Dave Jones]

Also, at least around here, chipboard is cheaper than plywood and doesn't warp unless it gets wet. MDF on the other hand is a fair amount more expensive than plywood and most other kinds of wood, so it surprises me that it would be used as a throw away covering for another kind of wood. It seems it would be cheaper to simply include an extra sheet of the other wood on the top and bottom of the pile, or protect it with plywood (or chipboard).

[Pete Thomas]

Dave, thanks for posting the pictures. I was on line yesterday looking for just that, the differences between the various types you have mentioned.

Thanks, pete

[Thomas Hempleman]

Is MDF any good for outdoor use or will it eventually fall apart when it gets wet? Can it be coated or treated to make it more weather resistant? I would like to use it as a backer board for small outdoor signs, but I've resisted using it for fear that it wouldn't hold up to the weather.

[Joe Pelonio]

Thomas,

MDF will work outdoors only if totally sealed, edges, face and back. Oil based primer and exterior topcoat. Any penetration including screw/nail holes will allow moisture in and it will swell up like a sponge. The letters I made from it are for outdoors, but are being installed under an overhang where they will not be in contact with water, but I still advised the customer to paint well on all surfaces and install with adhesive to prevent
humidity in the air and fog from attacking them.

For what you are doing I'd suggest using extruded acrylic (buy scraps from the bargain bin) or PVC sheet such as Sintra or Komatex. It's not cheap but for small sign backing goes a long way, 4'x8 sheet 1/8" $35. Can't laser cut but you can use a sharp utility knife and metal straightedge or saw.

[Tom Majewski]

Joe,
I worked for a custom cabinet shop and learned the 1/4" mdf you get from home supply stores, even though it's called MDF is actually MDF Lite. It's construction lends itself to delamination, and crushes easier when driving screws into it. We would order true 1/4" mdf from a plywood shop. Also look into Norboard brand moisture resistant MDF. Don't know what the resin is, but it's green and tough on sawblades and router bits. Never tried to laser it. The sawdust looks to have a mineral content in it. Mybe it's just glossy resin dust.

We would run 1/2" to 1" mdf through the cnc router and the edges were rock hard and sharp. The 1/4" stuff was usually soft and crushable.

We were also powdercoating mdf for that "dipped in gloss" look. Waterproof (as long as you didn't scratch through the surface) and a really great look for curved desktops that wasn't possible with laminate covering.

Tom

[Dave Jones]

How about Corian? That's an acrylic based material that lasers and can be worked like wood. Used for countertops and talked about in several threads here. I'm pretty sure Keith said he uses it for exterior signs all the time. It comes in various colors and even marble look. You can maybe get some scrap pieces from a local cabinet maker or kitchen installer.

[Joe Pelonio]

According to the manufacturer I can only cut 1/8" corian with the laser, so in the case of 1/2" thick letters I'd have to cut 4 of each and glue them up. Not sure if it's available that thin, it's hard to come by even in 1/4". Has anyone tried cutting 1/4" corian, and if so, how many watts on your laser?

[Dave Jones]

I think even the 1/4" corian is rare. Most of it is 1/2".

I was thinking more about Thomas' question where he wanted to use MDF as a backer for exterior signs rather than for the letters you talked about. I was assuming he would be cutting the MDF on a saw, and could cut corian the same way, but it would hold up in the weather better than MDF.

I've never tried corian at all, so have no idea of the power needed to laser cut it. I gather Keith uses a shopbot to cut it to size and shape.

[Mike Mackenzie]

Joe,

We have cut 1/2 corian it took 120 watts with very high air pressure. I would caution people about cutting this type of material even engraving it. The material produces a very fine dust that is very abrasive. If you work with corian you must CLEAN the motion system when you are finished otherwise it will wear out moving parts.

here is a pic of 1/2 corian cut.