# Finishing MDF edges



## Involute

Is there a product or technique which can be applied to the cut edges of MDF that will give them the same texture and appearance, after painting, of the uncut painted surfaces? The edges always stand out, no matter how much I sand and prime them. Thanks.


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## Rashed

You can seal them with a sanding sealer or use a dry wall mud and sand in both cases before priming.


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## Fred Hargis

Another option would be "glue size", simply diluted PVA (4 parts water is common) and rub it on the edge. Let dry, and then smooth.


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## Gilgaron

I've used the dry wall mud and it works pretty well, just try to make the edge good beforehand, because if it is too thick it can chip after it is painted. Spread it with a nice putty knife.


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## Sarge240

I've used edge banding, it's easier and it's getting painted, so it won't look odd. Some may not like that, but I've done it twice, and it looks normal.


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## Steve Neul

If the edges are square I second using edge banding tape. They make a paper tape that is the same material as the face of the mdf sheet for this purpose. If you have a lot of it to do it's too big of task without a edgebander though. If you have a molded edge then the only solution is to seal the edges so it doesn't soak up so much finish. You could use glue, sanding sealer or just primer if you are painting it.


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## Marv

High build up automotive primer is the quickest/easiest way I have found to seal MDF edges for paint.


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## Leo G

Any high quality hi build primer will do. You have to apply and sand and apply again. I use a professional product, MLC Clawlock, which is a post catalyzed hi build primer. One heavy coat, let dry, sand hard and then coat everything else 2 coats. That gives 3 coats on the edge and 2 everywhere else. This will take care of most everything up to birch grain fill. It won't take care of filling oak grain. It is a spray only product.


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## Involute

After going over all the replies here and browsing for other opinions, I decided to test the products I'd most likely use. I won't go into why I chose what I chose, or why I excluded others, except to say my priorities are speed, simplicity, and quality. If I can achieve acceptable results with one coat of something, I'll prefer that over a superior result with two coats of something else. So, this test was intended to address my own personal needs and wasn't intended to be a comprehensive test of all possible solutions. Despite the non-comprehensiveness, I thought I'd document and share my results since others may find them useful.

I began by cutting six 3" x 5" x .5" pieces ("samples") from the same sheet of MDF with a Freud 10", 3/32, 60-tooth, carbide-tipped, circular blade. All samples received an initial machine sanding with 220 grit paper and then were blown clean. 










Sample 1 was the control and was sprayed with one coat of gray Rustoleum Automobile Primer. The remaining samples were treated as follows, lightly hand sanded with 220 grit paper, then primed the same way as sample 1. All of these samples received a single coat of the associated sealer (68 deg. F, 50% rel. humidity):

Sample 2: Min Wax Wood Hardener, allowed to dry for 8 hours (at least four is the recommended dry time).

Sample 3: General Finishes Enduro Sanding Sealer, allowed to dry for 1.5 hours (at least one hour recommended). Note that the manufacturer recommends spray application but I brushed it on (no sprayer, and I'd be too lazy to use it if I had one).

Sample 4: Behlen Top Coat Lacquer and Sanding Sealer, allowed to dry for 1.5 hours (at least 30 minutes recommended).

Sample 5: "glue sizing" using 1 part PVA glue (Titebond Original Wood Glue) to 5 parts water (by weight).

Sample 6: "glue sizing" using 1 part PVA glue (Titebond Original Wood Glue) to 10 parts water (by weight).

Here you can see the samples drying after sealing, 1 - 6, left-to-right:










And here you can see the results after priming and drying:










With multiple coats, all of these sealers might perform well, but, as I said, I'm lazy, so I'll be going with the Enduro which clearly outperformed the others in this test.


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