[CJ Courtney]

Guys,is there any tips for treating the profile of mdf panels?My normal routine would be to sand the heck out of it,then brush on a coat of SW's oil base Prep Rite Pro Block,sand,brush on another coat and sand.Install the panel into a poplar wood frame.Then,spray a couple of coats on the whole panel and frame.Needless to say its time comsuming.What is your routine for painting mdf that has a profile 1-1/4 wide all around the panel?Thanks CJ Courtney

 

[vermontpainter]

Don't oversand...it gets real ugly.

 

[premierpainter]

coverstain works great on bevels or cuts

 

[NACE]

It is my understanding that alkyds in oil base coatings can disolve or soften the binding glue used in making MDF. I have always used a latex enamel underbody of some sort that sands into a fine dust like an oil, seals the surface more uniformly as it does not strike into the porosity of the MDF. Sometimes you can get flashing of the top coat with oil primer as it does not always uniformly seal the surface.

 

[slickshift]

That stuff is crap
Thanks again HGTV
I've had better luck with alkyd primers
I've had the acrylics activate the "glue" and have them puff up

Fortunately I don't get too much call for it
At this point I consider it a crap shoot

 

[DeanV]

I think latex primers are the worst. They will soak in to MDR "end grain" coat, after coat, after coat. On trim work, I will usually use latex primers, but will either smooth some caulk over the raw cut ends or brush a coat of BIN on them.

 

[Ron 2]

Fiberman, fiberman...

Ah...a subject to chime in on! I'm new to these forums but I've been fighting with fibre for as long as it's been around...or the late 80's at least!

Up here (in VOC friendly Canada) I use a product manufactured by ML Campbell's Canadian subsidiary called "Clawlock", specifically formulated for just this purpose. This is a high-solids, two component (post-catalyzed), Amino Alkyd formulation; I use standard (89C grade) premium lacquer thinner as the reducer in most cases (16-20 secs; #4 Ford Cup) although high-end ferbo reducer provides slightly better performance in some situations (i.e. boxes with the backs nailed on them). I spray conventional, one pass around the profiles and edges (cut surfaces), thirty minutes on the drying rack then sand til there's virtually nothing left (but there is ). I then shoot a full coat (20-24 secs viscosity) on everything (I hang most everything I can: doors, fillers, end panels) and allow for full cure (8 or so hours) prior to finish sanding. Depending on the quality of the fibre and the gloss level of the top coat, I may give the front faces a second pass to assure the necessary fill during finish sand. Finish is generally two coats ML Campbell "Resistant" high solids post cat, shot wet on wet with a Kremlin MX air-assisted airless; then 24 hour cure prior to packing or installation. For 95 point (i.e. mirrors), the "Resistant" is "watered" way back with ferbo and shot in two, two coat sessions with a cure and wet sand to 600 grit on day 2 and powerbuff when the second two passes have cured.

All that said, obviously this doesn't apply (whatsoever) to conditions "in the field", however this IS how I deal with MDF (in a shop with a booth).

IMO, if you have to deal with lots of fibreboard, high solids catalyzed primers are the only way to go (respirator is not optional :no and the investment in a pot, pistol and compressor will quickly pay for itself...Even if you are topcoating with more "conventional" products.

Cheers, Ron

PS: To prempt the inevitable "why would you use a pressure pot?"...superior fan control and superior atomization of high solids primers when doing cabinet grade finishes...(we're not shooting blockfiller here)...and besides, the customer also pays for the overspray when they pay for their doors!