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Finishing exterior MDF - Extira



Any of you guys sprayed exterior MDF? We are thinking of using this exterior mdf called Extira and wondered if it would take pigmented conversion varnish like regular interior MDF. One finisher told me it may have issues with adhesion , i imagine just like with any other mdf you would have to scuff the surface with a 120 grit sandpaper first but other than that i would be curious to know how this has turned out for you guys.

2/4/15       #2: Finishing exterior MDF - Extira ...

Just to add to my thread so its not misleading. The reason for using the exterior stuff is not to be used outside but rather to give our clients added assurance that their MDF doors wont swell like regular mdf. My question above is not about an exterior application.

2/4/15       #3: Finishing exterior MDF - Extira ...
Mitch Suber


I can not say about the varnish, but I just installed a set of exterior shutters we made from Extira. We used exterior primer and paint, but you might be interested to know that my research and actual experience showed that this stuff has a oiliness (for lack of a better word) to it. I would get sample pieces and test it with the finish in question. Other than the potential for finishing issues, I liked using it.
Another word of caution is that the corners and edges where it has been cut will be softer than regular MDF. A bump or knock will flake the material off where you hit it, you have to baby the stuff once it is finished.

2/4/15       #4: Finishing exterior MDF - Extira ...
Mitch Suber


Maybe this link will work for finishing information. Doesn't list varnish. But do follow their suggestion to ease any 90 degree edges.

Using Extira Panels

2/4/15       #5: Finishing exterior MDF - Extira ...

Hey Antonio, I can't help you with your exact question, but I thought I should chime in.

I used Extira for the trim/columns on my porch at home, and I have never seen material cup like this stuff can. It wasn't a problem for me because the columns pulled together and the trim boards aren't that noticeable, but I would hesitate to use it for slab doors if that's your intention.

I would definitely try a sample before anything. And the extra water resistance won't help your customer unless the room floods, and she's not insured, and she doesn't mind the water damaged CV....

2/5/15       #6: Finishing exterior MDF - Extira ...
Paul Snyder  Member

We used Extira on a large project a couple years ago and the two main thing I remember about it are how fast it dulled the router bits when we were cutting it and how it cupped when we tried to use it on an exhibit with removable panels. Because of the cupping, we had to use another product.

2/5/15       #7: Finishing exterior MDF - Extira ...
Max Neu

I would use Medex, it's a interior grade moisture resistant mdf.

2/11/15       #8: Finishing exterior MDF - Extira ...

Medex falls apart quick if it gets near real water. It is rated moisture resistant for a reason. We made a pile of exterior raised panels and they had to be replaced with Extira within a year.

I would use an epoxy primer on Extira and never think about it ever again.

2/12/15       #9: Finishing exterior MDF - Extira ...
Will Williamson

Use Plum creek double refined mdf for this application

2/12/15       #10: Finishing exterior MDF - Extira ...
Max Neu

Personally I think Extira is overkill for this application. Realistically, the MDF will never see a drop of water once installed in the house.If these pieces see so much water that only Extira will hold up, then the homeowners have much more problems on their hands than worrying about the mdf swelling!

2/12/15       #11: Finishing exterior MDF - Extira ...

I think a lot of this industry has to do with being able to sell a product with confidence and to have the client buy with confidence. For example, the MINUTE the letters MDF are mentioned in a meeting the clients almost ALWAYS say ''u mean particle board?? no way i dont want that in my house''. You (the builder) can either fold up and start stuttering or quickly respond with ''oh no, this is new moisture resistant MDF'' then you can pull out all the brochures etc to back it up. At this point they usually have a sigh of relief. I just wanted a 'go-to' product that will bring that 'sigh of relief' which so far i think i found with MEDEX and maybe extira for outside stuff. And as we all know, 'solid-wood' is not always the 'right choice' or the 'alternative', sometimes MDF is the best choice depending on the application.

2/18/15       #12: Finishing exterior MDF - Extira ...
jeff Takac


Hi Antonio,

We at Milesi high performance Italian wood coatings have a recommeded system for exterior MDFand products for your application. Contact me at

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