Smooth racing surface for MDF

[slothead]

I've decided not to paint my CNC routed oval because the natural light brown color of the MDF already resembles a dirt track surface. Since all my dirt oval cars have silicone tires I want the finished surface to be smooth. I have shellac and polyurethane to use but am unsure how to proceed. I'm leaning toward going with 1 or 2 coats of shellac as a sealer then top that off with several coats of polyurethane. The back and sides of the track sections have already been painted with a sealer & primer, so only the track surface needs to be done before taping and wiring.

Any input regarding how to get the desired smooth racing surface will be greatly appreciated.

[WB2]

Most, if not all, polyurethane manufacturers do not recommend PU over shellac.
Whatever you decide, do a test shot first. I sealed some MDF with tung oil. Two brands of tung oil, two different looks, and neither looked like bare MDF.

[slothead]

Yes, I watched a video in which the guy read the statement off the cans they they aren't meant to be used together. Then, he did a test on wood using 2 types of shellac (with and without wax) under PU and after 10 days saw no signs of adhesion problems. He admitted something could develop in the future but doubted it. He used 2 light coats of shellac just to seal the wood so the PU went on quicker and dried faster.

I'd be perfectly happy to just use PU if a sealer isn't needed under it on MDF. I guess that's the most important question along with how to get the top coat as smooth as possible.

I do plan on testing shellac, PU, and shellac under PU on 3 pieces of MDF first.

[Mickey thumbs]

Have you considered two part clear epoxy paint? Some folks have used epoxy paint for the durable, super smooth finish , main drawbacks are fumes and short window of time from mixing to application.

[slothead]

I heard about epoxy paint but have no experience with it. Is this what might be used on a bar or a live edge counter top that comes out looking like glass? That might be ideal if I could figure out how to do it.

[Mickey thumbs]

The pigmented epoxy paint is that super smooth stuff people paint fancy garage floors with. Not sure of uses of the clear

[noddaz]

https://sawmillcreek.org/showthread.php?185644-Finishing-MDF-with-Polyurethane

This might help...

[slothead]

Yes, the link you provided was helpful. I'm going to give diluted poly a test on spare mdf and hope for good results. Thanks.

[slothead]

Multiple options for a smooth racing surface still being considered. One thing I forgot about is having to fill a bunch of countersunk screw holes on every section. Then, the wood filler has to be painted to match the surrounding mdf. That got me leaning toward going back to my original plan to prime & seal first, then paint the racing surface with shades of brown. This would give good traction for rubber or urethane tires, but not the best for silicone which loves a silky smooth surface.

If I can paint the wood filler to blend in with the surrounding mdf I'll definitely try multiple coats of poly with light sanding between coats to try to get a really smooth, glass like, top coat.

[HO RacePro]

I have always painted MDF with a two-part epoxy. The smoothest surface I ever got was with a bathtub refinishing epoxy kit called "Tough As Tile". About as smooth as glass, and gives terrific traction with silicone tires. But the paint is white, so not the right color for you. The clear epoxy kits should work fine.

I have never sealed the MDF before painting. I do make sure I dust the surface beforehand. I've never had a problem with the paint peeling, -- this on tracks that are now decades old.

I always paint the MDF before routing. That avoids getting paint in the slots where it can cause problems. A plastic foot-plate on the router will not damage the epoxy. But I allow the epoxy 4 or 5 days to fully cure before routing. Rout too soon and you get strings of epoxy coming up. Not really an issue -- the slots still turn out good -- but I prefer to avoid it.

Ed Bianchi

[slothead]

Thanks very much, I'll test this with scrap MDF.