Finishing Cocobolo

The Achilles' Heel of Luthiery
btberlin
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Joined: Sun Dec 30, 2012 11:53 pm

Finishing Cocobolo

Post by btberlin »

I have a Cocobolo back and side set now in a vacuum press in my shop, and hope to start building a J45 with it early next year. I'm already looking into finishes for Cocobolo, knowing that it is a very difficult wood to finish. I have been thinking about an acetone wipe, followed by a blond shellac wash, followed by Target EM1000 sealer, and then EM6000 Lacquer. I'd appreciate cautions, ideas, descriptions of experience, and the like, on this topic. I am aware of the allergic issues, so, please, don't discuss that.

bert
B. Howard
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Re: Finishing Cocobolo

Post by B. Howard »

Bert, using shellac under a water born finish is not a good idea. Shellac and water are a bad combination and problems often arise when this combination is used. The acetone wipe down directly prior to finishing is almost mandatory on oily wood like coco. If you are going to be using target coatings, the best finish advice you can get on procedures and materials would be had by contacting their tech department and having them spec a finish schedule for you in this application. That's the beauty of staying within a finish system.
You never know what you are capable of until you actually try....

Brian Howard
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btberlin
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Re: Finishing Cocobolo

Post by btberlin »

Not sure where you are getting that information from. Target makes a WB shellac sealer (Ultraseal), shellac is often recommended as an isolation coat between, say, a tinted wb coat and a finish coat, and I have been assured by a few different manufacturers' support people that their WB coatings bond fine to shellac. Target support has been a bit difficult to get in touch with in the past, and, at any rate, i doubt that they've had any direct experience with Cocobolo, which is why i was looking for someone on this forum who might have gone through this already. I did purchase a few cocobolo cutoffs when i bought the back and side set, so i could experiment, but, i was looking for a good place to start the experimentation.

b
B. Howard
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Re: Finishing Cocobolo

Post by B. Howard »

Most of my knowledge on wood finishing comes from a 30+ year career in high end woodworking. Not sure how they make a WB shellac....Shellac is pretty universally known for it's lack of resistance to water. Mixing a bit of water into some shellac will turn it into a milky mess that is unusable. I hear from people quite often looking to determine the cause of a finish failure with a WB coating and a commonality is often the use of shellac as a sealer. A major company like Target should have a finish schedule for oily woods like teak, coco (or any other Rosewood). Putting shellac over a WB coating as a bond coat to tie in say a lacquer is completely different than using it as a sealer beneath it.
Which companies told you it was fine to put their product over a shellac? Did they mention a brand of shellac? I have dealt with most of the major coatings manufacturers at one time or another and none of them would ever confirm any finish schedule that uses a product from another manufacturer because their lab has not tested it to confirm functionality.
You never know what you are capable of until you actually try....

Brian Howard
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btberlin
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Re: Finishing Cocobolo

Post by btberlin »

Nonetheless, whether you are aware of the magic of how they dissolve shellac in a water-based solution, or not, they do it successfully. For directions of use of their water-based protocol using their emulsified linseed-oil-based stain and wb EM6000, see directions on the can of their 4000 product which describes its use over shellac. Also, conversation with long-gone tech support from Enduro WB varnishes, now owned by General Finishes confirmed the validity of the practice. See this article as well.
http://www.woodworkersjournal.com/Main/ ... -5129.aspx. Note the discussion of sealer, referring to shellac, and waterbased (it covers oil-based as well) finishes. Personally, over the past 45 years that i have been doing woodworking and applying fine furniture finishes, lately with an hvlp conversion gun, i have certainly used 1 lb cut amber dewaxed shellac from flake as a wash over raw and stripped wood, followed by WB varnish. It works quite well. IF you doubt the adhesion of a finish over shellac, try the "tape test."

Again, I was hoping to hear from someone who had actually finished cocobolo, and would be willing to share their actual experience and knowledge.

Bert
B. Howard
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Re: Finishing Cocobolo

Post by B. Howard »

I do not use WB finishes personally. Have tried the best from the best and do not like the way they look. I have however finished coco......just not with the schedule you want. As I stated earlier, If Target coatings lab techs don't know how to finish coco with their products it is likely no one does. According to the TDS for the sealer you mention it works with all domestic and exotic woods. http://www.targetcoatings.com/images/PD ... Master.pdf
Their prep instructions look like what I typically do on oily exotics, so I am not really sure what the shellac is for anyway...

Have not heard of the tape test, what is that?. Have done 90 day impact tests in the past to assess finish viability and also had field chemists come by the shop and run assessments as well and never seen it.


Anyway, Good luck with your project.
You never know what you are capable of until you actually try....

