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Back finishing problem
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=19319		 Page 1 of 1
Author:  vandenboom [ Sat Oct 25, 2008 4:41 am ]
Post subject:  Back finishing problem
The dreadnought I have been finishing has blackwood back and sides - not tasmaninan blackwood, I was told it is Gippsland blackwood.
I initially filled pores with LMI water based pore filler. Gave it 12 coats of nitro. But I found it had very deep small holes and slits in the lacquer - not just low shiny spots you see during levelling. I just couldn't sand them out - I even got down to using P240 and thought I must have done a lousy job of pore filling. So I scraped the back to bare wood and did several new applications of pore filler - 24 hours to cure after 3rd application, then a light coat of shellac and am now up to coat 8 of lacquer in this second attempt.
However I am having much the same problem, although I haven't seen slits quite as deep as previously.
Initially I started levelling with P600, but could see I wasn't getting anywhere, changed to P400, still not getting anywhere, so back to P240. Unfortunately, I sanded through to wood in a couple of spots. While I am now much closer to having sanded out the pits and slits than on the first attempt, I'm still not there.
This is my 4th guitar, but none of the previous were difficult as this. Sometimes I still don't feel confident that I understand some of the basic aspects of finishing. All I can think of is that the pore filling is ineffective for some reasons, and that this wood has very big pores. I have seen comments in other posts that don't regard LMI water based pore filler very well, but I figure lots of people must be using it, and I didn't experience this problem after using the LMI filler on 3 previous guitars, though the wood used on them was different.

Can anyone read anything into this situation?
Frank
Author:  Martin Turner [ Sat Oct 25, 2008 5:41 am ]
Post subject:  Re: Back finishing problem
Any possible source of silicon contamination during build/finishing process? Probably a stab in the dark but silicon release agent from a non slip mat I had a guitar sitting on probably lead to finish failure on the back of the instrument.

Hope you get it sussed.....

Martin
Author:  vandenboom [ Sat Oct 25, 2008 6:58 am ]
Post subject:  Re: Back finishing problem
I did not have this problem with the top or the neck and sprayed them at the same time. The sides had similar problems but the slits were not as deep and I was able to sand them out, but again it was a fair bit of work. So I don't think silicone contamination was at work.
I followed the suggestions in the Stewmac "Finishing Step by Step" book and cleaned the wood down with Naptha, metho and then ammonia before spraying and that is supposed to deal with silicone residue.

Frank
Author:  Hesh [ Sat Oct 25, 2008 6:59 am ]
Post subject:  Re: Back finishing problem
Hi Frank - the Stew-Mac water based filler which is probably much like the LMI filler gave me fits and I was never able to get good results with it. This included a guitar with an Aussie Blackwood back and sides......

What worked for me was switching to epoxy finishing resin for pore filling. System III was the first product that I tried and it worked great. It is unforgiving in the mix ratio and requires a gram scale to ensure an accurate mix. Next I tried Z-Poxy and liked that even better - Z-Poxy is more forgiving in the mix ratio. Both products gave perfect fills with two applications and any sand through was easily fixed by wiping on a 50/50 thin coat of the epoxy and denatured alcohol to even out the color. Use a lint free cloth to wipe the mixture on. Both of these products are "finishing resins" and not designed to be epoxy glues because of the thin viscosity. Be sure to get the finishing resins because both Z-poxy and SIII also make epoxy glue in other flavors.

West Systems epoxy, not a finishing resin, also works fantastic.

I guess the main point of my post here is that I never had any luck with the water based fillers but when I went the epoxy route the problems were solved immediately and pore filling was now something that let me keep some of my hair.....

Application technique is also a possible problem area until you get your technique down. I use a credit-type card (preferably without a high balance.... :D ) and instead of using it to squeegee on the epoxy I use it to "mash" the epoxy into the pores moving in all directions but especially at 45 degrees to the grain. Once a small area is done I then use the card at 45 degrees to the grain to squeegee off the excess. Wait a day and sand it back, it sands easily and you can sand back to bare wood or leave a thin coat of epoxy over the wood. Nothing pops the figure of the wood like epoxy.

Good luck.
Author:  cphanna [ Sat Oct 25, 2008 9:17 am ]
Post subject:  Re: Back finishing problem
Hi, Frank,
Is it possible that you sprayed your back coats a little more heavily--or more thinly-- than your top coats? Or that your individual coats were of different thicknesses? (thin coat over a thick coat over another thin coat...etc.?) I can only relate my experience. I shot my archtop with Target Oxford Ultima, and most of it was very easy and problem-free. I shot three thin coats a day, with an hour or more drying time between each coat, and then a 24 hour wait before the next three applications. I also sanded after each 24 hour layover. I tried to keep the coats very uniform, but I'm far from being an expert sprayer. Somewhere around the ninth coat, I found two slits in the finish, but they weren't deep. In fact, I think they were in the last coat only. The slits were parallel to the grain, and about a quarter or three eighths of an inch long. I didn't know what caused this, but I theorized that it must have been shrinkage of the top coat as the water evaporated. Interesting that the slits were parallel to the grain. That suggests that it might have had something to do with wood movement, too. In any event, I was able to sand them out during the leveling process. I posed a question about this on another forum, and several people reported that they had experienced similar slits in their finish applications. No one knew for sure what caused the problem, but no one attributed it to contamination. I know a lot of people don't like water-borne finishes, but I like the fact that it's pretty safe to use and it doesn't stink up my shop. I also like the way it polished out. I would use it again without too much worry. But I'd keep a sharp eye peeled for the development of these slits between each and every coat. If I detected one, I'd let it dry overnight and sand it out before continuing. If I noticed another slit later in the same place, THEN I would suspect contamination, but not until then.
Author:  cphanna [ Sat Oct 25, 2008 9:25 am ]
Post subject:  Re: Back finishing problem
Frank,
I just red your last comment a second time. No problem with the top or neck. Slight problem with the sides. Most of the problem on the back. Question: Is your neck wood the same as your back and sides? If so, then I am stumped. If the neck is different wood, then I would suspect slight wood movement at a critical time during the finish drying. And, because the back is a wider expanse than the sides, it stands to reason that most of the problem would show up there. Still just a hunch. Keep us informed as you work through it.
I'm sure a lot of people are reading this thread...even if they aren't chiming in.
Author:  vandenboom [ Sat Oct 25, 2008 5:29 pm ]
Post subject:  Re: Back finishing problem
Hesh
My decision last week to scrape the back down and start again was after reading an old post on pore filling which had lots of responses, including yourself. The bit I remember from you was that you proposed that lots of inexperienced luthiers reach this "Ah Ha" moment in pore filling. I really thought that was my moment, and that I had done a poor job of it, so decided to start again. I also moved from using a cloth for rubbing it in to credit card and razor blade with rounded edges (MichaelP method). Anyway, I will see if I can get something equivalent to Z-poxy finishing resin in australia, as I probably can't ship it internationally, and shipping tins of stuff is usually very costly. Any australians out there who know of equivalent products here?

