Extira experience dubious or not?

[jhicks]

I am about to build a substantial project and have been asked to fabricate it in extira. Have sampled a few pieces and except for the fuzz after routing it seems OK to me. Now it comes down to finishing and confidence in the product/process. I can't afford a finish or material failure here in our Chicago weather so I hope someone can throw in their comments. I have read a few posts which indicate major finish failures and extira's specifications so perhaps those failures were due to insufficient surface prep or in adequate/incompatible materials? I would appreciate input from Anyone who has a known good experience or process to cut, sand, prime, finish or anyone who has used a recommended process and found out it failed and the reasons why.
THANKS

[billp]

Jerry,
I have cut a bunch of Extira, and the ONLY finish I was able to get to syick to it reliably was shellac. A few coats of it. I believe it is the alcohol base in shellac which allows it to penetrate the "water repellant" surface of the product. If I were to cut the material again (which I won't because of it's other properties which I have commented on before in previous Forum threads....) I would topcoat the shellac with epoxy, and THEN a primer, color coat, etc.
If you check back on the Forum I believe Joe Crumley has also had considerable experience with the product, and mixed results.
The Extira company themselves are little help as they wound up asking ME how to coat their product
after I did that alligator project for them.....
If you have the time I would cut some samples, and test your proposed coating system first, before you get into slinging around those sheets...

[Brady Watson]

Jerry,
It is very hard on tools...so be sure to build in extra $$$ for bits. Dust collection is a must unless you want molasses colored dust on EVERYTHING in the shop.

As far as finishing goes, I'd use a base coat of shellac. You will probably need 2 or 3 coats to get a good seal. After than, brush or roll on epoxy (west brand is fine). This will hard coat the surface and provide a good base for any type of paint that you want to add to it. Automotive type primers and top coats work well.

If you need to glue pieces together, use Gorilla glue or similar polyurethane glue.

-B
(looks like Bill just edged me out...)

[robtown]

With all that shellac and epoxy, one has to wonder why do you need an exterior rated substrate?

[billp]

That's why many of us switched over to Trupan instead. If we're going to encapsulate something it might as well be something easy to deal with in the handling and cutting phases...

[jhicks]

Bill, & Brady, are you saying that trupan or medex will hold as well under weather as Extira if one applies an epoxy wash primer?
Under those circumstances I would choose Medex over Trupan simply becasue if the density and moisture resistance in the base material BUT if both hold as well with Epoxy wash, I guess I would agree with Rob.
Exactly what is the Epoxy wash routine if you can tell me. I'll also check previous posts.
Thanks for helping me avioid a disaster.

[billp]

Jerry,
The sign for my shop was made of two- 4'by 8'pieces of Trupan joined to gether with Bill Young's "stepscarf". This gave me a 4'by 15'sign which I coated with 2 coats of shellac, followed by two rolled on coats of MAS epoxy. I also brushed an additional two coats of epoxy along the edges of the Trupan since I knew the height of the sign would mean it might wind up standing in snow over the Winter. (See photo below).
I topcoated that with a marine polyurethane for extra protection (but I think that ANY good paint would have worked, and the marine stuff was expensive, and stunk up my shop...).
The sign lasted outdoors over 3-1/2 years before I closed the business, and took it down. At that point there was no delamination, or "rice crispie swelling" on the edges.
We also did another sign in our compound where that business used automotive primers instead of the shellac/epoxy treatment, and their sign is still up, looking glossy, and great...The point here being, with a good job of sealing, almost any substrate will hold up to the weather.
P.S. The letters you see on this sign were also Trupan, coated with the same treatment, and top coated with Sculpt Nouveau ...

6084

[jhicks]

Thanks Bill, I'm leaning toward KILZ primer over Medex or MDF and waiting for their process specs and reply to my specific questions. In the end, I guess there are a numbr of ways to accomplish this and appreciate your feedback as always.

[Brady Watson]

Jerry,
The Kilz is pretty good for priming MDF & Trupan, but I have not tested it outdoors. The best bet would be to test it. The shellac I know works (Kilz doesn't make a shellac-based product) and slap some epoxy on it & you are golden...literally!

-B

[tomj]

I tried some Zinsser BIN primer (which is shellac based)on MDF and it sure sealed good...I'm not sure how it holds up outdoors though.

keep us posted on what you do!

Tom.

[Brady Watson]

Tom,
It works well outside if you top coat with epoxy...that's the magic sauce for outdoor stuff.

-B