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Polyurethane..why cannot we just get along

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Forum topic by handystanley posted 09-06-2011 10:02 PM 4467 views 6 times favorited 38 replies Add to Favorites Watch
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handystanley

165 posts in 1601 days


09-06-2011 10:02 PM

It seems whenever I decide to use a polyurethane product…we just do NOT get along. My results are always substandard. This weekend I even read a previous article in Fine Woodworking by Lon Schleining (www.woodbender.com) on finishing. I applied a multiple coat of polyurethane using 300 grit sandpaper as he wrote…even had the artilce next to me as a reference …now I have scratch marks all over the door that I was refinishing….

To top off the frustration…this door is pocket door that needs to be installed before I can finish the trim work in my master bathroom…..

Frustrating….

-- "Projects beget projects and projects beget the need to buy new tools and that is what the cycle of life is all about." Stan Pearse, Novato, CA


38 replies so far

View gfadvm's profile

gfadvm

11234 posts in 1378 days


#1 posted 09-07-2011 04:24 AM

I never brush poly but prefer home made wipe on [Slower but goof proof] or spraying larger/intricate projects [like my chairs]. I use grey Scotch pads rather than sandpaper and dont bear down. The above have solved my poly problems. Hope this helps. I would wipe your doors and you probably wont need to sand/Scotch after the first coat unless in a dusty environ.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View Steven H's profile

Steven H

1114 posts in 1748 days


#2 posted 09-07-2011 08:36 AM

I assume you are using a brand new sandpaper?

Rub two sandpapers together until smooth. Then use that to sand.

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ajosephg

1854 posts in 2249 days


#3 posted 09-07-2011 12:15 PM

I never have a problem using 220 grit for the final bare wood sanding. After each coat of gloss poly (Minwax oil based) using a good brush I sand with 300 grit wet dry automotive sandpaper with one of those rubber block thingies. Usually I get a finish I like after three or four coats. I’ve tried finer grits on after several coats but can’t see any better results. The Minwax website has a lot good info on application, and they recommend 220 grit between coats. Besides the resulting super smooth finish, I’m told sanding is required to make sure the poly bonds well with the previous coat.

BTW – I change to semi-gloss or satin spray on (aerosol can) for the last several coats. That’s kind of expensive but the results are great. Some day I hope to get a HVLP system.

Also – Go easy on the sanding or you’ll go completely through the varnish down to bare wood.

-- Joe

View Fred Hargis's profile

Fred Hargis

1889 posts in 1181 days


#4 posted 09-07-2011 01:19 PM

Like yoou, I’ve never had good success with anything “polyurethane”. I’ve completely purged my shop of all products poly. For oil based varnish I now use alkyd/soya or alkyd Linseed oil formulas. For soya based P&L 38 is my favorite (when I can find it), but I’ve also used the Cabot 8000 series and like it really well. For a linseed oil formula the SW Fast Dry Oil Varnish is really great. If it wasn’t for the amber color it has (linseed oil) I’d use it exclusively. As it is, it only gets occasional use in my shop. But they are all top notch products.

-- Our village hasn't lost it's idiot, he was elected to congress.

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stnich

108 posts in 1612 days


#5 posted 09-07-2011 02:06 PM

I use Polyurathane products all the time and never have a problem. I use a foam brush to apply light coats on larger flat surfaces keeping a wet edge as I go. On mouldings and other detailed type surfaces I use a china bristle brush usually of the throw away variety. I sand with 320 grit paper and gray synthetic sanding pads in between coats. When I apply it I try to not go back into the poly to much that I’ve already applied so that in levels out naturally. I also use aresol spray cans of Poly with great success. Some of the things that I make are just to small to put a brush to. I combine the two finishes with no noticeable difference in the finishes.

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richgreer

4524 posts in 1763 days


#6 posted 09-07-2011 04:06 PM

I have pretty good luck with poly. Here’s my approach. I only use wipe-on poly and I apply it with a disposable foam brush. Right after I cover an area of about 2 square feet or less, I wipe the poly off with a lint free paper towel. I wait 3-4 hours, sand lightly with clean 400 grit paper, and apply another coat. Each coat is quite thin and I consider 5 coats to be the minimum for any visible area. I’ll get by with fewer coats on the underside or back of an item.

As an FYI, I like Minwax wipe on poly but I think the gloss is too glossy and the satin is too dull. I mix them 50/50 to get the finish I want.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

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Brett

884 posts in 1447 days


#7 posted 09-07-2011 04:29 PM

I’ll put in my $.02.

I used to get terrible results with oil based poly and I would get sooooo frustrated. Then I figured out, or was told, to thin it out. I do like many others have done, I make it into a wipe on poly, about 3 parts poly to 1 part mineral spirits, maybe even 2 poly to one spirits. I like to let each coat cure for at least 24 hours and sand lightly between each coat with 400 grit. I do AT LEAST 3 coats minmum. For my final coat and sheen (I like satin so I use satin sheen from the can) I dilute to 1 part poly to 3 parts mineral spirits. I wipe the whole piece down making sure to check the evenness of the application by making the piece look “wet”. Using a good light source at a low angle to the piece is how I check for “wetness”. I let this coat dry and I have always had good results. If I have noticed after that final coat that I have missed a spot, I very lightly sand and wipe the piece down again with the 1/4 ratio and check again when dry. The last coat is so thin that it is like wiping with just mineral spirits but there is just enough poly in it that it lays down a thin layer and gives it the final sheen that is indicated on the can.

