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Polyurethane finish is not coming out smooth.

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Forum topic by deeker posted 01-04-2009 02:46 AM 16742 views 0 times favorited 10 replies Add to Favorites Watch
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deeker

43 posts in 2437 days


01-04-2009 02:46 AM

Almost like it has tiny lumps in it. It is Minnwax poly…...from a gallon can I have had for a couple of years. Has a skin on the top, broke through it and opened it enough to dip the foam brush.

Cannot see any lumps when I start.

I am using it on rustic table tops from dry spruce.

Any ideas and suggestions would be helpful.

Thanks

Kevin

-- To those who fight for it, life has a flavor the protected never know. Unknown, on an empty C-ration box. Khe Sahn 1968


10 replies so far

View jeffthewoodwacker's profile

jeffthewoodwacker

603 posts in 2456 days


#1 posted 01-04-2009 02:50 AM

If the can is old and has a skin on top I would recommend tossing it. Sand your table top down with 220 or 300 grit sandpaper and start over. Option two would be that the poly raised the grain and you could lightly with 0000 steel wool, wipe the sanding dust off and try another coat of poly. I would try option two first – if there are still lumps then pitch the poly and buy some new.

-- Those that say it can't be done should not interrupt those who are doing it.

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lew

10027 posts in 2407 days


#2 posted 01-04-2009 02:55 AM

Kevin,

Recently had the same problem. I attributed it to the cold temperature in the work shop- between 55 and 60 degrees- not allowing the poly to flow. Mine was also old but not film on top.

Lew

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

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deeker

43 posts in 2437 days


#3 posted 01-04-2009 03:14 AM

I keep the table tops in the house for about three days to make certian they are not cold prior to finishing.

I will probably keep using the can until gone, just won’t use it for the finishing coats. Sanding each previous coat.

The epoxy I use to fill in the cracks…bark encasements and branch/knots…..looks great and comes out smooth and clear.

The Poly is probably just too old.

Thanks for the comments

Kevin

-- To those who fight for it, life has a flavor the protected never know. Unknown, on an empty C-ration box. Khe Sahn 1968

View ajosephg's profile

ajosephg

1852 posts in 2213 days


#4 posted 01-04-2009 04:10 AM

My process is:
1. Let dust settle in shop settle before finishing
2. Wipe surface with cloth soaked with mineral spirits, let dry. (Properly dispose of cloth to prevent spontaneous combustion. – Since I don’t have a sealed metal container, I take them outside and spread them out flat on a concrete or rock surface until dry.)
3. Apply varnish with quality brush, don’t mix (Mixing puts air bubbles in) I have not had much success with foam brushes.
4. Don’t worry about “specs” and lightly sand.
5. Repeat above for at least 3 coats. (I usually go 5)
6. After final coat rub out with 0000 steel wool and wax with carnuba. Any slight specs after the final coat will be rubbed out.

While it’s good practice to use fresh varnish, I recently used some that had been sitting around for 15 years and it worked ok.

-- Joe

View Scott Bryan's profile

Scott Bryan

27251 posts in 2474 days


#5 posted 01-04-2009 05:36 AM

Once the poly skims over it is starting to cure out which is caused by exposure to oxygen. The remainder really should be tossed since this process is irreversible and it will only continue to spread throughout the remainder. But if you are set on using it then you should filter it to remove as much of the cured product as you can.

It is better to transfer the poly, once the can is opened, (1) to smaller containers and try to eliminate as much air as possible or (2) remove the oxygen by using bloxygen to displace the air before putting the lid back on. Here is a posting where topic has been discussed. There is also a school of thought that adding inert fillers such as marbles to eliminate the air in the can will work but I have never used this.

-- Challenges are what make life interesting; overcoming them is what makes life meaningful- Joshua Marine

View bbqking's profile

bbqking

328 posts in 2375 days


#6 posted 01-04-2009 06:51 AM

For what it’s worth, once I start the finish on a piece, I treat it like when I was building bikes. I use 1200 grit wet sand between coats, building up 2 or 3 coats. The last coat I rub out with a really used piece of 1200 grit or even newspaper. You can buff finish out brilliantly with newspaper. I might wax something up before I deliver it or before they pick it up but usually not till it needs it. bbqKing

-- bbqKing, Lawrenceville

View John Ormsby's profile

John Ormsby

1279 posts in 2389 days


#7 posted 01-04-2009 06:55 AM

I have been using the glass marbles trick for years. This will keep the material as close to full as possible in the can. This keeps the air volume low and thus longer lasting material. It does work well.

