I posted this over on the Veneer forum, but don't know how many people regularly follow that forum.
I'm needing to get started on building a 12' long kitchen island which will be veneered with some very nice figured Bubinga.
The builder has specified that I use Extira for the substrate, which would be fine with me, since there is a sink in it. When I went to pick up materials, the bundle that my supplier had pulled for me was so warped that I wouldn't accept it.
Then we went back to get a new bundle, and cut the bands on it. It had been sitting on a level floor, and showed no reason for the whole bundle also being warped. Every sheet had 1.25" bow down the long side, and 7/16" across the short axis, creating a bulge.
I'm wondering if I should expect the face veneers to hold this amount of bulge out?
I don't have any extra veneer to do the project over, if it just comes out curved again.
I always thought one of the wonderful things about mdf products were that we could always expect them to be flat.
My local supplier says he hasn't had any complaints, and that he even has one shop using it for exterior doors.
Seems like life is hard enough without having to fight problems like this. Not to mention that with a price over $50 per sheet, flatness would be nice.
What do you think? Are any of you regular users of Extira, and is it always warped when you get it?
The product specified is for exterior use. It is also treated with zinc borate as a wood preservative. I do believe it is not the correct product for a countertop substrate. Note that if it were dried to 6% MC it would not warp, so we know it is at a higher MC, which would typically be ok for exterior use. It also uses phenol adhesive...I have always seen that this adhesive uses formaldehyde as a catalyst. Their ads say "no added formaldehyde" but does this include the PF adhesive?
I think it is wise to not let customers specify materials or methods beyond generalities. It is also best if the woodworker uses materials and methods he/she is familiar with to produce the best product for the job.
It would be good for you to gently explain this to the builder/customer. No doubt, as a result of marketing, he envisions the Extira as fending off waves of water over the years, whereas the core stock you might use would fall apart with the first bit of dampness. Your job is to convince him that you are a professional and he can trust you to execute the work in a professional manner.
Beyond finding another vendor, you can easily photograph the panels you have seen and rejected, and ask him if he is sure he wants you to use this marginal material.
I haven't used Extira, (my main supplier doesn't carry it), so I use a "water resistant" mdf product for my bath cabinetry instead. Unfortunately I don't know the name off the top of my head. Anyway it's about as flat as normal mdf and for my needs, usually veneered vanities and such, it works well. I always sand the face before veneering, 120 grit on the ROS. Using TB Cold Press in a vac bag with paper backed veneers I haven't had any problems with itů..but will admit I've only used it the last few years.
I honestly don't know if the face veneers will hold the panel flat? I would probably consider design changes that would allow for structural support behind the panel.
I have not noticed any of my Extira sheets coming in warped, always seemed pretty flat. I do use 2 different thicknesses, both 3/4" and 1 1/4". It appears that this product is not as rigid as regular mdf. I would also be concerned about gluing anything to it, as the material has an oily feel to it. This is addressed in the paint recommendations.
Moisture content! Extira is an exterior panel, manufactured for average exterior moisture content 10-12%. Good thing you're supplier has had this lot inside for a bit, as it's already starting to warp while reaching indoor moisture content unevenly. It will get 6-7% eventually. Expect buckled veneer if you don't somehow manage to dry it evenly before veneering.
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