Help! Spar urethane didn't cure right on MDF desk/table


Hi all,
I built a work table in my basement (really a kind of desk) out of MDF. It turned out really nice. I used a helmsman indoor/outdoor spar urethane to seal the MDF. I applied several thin coats when I noticed that what I thought was the bottom of the can (gallon) was actually a hardened translucent layer of material that had settled to the bottom, it was hard work but I managed to stir it up after that for the remaining 2 coats.
The problem is that 6 months have gone buy now and the table still reeks of urethane smell, this can't be good. With the window open it's ok, but if you put something down on the table for even 5 minutes and then pick it up, you catch a strong whiff of urethane in the air and on the object itself.
I'm now prepared to sand this down and restart but it's a HUGE job, the room is full of stuff that needs to be moved.
Is there anything I can apply to 'post cure' this flawed urethane? Without having to do a bunch of sanding?
PS. the 'table' is built in, can't be moved. It's 15' long with l extensions on each end, bolted to the wall.
Thanks,
Zander
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Spar varnishes are designed to not harden and remain flexible.

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Not that flexible. Mine is just fine after a couple of days.
From the MinWax company:
Ideal for: Doors, windows, trim, bathroom cabinets, bar tops, kitchen countertops and outdoor furniture
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Thanks everyone,
I have a feeling I am going to have to recoat - too bad as I mentioned it's a huge undertaking and this is my home office so I can ill afford the time - but also can ill afford the smell.
Assuming I do strip or scrap or sand this all away what would you recommend as a hassle free replacement, considering the the pigment of spar urethane gives the natural MDF a really nice look.
Also, I simply used latex paint on the bottom of the desk but later read that only polyurethane adequetly seals mdf against formeldahyde (sp?) release. Is there any thing to do about that?
Thanks,
Zander
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snipped-for-privacy@gmail.com wrote:

rip it out and start over.....

if you can smell it it means you are absorbing it via your lungs into your bloodstream..... nice thought, eh?

"natural" MDF? <G> varnish is probably the best bet. it needn't be spar or polyurethane. consider a tabletop varnish:
or McCloskey heirloom varnish (about halfway down: <http://www.o-geepaint.com/ArchiCoats/McCloskey/McCloskey.shtml for some more data, try: http://www.woodzone.com/articles/wood_finishes.htm

here's georga pacific's MSDS for MDF: <http://www.gp.com/BUILD/DocumentViewer.aspx?repository=BP&elementidE03
basically, the formaldehyde is released when you cut, sand or burn the stuff. just sitting there it doesn't present a hazard. sealing all surfaces is not a bad idea though, because it absorbs moisture. you are breathing a lot more toxic stuff by having that improperly cured polyurethane in your house than you will ever get from the MDF.

hope it helps.
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bridger wrote:

Agreed.
It is the only way you are going to solve the problem.
Wear protective clothing when you do it.

Agreed.
Lew
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I had read somewhere that a urethane was 'required' to prevent formaldehyde release from MDF. I believe the MDF does release formaldehyde just sitting, because, as an example, if I buy a sheet of MDF and put it in my downstairs workshop I can smell it the next day as soon as I open my front door. I find the odor really powerfull. Although some brands don't seem quite as smelly.
Thanks for your reply.
Zander
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On 9 Jul 2005 11:53:15 -0700, snipped-for-privacy@gmail.com wrote:

I had some trouble on a piece that I sprayed with the stuff in a can reamining sticky for weeks, and I finally rubbed it down with paste wax so I could handle it. Couldn't tell you how the poly underneith reacted chemically, but it now feels dry and the smell is gone. Might be worth a try- worst case senario, you just have to sand it off like you were going to in the first place.

What is "natural" MDF? :)
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When I said 'natural' MDF I meant 'unfinished' <G> As a person who used to cnc cut hundreds of 3/4 MDF laminated blocks into 3d patterns I remain thoroughly disgusted by the smell.
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Edwin Pawlowski wrote:

flexible is a relative term. spar varnish was developed as a finish for spars on wooden boats. spars are working members- that is, they are under load, enough load to cause them to flex about. so the finish needed to be able to flex with the spar without cracking. now, flexibility is also a great characteristic for a finish for doors, since they get slammed, hung in jambs where stress is applied and such. it's not good for floors, though. it's too soft and will quickly get scratched and scuffed up. I'd hesitate to use it for a bar top or countertop for the same reason, but it's just fine for trim. spar is a long oil varnish- it has a lot of oils in it. for hard wearing surfaces like floors and counters use a short oil varnish.
I spent several hours today prepping a door I built and installed a few months ago for a final coat of gloss spar. I scraped and sanded to 320 grit. tomorrow I'll apply a wiping coat to get the final gloss. it's been a couple of months since the last coat went on and although it's totally dry to the touch and impervious to thinner it definitely gums up the scraper blade and clogs up the sandpaper. it's never totally dry, I guess.
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snipped-for-privacy@gmail.com wrote:

contact the manufacturer of the finish for the specifics of the finish chemistry. I'll bet that there isn't much you can do to it now to cure the bottom layers, but you might just get lucky. probably you are going to have to remove what's on there and start over. given the labor involved and the cost of MDF it might be best to start completely over.
sanding isn't the only way to strip it, should you go the refinish route. scrapers can be faster and much less dusty than sanding, and chemical strippers will do a dust free job, though they make fumes of their own.
when you get to the point of applying a new finish, start with a fresh can. read and follow the directions printed on the side of the can, which almost certainly involve stirring frequently during use.....
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Spar varnish was probably not the best for the job, but now you have to work around that. I'd try some heat. Not a lot, but a lamp that would raise the surface temperature a bit for a couple of hours. Another method is to contact MinWax and as for help.
http://www.minwax.com/listserv/askminwax.cfm
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Hi Edwin,
What I'm trying todays is: I removed 1/3 of the table and carried it outside where it is currently sitting in the very hot sun baking away. I'll see what happens!
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Hi All,
I spoke to MinWax and the women was extremely knowedgable. She said the following:
1: The stuff on the bottom of the can that was so hard I didn't know it was there was only the flattening agent (silica) 2: The solvent in spar urethane is mineral spirits, it soaks into the fibres first and can take a while to off gas 3: What it needs is air circulation - eventually it will cure 4: Wiping the surfaces down with mineral spirits now can help it cure faster
So, I'm going to leave these table tops (1 at a time) outside until they have cured. I still have enough table space with 2/3 of my desk (my whole desk is about 60 square feet!)
Thanks to all for your help in this matter.
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snipped-for-privacy@gmail.com wrote:

Since the solvent hasn't evaporated in the last six months I don't think you'll have much luck. Unless you have been keeping them hermetically sealed all that time :)
-- dadiOH ____________________________
dadiOH's dandies v3.06... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico
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snipped-for-privacy@gmail.com wrote:

Did the MinWax lady suggest what you should breathe in the meantime?
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