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Trouble rubbing out Urethane Varnish

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Forum topic by Vindex posted 08-09-2017 05:56 AM 488 views 0 times favorited 19 replies Add to Favorites Watch
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Vindex

76 posts in 656 days


08-09-2017 05:56 AM

Topic tags/keywords: question walnut finishing

I have started practicing rubbing out a finish on test pieces, and the results have not been very good. The scratch marks just make the finish look hazy.

Here is one that I tried today:

I brushed on this varnish on July 25th—that’s 15 days. According to Dresdner’s book, I should have been able to rub out a satin finish after 7 days (but he recommends waiting 14). I used soapy water as a lubricant, flattened the surface with p800 grit sandpaper, and then rubbed the surface with 0000 steel wool (also lubricated with soapy water). What am I doing wrong? Am I sanding too much or not enough? Is this an indication that the finish is insufficiently cured? Is there something else I missed?


19 replies so far

View Loren's profile

Loren

9606 posts in 3482 days


#1 posted 08-09-2017 06:06 AM

How many coats of varnish?

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Vindex

76 posts in 656 days


#2 posted 08-09-2017 06:25 AM

The test piece pictured just had one brushed coat of varnish. The real thing (kitchen table) has nine wiped coats. I have other test pieces with multiple wiped coats of varnish on them, and the results have been similar to the pictured test piece. Everything got a wash coat of dewaxed shellac before the varnish.

View Loren's profile

Loren

9606 posts in 3482 days


#3 posted 08-09-2017 06:34 AM

It looks to me like you’re sanding through
the varnish.

Excessive sanding between coats could be
a culprit. All that’s required is a light
de-nibbing with 180 or 220 grit paper.
I fold a quarter sheet into quarters and
do it by hand. I’ve also used a felt block.
Harder blocks can be too aggressive.

View pontic's profile

pontic

500 posts in 442 days


#4 posted 08-09-2017 08:35 AM

Nylon scrubpads work too.

-- Illigitimii non carburundum sum

View dhazelton's profile

dhazelton

2607 posts in 2130 days


#5 posted 08-09-2017 10:48 AM

One coat isn’t enough, but…

When you get down to the final finishing it will look pretty much like what you have now. When you put paste wax over that it will be pretty gorgeous.

View bondogaposis's profile

bondogaposis

4475 posts in 2185 days


#6 posted 08-09-2017 01:57 PM

You need to put down more than one coat, you are sanding through the finish. Personally, I lightly sand w/ a 400 grit foam pad between coats, then rub out the final coat with a brown paper sack. I consider 4 coats to be a minimum for a film finish.

-- Bondo Gaposis

View Planeman40's profile

Planeman40

1034 posts in 2595 days


#7 posted 08-09-2017 02:12 PM

Provided there is enough varnish on the surface, you are doing the right thing but you are not going quite far enough. Be aware that sand paper cuts using pointy bits of grit. This can leave scratch marks that are relatively deep, particularly if the sandpaper is new. Try following up each grit of sandpaper with a worn bit of the same sandpaper. The larger grits have been removed with use and what is left doesn’t cut so deep. Steel wool cuts using a scraping cut from the edges of the steel fibers. This is why it is used after the sandpaper to remove the sandpaper scratches. BUT . . the steel wool does leave very fine scratches! For this you need to use a fine grade of rubbing compound. Car polishing compound for car finishes works fine. You can hand rub (in straight lines is best to avoid leaving noticeable swirl marks that can be seen in a bright light) or you can power buff with a lambs wool pad. BUT be aware that power buffing can build up heat from friction and melt the finish if you are not careful. Finish by burnishing by rubbing briskly with a piece of paper towel. This rubs our any ultra fine scratches left by polishing. At this point you should have a mirror surface – IF you have leveled out your varnish surface before sanding.

NOTE:
Rather than going to rubbing compound which is a lot of work, on lesser projects I usually just apply one last coat of varnish using a soft artist’s brush that will leave no brush marks. Standard brushes from the paint store usually have stiffer bristles that can leave brush marks. One other thing. I often build up the surface beginning with a number of coats of shellac before scraping ad outlined below. Shellac dries quickly (I can usually re-coat in five to ten minutes) and “builds” well. It also”chalks when sanding and avoids the clogging of the sandpaper. I then do my scraping, then move to the sandpaper and steel wool. For that final coat at the end I use polyurethane varnish as it is relatively thin and dries slowly, giving the finish time to level out before drying. Shellac dries so quickly that it doesn’t level out well.

