Ongoing neck finish problem

[vandenboom]

A post that I put up earlier this year, but was lost, concerned problems I have had with the finish on the back of a neck on a dread I made for my own regular use.
Here is a picture of the neck taken immediately after finishing in Sept 2009 when everything was wonderful.

176_NeckbackF_1.jpg (68.96 KiB) Viewed 4415 times

The neck is a blackwood (don't know which variety) with silver wattle lamination up the centre.
The first finish was with Mirocat after filling with zpoxy. Everything was beautiful.
So here is what happened....
- in the months following, I noticed a gradually roughening of the back of finish, but only in the areas where my hands make contact. The heel and back of headstock remained perfect. The affected areas eventually developed a type of pitting or very tiny blisters. I don't have a photo any longer, but I put it up for your consideration at the time. However there wasn't any concensus on the likely cause, though a form of 'amine blushing' attributed to the zpoxy was one confident view from memory.
- so I stripped the neck finish back to bare wood, refilled pores with zpoxy, but made a point of doing a few steps to avoid the blushing from reoccuring. (eg. wipe with naptha before sanding back). Instead of reapplying lacquer, I then applied Whittle's hard oil/wax, as I was keen to try this as a finish as I like oiled necks. But a similar problem has gradually unfolded, where the surface is becoming increasingly rough in the areas where my hands make contact. Unlike the lacquered neck, it is not obvious in this case when looking at the neck i.e. no obvious pitting etc.

I would love to solve this problem. Don't know if it is something in the wood, the zpoxy or in my skin!! Any further thoughts would be greatly appreciated.
Thanks. Frank.

[Kim]

Sorry Frank, I just spent an hour drafting up a reply. When I went to upload a file, I lost the lot

A condensed version:

No one will be able to say for certain that the problem with the neck of your guitar is amine blush.

Amine blush is caused by sorbtion of CO2 and H2O present in the atmosphere by amines (amino acids) found in 'all' epoxy hardeners during the mixing, application and curing process.

Amines are very effective at scavenging CO2 from the atmosphere, so much so that "An entire industry, “gas treating”, relies on the use of amine compounds as scavengers of carbon dioxide and other contaminating gases [e.g. 7]. Although overlooked by many end-users of epoxy resins, amine compounds used as epoxy curing agents readily scavenge carbon dioxide (and sometimes moisture) from the atmosphere." (ref: see attached .pdf)

Some epoxy products are more prone to blushing than others. 'Low blush' formulations contain more refined amines meaning that they are less able to separate from the mix to scavenge CO2 from the atmosphere while those products that are more prone to blushing have crude amines which, as I understand are a larger molecular structure allowing them to free themselves more readily. (as an analogy, think of how larger bubbles rise more quickly to the surface of water) Those products categorized as "Low Blush" are known to cure to a higher modulus of elasticity which makes them more flexible and therefore more resistant to abrasion...Zpoxy sands wonderfully.

If amine blush is the problem, the reason it may be occurring only on the neck shaft could be related to how much epoxy was left on/in the wood prior to the finish being applied e.g. the flat surface of the rear of the headstock is easier to sand, the heel transition area is often more heavily worked than the shaft. It could also be that the whole neck is actually being effected by amine blush, but the oils/sweat/heat/friction from your hand is accelerating the affect on the shaft or otherwise breaking down the thin outer surface of the finish that is perhaps acting as a barrier to prevent its effect elsewhere.

It should be clearly understood that amine blush is a formation of 'salts', the exact make up of which depends entirely upon the type of amines that have been used in the hardener of the product applied, but it is always salts. Salts dissolve in water, they will not dissolve in thinners or spirits based products. To remove amine blush the accepted method is to use water and agitation of the surface with a nylon scouring pad. To assist in making free amines more soluble, a little citric acid or vinegar can be added to the water.

Anyone who uses epoxy products should make themselves aware of epoxy amine blush. The attached .pdf does not offer any silver bullet but it does explain the issue and identify the problem well and the first part of any successful strategy is to know your enemy.

Blushing_of_Amine-cured_Epoxy_Resins.pdf

(319.41 KiB) Downloaded 6156 times

Cheers

Kim

[J.F. Custom]

Hi Frank.

First point I'd make is that Amines in the epoxy are dissolved with water, not naptha. Therefore if your wiping with naptha before sanding was to remove this potential problem, it won't have had the desired effect. As a result, you can't as yet rule out that as the cause of the issues you are experiencing.

Otherwise, all I can offer is pure speculation. You would think if the same issue has occurred under this re-finish, the problem was unlikely to be the Mirocat or the oil; unless it was incompatability in the finish combos. It should not be this as many use Zpoxy followed by lacquer at least. If we consider then the common factors we have - Zpoxy; the timber species; and your hands/sweat/friction.

How old is the Zpoxy? Has it been stored correctly? Are you confident in the mix ratio? I have not used it so am unsure as to how 'forgiving' it is in mixing. Could it be that the Zpoxy is not curing properly thereby causing issues with finishes placed over it? This is more likely to show gradually as you have experienced, possibly exacerbated by the friction from your hand.

Sweat can and does affect finishes adversely, though you would usually associate it with something like French Polish. Lacquer should provide a much more efficient barrier to sweat; unless you are particularly corrosive Frank?? Perhaps your lead death metal licks are heating the lacquer up and melting it off?

Some timber species can be more problematic with finishing than others due to high oil/resin contents etc. I have not experienced that with Acacia Melanoxylon though. It can help on some of these to wipe the surface down with say naptha or a similar solvent, prior to any grain filling/finish to remove and/or dissolve any surface residues. Some timbers can continue to bleed resin/oil long after too but I'd have thought if the Zpoxy is fully cured and followed by mirocat; you should have a reasonably impervious finish.

Finally then, is this something you have experienced on any other instrument? Can you isolate what you may have done or used in your finish process that was different to other instruments you have made where the problem has not occurred?

Otherwise I'd suggest before re-doing the finish once more, do some sample testing. Have you got some offcuts of the same 'blackwood'? Try using a water based grain filler such as those mentioned recently instead of Zpoxy. Then try the lacquer on one and the Whittles on another. Do a few experiments on this timber and try to isolate the problem, of course you'd need to add in your 'handling' there too. Long process though and I don't envy you for it.

Hope this may spark something Frank, otherwise good luck.

Jeremy.

PS - I've just spent an hour between other tasks and found Kim did too! This software 'warns' you when someone has posted while you were writing... Haven't read his post yet so not sure if my effort is redundant but here it is. Read the first line though Kim I've experienced that too ( ) so now I highlight and copy my text to the clipboard before attempting the post.

[vandenboom]

Kim, thanks for taking the time to put this response together - twice!
By elimination, it can't be the finish as the same thing has happened to two completely different finishes with different application procedures.It is unlikely to be the wood, as it occurs on 3 types of wood being used - the Wenge fb binding, blackwood shaft and silver wattle lam.
So I agree, that the culprit is something to do with zpoxy and my approach to applying it.
I will probably sand the whole neck back again, fill it with something else and re-oil.
Thanks again. Frank.

[Kim]

Sorry for you Frank..this is such a bummer...I do know from personal experience.

Just a further tip for all seeking to avoid problems with amine blush and to help protect yourself from sensitivity issues.

USE A FAN AT ALL TIMES DURING THE MIXING, APPLICATION AND CURING OF EPOXY

I know I have said it before but seriously, to apply epoxy 'indoors' without a simple fan running to push the CO2 from your breath away from the work piece and the toxic epoxy fumes away from your skin is just asking for trouble.

Cheers

Kim