-- Oldworld, Fair Oaks, Ca

View John Gray's profile

John Gray

2370 posts in 2537 days


#8 posted 01-04-2009 08:00 AM

First strain the Poly though a paint strainer into a CLEAN container that will get most of the lumps. If you want to use the same container it was in CLEAN it thoroughly (I would suggest a new container they sell them at the BORG) including the rim and lid and pour it back into that through a NEW paint strainer. You can use Bloxygen http://www.bloxygen.com/ i to purge the container of oxygen just before you seal the can. I’ve heard recently that you can use your breath to purge the can of oxygen because your breath is mostly CO2 (carbon dioxide and that is what Bloxygen is), haven’t tried that yet but it is cheap…..did I say I’m a cheap skate?
I’ve done the above straining to lumpy varnish with a skim on top and it worked for me. MY 2 CENTS.

-- Only the Shadow knows....................

View alanealane's profile

alanealane

365 posts in 2542 days


#9 posted 02-25-2010 11:06 PM

I know it’s been a long time since anyone posted on this topic, but I owe Kevin (deeker) a HUGE thanks for starting it. I also want to thank Joe (ajosephg) for his response, especially the point about NOT WORRYING IF THERE’S DUST IN THE FINAL COAT. Just rub out the finish after it’s completely dry, and the dust specs should be removed.

I’ve heard many people say that Meguiar’s brand and 3M automotive polishing compounds (like “Perfect-It” or “Finesse-It”) work very well in giving the glassy appearance on finishes. I might try one of these. There is also a product called Novus that is made for re-clarifying plastic and polycarbonate surfaces, such as headlight lenses. That system has two abrasive compounds and a cleansing polish, and worked great on my old Buick’s headlight covers! I may give it a try on a scrap finished with polyurethane to see if it works. Whether the Novus works well or not, I’ll first wet sand with some 1200 to 2000 grit waterproof silicon carbide paper and soapy water. Then I’ll apply either the Novus system or the 3M polishing compound.

I’m finishing a large desk top made of ribbon-striped Afromosia veneer over a solid-core door, with the edges wrapped in White Ash. I used Zinsser Seal Coat first, followed by 4 coats (and sandings) of Crystal-Lac clear grain filler. I just put the 3rd coat of Minwax clear poly on this morning. I WAS EXTREMELY CAREFUL TO LET THE DUST SETTLE OVERNIGHT AND WIPE IT OFF WITH A DAMP CLOTH, AND IT STILL HAD DUST NIBS SETTLING IN THE FINISH!! AAARGH! I even took a single bristle from my brush and tried to lift out the dust particles while the finish was wet, but I couldn’t get to them all before it started to cure.

I’ll just put one or two more coats of poly on and then try the Novus polish system (if it works well on the test scrap). Whatever I do, I’ll be trying some sort of fine polishing compound to get the shine I want. I’ll probably stop before I get to “mirror” quality, since this will be used as a writing desk. I don’t want the person’s desk lamp to reflect off the desk top and BLIND them…LOL
I just want the dust nibs GONE. By the way, the dust in the finish is NOT sanding dust or sawdust, it’s FIBERS FROM NORMAL HOUSEHOLD DUST. The few pieces I was able to pick out of the finish were tiny strands. I have forced-air heat in the house, but the shop is in the basement and I have no registers heating the basement. I suppose the cold-air-return is sucking plenty of dust back into the basement from the rest of the house, and circulating it around constantly.

If I happen to gain more insight into this area of finishing, I’ll make sure it gets posted here.

Once again thanks for this topic!!!
I LOVE LUMBERJOCKS.COM

-- Lane Custom Guitars and Basses

View SnowyRiver's profile

SnowyRiver

51451 posts in 2132 days


#10 posted 02-25-2010 11:33 PM

I would have to agree with the others that once the poly starts to skim over, I toss it. Its just not worth the risk after you have spent so much time building the project. I would sand it off too and get a new can of poly. Also be sure all the dust has been removed from the piece before starting.

-- Wayne - Plymouth MN

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