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Stripes in finish

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Forum topic by wastedalf posted 08-31-2013 12:22 AM 616 views 0 times favorited 7 replies Add to Favorites Watch
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wastedalf

53 posts in 389 days


08-31-2013 12:22 AM

This may be an easy question to answer but please don’t make fun of me for it, I’ve only recently gotten into woodworking (about 3-4 months).

Here goes: I’ve made a sign out of walnut using my router. I’m finishing the back of it, it’s basically a 1×10 board, 2 feet long. I did what I thought was a seal coat; 25% mineral spirits with 75% polyurethane (minwax). That dried for 2 hours, then I applied a normal coat of polyurethane. I let that dry for about 6 hours, then I did a very light sanding with 320 grit 3m paper.

What’s worrying me is that after the 320 grit sanding, there is an extremely clear stripe pattern in the wood. The stripes are about 3/4 inch in width.

So my question is, why is this happening? Is it my technique? Or is it the board?

Thanks for your help,
alf

-- If the iron is blunt, and one does not sharpen the edge, he must use more strength, but wisdom helps one to succeed.


7 replies so far

View Marcus's profile

Marcus

1048 posts in 676 days


#1 posted 08-31-2013 12:40 AM

Maybe tool marks in the wood? Did you out the board through a planer?

My first thought was maybe the finish was too thic, but your mix sounds fine. Are you sanding between coats?

View redSLED's profile

redSLED

687 posts in 549 days


#2 posted 08-31-2013 02:34 AM

Tool/jig marks from before or during the routering? I also might have waited much longer than 2 hours for the 1st coat of poly to dry before re-coating – but that may have nothing to do with the stripe pattern.

Flip the walnut sign over and start again?

-- Perfection is the difference between too much and not enough.

View wastedalf's profile

wastedalf

53 posts in 389 days


#3 posted 08-31-2013 02:58 AM

My first mistake was that I did not take any pictures. The sign is finished and up on projects. As I thought would happen, the stripes essentially disappeared when I added the next coat.

I could have waited longer after the sealer coat, but there was no tackiness, it seemed completely dry. I had a ceiling fan on high directly above it. I sanded lightly with 320 between coats.

I used the router, then sanded the board thoroughly prior to finishing. 100, 150, 220, 320. I sanded the back the same way, then applied finish to the back first; this was where the stripes appeared.

What throws me off is how precise the stripes seemed to be. The lines were perfectly straight, perfectly parallel, and perfectly the same width. I used no tools on the board in this fashion at all.

Thanks for the input, I suppose for now I’m just going to chalk it up to my inexperience. Brushing or sanding technique, perhaps.

-- If the iron is blunt, and one does not sharpen the edge, he must use more strength, but wisdom helps one to succeed.

View Dave's profile

Dave

115 posts in 1854 days


#4 posted 08-31-2013 09:08 AM

How did you apply the polyurethane? I use the General Finishes wipe-on poly, which is great, and it warns about something that sounds pretty similar to what you’re seeing if you work the finish too much while applying it. If that’s what happened you might be able to sand off and re-apply.

That’s also the first time I’ve ever heard of thinning polyurethane with mineral spirits as a seal coat. Maybe that’s a factor? If you’re doing a clear poly over it anyway and not a stain you might be able to skip that step and avoid some issues.

-- "I'm not afraid of heights. I'm afraid of widths." - Steven Wright

View JustaLilJoinery's profile

JustaLilJoinery

31 posts in 413 days


#5 posted 08-31-2013 10:04 AM

So sorry that you have cause to have the first sentence of your post asking that no one mock you for your question…

I’m happy to see you had 3 very sincere and helpful fellow workers so willing to lend their thoughts. I hope your future experiences reinforce a positive and supportive experience and that you continue to grow in confidence!

Cheers,

-- Genius may have its limitations, but stupidity is not thus handicapped. -Hubbard

View SamuraiSaw's profile

SamuraiSaw

457 posts in 621 days


#6 posted 08-31-2013 02:09 PM

Good job on the sign. The freehand use of the router certainly doesn’t detract from the sign. I think it enhances it.

I’m inclined to believe the stripes are machine marks that were somewhat deeper than your sanding. It sounds like the surface was absorbing finish differently, thus causing the stripes to appear but diminish after multiple coats.

The current Minwax formulation is “quick drying” and has a tendency to resist thinning. I hate the stuff. Look around and see if you can find some Olympic poly. It has a slower drying time, levels much better, and thins nicely.

-- Artisan Woodworks of Texas.... www.awwtx.com

View wastedalf's profile

wastedalf

53 posts in 389 days


#7 posted 08-31-2013 05:05 PM

Dave: I used a white china bristle brush (Wooster brand). Not a top of the line, but not a foam brush either. I lay down one smooth coat, overlapping each brushstroke by 1/4 inch or so. After the coat is applied, I run the brush the length of board again to smooth out the overlaps. The entire time, I don’t press on the brush, it touches the board under its own weight. As far as the seal coat, I’ve read that this helps the wood absorb the poly more uniformly. Maybe the second run is working the poly too much? It’s still completely wet though.

JLJ: Since this was my first post, I suppose I just said that by habit. That’s not a reflection of this forum, that’s a reflection of other forums I’ve been on (video game forums are notorious for bashing).

Samurai: Thanks for the positive comments. Your theory makes sense to me, that the board was absorbing finish at different rates maybe. The stripes never appeared on subsequent coats and sanding. Luckily, I only have the small can of Minwax, so it’s almost gone regardless. I’ll look for Olympic next time I do a furniture-type piece. On my next couple projects I’m going to want to use a food grade finish, so I’m going with George’s Club House Wax that I found at Woodcraft. I think I’m going to make another post about that in the forum.

Again, thanks everyone so much for all your help!

-- If the iron is blunt, and one does not sharpen the edge, he must use more strength, but wisdom helps one to succeed.

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