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

Spar varnishes are designed to not harden and remain flexible.


wrote in message
ups.com...
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

wrote:
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




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.....

wrote in message
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.

Is there anything I can apply to 'post cure' this flawed urethane?
Without having to do a bunch of sanding?

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

"Leon" wrote in message
. ..
Spar varnishes are designed to not harden and remain flexible.


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

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

wrote:
Thanks everyone,

I have a feeling I am going to have to recoat - too bad as I mentioned
it's a huge undertaking

rip it out and start over.....


and this is my home office so I can ill afford
the time - but also can ill afford the smell.

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





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.

"natural" MDF? G
varnish is probably the best bet. it needn't be spar or polyurethane.
consider a tabletop varnish:
http://www.woodcraft.com/family.aspx?DeptID=4043&FamilyID=751
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




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?

here's georga pacific's MSDS for MDF:
http://www.gp.com/BUILD/DocumentViewer.aspx?repository=BP&elementid=4503

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.




Thanks,

Zander



hope it helps.

bridger wrote:

rip it out and start over.....

Agreed.

It is the only way you are going to solve the problem.

Wear protective clothing when you do it.


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

Agreed.


Lew

"Leon" wrote:
Spar varnishes are designed to not harden and remain flexible.



Edwin Pawlowski wrote:
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

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.

On 9 Jul 2005 11:53:15 -0700, wrote:

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.

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.

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.

What is "natural" MDF? :)

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.

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

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!

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.

wrote:
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!)

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

wrote:
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.

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