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First time using nitro finish here.
History/Rant first (Can be skipped to question below)
I've had a problem filing a tiny gap on the outside of the rosette with a well know finishing CA, the thin one.
I levelled then left to dry for 1 1/2 hrs before start build coats, and the area of the CA rejected the nitro (I'm using Gluboost Flash Coat - sprays really quite well)
Contacted the manufacturer and received a reply which first suggested not enough time had been left for the CA to dry first and did I use the accelerator (Yes)
I there was a bit of to and fro between us as I gave them some details of the schedule (sanding grits, lubrication etc) and that I had waited more than the suggested hour and asked could I try a thin coat of shellac over the CA, and I was then told "[u]

Quote:

its clear to us that you aren’t using consistent techniques and not following our instructions. Please try it again using our instructions and watching the videos first and please don’t add any steps or other products to the technique

They forwarded 4 video links, one of which was more or less related to my use.
(P.S. I watched a well known sponsored instructor's related repair video using the thicker finishing CA and flash coat probably 20 times before attempting the procedure and all the other videos provided by the manufacturer many times and have used their product for several years - I really like it)
I'm going to leave it for another day or two after the 2 days it's already dried before attempting again to spray the nitro.
If it has the same results, I'm be forced sand back and to buy yet another rattlecan as I have only enough left for mabye 3 coats, and I suspect that won't be enough for final sanding/buffing (using Assilex?buffex to 1500 before buffing
Question
So, Can anyone tell me, if I had a small accidental sand through between the nitro/shellac/nitro layers, am I likely to get witness lines?

P.S. I had no such problem with the BSI super thin used for gluing the rosette in.(edit - but of course I used shellac as a sealer/base on the bare wood)

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

There are NO shortcuts in finishing. That's why it takes so long, and why a properly applied finish looks so good.

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"Act your age, not your shoe size" - Prince

Try clear nail polish.

Colin, I would doubt you would get witness lines. I believe there would be at least some burn in between shellac and nitro. Maybe not a lot but probably enough. Go for it.

Sorry, where was I asking for a shortcut?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Can't be bothered with the maintenance, doing my nails is so time consuming

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Colin, you can just drop fill using the nitro. It will burn in the best and should become invisible once you sand back the excess and finish over it.

Cal

Just noticed you are using rattlecan nitro……just spray some into a small container and use a small artists brush to drop fill the void. Build it up a bit as it will shrink back some in a couple days.

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Remember, there are no stupid questions, only stupid answers!

Hey Colin,
A bit late, but I agree with Cal:




I lived 2 lives... Until I was 35 I was a painter in a body shop, then I went to college and got an Industrial Design degree. I have easily sprayed 1000's of gallons of laquer as well as other finishes. I was paid commission so I got paid for doing the job one time. If It came back, It was on my dime, and in some cases I had to buy the materials as well. So it didn't pay to not follow a manufactures suggestions. I have actually had finishes fail, but because I used all of the reccomended products and procedures they suggest, they had to pay me to fix the problem. So I personally understand the manufactures response to you.

Now in all of this time I have also been in wood working and repairing guitars so I have a fair amount of experience in finishing wood. With all of that in mind, I have always had a hard and fast rule.

Never Mix Finishes. The only 2 exceptions to that are

1. If the manufacture suggests you us X, Y or Z product.

2, Shellack is probably the best sealer you can get. (even if the manufacture doesn't recommend it.

Back in the (I'm dating myself now) 60's I worked for a semi truck repair shop. They would buy used fleet trucks to refurbish and sell on their used truck lot. Most of those trucks were always red. It didn't matter what you tried sealing red with it would bleed through so a white truck would turn pink or blue would turn purple. The only sealer we ever used on those was dewaxed shellack. One light coat and it would be sealed and no more bleed. As well as if you had a problem finish that wrinkled from a reaction to the thinners, one lite coat to the effected area and it was sealed.

So with your original question about whitness lines. Yes, you can end up with whitness lines if you get a build up of any "different" materials but most likely you will be just fine. Where I would be a bit concerned would be if you already have a buildup of lacquer(clear) then added a buildup of shellack (yellow) and build up more layers. You very well may see the difference where you burned (or sanded) through.

One last thing,

You are using rattle cans which is a good way to experiment. However Spray cans will almost always give you some ammount of orange-peel. That is because the finish isn't as atomized as if you were using a spray gun. It just means the finish will not be as smooth and you will have more leveling to do (and chance of sanding through).

You can drop fill any small spots with lacquer but it needs to be thick. I have touched up many many stone chips in my day and the thing to do is pour out about a small puddle of the finish on something like a lid of a can. Let it sit for a while and evaporate until it becomes thick like honey. Now do you drop fill and let it dry. It will only take a few drop fills to level it out.

Using spray can lacquer it will take longer because it is much thinner and it will have gasses in it from the propellant which could become little micro bubbles in your drop fill.

