# Sealing MDF



## Eric Grum (Oct 14, 2013)

I've never used MDF before. I'm just setting up a Freud router table, which has a laminate covered MDF table with raw edges. A label on the bottom of the table top warns to seal the bare MDF in circumstances of high humidity and/or low temperatures. Out of an abundance of caution I'd prefer to seal the edges even though the table is unlikely to be exposed to the environments warned against. I'm wondering what I should use to seal the edges. Some sort of varathane is what I'm thinking. Does it matter if it is water based, or not?
Thanks!


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## fire65 (Oct 29, 2008)

Why not just add some solid wood banding to it? Lots of our home made router tables do this. It will also add some protection to keep from chipping the edges.


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## MAFoElffen (Jun 8, 2012)

fire65 said:


> Why not just add some solid wood banding to it? Lots of our home made router tables do this. It will also add some protection to keep from chipping the edges.


fire65-
Because, unless you are liberal with the adhesives, edge banding will not "seal" the edges... Alongside that, most edge banding tape is iron-on which is far from "sealing" it. Most commercial edge banding machines are a hot glue, which is applied just enough to stick... not to seal it. (Excess glue takes time to clean up and slows down production) Like you said, good chip protection and prolongs life, but in itself, does not seal the edges.

Eric-
You could just use a seal coat finish. We use MDF in a machine table because the surfaces across it's thickness are parallel to each other and the surfaces are consistently flat. Those qualities are important in a machine table. If you do a paint-out or other finishes (without sealing first), then if it is thick in one spot or you overdo it with too much at one time... then besides the MDF soaking in more and risking swelling, the thick finish itself risks it not being that flat anymore from the inconsistent thickness of the finish. (If you were real picking about that minute amount... talking brush-on application.)

Even in a paint-out, with MDF, you seal it with a primer or some other type of sealer first. Sealing it will a seal coat would be the best option for that in that application. That would seal the material without adding anything to it's thickness. If any finish was applied after being sealed with a seal coat or primer, finished over that sealer, then it would take less and be more consistent, without risk of that finish soaking in too much. 

Do not use paste wax. A lot of times paste wax on MDF tends to soften it's surface and ends up making it's surface somewhat gummy. The material will then stick to it. Not all the time; but often enough for me not to do that again.

Unfinished MDF has a tendency to soak in any moisture very well. That is why gluing is so easy with mdf. Even if you think you live in a low humidity area... sealing = good protection, material slides better, reducing drag and causes the table to wear less. It doesn't hurt anything to seal it and be safe.

Did you call the number of Freud customer support in the docs that came with the table? What did they recommend?


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## walowan (Jan 21, 2011)

I would use rattle can spray paint... coat, sand, recoat sand several times. Make sure to let it dry completley between coats. There are many other options but this seems best for a one time non production fix. Just about anything will make MDF end grain expand a bit.....so make sure not to use anything water based.


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## fire65 (Oct 29, 2008)

I do not mean tape, I mean 3/4" solid wood. It must be ok, I been putting solid oak on counter top fronts for many years.


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## geoff_s (Apr 14, 2012)

I usually give MDF a coat of polyurethane unless there's some other covering going on it e.g. laminex/formica or some other paint.
On my router table, the exposed MDF edges have a coat of polyurethane which will be covered up with a solid timber edge.
Today I'm cutting some kitchen cupboard doors out of MDF. They will have a coat of primer and then two coats of semi gloss enamel. In my last kitchen, this door treatment lasted 10 years or more.


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## tje (Apr 29, 2013)

Try thin CA. But use an accelerator for cure


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## rwbaker (Feb 25, 2010)

use shellac - it is alcohol based and I have used it on MDF for years as a sealant. Just brush on until it stops drinking. Do not use sprays as they are meant to dry very quickly. The Urethane family will work as will oil based enamels. Anything tha is non-water based should work.