Leveling your varnish surface:
If you are ultimately trying to achieve a mirror surface, you must level the varnish surface before you begin sanding. It is best to view the surface while you work under magnification. I use a 2X (two power) magnifying visor from Harbor Freight (which works just as good as the $40 versions). The object is to fill up the low spots and trim off the high spots. Begin by scraping the varnish surface using a single-edge razor blade (box of 100 from Harbor Freight). Scrape the surface while viewing the light from a strong source bouncing off the surface. Scrape until there are no “shiny” spots or areas. If some shiny spots are to deep, apply another coat or two of varnish and re-scrape. Keep doing this until there are NO shiny spots!
Now you are ready to do some light sanding as outlined above to remove the scraping marks.

-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

View Vindex's profile

Vindex

76 posts in 656 days


#8 posted 08-09-2017 02:42 PM

Thanks for all of the responses, everybody!

I had been thinking I would go for a satin finish since I’ve read that gloss finishes are very difficult for beginners to rub out.

I had hoped to avoid the paste wax because I was under the impression (for no good reason, now that I think about it) that paste wax would not work well on a heavy-traffic kitchen table. I had assumed that the wax would be removed unevenly as we clean the table each day. Am I just wrong in those assumptions? If so, what paste wax would you all recommend for use on walnut?

My table’s surface is pretty darned flat, and I used grain filler before applying any other finishing product. There is one small patch near a corner where the pores are not completely filled (must have sanded too much there). The finish looks pretty good as is, but those dust nibs still bother me. Here is a picture of one of the larger nibs (wth a dime nearby for size comparison):

Edit: Bondo, is this good enough for the brown paper sack to work? This is after nine wiped-on coats.

Here is the project page if that helps: http://lumberjocks.com/projects/330793

View AlaskaGuy's profile

AlaskaGuy

3633 posts in 2143 days


#9 posted 08-09-2017 02:46 PM

Doesn’t the finish have to cure before trying to rub out? Doesn’t urethane finish take 3-4 weeks to fully cure? Its it true urethane finishes are tough but not hard and it’s hard to rub out to a high gloss finish?

-- Alaskan's for Global warming!

View Vindex's profile

Vindex

76 posts in 656 days


#10 posted 08-09-2017 02:53 PM

Alsaskaguy, I’m not touching the real thing for at least a month, but I was hoping to practice before that. According to Dresdner, varnishes can be rubbed to a satin finish after 7 days, so I thought it would be enough time to try rubbing out some test pieces.

View Planeman40's profile

Planeman40

1034 posts in 2595 days


#11 posted 08-09-2017 02:54 PM

You are right about that AlaskaGuy. Urethane finishes are tough and chip resistant, but they do take some time to really harden. You can gently handle them after an overnight drying, but you have to treat them gently for a couple of weeks before you can polish them or bang them around. I have also found this to be the case with water-based acrylics. I guess the chemical reaction is slow to complete.

-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

View Vindex's profile

Vindex

76 posts in 656 days


#12 posted 08-09-2017 02:58 PM

So am I just jumping the gun on practicing the rub out?

View AlaskaGuy's profile

AlaskaGuy

3633 posts in 2143 days


#13 posted 08-09-2017 07:46 PM



So am I just jumping the gun on practicing the rub out?

- Vindex

I’m no expert but that’s what I’m thinking.

http://homesteadfinishingproducts.com/rubbing-out-finishes/

-- Alaskan's for Global warming!

View Vindex's profile

Vindex

76 posts in 656 days


#14 posted 08-09-2017 08:42 PM

Okay. Thanks, AlaskaGuy. I’ll prepare a few more test boards and wait a month before I try again.

Thanks again to everybody for the advice!

View jimbrown's profile

jimbrown

20 posts in 129 days


#15 posted 08-09-2017 09:04 PM

I did a project like this a long time ago. I used a pumice powder slurry for the last rub out which gave me the soft velvet look and then waxed with paste wax. I haven’t done one since, toooo much work. So much for daughters.

-- JimBrown

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