Hopefully this gives you another method to try and I hope that you get the results that you are looking for.

-- Hand Crafted by Brett Peterson John 3:16 http://www.TheCrookedNail.blogspot.com

View Steven H's profile

Steven H

1114 posts in 1748 days


#8 posted 09-07-2011 04:44 PM

I love screwing up, because you get to learn newer things.

Apply another coat, you willl probably see the scratches gone.

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helluvawreck

15960 posts in 1555 days


#9 posted 09-07-2011 04:53 PM

Thanks for this thread – good info from it.

-- If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music which he hears, however measured or far away. Henry David Thoreau

View handystanley's profile

handystanley

165 posts in 1601 days


#10 posted 09-07-2011 08:25 PM

I have really appreciated the feedback that I have received so far. What I am planning on doing tonight is to try sanding out the scratches with 300 grit sand paper and then moving up to 400. I was thinking to sand until I see no more scratches on the door frame. Feedback welcome.

Question: Does anyone see an issue if I use my Makita palm sander instead of doing it by hand????

@cr1: Will consider using the General Finishes product the next time I need to use a polyurethane. The main issue is that no one in my county carries it. However, it will give me an excuse to go up one county to a wood store that I have not been to in a while.

@gfadvm: I originally used Old Masters wipe on Poly…followed the instructions and ended up having “ridges” which I did not discover until my third coat…that is when I started having my scratch problems…when family members wanted to “help me out”...ahem…

@StevenH: What is the purpose of sanding two pieces of sandpaper together? To dull the grit??

@josephg: thanks for the concern about sanding too much. I am also using a satin finish.

@brett: That is what I have been doing this week to a mirror frame that I am working on. Instead of applying Poly straight…I have been using 3 parts Poly to 1 part paint thinner / mineral spirits. It seems to be working better that way. I am applying the final coat tonight so we can get a mirror cut for the frame tomorrow.

-- "Projects beget projects and projects beget the need to buy new tools and that is what the cycle of life is all about." Stan Pearse, Novato, CA

View Steven H's profile

Steven H

1114 posts in 1748 days


#11 posted 09-07-2011 09:24 PM

I asked you are you using a brand new sandpaper?

Most sandpaper brands 320 grit and 400 is too aggressive when new.

I never use a brand new sandper when sanding between coat.
Don’t throw away your beat up sandpaper, they re perfect for this.
Yes sanding them together to dull them.

I bet 100 dollars that if you apply another coat, you will see the scratches gone.

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bandit571

7146 posts in 1371 days


#12 posted 09-07-2011 09:42 PM

All I have ever used is Poly. I’ll sand down to 150 grit on bare wood. Between coat #1 and #2 , 220 grit HAND sanding. Between #2 and #3, steel wool. After each sand ing/scruffing, I CLEAN the surface with a tack cloth. That is, one wipe, change to new areas of the tack cloth, wipe another section. Use a clean section of the TC each time. After coat #3 is on, I’ll let it dry until it is just barely tacky to a finger tip. Then I grab an old T-shirt, and a big batch of elbow grease, and start rubbing things down, HARD. That was the way I was taught.

-- A Planer? I'M the planer, this is what I use

View A Slice of Wood Workshop's profile

A Slice of Wood Workshop

897 posts in 1861 days


#13 posted 09-07-2011 09:53 PM

I also used to have major problems with poly. I never thinned it. Poly straight out of the can dries quickly and that is usually where the brush marks come in. If you thin it and go extra light on the sanding between coats it should help a bunch. The poly will have time to fill any small voids. Good luck. If you can, snap a before and after pic to put into the thread so everyone can see the difference.

-- Tim- http://www.asliceofwoodworkshop.com; Twitter-@asliceofwood; Facebook-http://www.facebook.com/asliceofwood

View handystanley's profile

handystanley

165 posts in 1601 days


#14 posted 09-07-2011 11:52 PM

@ Steven H: Yeah…I have been using new sandpaper. I will try your suggestion tonight. BTW…your bet is tempting but my personal economy right now is stretched just like everyone else’s…LOL!

@bandit571: Thanks….may try the elbow grease tonight.

@The Head Chuck: The best I can do in pictures is show everyone where I am right now and hopefully an improvement picture afterwards.

Boy…I got to get this door done so I can finish the bathroom and move on to getting the baseboard and window trim finished in the bedroom so the wife and I can move back in. We started a “remodel / repair” of both rooms a YEAR AGO last Memorial Day weekend and had a contractor totally screw it up. They say if you want it done right do it yourself. Well, I am certainly trying. LOL!

-- "Projects beget projects and projects beget the need to buy new tools and that is what the cycle of life is all about." Stan Pearse, Novato, CA

View gfadvm's profile

gfadvm

11234 posts in 1378 days


#15 posted 09-08-2011 04:13 AM

Stan – If you’re getting ridges with wipe on, you are probably applying too much at one time or it is not thinned enough to flatten out before it dries. Runs are a huge problem on vertical surfaces so I hope the door is lying flat rather than hung on its hinges. Good luck!

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

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