Good Luck - Baker


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## harrysin (Jan 15, 2007)

I'm with Richard on this, I always use Shellac if I don't use wood edging strip.


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## Eric Grum (Oct 14, 2013)

*Sewing question/answers*

Thanks for those answers, guys. A common thread seems to be -no water based sealers. Pretty well what I was looking for. 

The edge of this table top is contoured, and the corners rounded, so edging would not be applicable. Also, the top and bottom surfaces of the table are laminated, so there is no need to seal them. 

Thanks again.


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## Slappy (Nov 2, 2013)

Eric Grum said:


> Thanks for those answers, guys. A common thread seems to be -no water based sealers. Pretty well what I was looking for.
> 
> The edge of this table top is contoured, and the corners rounded, so edging would not be applicable. Also, the top and bottom surfaces of the table are laminated, so there is no need to seal them.
> 
> Thanks again.


 always use Shellac , thin it with alcohol , keep applying while it's still wet till it drinks no more , let it cure your done . the more it soaks in the better as this hardens the MDF fibers & makes them resistant to bumps that will break down the edges , remember to seal the router base cut out edges as well . you don't want the cut-out area to swell there Too ! :blink:


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## MAFoElffen (Jun 8, 2012)

Slappy said:


> always use Shellac , thin it with alcohol , keep applying while it's still wet till it drinks no more , let it cure your done . the more it soaks in the better as this hardens the MDF fibers & makes them resistant to bumps that will break down the edges , remember to seal the router base cut out edges as well . you don't want the cut-out area to swell there Too ! :blink:


...which _is_ the recipe for making diy "seal coat"... I think I remember the ratio to premixed shellac at being 1 part shellac to 1 part alcohol. Remember to use denatured alcohol. 

I mix up and use seal coat a lot... on various materials.

I buy Shellac flakes and just mix up what I need. My usual shellac recipe for brush-on is 1/2 lb. flakes to 1/4 lb. alcohol. To make a seal coat, I do 1/2 lb. flakes to at least 1/2 -3/4 lb. alcohol.

It should dry just below the surface and not leave a hard surface above it. What you are trying to achieve with a seal coat is to seal the material... but have enough of the surface left to accept a stain and a finish coat. It's important while doing a sealcoat, that if you see that after a resonable sort time that it sin't soaking in... like puddling on the surface... to wipe that excess off.

I used to use wood conditioner, but found this works a lot better and I get better results.

I suggest you play with it and practice on scrap before coming up with your solution that you are going be happy with and to apply to your table. Too much alcohol of an inferior quality or the wrong type... soaked... and it _will_ swell MDF. That's why is important you use denatured alcohol (about 93%). Some do 200 proof, but I think that is just overkill and adds cost.

I've also done this with thinned down "wood glue"... That is probably considerred the DIY to DIY... but sometimes you do with what you have.


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## Eric Grum (Oct 14, 2013)

*Shellac sealing*

10-4. Sounds like a plan. Thanks for that!


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## TinyTiger (Mar 9, 2013)

I also use shellac (several coats).


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## Slappy (Nov 2, 2013)

MAFoElffen said:


> ...which _is_ the recipe for making diy "seal coat"... I think I remember the ratio to premixed shellac at being 1 part shellac to 1 part alcohol. Remember to use denatured alcohol.
> 
> I mix up and use seal coat a lot... on various materials.
> 
> ...


+1
but stay away from watered down wood glue on the edges as tends gets soft in high humidity & water will pass thru it . I wouldn't put any water based on raw MDF at any time , the edges are the worst as the top & bottom of MDF has a sealer on it that is applied to keep it from sticking to presses that compress the stuff 

I plan on building a large router table here soon & will seal all the edges with Shellac & laminate the top & bottom surfaces as well . 
blue painter tape the surface around the edges to keep the laminate free from Shellac .


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## Eric Grum (Oct 14, 2013)

Sounds good. Thanks guys.


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