Replies

1. 
   highfigh | Mar 27, 2005 04:31am | #1

   You can use a slightly thinned paint or a clear finish. Then, sand lightly. Once the edge has been sealed and the feel is the same, it should take paint the same way.

   "I cut this piece four times and it's still too short."
2. 
   sawdustmaker | Mar 27, 2005 03:22pm | #2

   I've used a slightly watered-down drywall compound, coat the edges, let dry, and sand. It does a pretty good job of filling the pores and won't swell up with a water based paint. I have tried treating the edges with an oil based primer, but that didn't work as well for me.

3. 
   Fingrs | Mar 27, 2005 04:07pm | #3

   I like the response from highfigh: "it should..."  To my ear that sounds like a theory or something, rather than actual experience.

   In my actual experience, the milled edge of MDF is a bear to prep for a smooth finish.  I've tried shellac, spray primers, and so on.  Even after sanding, the edge is still rough.  Using drywall compound is probably the best idea (I hadn't gotten around to that one yet...I put my project on hold due to extreme frustration!). 

   I used this trick on some plywood from HD, stuff called sandply.  While sold as a hardwood veneer plywood, the grain would never "settle down" when the finish was applied.  Someone here suggested I slather drywall compound over the surface, sand smooth, prime and paint, which I did.  The results were excellent.  It was a lot of work, though!

   Please let us know how you achieve success.

    

4. 
   Pondfish | Mar 27, 2005 04:19pm | #4

   Try a 50/50 mix of yellow glue and water; two applications may be needed before the thirsty edges are filled.  Once dry, it can be sanded.

   MDF edges will drink shellac till the cows come home, so I use the glue step when putting a protective shellac finish on my MDF-made jigs. 

1. 
   nikkiwood | Mar 27, 2005 05:42pm | #6

   There was a FWW article about painting MDF (sometime in the last year).There are two techniques I have used with a good result:1) Band the edges -- I use 1/8" strips, glued and nailed. Spackle the nail holes, as well as the seam between the edge band and the MDF.2) Prime the edges; sand, coat with drywall compound -- I generally use a 1" knife, but I have smeared it on with my finger. Then prime the whole piece (which means a second coat of primer on the edges). If I am being real fussy, I will brush a third coat of primer over the edges, sometimes preceded by a second smear coat of the drywall compound. Lee Valley makes a filler specifically for this purpose, but I didn't think it worked any better than the dw compound. For all this priming, I use a Benjamin Moore "First Coat" product -- "latex enamel underbody", which is pretty thick and gloppy. ******************************The second technique will get the edges looking pretty smooth, but the wood edge band will yield the best result.For either, I use an alkyd enamel (BM Satin Impervo) for two top coats.

5. 
   ring | Mar 27, 2005 05:23pm | #5

   there may be other good ways but drywall compound has proven itself many times for me.

   DR

6. 
   dondownunder | Mar 28, 2005 04:48am | #7

   asar

   Two methods are used in my workshop depending on top coat.

   For 2 pack finishes sand job to 240G with a ROS, spray primer to edges only, sand with 320 & then prime all surfaces. Sand again with 360 & finish coat.

   For other paint finishes we use a good acrylic primer, again double coating the edges. We havn't had a problem with swelling & the grain raising caused by the first coat is easily sanded off to give a good substrate for further finishes

   Don

1. 
   UncleDunc | Mar 28, 2005 05:34am | #8

   >> For 2 pack finishes ...Is this what we in the US would call a two part finish, i.e. epoxy?

1. 
   dondownunder | Mar 28, 2005 08:16am | #10

   Uncle Dunc,

   In this case polyurethane paint & hardener is what I was referring to however epoxies are of course 2 part as you mentioned. It is pretty common practice to use 2 pack polyurethanes to coat MR MDF kitchen & bathroom cabinet doors, most trade suppliers are putting a 7 year warranty on them as well & to date I haven't had a come back on any.

   Don

7. 
   cowtown | Mar 28, 2005 06:53am | #9

   well, as to what is the best way, God only knows.

   If you use a latex primer sealer, you will undoubtedly experience some real long delays in curing time, compounded if you use latex paint.

   If you use oil base or expoxy based stuff, you got a long curing time, like next day

   Ergo, you can use a laquer primer, in spray bombs or pressure pot , or use a shellac based primer sealer like ?kilz which dries in a few minutes, sand smooth, apply another coat. etc. Warning, don't opt for the latex versions of these stain sealers- look for the one that says to use methyl aclohol to clean up.

   whatever primer you use, if yer using latex paint on MDF, you cannot stack the doors together, even after a week OR EVEN TWO of drying. they will simply bond togeether. Put cardboard in between em, and the cardboard will meld with the paint. For whatever reason, latex paint really takes a horrendously long time to cure hard on MDF, regardless of the primer used.

   MDX is rumoured to be an exterior grade MDF, and lots of trades folk think that that is the case. The info from the supplier gives another version. They state that the product is NOT recommended for exterior application UNLESS all surfaces (including edges) have been treated with an epoxy covering. The practice is far from the recommendation, but yet it seems to work.

   that merely points out that painting this stuff is not fully understood by even the folks who make it.

   Just some observations based on my experience.

   Eric in Calgary