# sealing MDF?



## oldnovice (Mar 7, 2009)

*What if anything will protect MDF? *

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


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## renners (Apr 9, 2010)

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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## RonInOhio (Jul 23, 2010)

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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## MarceloRibeiro (Dec 5, 2012)

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


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## kizerpea (Dec 2, 2011)

MDO its for outdoor projects signs an such….


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## wapakfred (Jul 29, 2011)

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.


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## bluekingfisher (Mar 30, 2010)

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


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## bondogaposis (Dec 18, 2011)

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


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## Earlextech (Jan 13, 2011)

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.


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## blackcherry (Dec 7, 2007)

Sand & Sealer works great !!!


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## DS (Oct 10, 2011)

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.)


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## blackcherry (Dec 7, 2007)

High end finish on MDF that's funny!


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## oldnovice (Mar 7, 2009)

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!


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## NiteWalker (May 7, 2011)

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


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## DS (Oct 10, 2011)

*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.


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## DS (Oct 10, 2011)

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.


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## bobasaurus (Sep 6, 2009)

I use a whole lots of polyurethane. Soaks up a ton the first few coats, then adheres and builds normally.


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## blackcherry (Dec 7, 2007)

DS251 I sure you could put a high end finish on just about any surface if its worth it…but to me MDF would not be worth the time and effort. We mostly used mdf for our work surface in the shop each yr replacing them with new and applying a few coats of sand and sealer and a coat of paste wax. I myself refuse all and any mdf jobs period the stuff is just worthless !


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## Rick Dennington (Aug 27, 2009)

Five coats of polyeurthane on my bench tops….2 coats on my jigs…...


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## oldnovice (Mar 7, 2009)

*DS251* my spoil board is bolted to the table with brass lots an Tee nuts on the bottom side of the table and are recessed 3/8" from the top surface. The top has been flattened and is as smooth as the original surface or the MDF and that's how I would like to keep it. The MDF was 1" thick and only cost $12.

I did not use a fly cutter but a cutter as they then to unbalance the spindle at 12K RPM.
Adding another spoil board on top of the one I have will reduce the Z height.


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## Knothead62 (Apr 17, 2010)

I have a bench made of inexpensive/cheap MDF or particle board. Made it several years ago and just used cheap white paint. It's looking cruddy and I'm thinking about sanding it down or replacing it, whichevery is easiest. I'm not only cheap but lazy, too.


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## roman (Sep 28, 2007)

almost anything will seal MDF except water : ) , left over paint, varnish, lacquer, and an endless list. I prefer primer of some sort, easy to sand, followed by your own poison.

for those who think MDF isn't used in high end finishing, you don't get out much : )) but i do love frugality.


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## RonInOhio (Jul 23, 2010)

I have also heard a lot of people cut a piece of hardboard to the size of the tabletop. Then attach 
trim pieces around the perimeter of the table that are raised 1/8" or whatever the thickness of the 
hardboard is above the tabletop . Then just lay the hardboard down on top of the MDF.

The trim keeps it in-place.
Hardboard is super flat and smooth and when it gets bad , just pull it out and put in another piece
of hardboard or possibly flip it over.


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## DS (Oct 10, 2011)

It is a bit of a side topic, but, I have a client who wants a High Gloss Grey/Blue lacquered credenza (With silver accents). The structure will be solid hardwood, but the panels will be MDF.

Why would I use an expensive veneer plywood only to completely hide it with an opaque finish? 
MDF has its place.

It also works well for CNC router spoil boards… ;-D


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## DS (Oct 10, 2011)

BTW, they do make balanced "fly cutters" for CNC machines. There are also "planer" or "bottom cutting" router bits that work well too.

I have this one.


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## dhazelton (Feb 11, 2012)

Oil on MDF? I would think it would absorb and swell up the sawdusty stuff that makes up MDF. I would use latex paint, whatever is laying around, the cheaper the better,


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## oldnovice (Mar 7, 2009)

That's similar to what I used but what I used in the model shop which is more like this

*I think these may both be called fly cutters just not the term I was used to seeing for the cutter in you picture above!*


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