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I’m new to this forum and work mostly in the film industry. So often pieces are built from MDF and then we are asked to make it look some kind of highly polished surface like metal or ceramic tile etc. The edges/end grain in particular are a real problem no matter what the end result is supposed to be. I’ve used various things, in various combinations—watered down glue (doesn’t sand very nicely), sanding sealer, shellac, watered down spackle, etc. I’m curious what others have done and if there’s something easy and fast out there In the end, it’s just a lot of work to deal with all those edges.
thanks!
Hey, Peggy, welcome to the forum!
I don’t know what the tolerances are for finishes in film work, but I do work with a lot of MDF, and I agree it’s tough to make the tooled edge as smooth as the surface. And, since the surface is so smooth, if you accidentally scratch that surface, you get to decide if you’re now going to sand everything…
If we have edges that need to look particularly “up-close smooth”, we might sand both before applying anything and after applying a few coats of a sealer like shellac, or Rosco toughprime, which has a similar lack of body and therefore leaves fewer applicator marks, while “stiffening” the material enough to sand nicely. I like shellac because it dries quickly (and we have a walk-in spray booth), but it still does tend to get “gooey” under intense heat and friction, like with a palm sander….
I don’t know any way to short-cut the process, except maybe dipping the whole piece in bar varnish? LOL
Looking forward to hearing what else comes up for people– I bet it’s a pretty universal concern.
Cheers,
Claire
Hello!
I worked for a TV studio in Chicago where the carpenters Bondo’ed every MDF seam. That did the trick. But a lot of work!
I found a primer made by a compnay that supplies the CNC world. They make all sorts of different sheet goods to make fancy CNC things.
The company is called Coastal Enterprises. The product is called FSC-88. It is brushed or rolled on and then sanded. It works really well.
https://precisionboard.com/products/primers-fillers/fsc-88-wb/
One more thing I accidentally found, Sherwin Williams makes a primer called Wall and Wood Primer that worked better than I expected. Apply one coat, sand and then apply one more. Then top coat.
Good luck!
Scott
Thanks for the tips! I am going to try the FSC-88. Sounds like it was made for exactly this issue! This piece I’m working on now was CNC’d. It’s even worse than endgrain/edges because of the odd tool marks left in the (should be smooth, flat) channels that were cut away that weren’t even visible until I shellacked it. Anything to avoid Bondo…
We deal with quite a bit of MDF end grain. My favorite way to make it go away is to sand it with 220 grit on an orbital first. Then, use an air nozzle to blow out any dust. We use a Sherwin Williams Shrink-Free Spackling and apply it liberally with a putty knife. Make sure you’re pushing it into the end grain and build it up a bit. It takes little while to dry but once it does, I sand again with 220 grit on an orbital. Be careful not to over-sand it.
I like the Sherwin Williams Shrink Free Spackling for a few reasons.
- SW stores are all over the place. It can be had anywhere.
- The spackling compound is fluid enough to move around nicely and has enough body to hold in place.
- It sands very quickly and isn’t anywhere near as messy as Bondo sanding.
I enjoy this particular spackling paste more than other brands like Red Devil. It has a really nice consistency and sands well. No issues with it accepting paint.
Also….
To add to my last post. We use the Sherwin stuff for pieces of stacked MDF as well. Sometimes we get light boxes or signs that need to be built up and this is done with several layers of MDF. The spackling paste works well applied with a wider putty knife like a drywaller might use. You can also grab a pair of gloves and just use your hands to apply around curved surfaces. Don’t be afraid to make a mess. It sands so easily.
I consulted with the other scenics back at Universal Orlando before offering this tip (to make sure I wasn’t just making it up). In general we would paint the edge with XIM in a heavy coat. A fresh can of XIM is really thin but one that’s been used is usually like standard latex or glue in consistency. It covers and sands well.
Thank you for all the tips. We actually just purchased the Precision Board product and are loving how easy and effective it is. Its a game changer for us!
I know I’m late to the party but I work with MDF constantly (my designer loves smooth surfaces), and I feel your pain with the edges. I have recently found that a quick pass with a piece of 220 sandpaper to get any proud corners down, and then a healthy skim coat of Sculpt or Coat helps immensely!
Rae
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