sealing MDF?

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Forum topic by oldnovice posted 12-06-2012 07:56 AM 15908 views 2 times favorited 26 replies Add to Favorites Watch
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6764 posts in 3332 days

12-06-2012 07:56 AM

Topic tags/keywords: finishing mdf sealing

What if anything will protect MDF?

My first inclination is shellac but I don’t really know …..

-- "I never met a board I didn't like!"

26 replies so far

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404 - Not Found

2544 posts in 2934 days

#1 posted 12-06-2012 10:41 AM

What’s it for oldnovice?

If this is going to get wet, you’d be as well using moisture resistant mdf. If it’s just for workshop fixtures and fittings you’d be ok with shellac and maybe even a topcoat depending on how far you want to go.
Paint is another option – Zinsser B·I·N as recommended by LJ’s is great for priming.

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721 posts in 2829 days

#2 posted 12-06-2012 11:04 AM

I threw together a utility bench a few years ago . The top is MDF. The tip I came across was to brush a few coats of wood glue on the surface. I know you are probably thinking. Wood glue ? It dries and forms a shiny transparent shield (much like poly) and that protects the mdf from water or moisture. So far it still looks great .

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4 posts in 1963 days

#3 posted 12-06-2012 11:16 AM

It depends on what use it will be assigned for….if your´re doing a kitchen cabinet for example, it´ll be nice to seal the pieces that could wet on a leaking accident…the cabinet base and the columns could be a lamineted MDF with border tape even the faces that will “glue” toghether…so the columns don´t absorve water from base surface…
I use to seal these bordes with contact glue….2 coats

-- "Everyday we make it, we try to make it the best we can" Mr. Jack Daniel

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774 posts in 2332 days

#4 posted 12-06-2012 12:48 PM

MDO its for outdoor projects signs an such….


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Fred Hargis

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#5 posted 12-06-2012 01:02 PM

What are you trying to seal it from? A lot of things won’t be too hard, others impossible. I have an assembly table that is now 6 years old, made from MDF. The only thing I’ve ever put on it was a mixture of beeswax/BLO/turpentine. The only damage it has is scrapes/scratches from the work I do on it.

-- Our village hasn't lost it's idiot, he was elected to congress.

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1250 posts in 2944 days

#6 posted 12-06-2012 01:02 PM

There are commercial sealers avaialbale, primarily to prime the surfaces if you are intending to paint.

If, from the previous replies, you are looking at sealing the edges (known as sizing) thinned down PVA (with water) will do a pretty good job. One coat should be enough but two maybe required depending on how tight you need the sealing to be. Even poly take several coats before an edge is suitable sealed. Using glue will dry out quickly too.

Good luck

-- No one plans to fail, they just, just fail to plan

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4682 posts in 2316 days

#7 posted 12-06-2012 01:28 PM

I use spar varnish thinned 50/50 w/ mineral spirits. It really drinks it in and seals up nice.

-- Bondo Gaposis

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1160 posts in 2655 days

#8 posted 12-06-2012 01:37 PM

If you’re asking about the edges, it’s called gluesize. 50/50 wood glue and water, brush it on heavy, let it dry and sand it smooth. Any old sealer will protect the top, it’s the edges that are a problem.

-- Sam Hamory - The project is never finished until its "Finished"!

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3337 posts in 3788 days

#9 posted 12-06-2012 03:16 PM

Sand & Sealer works great !!!

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2894 posts in 2385 days

#10 posted 12-06-2012 04:00 PM

Depending on what I have on hand, I use either Vinyl Sanding Sealer, or Lacquer Primer.
To make it a durable finish you’d need a top coat of either Lacquer, or Paint.
(I’m assuming this is a utilitarian application and not a high-end finish.)

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

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3337 posts in 3788 days

#11 posted 12-06-2012 04:11 PM

High end finish on MDF that’s funny!

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6764 posts in 3332 days

#12 posted 12-06-2012 06:59 PM

I wouldn’t normally be concerned about sealing it but with the rain we have in the last few days everything in my garage feels “clammy”!

The MDF in question is the spoil board on my CNC and I don’t want it to “grow” fuzz and get out of flat. It took three passes to get it flat “flat as a board” and remove about 0.045” off the top surface! I would like to keep it that flat at for a little while after all it is a spoil board and, as the name implies, it is supposed to get spoiled.

I thank all that responded and since I have the primer I will use that and see what happens!

-- "I never met a board I didn't like!"

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2736 posts in 2541 days

#13 posted 12-06-2012 07:15 PM

Pat warner uses danish oil on his MDF router table and it holds up extremely well.

-- He who dies with the most tools... dies with the emptiest wallet.

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2894 posts in 2385 days

#14 posted 12-06-2012 09:32 PM

blackcherry: Actually, you’d be surprised how you can get a high-end finish to take to MDF. I can get a pretty high gloss on a lacquered top made from MDF. Smooooth and flat and shined to a mirror finish.

oldnovice: I assume you don’t have a vacuum sucking through the mdf to hold your parts. If you did, I’d say to just edgeband or seal the edges with glue. That might still be a good idea to limit moisture absorption.

If this were my machine, I’d leave the face raw. It’s called a spoil board for a good reason— It will get spoiled (ruined) with use. Don’t spend too much time on it. It is actually to your advantage to have a bit of friction between it and your parts. If it’s too slick they won’t hold still as well.

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

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2894 posts in 2385 days

#15 posted 12-06-2012 10:07 PM

If you bolted your spoil board to the table, be sure to inset the bolt heads so you have room to fly cut your board a ways before needing to replace the spoil board. If you notice it is getting rough or “fuzzy”, as you call it, you can fly cut it again with little effort.
(I presume you have a fly cutter and a spoil board cutting program made by now.)

It might be a good idea to have a dedicated spoil board which has finish on it and then a disposable spoil board on top of that which can be replaced often—just a thought.

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

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