What to use to seal MDF?

[Greg Koch]

From the thread on Forrest blades, this bit of information was interesting...http://www.design-technology.org/mdf.htm

I just bought a Rockler offset router table, made of solid MDF, that has exposed edges. http://www.rockler.com/gallery.cfm?Offerings_ID=16372&TabSelect=Details

So...what would you guys recommend I use to seal the edges? Would Poly work? I really don't want to paint it.

[Alan DuBoff]

Greg, I used some Thompson's Waterproofing recentely on some mdf I used for a sheet of flooring in a small area. Seemed to work fine, not sure if that was the right stuff to use or not, but that's what a friend told me he uses, so I thought I would give it a try.

[Tom Araya]

Many recipes to seal MDF edges.

1. Sanding sealer
2. Yellow wood glue diluted with water
3. Minwax wood hardener
4. High build primer
5. Kitchen sink :p

[Jim Cunningham]

I have used sanding sealer several times and it worked fine. I have used lacquer based and mineral spirits based sanding sealer. My experience has been trhat the mineral spirits based product is useless. Lacquer based goes on better and dries in a few minutes which means you can recoat it almost immediately

Jim

[Cliff Rohrabacher]

Seal it against what?
Normal HVAC controlled humidity or Really high celler type humidity? It matters quite a lot what you have to seal it against.

If you must seal against high humididity conditions use a penetrating epoxy or a penetrating two part urethane. They aren't cheap but they will seal it. They will also provide a really tough surface.

[Alden Miller]

I have some MDF edges I need to seal. I have heard of using sizing to seal them but was wondering about a 1 lb cut of shellac.

After all, I use that for a sealer on cherry or oak before moving on, why wouldn't it work well for MDF? It shouldn't raise the fuzz. It's a universal undercoat...

I think I'll give it a try unless someone says otherwise.

-Alden

[Greg Koch]

Seal it against what?

Cliff....the Urea Formaldehyde that is always "leaking" is what I want to seal against:

"Urea formaldehyde is always being slowly released from the surface of MDF. When painting it is good idea to coat the whole of the product in order to seal in the urea formaldehyde. Wax and oil finishes may be used as finishes but they are less effective at sealing in the urea formaldehyde"

[Dennis McDonaugh]

I have used two coats of polyurathane followed by a couple coats of oil based primer. Works pretty well. You can sand it smooth so a gloss topcoat looks good.

[chester stidham]

try this mix yellow wood glue 50 = 50 with water and brush it on the edge of the MDF this well seal it them use poly if you try just using poly it well take a number of coats to seal it got this idea from wood mag. and it works well also if the bottom is not lamanated use tung oil three coats well do.:rolleyes:

[Rick Schubert]

Somewhere recently I read to seal in the formaldehyde outgassing from MDF use two coats of full strength oil-based polyurathane. Water-based will not do it.

Rick

[Mark Hulette]

Not to hijack the thread but what prep work do you do for painting MDF? I've read to sand to a higher grit but wondered if there is anything else or other tips.

Thanks!

[Mark Pruitt]

From the thread on Forrest blades, this bit of information was interesting...http://www.design-technology.org/mdf.htm

I just bought a Rockler offset router table, made of solid MDF, that has exposed edges. http://www.rockler.com/gallery.cfm?Offerings_ID=16372&TabSelect=Details

So...what would you guys recommend I use to seal the edges? Would Poly work? I really don't want to paint it.

I've been kind of lost on this entire thread. Could someone tell me why I would NEED to apply a finish of any variety to MDF? What are the risks of leaving it unfinished? It's not like a board, where you would want to control the movement of air in and out of the pores--there are no pores. If there is a constant emission of urea formaldahyde that poses a health risk, what does that say about the stores that stock piles and piles of the stuff? Are they putting their employees and customers at risk? If not, then why am I at risk for having a 36x26x20 cabinet made of MDF sitting in my shop unfinished?

