Melissa,
I would not recommend thinning except with heat as this could alter the chemical composition in such a way that it might not cure properly and then you would have a real mess on your hands. Most manufacturers do not recommend thinning their epoxy. Do so at your own risk.
If you are intent on using epoxy this way here is what I would do:
1) Widen the cracks a little with a standard shinning tool (don't go bananas...just a bit)
2) Thicken the epoxy like Chris suggested with wood dust or micro-balloons. You dont want it runny for this.
3) Use a putty knife to work it into the cracks (save yourself some cleanup trouble by putting masking tape on either side of the crack but very close to it). Build up to level of tape.
4) Let it cure, pull off tape, scrape off excess with the scraping of the rest of the board. (This assumes you are scraping and finishing the board. If not, I have no clue as to how you would do otherwise).
This epoxy has a long cure time. Simply putting it in the cracks as is will mean it's going to come out the other side. You'll need to stop that from happening, and that's hard with a long cure time.
I like to use Lakeone wood rebuilder for this purpose. You can regulate the thickness of it by the proportions you mix. The only caveat is that your window for cleanup is short (but sweet). There is a period between hardening and full cure where it can be scraped perfectly flush with the top of the board with virtually one stroke of the scraper. Then you're done. If you let it go to full cure before scraping off you'll be really sorry as it cures extremely hard and durable. It is also VERY SMELLY as it is a polyester based substance.
I only use epoxy as a full coating on the board (coating epoxy) as per Del Fandrich's protocol.
Anyway, this is simply an opinion. Others are free to disagree.
Pwg
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Peter Grey
Stratham NH
603-686-2395
pianodoctor57@gmail.com------------------------------
Original Message:
Sent: 01-04-2018 08:50
From: Philip Jamison
Subject: Soundboard cracks
I've never thinned epoxy with mineral spirits, but acetone or MEK both work well. You can also use a heat gun to thin it out. In my experience, the buzzing from a soundboard crack occurs where it pulls away from the ribs.
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Philip Jamison
Philip Jamison Pianos
WEST CHESTER PA
610-696-8449
Original Message:
Sent: 01-04-2018 08:29
From: Melissa Warren
Subject: Soundboard cracks
Thanks everyone. Since they won't be too visible I'm using it in the hairline cracks. I've also read that it's ok to to thin it a bit with be mineral spirits to aid penetration.
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Melissa Warren
Lawrence KS
785-749-5000
Original Message:
Sent: 01-03-2018 17:09
From: Philip Jamison
Subject: Soundboard cracks
How are you using G-Flex epoxy for soundboard cracks?
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Philip Jamison
Philip Jamison Pianos
WEST CHESTER PA
610-696-8449
Original Message:
Sent: 01-02-2018 13:17
From: Karl Roeder
Subject: Soundboard cracks
My good friend and mentor in NYC uses it for small cosmetic cracks with excellent results. I've used it several times in my shop for other repairs and have been very pleased with the product.
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Karl Roeder
Pompano Beach FL
Original Message:
Sent: 01-02-2018 10:12
From: Melissa Warren
Subject: Soundboard cracks
I am working on an old upright. Some cracks clearly need shims. What do you think about using Gflex epoxy on the really thin ones??
Melissa