Sealing/protecting MDF

[toni_k]

Hi all,

I was hoping someone can offer some advice on best way to seal/protect MDF.

I'm making a router table and I've laminated 2 pieces of 18mm MDF for the table top. I was initially planning to just get some spray-on varnish and give it couple of coats but then I read somewhere that there are actually primers/sealers designed specifically for MDF. Do you think this is required or can I just coat it with varnish on raw MDF? The MDF is just standard 18mm stuff from Bunnings.

Thank you,
Toni

[GraemeCook]

Hi Toni

MDF is just a high grade chipboard, aka wheatbix. Anything to make it tougher is worthwhile.

I would use wipe on polyurethane - WOP - poly because it gives a tough finish and wipe-on because it is thinner and penetrates a little and gets some of the finish below the surface. You can buy WOP or make your own - just mix equal volumes of polyurethane (eg Estapol) and turps. My technique is:

1. Paint WOP onto edge-grain, top, bottom and edge-grain again (it soaks in really quick) - brush or small roller.
2. Wait ten minutes and, with clean rag, rub off WOP - this fills pores.
3. Next day, lightly sand and repeat steps 1 & 2.
4. Ditto - next day. Edge-grain should now be full of poly - visibly.
5. Next day. Dip 400 grit sandpaper into WOP and wet sand.
6. Repeat next day.
7. Surface should be very glossy and as close to bullet-proof as is possible with MDF.

If you want to go to an even better surface finish just continue the daily wet sanding up through the grits - 400, 600, 1000,1500, 2000, 3000, 4000, now we are getting ridiculous. Worth doing with real timber or plywood, but MDF is MDF.

[toni_k]

Great, thanks for the detailed instructions Graeme! I will give this a go.

[GraemeCook]

Great, thanks for the detailed instructions Graeme! I will give this a go.

Good luck, Toni.

I have used it on the assembly benches in my workshop. Just remember MDF hates water - wheatbix.

With good timbers, running up through the grits to 5000, I can get a faux French polish finish, polished with antique wax. Most people cannot tell it is not French polish, but it is not sensitive to heat or alcohol, the great enemies of real French polish.

[justonething]

I'd pay special attention to all edges and give them extra coatings whenever you can.

[yvan]

Hi Toni

MDF is just a high grade chipboard, aka wheatbix. Anything to make it tougher is worthwhile.

I would use wipe on polyurethane - WOP - poly because it gives a tough finish and wipe-on because it is thinner and penetrates a little and gets some of the finish below the surface. You can buy WOP or make your own - just mix equal volumes of polyurethane (eg Estapol) and turps. My technique is:

1. Paint WOP onto edge-grain, top, bottom and edge-grain again (it soaks in really quick) - brush or small roller.
2. Wait ten minutes and, with clean rag, rub off WOP - this fills pores.
3. Next day, lightly sand and repeat steps 1 & 2.
4. Ditto - next day. Edge-grain should now be full of poly - visibly.
5. Next day. Dip 400 grit sandpaper into WOP and wet sand.
6. Repeat next day.
7. Surface should be very glossy and as close to bullet-proof as is possible with MDF.

If you want to go to an even better surface finish just continue the daily wet sanding up through the grits - 400, 600, 1000,1500, 2000, 3000, 4000, now we are getting ridiculous. Worth doing with real timber or plywood, but MDF is MDF.

Graeme,

Would Laminex be a good, tough & smooth surface for a router table, if available of course?

Cheers,
Yvan

[Jaded62]

What about form ply?

Graeme,

Would Laminex be a good, tough & smooth surface for a router table, if available of course?

Cheers,
Yvan

[GraemeCook]

Would Laminex be a good, tough & smooth surface for a router table

Toni asked for advice on finishing a router table top made from laminated MDF.

I hate laminex - a pathological hangover from those horrible 1950's kitchen tables - and modern laminex is so thin it just confirms my prejudices.

[toni_k]

I used MDF because I read somewhere it would be the flatest and remain most stable over time, provided it doesn't get moisture of course. I laminated 2 sheets together to get more strength and stability and I was able to use my frined's welding table for a very flat surface to clamp to when gluing the 2 sheets together. I'll post a photo here when I'm done.

Toni

[toni_k]

Just a quick update on the router table top. I ended up doing about 6 coats on the top and bottom surface and double that on the edges. I sanded the top and bottom with 400 and later 600 grit between each coat. The diluted wipe-on-poly seemed to stay a little sticky even after couple of days of drying so I did the last 2 coats with undiluted polyurethane and it has come out quite nice.

Couple of photos in case anyone is interested to see it:

d4732a1a-adbb-47a7-b8ae-bd05c2d52541.jpg 8846612b-ab16-4132-a4ba-05a565b58259.jpg 9ed47070-4454-4f9e-b8b1-1a1ded968452.jpg 1adb307e-5971-496b-a649-9f70871d6c2f.jpg b9dc68b4-6d41-4923-bea5-fd7fc315e74a.jpg

[GraemeCook]

Looking good Toni; nice job.

The diluted wipe-on-poly seemed to stay a little sticky even after couple of days of drying so I did the last 2 coats with undiluted polyurethane and it has come out quite nice.

Strange, I have never actually had this happen with wipe on poly - WOP. My experience is that WOP is touch dry after about half an hour or so, longer when cold or humid. Specifically, what did you dilute it with?

I have had it happen with Danish oil simply because I put it on too thick and the oil just sat there. Lots of thin coats is the answer.

Poly is as tough as anything short of two-pack poly so your table should be good for years.

Now that you have a router table, your collection of router bits is about to explode - they breed like rabbits. You will be amazed at what you can route edges to, and the array of trench options, and the regret - why did I do that?

[toni_k]

Thanks Graeme!

Strange, I have never actually had this happen with wipe on poly - WOP. My experience is that WOP is touch dry after about half an hour or so, longer when cold or humid. Specifically, what did you dilute it with?

I used Diggers mineral turpentine from Bunnings. The polyurethane varnish was Bondall gloss that I had left over also from Bunnings. I now see it is the cheapest one they sell so perhaps that's the reason I used 50/50 mix.

892fc6fc-cfac-49d6-8cc9-2e07cb6aba8b.jpgWhatsApp Image 2024-04-01 at 11.17.43 AM.jpeg

Cheers,
Toni