You have my curiosity up on this one!

[Howard Acheson]

There is nothing better than a couple of coats of oil based varnish, poly varnish or oil based paint. It's not a big deal which you use.

You can also use a couple of coats of a dewaxed shellac (dewaxed shellac is much more water vapor resistant then natural shellac).

[Al Willits]

I have a friend who suggests Tung oil and Valspar mixed about 50-50, says he uses that on woods that are outside also.
Haven't tried it, but sounds good....

Al

[Dennis McDonaugh]

I've been kind of lost on this entire thread. Could someone tell me why I would NEED to apply a finish of any variety to MDF? What are the risks of leaving it unfinished? It's not like a board, where you would want to control the movement of air in and out of the pores--there are no pores. If there is a constant emission of urea formaldahyde that poses a health risk, what does that say about the stores that stock piles and piles of the stuff? Are they putting their employees and customers at risk? If not, then why am I at risk for having a 36x26x20 cabinet made of MDF sitting in my shop unfinished?

You have my curiosity up on this one!

Mark, I seal it because the edges are not very durable.

[pat warner]

GF poly/tung x 3 days + wax on this surface (http://patwarner.com/images/rt_topgf.jpg). Will add substantially to life, service and slip to the work.
Routers (http://patwarner.com/)

[Steve Clardy]

A lot of the manufacturers are supposed to be phasing out formaldehyde.

[glenn bradley]

I have a work surface of MDF with exposed edges. Two coats of poly on the surface and repeated coats on the edges till they stopped soaking it up. Its been a year, no problems. One caution; take it slow, the edges will soak up too much and swell if you allow it.

[Ted Jay]

Laminate it!!!

[Byron Trantham]

Laminate it!!!

There you go!:D

[Greg Koch]

The top and bottom of the table are laminated...it's the edges that I want to seal. The edges are all round (half rounded top and bottom) and so I would not know how to laminate them....

http://www.rockler.com/gallery.cfm?Offerings_ID=16372&TabSelect=Details

[Steve Clardy]

Laminate will bend around those corners.

[Greg Koch]

I'll try to take some pics of the top, cause to me it would be like trying to laminate an egg! Beyond me...

[Alan Turner]

At the suggestion of Mark Singer, and perhpas others, I use shellac. 2 or 3 coats is fine. I have done this on my table saw sleds without problem.

[Alan Tolchinsky]

I've read in several places about using dry wall compound for this. You just apply it and sand. I haven't done it myself but it seems like a good method and as I said suggested by several sources.

[Steve Clardy]

I'll try to take some pics of the top, cause to me it would be like trying to laminate an egg! Beyond me...

So the edges are rounded over, top and bottom, as well as the corners rounded off?

[Greg Koch]

Exactly, Steve. That's why I never considered a laminate edging. Only way I could seal it is with some kind of "application of a liquid" that I could imagine. But what...was the question.

This is not the best pic, but you can see that the bottom of the T-rail is not flush with the edge of the table... This is because the edge rounds outward and then curves back under to where it meets with the bottom of the table.

Looks like Shellac or Poly is the way?

[Steve Clardy]

Ok. Laminate is out. I understand now.
2-3 coats water base poly, or shellac, whichever you have on hand.

[Mark Pruitt]

I'm attaching a MSDS that I found for MDF......Section 7 has a brief statement about vapors and ventilation. This was news to me.

[Bruce Wrenn]

In my shop MDF gets a white/ yellow mold growth on it during periods of HIGH humidity. To seal edges prior to painting, I use a runny coat of drywall compound, spread with finger. After it dries, sand edge and paint. For primer, I use Wal-Mart's spray paint that is $0.97 per can It dries in 15 minutes. Paint (also $0.97) dries in 15 minutes, very similar to Krylon, only a lot cheaper Limited number of colors though.

[Todd Burch]

I use ClawLock by ML Campbell. Search this forum ("clawlock") for multiple threads on this same subject.

Todd