Preserving MDF

What are you going to do with the final product? Paint it? If so, that would probably do the trick.

-- Beer, Beer, Thank God for Beer. It's my way of keeping my mind fresh and clear...

Make the torsion box then coat the outside of the box. I made an off feed table from MDF and put laminate on the top and backer laminate on the bottom. I had it stored in an unheated garage for 5 years and one year the garage flooded in winter. The torsion box was off the ground but it did stay as flat as the day it was made. Except for the laminate there was no finish on the other exposed sides.

-- Few folks really know how to maximize the potential of their tools!

What should I coat the outside with? I may eventually paint it, but right now, I’m just concerned in preventing the MDF from absorbing moisture.

I would just shellac the heack out of it. If ya want, apply a couple coat of a waterbased poly. All ya really want to do is seal the mdf. If you really want a bullet-proof surface, use the exterior grade MDF. I used a product (Extira) for some trim. It is tough and heavy. Very stable.

-- bill@magraphics.us

i typically use an exterior grade poly, although I agree shellac should work just fine as well.

-- There is nothing like the sound of a well tuned hand plane. - http://timetestedtools.wordpress.com (timetestedtools at hotmail dot c0m)

MrRon—Shellac. Remember that shellac is a material you can use under virtually any other finish.

—Gerry

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

I would also say shellac. I have a couple of steam bending forms that are made of mdf and I sealed them with shellac. They are about 6 years old and look like the day I built them.

-- Tim-- http://www.tmuli.com

Thin some wood glue with water and apply that to the edged because they will soak up a lot of finish. As for the large faces I use 50/50 poly/mineral spirits just wiped on and let soak in for 10 minutes and remove the excess. Works great for my MDF jigs and never had a problem.

-- Chief Petty Officer USN(RET) 1991-2011

Hey Ron,
Shellac is always a win win. Edges are the biggest offenders, but best to do it all. Don’t use any water based poly or latex paint.

I have built three CNC machines and learned a lot. You will probably use a spoil board on the bed, and then you level it with the router. It will then be flat and level as far as the router is concerned, so you will be able to recover a slight warping/bowing.

Rick L mentioned a technique above that I really like. Coat both sides of MDF with plastic laminate (Formica). I just used white glue and then iron-on maple edge banding – looks great. This forms a mini torsion box (two skins separated by a membrane). It forms an amazingly strong panel for use in gantry walls and stuff like that. And waterproof. Give it a try.

Good luck and keep us informed,
Steve

-- -- I'm no rocket surgeon

Thanks for posting this. I built a TS outfeed table with an MDF top and never thought about sealing it. I did put edge banding (pine) on it, biscuit joing and glued. But there are still edges on my mitre slots. Time to bust out the shellac again. Does it need to be de-waxed or is it better to leave that in?

-- Don, Royersford, PA

Another thanks here as well. I am +80% complete on my first MDF mortising jig and was wondering about sealing/finishing as well. 8-)

-- HorizontalMike -- "Woodpeckers understand..."

Thanks all for your time and great advise. Way back before the fancy finishes were invented, shellac was the finish of choice. There wasn’t much else available other than paint and whitewash. I guess I got side tracked along the way.

Maybe consider MDO which is what is used for outdoor traffic signs.
Very sturdy, already water proof and extremely stable.
Sounds like a good option to me.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

I use an exterior grade MDF called Extira (?). A coat or two of shellac is a winner. This stuff (the Extira) is tough, water proof, and heavy. Look it up.http://www.extira.com/pageBuild.asp?PageID=B_extiravmdf_e

Bill

-- bill@magraphics.us

DS221: The torsion box is already built. MDO costs about 2-1/2x the cost of MDF. I used 3 sheets of MDF. 3/4” MDO costs around $75 a sheet vs $30 for MDF.