Compatability of Tru-oil with other finish materials

[tim mullin]

I know luthiers in Canada and the US who are using Tru-oil on the neck shaft of guitars where the remainder of the instrument is finished in gloss lacquer, to achieve a "fast" feel. I've been doing this on the last few guitars, but have learned some hard lessons about compatability. (If you look at the posting I made recently on the Gallery, my recent OM has a Tru-oil finish on the neck).

For those not familiar with Tru-oil, it's a polymerizing oil (i.e., varnish) that cures very quickly and is highly resistant to moisture once cured. It is manufactured by Birchwood Casey as a rifle stock finish and readily available from gunshops. Some folks are using it on the entire instrument, but many more are using it on neck shafts for improved feel over lacquer.

A quick search at the OLF will confirm that Tru-oil is not really compatible with Zpoxy epoxy resin -- it can develop fuzzy spots after a few months, although these can be buffed out. I should have sorted this with better research before I made the same mistake on my first attempt. The solution is easy -- a barrier coat of shellac does the trick.

More difficult is the incompatability between Tru-oil and the Mirotone 3220 precatalysed lacquer that many of us use in Oz and NZ. I've been spraying the headstock and heel areas with lacquer. Once the lacquer build is complete, I then apply Tru-oil in several thin coats, leveling every few coats. Problem is, where the Tru-oil is applied in the transition area at the nut and heel ends, it doesn't cure properly and remains sticky. When you level, you can rub the sticky layer right off the lacquer. Doesn't seem to matter how long the lacquer has cured, or how long you leave the Tru-oil to dry. If done very carefully, this works OK, but there is a very fine line between rubbing the sticky stuff off the lacquer, and going too far and exposing bare wood. My contacts who are using this technique in Canada don't seem to have this issue -- Tru-oil cures just fine on their lacquer.

I've tried cleaning the surface with alcohol, napatha, etc., but nothing seems to encourage the Tru-oil to cure properly on the 3220. If anyone else has experienced this problem, and especially if they've found a solution, I'm all ears. I can get a good finish at the transition area with something of a fiddle, and I really like the feel, but I'm not sure I'll be doing it again.

[Bob Connor]

Maybe use Mirotone 3220 30% gloss on the neck Tim.

Regards

[Kim]

A quick search at the OLF will confirm that Tru-oil is not really compatible with Zpoxy epoxy resin -- it can develop fuzzy spots after a few months, although these can be buffed out. I should have sorted this with better research before I made the same mistake on my first attempt. The solution is easy -- a barrier coat of shellac does the trick.

If you read those topics at the OLF more closely Tim you will find that what you are talking about is epoxy amine blush (google it). You can buff the effected finish but the fuzziness will most often return eventually and because the effect of amines (amino acids) is to retard or even reverse the polymerization process, sealing with shellac will often prove ineffective in the long run as well because it too will at first cure on the surface and then soften through from beneath.

The only way to properly deal with epoxy amines is to first of all make sure that you apply epoxy in a well ventilated area to keep down the carbon-dioxide count in the air, keep a fan running to keep carbon-dioxide from your breath off the work and just as important, the epoxy fumes from your skin, and don't apply epoxy at times of high relative humidity.

This is the reason why some people report no problem with truoil over epoxy yet others experience major problems, the cause is mostly environmental and if you just happen to apply amine cured epoxy in the right conditions with low moisture and low carbon dioxide count in the air, then there will be no problem. But, my advice is that if you are unsure if these preventative measures were enough to prevent amine excretion during the curing process..DO NOT SAND WITH ABRASIVE UNTIL AFTER THE SURFACE HAS BEEN WASHED THOROUGHLY WITH WARM SOAPY WATER AND A NYLON SCOURING PAD AND THEN RINSED WITH FRESH WATER.

Cheers

Kim

[tim mullin]

You can buff the effected finish but the fuzziness will most often return eventually and because the effect of amines (amino acids) is to retard or even reverse the polymerization process, sealing with shellac will often prove ineffective in the long run as well because it too will at first cure on the surface and then soften through from beneath.

Certainly I missed anything on OLF that would suggest shellac would be ineffective, but my most recent use of Tru-oil has avoided the Zpoxy compatibility issue altogether by using another water-based pore filler on the neck.

[tim mullin]

Maybe use Mirotone 3220 30% gloss on the neck Tim.

