Sealing MDF Edges

drywall compound. its messy but it works. make it a little watery, slather it on with a finger, let it dry, buff it smooth. got it from FWW, i dont remember which issue.

-- "Democracy is by far the worst system of government. Except all the others that have been tried." ~ Winston Churchill

I thin some solvent base or water base wood filler and spackle it on all the edges (very time consuming). You don’t have to put it on thick, just enough to fill. Or I use a thickened type of sealer ( something compatible with your top coat paint). Once both methods are dry (using either-or), sand smooth and paint(seal) the entire surface. Let dry, sand, and refill any areas that need it again. Now move to the first top coat. Check for imperfections, fill and sand, then apply finale top coat. I use Lacquer, and I use this method on high gloss finishes. Of coarse there is wet sanding and buffing in that process also. Painting MDF to a flawless finish takes time and patience and a lot of filler or numerous base coats and sanding. Good luck. Bob

-- Built in a Barn Bob

More, more, and then some more. I spray 90% of my finishes. When I’m painting mdf I always go around the pc giving the edges a good coat (sealer or primer) first and then spray the surfaces and then giving the edge 1 more shot. (Basiclly giving the edges two coats per setting) After the first coat I look for any pitting or open pores and sometimes they need to be filled before the second coat. Then I sand the edge real good and then do a second coat the same way. Usually 2 good coats in this manner seal the edges pretty good. I finish with at least 2 – 3 coats of the final finish depending on how it’s looking and the product The higher the quality of your finish will determine if you need more edge work before your final coats.

I have tried filling the edges first but I end up sanding it all off before I paint anyway, maybe it does help seal it though, or maybe I just shouldn’t sand it so much. lol
But it’s going to depend on the product your using and how you use it. The variables such as how thin it’s mixed, how much solids are in it, how heavy you spray, etc. You just have to get a feel for what it takes to make sure the edges are ready using the method you use.

to be honest, it wasnt worth the hassle for me….i did the trim in my kitchen like that, and then swore i’d stay away from mdf and just use poplar from now on, to hell with the cost. thats just me tho. i love to cut, love to install…hate hate HATE to finish.

-- "Democracy is by far the worst system of government. Except all the others that have been tried." ~ Winston Churchill

I have not had that problem at all with MDF. Could be that my projects are finished with conversion varnish or lacquer and not paint.

-- http://www.woodsongsfurniture.com

I second what sean said. 5 minute hotmud is what I use and it works pretty good

-- Childress Woodworks

A painter I know showed me how to seal the edges of plywood and mdf with latex painters caulk if you are painting it.

-- Dan, Sterling Alaska, http://sullcon.homestead.com/ Before you criticise some one, walk a mile in their shoes...then you will be a mile away and you have their shoes!

Have you tried using glue sizing? Basically watered down glue. Sand your edges really well, put the sizing on and let it dry then lightly sand and add another coat and let dry and sand again. You should now be ready to finish.

I sealed the MDF on the project below using this process and it is 90% MDF.

-- //FC - Round Rock, TX - "Experience is what you get just after you need it"

cool shelf

-- Dan, Sterling Alaska, http://sullcon.homestead.com/ Before you criticise some one, walk a mile in their shoes...then you will be a mile away and you have their shoes!

yes, maybe painting is good , (this is not in line of my business , i just work at plywood manufacture in china)

-- Everything is possible!

I read in one of my wood rags that this guy uses water putty (same as plumbers putty?)to seal it but he was gonna spray paint his project so not sure if that will work for you.

-- Pie

I’ve used the drywall mud method. Definitely works but as stated very messy. Next time I’ll try the glue sizing method using watered-down yellow glue.

-- You're a unique and special person, just like everyone else.

This is what I’ve used, you can mix as little or as much as you want, Durham’s Putty, this is what we used in woodshop at school. http://www.waterputty.com/

-- Only the Shadow knows....................

Durham’s Rock Hard. Great stuff. Works well to seal MDF edges.
Spackle, right out of the can, is faster for edges, IMO.

-- Gene

there are several sealants made…but the best i have ever found is using BIN primer sealer…it is a white shellac base, several coats and give it a good scuff sand with some 320 and you are good to go…works well…as well shellac in about a 3 lb cut does well…

SHELLAC is awesome for sealing mdf and easy to apply. I have used all kinds of fillers and muds and pastes and other junk I had heard of but shellac is hands down the best solution. In fact I’m about to use it on some cabinet doors I’m building for a client. GOOD LUCK!!!!!

-- Jed,Ala,jmwoodworks057.com

OK, I have to offer another solution. We do a lot of MDF doors and drawer fronts that we process on the CNC to look like paneled doors. These are always used on painted cabinets. We sand the MDF down with 150 grit sandpaper and then use 400 grit Abranet on all edges and front and back. Our finishing department then sprays them with a sanding sealer. The mdf is then sanded again with 220 grit sandpaper and a primer put on. Then a coat of paint and a coat of lacquer. We almost never have a problem with the edges after this process. I have seen doors that are over 5 years old and the edges still look good.
Hope this helps.

-- Jerry--A man can never have enough tools or clamps

sIKE – I made the same shelf for my nephew. He loves it. I used glue sizing too and a couple coats of bright spray enamel. Seemed to work well, not too gritty after sanding before the first coat of paint.

-- If you think healthcare is expensive now, wait until it's free! PJ O'Rourke

boy am i coming into this late. But it was on the front page so I’ll toss my two cents in. Best thing is auto body compound called Icing. The stuff is great. Its just like drywall compound but you add an activator to a little bit of it then spread it on. Benefit is it drys in 15 minutes. Sand. Paint. Done. I get a 3in diameter 10 inch long tube of it for 15 bucks. More expensive but much nicer since you don’t have to wait as long nor make as big a mess.

-- Jerry Langfitt, Canton, OH

I just recently completed an MDF shelving system for a client. I applied a wood stabilzer/hardner made for rotted wood repairs. It sealed well, sanded good and did in fact harden the edges to help reduce chipping and dings. Finished with SW White Opex lacquer with no problems.

Glue sizing light sanding then thiner water base wood filler light sanding then touch up and paint.

-- Jim from Heirloom Woodshop Southern Oregon

I have used watered down wood glue on the edges of MDF and I also seal my board ends with this solution to prevent checking.

BONDO! A trhin coat of bondo, well sanded will do the trick. A 1” stripe of hardener to a golf ball size glob of putty is about the right proportion.
Good luck Kimball