Best methods for finishing MDF

[lunchmoney]

Re: Best methods for finishing MDF

How about routing along the joint with a shallow 1/16" to 1/8" deep recess and filling with your favorite filler?

neat idea... but would those new seams eventually show?... not sure why they wouldn't

[ocdSCHACK]

Re: Best methods for finishing MDF

FSC88 is a water based filler primer. under $30 a gallon. Can be used on wood also. Wonder if it is the stuff.

That's not it, but if I can find it, I'll post a link.
I'm tempted to try the Transtar stuff. Their products are pretty good...they're meant for repair shops and industrial use, so you usually don't get so suckered by some marketing scam. I've used Transtar, but never any waterborne products.

As for a tip: I would seal the entire enclosure with whatever you use, not just the outside. That should help minimize the expanding and contracting that you always get from temperature and humidity changes. The goal is to prevent any moisture from seeping into the wood after it's sealed and dry, not just the part you are painting. Sealing only one side can theoretically make it worse, because the wood can't absorb and release moisture(or expand and contract) symmetrically.

[davepellegrene]

Re: Best methods for finishing MDF

That's not it, but if I can find it, I'll post a link.
I'm tempted to try the Transtar stuff. Their products are pretty good...they're meant for repair shops and industrial use, so you usually don't get so suckered by some marketing scam. I've used Transtar, but never any waterborne products.

As for a tip: I would seal the entire enclosure with whatever you use, not just the outside. That should help minimize the expanding and contracting that you always get from temperature and humidity changes. The goal is to prevent any moisture from seeping into the wood after it's sealed and dry, not just the part you are painting. Sealing only one side can theoretically make it worse, because the wood can't absorb and release moisture(or expand and contract) symmetrically.

The Transtar primer I posted a link to, on my first post, I have left over. I used it on my Nightmare speakers. Great stuff for fill and no toxic smell. Very low over spray. Sands nice and doesn't seem to stick to your skin like regular primer does. I dry sanded up to 600. No thinners for clean up either. If you do use it make sure you run water through your gun to get the solvents out , then after you are done and clean up with water, run thinner through your gun to get the water out.
On the Nightmare speakers I coated the inside with Bin123 and the outside with Minwax Hardener, then two coats of Bin123, then several coats of the Transtar primer. I top coated with base coat clear coat. I left a lot of dry time between products. I was looking at them with a flashlight last night and can see every seam on them if I look really close. Even the one between the the two layers on the baffle. From two feet away I don't see any off them. Had I painted them with less of a sheen it would really be hard to see the seams. I agree that all exposed surfaces need to be sealed with a good build up of material to help control the humidity absorption.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

How about routing along the joint with a shallow 1/16" to 1/8" deep recess and filling with your favorite filler?

Not sure how I missed your post. I have been thinking about this method. From what I can see on different boxes were the seam shows the piece b u t t ing into the back of the exposed end grain piece either sets back a hair or protrudes out a hair. Depending on how much humidity is in the MDF. On some of the samples I am going to groove out as you suggest then fill with different fillers. The first that comes to mind is automotive seam sealer. Something that is flexible but a top coat of epoxy will stick to. I am also going to try auto body filler to see if it will bridge the seam and not crack.
Someone explained to me that basically the glue joint restrains the mdf right at the joint then a few hundreds of an inch away it expands or shrinks to show the line. So if I can find something that will flex and bridge the joint I may be in luck.

I have 16 pieces of six inch long 90 degree joints glued up and drying in the house.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

I've tried a number of different methods of sealing the seams and the only one I've found that is permanent is 1/8" MDF. I cap the ends/surfaces with all of the seams using 1/8" MDF and then you just have a 1/8" seam that is on an edge to worry about.

BTW, bondo is the best solution other than 1/8" MDF I've found for seams.

Jim

I think you may end up having the simplest solution with the 1/8" MDF. Cap the sides with it. Round over the front edge and I would think it would be difficult to see the seam. We'll see.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

I made up 16 sample pieces a couple of weeks ago and set them in my house to acclimate. Today I got a chance to work on 7 of them. I sanded them flat with my table belt sander with an 80 grit belt. 1,2 and 3 have the seam indented for filler. 4 through 7 are just coatings. Not sure what I am going to coat the rest with yet. Does anybody know any process I have missed. I am trying to keep the methods to processes that anybody can do and get the materials easy.
1. Epoxy in indented seam
2. Body putty in indented seam with fiberglass resin coating.
3. Body putty in indent.
4. Tightbond II coating.
5. Bin 123 white pigmented shellac coating.
6. Fiberglass resin coating.
7 Benjamin Moore sanding sealer coating.
Unlabeled one is just showing the indented seam.



The one to the right is showing the indent I put on the seam so I could add filler over the seam. I am going to do one more with auto body seam filler with probably fiberglass resin over top. The auto seam filler will be flexible so the seam can move if needed.


Dave

[evilskillit]

Re: Best methods for finishing MDF

Now that is awesome, testing with results you can see can't wait to find out how this goes.

[patrickm]

Re: Best methods for finishing MDF

one thing that helps, but doesn't completely solve the problem, is to get rid of indented seams altogether. when i build MDF cabinets, i usually try to cut 3-4 extra pieces the width of the top/bottom panels. when you go to cut the side panels, make them 1/4" oversize. when you go to glue, use the extra pieces to square up the top, and let the sides overhang about 1/8". then use a flush trim bit to take them off. it makes for some nice sharp edges. i'll also second wolf's hand-rubbed glue method. and for baffles, do the same -- overcut about 1/4"-1/2", and flush trim the entire thing. i think i used to spend about 20-30% of construction time measuring accurately to make perfect baffles and corners, and now a $17 bit shaves most of that off. rustoleum appliance epoxy paint is also good stuff. goes on nice and thick. it only comes in a couple colors, but you can always paint over it again.

[Wolf]

Re: Best methods for finishing MDF

i'll also second wolf's hand-rubbed glue method.

What can I say- I can get some very solid and sharp right-angles doing it this way, and it works well for me!
Later,
Wolf

[djg]

Re: Best methods for finishing MDF

Thanks for all your hard work. It will be interesting to see your results.

[sbrtoy]

Re: Best methods for finishing MDF

Not sure if these would be as good structurally on a big cabinet but perhaps on a small one?

http://tapeease.com/cabinet1.htm

[lunchmoney]

Re: Best methods for finishing MDF

Excellent, Dave!

Thanks for all your hard work. It'll a tremendous contribution to this community.

Can't wait for the results...

The bad news is that you really won't know for sure what the long term results are for a good 6 months at least

[skatz]

Re: Best methods for finishing MDF

Dave
What epoxy method are you using? I wrote to tech support at West Systems epoxy to ask them about edge sealing on MDF, they responded that their 105 with 205 hardener would likely do a good job, but I haven't tried it.

Steve

[ocdSCHACK]

Re: Best methods for finishing MDF

FSC88 is a water based filler primer. under $30 a gallon. Can be used on wood also. Wonder if it is the stuff.

I found the stuff, but can't imagine it seals mdf edges. I've used Evercoat metal glaze, a two-part polyester finishing/glazing putty, and edges eventually showed up. Anyway, the stuff was was Duratex, I think this one - http://www.acrytech.com/catalog.asp?prodid=547778

[donparsons]

Re: Best methods for finishing MDF

We know that miter cuts will eliminate this problem. I mentioned that to Lunch in one of these converstations and he said he likes roundovers. I have been wondering what would happen if you did a roundover on a miter cut. You would only have one seam to measure and it is the seams that show not the end grain. What say you?