Regards

Good suggestion, Bob, although I'm not sure how the "feel" would compare between that and Tru-oil, which is the main reason for the Tru-oil on the neck. If it was comparable, I would still have something of an issue trying to spray 2 different gloss levels on the instrument, as my necks are already attached when sprayed -- for those who assemble after finishing, this would of course be a non-issue, provided they like a satin finish on the entire neck. Of course, I guess they could also finish the entire neck in Tru-oil, and not just the shaft, which also avoids the compatability issue.

[Kim]

You can buff the effected finish but the fuzziness will most often return eventually and because the effect of amines (amino acids) is to retard or even reverse the polymerization process, sealing with shellac will often prove ineffective in the long run as well because it too will at first cure on the surface and then soften through from beneath.

Certainly I missed anything on OLF that would suggest shellac would be ineffective

That's because until amine blush/bloom had been bought to the attention of the folks at the OLF in a number of separate threads started at that forum by people who had experienced issues with oil based finishes, 'most' at that forum seem to have never even heard of it. In fact it is fair to say that most at that forum still do not seem to understand or want to understand what amine blush is, how it happens, or that when it does happen it will effect the curing of any finish which relies upon a process of polymerization e.g; any oil based finish and, to some degree, shellac also. This is why some people who have used french polish over zpoxy have also reported the same fuzziness in some of those same topics.

So yes, an obvious solution is of coarse to avoid epoxy fillers if you plan to use these type of finishes, but my post here at the ANZLF was made simply to clarify that the fussiness you had mentioned in your post has nothing whatsoever to do with any incompatibility issues as you had suggested. Rather that the issue is the direct result of a reaction to a bye product of the amine curing process upon which all epoxies rely to varying degrees, and that this bye product can be avoided or controlled by understanding the importance of the environmental conditions during application and curing of epoxies.

One thing I will say about those people not wanting to understand the issue of amine blush is that they generally do so pointing to the fact that they themselves have used oil based finish or FP over epoxy filler and not experienced any issue whatsoever. In that they feel they 'know' conclusively that the whole amine blush suggestion is complete rubbish and that the problem others are experiencing 'must' be caused by something else such as out of date product, application techniques, or a host of other possibilities. But as I have suggested, amine blush is a direct result of environmental influences during application and curing so the bottom line is that sometimes you can just get lucky, and in the right place, that could even be most of the time, but its a prick of a job to have to rub back your pride and joy to bare wood when your luck runs out. So IMO its better to take the time to understand what the problem really is before it happens to you rather than to assume that it can't happen because it hasn't yet.

Cheers

Kim

[rocket]

Hi Tim,, a suggestion from a relative novice in this area. What about spraying the whole neck in gloss as normal and the area you want the tru-oil on, instead, rub back with a very fine w/d and then polish with a series of fine polishing cloths. Should turn out very shmooove and a semi gloss.
Cheers,,,, Rod.

[tim mullin]

Hi Tim,, a suggestion from a relative novice in this area. What about spraying the whole neck in gloss as normal and the area you want the tru-oil on, instead, rub back with a very fine w/d and then polish with a series of fine polishing cloths. Should turn out very shmooove and a semi gloss.
Cheers,,,, Rod.

Thanks for your thoughts on this, Rod. Indeed, your suggestion would indeed give a nice semi-gloss finish to lacquer, but on a neck the effect will quickly become non-uniform as playing would cause the lacquer to regain its gloss in worn patches. Bob's suggestion of using lacquer formulated with flatteners is the only real way to maintain a satin finish on a wearing surface.

But, a satin finish is not really the goal. Lacquer of any kind is still lacquer, and doesn't have the "feel" of Tru-oil -- that feel really is quite different and I now appreciate why so many players like it. It seems that Tru-oil application may be made over areas sprayed with some brands of lacquer -- but this is apparently not the case with Mirotone 3220, as the Tru-oil doesn't polymerize properly.

If I were to do this again, I suspect I would apply a barrier coat of shellac over the lacquer in the transition areas first -- Tru-oil cures just fine over shellac, and shellac gets along with lacquer. When I level the finish, I suspect there is a risk of witness lines as the shellac is exposed between the Tru-oil and lacquer layers -- probably most noticable over dark woods like ebony binding. I have some experiments to do first.

Meanwhile, if someone has insight to share on how treat Mirotone 3220 so that it accepts Tru-oil, I'm all ears. Or perhaps other lacquer formulations that are as suitable as 3220, but yet might accept Tru-oil in the same way that other formulations from North America apparently do.