How to Seal Your Shapeoko's MDF Baseplates / Wasteboard

[MarkDGaal (Mark David Gaal)]

I’m learning very quickly that often the CNC discipline and the woodworking discipline are not always possessed by the same person I’m watching do a tutorial or how-to video.

My biggest pet peeve thus far… sealing wasteboards/ spoilboards/ baseplates. Here’s a few friendly tips about what you should and shouldn’t do…

1. DO NOT use Plywood over MDF, regardless of how each responds to humidity MDF is FAR more dimensionally stable and is generally flatter than even the highest grades of plywood after manufacturing.

2. There are different grades of MDF. LDF, MDF, and HDF (low, medium, high) Density are all colloquially known as “MDF”. There are also big differences in quality depending on who the manufacturer is. Call your local Woodcraft store to see if they stock some of the better quality panels.

3. DO NOT go to home depot and pick up your garden variety of urethane finish. There are massive differences in the quality of finishes. Nothing annoys me more than about someone wanting a flatter reference surface then using a finishing product that is not Self-Leveling. Many of these products are meant to be applied with multiple coats with sanding in-between coats. Master finishers can’t achieve perfectly flat results with them and neither will you. Instead…

4. Use a SEALER not a buildable finish. Something that will soak into the MDF and seal it is a better idea then a finish that sits on top. My recommendation is Smith’s Original Epoxy Sealer. Know in woodworking circles as “CEPS” https://amzn.to/37b8hJm. It’s not thick like the epoxy you’re thinking off, it can be applied with a foam brush, applicator pad, t-shirt, whatever really. Mix it well and you can’t screw it up. My XXL baseplate just took a soup-bowl amount so the pint size is plenty.

5. DON’T forget to do the edges! The end/edge grain of MDF is most susceptible to humidity apply a generous amount to get it sealed.

6. Make your life easy, do the edges first, then the backside, then the topside. Use something like this to get it all done at once! Painters Pyramids

#EndRant hope you find this helpful.

[cnc-life (Robin)]

I found that the MDF i purchased seemed to have some sort of seal on as it had shine.
However the bit I levelled was exposed, so I used a waterbased wood seal for outdoor use (timber decking and facias). Its very slightly tinted with a very pale yellow so its looks close to a natural wood colour. Happy with result.

[MarkDGaal (Mark David Gaal)]

Good on you for using a sealer; but if it were me, I wouldn’t have used water-based. With normal wood/plywood you would raise the grain using anything water-based. And since all other wood has a non-unform grain it would feel very slightly bumpy or fuzzy to the touch after applying.

Luckily MDF is very-uniform so you likely raised everything by the same amount … Even still non-waterbased would be a better idea.

[cnc-life (Robin)]

Yes I had thought of that but did not want to buy something else when I had 5L of it sitting in cupboard. As it happens the surface feels the same afterwards, did not lift the grain like some sealers.
It could be because this one is a thick gel.

[mikep]

That hard surface is from how it’s made, there’s more pressure on the outside surfaces of the material when it goes through the press. There is also “tempered hardboard” which has very high density, a very strong surface and is very stiff - but I’ve only ever seen it in ¼" thickness.