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Anybody know definitively what solvent in CA causes it to melt into lacquer? We've observed this many times in doing CA repairs over nitro, that if the CA is leveled and buffed a day or two after it's applied, a few days later the CA repair has shrunk back below the surface of the lacquer. I'm fairly sure it's not the CA continuing to shrink, but that it's eating into the lacquer underneath.

We have a few questions around this.

-- What's eating the lacquer? I've heard some ca's use acetone, which certainly will eat lacquer, but the brand we use, Starbond, says they don't have acetone.

-- Does viscosity play into it? We've noticed significant "melting" when using thin CA, and little melting with the thick stuff, but not enough to substantiate any theories around that.

-- Does the age of the lacquer play into it? We've noticed more shrinkage with new finishes, but again, not definitive evidence that older finishes are less prone than new.

-- Are solvents or additives used to thicken thin CA, or vice versa?

Worth mentioning that CAs intended for finish repair seem to actually shrink back more than Starbond. Go figure.

Any insights folks can offer are much appreciated. Inquiring minds want to know!


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Mountain Song Guitars www.mountainsongguitars.com

Can't say what causes it. I use Starbond as well (not on nitro) and have added Glu-Boost to my arsenal. It is supposed to be safe on nitro.

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"I've been had again"
Tim Benware
Creedmoor, NC

I only use CA to repair poly finishes, never lacquer and have no issues with shrink back.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Speaking from experience, Glu-Boost CA Adhesives and Glu-Dry accelerator will melt nitro lacquer finish, especially new finishes. The only safe accelerator that I use is ZAP brand. It will not melt or dull nitro finishes.

An additional lacquer-safe CA accelerator is BSI's (Bob Smith Industries) 151/152 accelerator, which has a light hydrocarbon (naptha-based ?) carrier in a pump bottle (we prefer to avoid spray cans...more expensive, and some propellants with cloud lacquer finishes), and is safe on any finish. Look for the 2 ounce pump bottle or 8 ounce refil brown plastic bottle in hobby shops or on Amazon.

Our experience with GluBoost is that - if applied as a light mist - it is safe on lacquer, but a heavy application that leaves the surface damp with excess carrier will dull even well dried lacquer. Very little of the accelerator is needed to get the job done - if any liquid ends up on the surface, it is being applied too heavily and at too close a distance. The trick I learned from one of the gentlemen in the shop was to carefully modulate the spray to minimize the amount of accelerator used - just a bit of mist is required at about twice the distance used for other accelerators.

On lacquer settling - we see this in the shop, but suspect it is as much a surface tension issue with the applied lacquer as it is the lacquer being softened by the CA taking a bit of time to out-gas whatever it picked up from the CA - the lacquer topcoat will flow towards the edge of the repair, requiring additional finish to level even on well-prepared and well cured CA fills. CA can take several days to full harden - especially on a deep repair - so waiting for the fill to fully cure before scraping and sanding helps to minimize settling. If in doubt, try making up a test panel with a variety of CA repairs...try scraping at 20 minutes, a few hours, a day, etc. to see the differences.

Last thought - filing CA drop fills level in areas where a small mill bastard can be used is often easier than scraping, and produces a level surface quicker. The CA debris loads the file up, but that cleans out well with carding of the file.

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