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Scratches/Grooves Appearing in Shellac? HELP!!

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Forum topic by customturnedwork posted 04-08-2016 07:10 PM 1094 views 0 times favorited 25 replies Add to Favorites Watch
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customturnedwork

43 posts in 1004 days


04-08-2016 07:10 PM

Hi guys,
This is the first time this has ever happened to me, and I was wondering if anyone has experience this before. I’m finishing a piece of oak; grain is filled, several coats of shellac brushed on, then rubbed out with 400, 600, 1000 grit. I then leave the piece overnight. When I return there are relatively deep scratches all over the piece that weren’t there when I left. This also occurs when I use shellac to as a clear coat on painted metal, so it isn’t the grain of the wood that’s the problem.

I’d really appreciate some help on this issue, I’ve brushed shellac before without issues.

Here’s an image: http://postimg.org/image/iugfp1zlp/


25 replies so far

View ClammyBallz's profile

ClammyBallz

309 posts in 602 days


#1 posted 04-08-2016 07:14 PM

Looks like stress cracks from laying it on too thick. How many coats did you put on?

View customturnedwork's profile

customturnedwork

43 posts in 1004 days


#2 posted 04-08-2016 07:26 PM

Thats probably about 10 coats on there…. I want the extra thickness so the shellac will properly fill the grin nice and flat….

If they are stress cracks, why did they develop and what can I do to fix/prevent them?

View bbasiaga's profile

bbasiaga

757 posts in 1461 days


#3 posted 04-08-2016 07:54 PM

Are you sure the coats were fully dry in between? The top could be cracking as solvent from below is trying to escape.

-- Part of engineering is to know when to put your calculator down and pick up your tools.

View BenjaminNY's profile

BenjaminNY

55 posts in 868 days


#4 posted 04-08-2016 08:04 PM

It’s the shellac. Are you absolutely sure it’s dry? How old is the shellac? Also, what pound cut are you using?

View customturnedwork's profile

customturnedwork

43 posts in 1004 days


#5 posted 04-08-2016 08:18 PM

I’m using what is about 2lb cut, freshly mixed from flakes under a month ago, with fresh alcohol. Shellac has been drying for a week now, and the scratches only appear AFTER beginning to rub out.

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customturnedwork

43 posts in 1004 days


#6 posted 04-18-2016 04:42 PM

Any other ideas? I’m still havig this occur

View pintodeluxe's profile

pintodeluxe

4859 posts in 2279 days


#7 posted 04-18-2016 04:57 PM

What are you rubbing out the finish with? I had a similar problem using synthetic pads to rub out a finish. I found them much too aggressive and coarse. I switched to a 1500 grit soft sponge sanding pad and wet sand with the grain. I haven’t had an issue since with lacquer, poly or shellac.

I would get a can of pre-mixed shellac and make a test sample using the same finishing schedule. This may help you further trace down the source of the problem. I usually spray pre-mixed shellac (two coats) and it dries very quickly. However heavy brush coats may need ample time to dry between coats.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View customturnedwork's profile

customturnedwork

43 posts in 1004 days


#8 posted 04-18-2016 05:16 PM

I’m rubbing out with 400 grit sand paper lubricated with oil to begin with, then work up with sandpaper to 1000 grit;

View Aj2's profile

Aj2

692 posts in 1263 days


#9 posted 04-18-2016 07:55 PM

Just looks like your finish is too thick all the layers aren’t drying.So your getting corns on your rubout pad.

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customturnedwork

43 posts in 1004 days


#10 posted 04-18-2016 07:58 PM

The problem with your theory, Aj2, is that these scratches only appear a day or two after rubbing out.

View pintodeluxe's profile

pintodeluxe

4859 posts in 2279 days


#11 posted 04-18-2016 08:57 PM

Try starting with 1500 grit soft sponges. Wet sand with water from a hand spray bottle.

The problems with introducing oil to a new finish are numerous. It may affect the curing of the finish, and it will certainly foul up any further topcoats that may be necessary.

Best of luck with it.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View Aj2's profile

Aj2

692 posts in 1263 days


#12 posted 04-18-2016 08:59 PM

Then try a little paste wax to blend back in.Just looks like moisture dried in the bottom of the scratch left by the corn on your pad.
Just my guess hope you get it figured out.

View TripH's profile

TripH

5 posts in 286 days


#13 posted 04-18-2016 10:36 PM

Keep the cat out of your shop?

Sorry…

I’ve been finishing w/ shellac for maybe fifteen years—never seen anything like it… But I’ve never seen shellac applied so thickly wither… From your description, sounds like some sort of surface stress cracking as the under-coats are drying…

I’d eMail Jeff Jewitt: info@HomesteadFinishingProducts.com—he’s Mr. Shellac and he’s always answered my questions within a day or so…

Good luck…

View customturnedwork's profile

customturnedwork

43 posts in 1004 days


#14 posted 04-18-2016 10:48 PM

Thanks for the advice, I’ll email Jeff; and just to confirm, no cat in my shop :)

View customturnedwork's profile

customturnedwork

43 posts in 1004 days


#15 posted 04-26-2016 02:29 PM

UPDATE: I talked to Jeff, and he said my problems were due to the use of methyl hydrate as my solvent. Since methyl hydrate flashes off quicker than any of the other two common solvents for shellac (denatured and isoproyl) apparently it forms a more brittle film. Especially with thicker films like mine, it is liable to have this problem. So I cut my methyl 50/50 with isopropyl, and it’s worked just fine. Takes longer to dry, but after rubbing out and letting it sit for a couple days, no cracks have can be seen. Problem Solved!

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