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Blister in Nitro Lacquer on the Back of Mandolin Neck

Hi,

I am a new member to the site (although I have been a regular visitor to Frank Ford's wonderful website for years to get me through my mandolin building projects).  I have blister in the nitro finish on the back of my mandolin neck that I believe was caused impact to the neck cradle of an instrument stand.  I don't think it was a particularly hard blow, but is seemed to cause the finish to separate from the wood.  I don't mind a few dings and such that come with honest play wear--but this is so noticeable.  Its probably 3/8 by 1/2  inch in size 

From what I understand the way to basic process for fixing  this is:

1.could amalgamate the lacquer using a finish retarder or similar product (acetone, lacquer thinner, "blush preventer" )  and the lacquer would again bond to the wood surface.

2. I understand that lacquer build up would then need to be done using the drop fill method and then allow for sufficient dry time during the process.

3.the requisite sanding and polishing would be done.(progressively finer grits--then fine polishing).

I would practice on scrap first..

Question--am I basically approaching this the right way?  Can you provide any corrections or suggestions.  

I appreciate any help you can provide to me.

Thanks!

Andy Morton

Madison WI

Here is a picture of the blister---

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May I jump on and do some hijacking of this thread? I know good repair advice is coming -

My question is - say that someone encounters this situation, but the instrument is about to be seriously played in grimy conditions for a week, perhaps at a camp or a bar tour. What would be the best way to prevent contamination of the bare spot while allowing playability? I first thought that basic invisible tape might work, but that seems like a bad idea for the surrounding finish.

Mark, I'd use a small brush to touch it up with a coat or two of shellac. It's quick drying and the lacquer could be done right over the shellac if it's clean enough after the "camp". 

Andy it sounds like you are on the right track .Just go for it . And to answer Marks ? you would just clean the neck off with Napta and go back to repairing the neck..Bill...................

I think the issue is about a de-laminated finish, where the lacquer remains in place but is separated from the wood/substrate rather than a missing piece of lacquer or 'chip'.  In which case the repair is not simple as it requires the treatment of a 'blind' area rather than an exposed area.   You will need to make access to the separated area and wick in some "thin" CA - treating the surface will do nothing to remove the 'haze'.   Not an area I'm otherwized knowledgeable about - someone has done this and they will , no doubt, give the good OK repair schedule for this.

Rusty.

I typically get my best results by cutting through the finish with a sharp blade and running in some Cellosolve, which flows way in by capillary attraction, softens the finish and allows it to regain adhesion.  Cellosolve is a high boiling point lacquer solvent, so it has lots of time to do its job.  Acetone or MEK may also work, but it's fairly common for them to be a bit incomplete in penetration or softening before they dry out.  If you don't have Cellosolve, a retarder thinner will work reasonably well.  Any residual unevenness or holes can be drop-filled after the Cellosolve has dried.  Unfortunately, there is a possibility of color change with the change in adhesion/penetration of new/restored finish. . .

Thanks everyone for the advice---yes this is a de-lamination that occurred and not a "chip,"  I didn't think that Cellosolve was still readily available,  Is it possible to obtain small quantities.

Andy

I guess youd have to know whats in cellosolve, which Id like to know as well, and find a retarder thinner with a similar makeup (check the msds). Id like to know where to find cellosolve of the like in Canada, without having to buy a gallon.

 If I was tackling this and trying for least visible outcome, I would cut the finish completely away, scuff with red scotch bright and seal with something thick and non-penetrating prior to building clear coats. There is a good possibility that a slow solvent would interact with the dyes or the wood and change the UV profile creating a dark spot.

I also don't see a ding. I think this may be the result of a missed scuff step in the finish schedule. If this was the case, and I owned the instrument, I would seriously consider moving this one on down the line. This may be the first of many blisters. 

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