Brian Howard
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Custom finishing services

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btberlin
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Re: Finishing Cocobolo

Post by btberlin »

There are two short forum topics on the subject of finishing Cocobolo on the Target forum. In one reply, the author wrote, "PostPosted: Sat Aug 27, 2011 10:34 am Post subject: (EM1000 and) EM6000 on Cocobolo Reply with quote
Used many times ..no problem ...really brings out the many colors
of the wood." http://www.targetcoatings.com/forum/vie ... t=cocobolo

The other reply was, "Welcome-
You can put any of our finishes over epoxy base coats. Ensure that the epoxy is cured and that any amine blush that rises to the surface of the epoxy is washed and neutralized with denatured alcohol. Fine sand with 320 grit then apply the coatin of choice.
JW" http://www.targetcoatings.com/forum/vie ... t=cocobolo

That said, I will go ahead with a test on the Cocobolo cutoffs that i bought when i purchased the back and sides.
As usual in my experience, response to my direct question through the target customer support "contact us" is not very good, but i think the forum gives me what i was looking for.

As for appearance, you may not like the water-clarity of WB finishes, and bluish cast some of them have. To overcome that there are a couple of tricks you may want to try - if you have any motivation to try WB again. First, an amber dye referred properly to as "overprint" can be added. I bought a lot of it years ago before Enduro sold out to General Finishes. I don't know if GF still makes the tint available as a separate item, but, it could be duplicated, IMHO, by any compatible amber dye added to the finish. Second, and I have used this with very good results on oak cabinet doors, to match the effect of light-aging when I added two cabinets to some that had been in place for several years. Flake dewaxed shellac comes in various shades from blonde to ruby. I have used the reddish-amber shellac as a sealer on oak, under WB, to match the effect of light. Worked out quite well. I have also used the overprint addition (without shellac) on freshly milled hard maple again to mimic the effect of light-aging. Doing so i was able to pretty closely match the color of 6 kitchen chairs i built to go with a hard-maple table made elsewhere, and at another time period.

As for the tape test, it's a simple test often used to test the adhesion of a finish to the underlying substrate. It's simple, and here is an example - some years ago we were about to re-finish oak flooring. The only source of the stain color we liked was an oil-based stain. The most highly recommended finish was a high gloss water based. HOw to determine that the WB would adhere over the oil-based stain? The manufacturer of Varathane was not able to make any guarantees that it would. So, I sanded a piece of oak to the same grit the floor would be sanded to, and stained it with the Oil-based material. It was allowed to dry for one day. Then a few coats of the Varathane were mopped over the stain. When that had dried hard, after the recommended period, a series of cross-hatch scores were made in the varnish with a razor, with the lines about 0.25 inch apart. A piece of clear packing tape is pressed over the hatched area. And then you pull. You can assess very well if the finish is adhering to the underlying substrate. in this case it did, and has held up quite well for years. This is a pretty standard test, to which you may find reference in some of the woodworking journals' archives, although I think i found it first in a test report article in Fine Woodworking which was dedicated to WB finishes.

bert.
Kevin Sjostrand
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Re: Finishing Cocobolo

Post by Kevin Sjostrand »

I just noticed this exchange.
Bert, I made a coco guitar and finished it with epoxy as a porefill and sprayed Deft nitro lacquer as the finish. That was 3 years ago and it has held up well, it's life thus far in India in high humidity.
I don't recall wiping it down with anything prior to the pore filling other than to get the dust off, however Coco does have some natural oils that could be considered. I did use a special adhesive for gluing the coco bridge to the top, and I did wipe it down with acetone right before gluing. I also used epoxy to glue the back panel joint and the back to the sides, just for some security.

Hope this all helps in some way.

Kevin
btberlin
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Re: Finishing Cocobolo

Post by btberlin »

This is very helpful information. It coincides well with a response on the Target coatings site, in regard to using their materials over epoxy filler (quoted in an earlier posting).

I was considering one of the epoxy fillers that LMI carries, and was a bit concerned about how easy they are to sand back. I believe they carry two types, one recommended by O'Brien in his DVD about building a kit steel string guitar. I would be sanding by hand, not machine, so, i would want to know that epoxy fillers are not really difficult to sand. I do, as I have mentioned, have coco cutoffs for testing the finish protocol, as well as a stick of Koa that i am planning to cut into strips for binding and tail wedge.

Do you happen to recall which epoxy you used?

I purchased the System II (or is it III?) epoxy glue for joints involving the coco, and would be using hide glue for the fingerboard to (sapele) neck and fingerboard to (Sitka) top (the neck from LMI, is a bolt-on), and possibly for the top to ribbon joint and certainly for the bridge to top, joint. I figure that this leaves the guitar repairable should the need arise.

b
B. Howard
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Re: Finishing Cocobolo

Post by B. Howard »

I use epoxy as a filler, and sometimes a sealer quite often. I use system 3's SB112. I prefer it over z- poxy for its clarity. I add fumed silica to it to expand and thicken it. This also makes sanding a little easier. The first coat I will usually scrape after about 12 hours while it is still a bit soft. The second coat I will sand after 24. There are two ways to use it. Strictly as a pore filler where the epoxy is only on the pores and the rest is bare wood or you leave a thin cost on the entire surface.
You never know what you are capable of until you actually try....

Brian Howard
www.brianhowardguitars.com
Taylor authorized service
Custom finishing services

Brian howard's guitar building & repair blog
http://www.brianhowardguitars.com
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