WHEW... Sorry for the long dissertation ...

Cheers,
Bob

Sorry folks, didn't mention my schedule and the stage I'm at so of course people have misunderstood a bit.
Raise grain, sand P320
3 coats 1lb cut shellac, light sand P320
8 coats Gluboost flash coat as a base coat (it's very thin and the spray is excellent, virtually no orange peel).
Levelled P600
Then I noticed and filled the gap mentioned in rosette with thin gluboost F n Finish thin, levelled, sanded Tolex P800,
Prepared spray shop 1 1/2 hours
Sprayed 8 (build) coats Flash Coat when I noticed the rejection
Contacted Gluboost
Apart from the shellac used as a sealer, this is a very similar schedule as used in the O'Brian video they sent (which I had watched many times
- light bulb moment maybe
Except the Tolex 800 - O'Brian used P320 to sand the CA -- could that be causing the rejection problem?

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Yea, I completely missed that, I thought you used the Glueboost to repair the divot and was asking about whitness lines under lacquer..

As I said, when it comes to finishes I rarely mix different types of materials. To me, there are just too many variables to trust my finishes to go beyond the "tried and true".

But I have no problem with anyone doing what ever they like.

Without seeing it it is hard to tell but it sounds like it could be some kind of contamination.

But I have no experience with Glueboost so there's that...

Hope you find the issue

Cheers,
Bob

Sounds like the guy I talked to way back ... and four links to information I had already read. But I did get this useful information:

Paraphrasing what he told me:
Fill N Finish has plasticizers that significantly retard the cure rate/ time. Accelerator should go on first and again after fill. He said to plan for a 24 hour cure time without accelerator first. Accelerator on the bottom and the top causes FIll N Finish to cure from both directions and ensures a full cure in a minimal amount of time.[/i]

I have never stacked Nitro/ shellac/ CA so I can't really speak to that, but the accelerator first and last drastically improved the product performance of FIll N Finish when leveling!

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Measure Twice,

Karl Borum

Colin, not answering your question, but trying to understand the problem.



I've used nitro over CA, but never had a "rejection" problem. But it was ordinary CA and spray gun nitro.

Typically, one has to wait a minimum of 24 hours, preferably 48 before trying to level CA. CA over nitro keeps on shrinking for that long. So if you level after a couple of hours then spray I find I get a sunken "pocket" over the CA. Is that what you mean by rejection?? The nitro around swells up as new lacquer is sprayed (solvent absorption), but where there is CA over the lacquer it prevents the lacquer beneath from absorbing and swelling. So a few hours later after the initial solvent flash off, there is a pocket where the CA is, or was. I say was, because even where you think you scraped/sanded off all the CA, it still seems to seal the lacquer at that point. If you wait long enough (days to weeks) all the solvent flashes off and the pocket gets shallower, but seldom disappears.

If, on the other hand, you wait a couple of days, the CA over nitro shrinks back down, you can level it, and then usually cover it to properly level (after it is also properly dried) with a couple of sprayed coats.

Is that the sort of thing that is maybe happening? If it is, shellac is unlikely to help.

The best fix is to CA fill those hairline gaps prior to any finishing. Wetting out the area with naphtha (or similar) will help you spot the gaps, as the solvent disappears into the gaps. Then you can level after a couple of hours and all will be good when you hit it with lacquer. I normally spray nitro onto tops after a few FP passes of shellac first. That also helps reveal any hairline gaps, but won't fill them. Residual CA over shellac, covered with more shellac tends to leave a high spot which is hard to hide with nitro.

Finishing can be fun!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I can't give an opinion on your specific question, I'm afraid.
I will say though that I have used shellac (French polish) over gluboost CA and have found that the shellac started to flake of in the areas where the CA was applied (in my case a rosette), after some time. So I would be worried about adhesion problems of the shellac to the CA, even if the adhesion of the nitro to the shellac would be fine. (if I understood the question correctly)

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http://www.vanguyseguitars.com

Thank you for the information, appreciated because I like and use Gluboost in repair work.
I've solved my "problem".
It was not rejection of the shellac, but a sand through to bare wood which was absorbing the lacquer, causing a pocket in the nitro,
My mistake, and yet another lesson learned.
I have informed Gluboost what my problem actually was as I did say I would keep him involved.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Glad you got it sorted Colin,

Finishing can be an interesting challenge sometimes. As I said I am not familiar with Glue Boost products but if what you are spraying is lacquer it is still (in my opinion) the best all round finish there is because it is so easy to repair. The biggest issue I have seen with people that use it is impatience. Because it flashes off very fast some think it cures fast and can sand and buff it earlier than they should. After a coupld of weeks the finish will dull out a bit or shrink back to show scratches or imperfections that were not there when they buffed it out the first time. But because it is lacquer it is simple to fix

I hope you find you like finishing with it

Cheers,
Bob