Cphanna
The slits are parallel to the grain and vary in length from tiny holes to 1/4".
The neck timber is different (silver wattle). Back and sides are gippsland blackwood. I see what you mean about movement of the wood. If this is the case, does it mean this wood is unsuitable? If it is due to movement, presumably it will continue to happen after it is finished (if I ever finish it!!) - will the lacquer flex, it maybe develop fine cracks as a result.
The wood didn't cost much but I have enough for about 5 more guitars.
Author:  cphanna [ Sat Oct 25, 2008 7:19 pm ]
Post subject:  Re: Back finishing problem
Frank,
Again, let me stress that I am not an expert. I'm just responding based on intuition. If I had your guitar in my shop and noticed these things, I think I would just slow down, maybe take a couple of days off, and re-evaluate. I wouldn't abandon the wood. I certainly did not abandon the guitar I was finishing, even after a similar problem occurred. In my case, the two slits were very shallow, and I easily sanded them away. Sounds like your slits were deeper. Maybe you were applying finish too quickly, too thickly, or too thinly. I just don't know. Do you have an experimental scrap on hand? You should be applying finish to a test strip at each phase of the process, so that you can work your way through these problems on the test strip as you go along. Do everything to the test piece that you do to the instrument. That way, you can experiment with solutions on the test piece. The test piece must be the same wood as your guitar--maybe a cut-off from one side. Don't abandon your guitar. You'll get a nice instrument out of this if you work the problem out, and then you will get several more nice instruments out of your supply of wood. I think you will be fine.
Author:  Howard Klepper [ Sat Oct 25, 2008 7:53 pm ]
Post subject:  Re: Back finishing problem
No mystery here. Water based grain filler sucks. Don't keep using it and expecting things to turn out differently.
Author:  Alexandru Marian [ Sat Oct 25, 2008 8:17 pm ]
Post subject:  Re: Back finishing problem
If you can't get epoxy, how about pumice. I just used it and i think it is great.
Author:  joe white [ Sat Oct 25, 2008 8:52 pm ]
Post subject:  Re: Back finishing problem
Howard Klepper wrote:
No mystery here. Water based grain filler sucks. Don't keep using it and expecting things to turn out differently.


Now that's right to the point! laughing6-hehe laughing6-hehe

I can't offer anything positive to you other than if you are going to top coat with a solvent material like nitro, maybe a solvent based filler might work best. Epoxy is nice.
Author:  vandenboom [ Sat Oct 25, 2008 10:06 pm ]
Post subject:  Re: Back finishing problem
Ok Howard - pretty clear message - never again!!

Cphanna - thanks for sticking with this. I have no intention of abandoning it. I know the process will eventually end, and I am pretty close now. The main reason I went back to square one is because I thought I had just had my "Ah-ha" moment regarding pore filling, and wanted to do it properly. But, based on Howard's feedback, it's the water based filler that is the main problem.
Author:  Martin Turner [ Sun Oct 26, 2008 5:44 am ]
Post subject:  Re: Back finishing problem
Z-poxy finishing resin is available here in Oz. Try Barnes on line. Theyre currently rejigging their website so you might not see it listed but give them a ring to verify theyve got stock and place order. I found their service good.

http://www.barnesonline.com.au/InfoPages/infozpoxy.htm

Cheers Martin


vandenboom wrote:
Hesh
Anyway, I will see if I can get something equivalent to Z-poxy finishing resin in australia, as I probably can't ship it internationally, and shipping tins of stuff is usually very costly. Any australians out there who know of equivalent products here?
Author:  Hesh [ Sun Oct 26, 2008 6:32 am ]
Post subject:  Re: Back finishing problem
Thank You Howard :D

And thank you Martin - now you have a source for Z-Poxy "finishing resin" in OZ.
Author:  Richard Wilson [ Sun Oct 26, 2008 6:57 am ]
Post subject:  Re: Back finishing problem
I've ordered Z-poxy from LMI in the past no problems... only thing is with the current exchange rate it'll cost you an arm and a leg to do so.

I've also ordered locally from this company:

http://www.amcsupplies.com.au/catalogue ... =7_553_556
(you're looking at the 12oz finishing resin for $25)

It arrived the next day if I recall correctly which isn't bad for Australian delivery. With the dollar where it is this'll probably be your best bet.
Author:  Michael Dale Payne [ Mon Oct 27, 2008 4:35 pm ]
Post subject:  Re: Back finishing problem
YOu might try what I use Starbond Medium Thick CA applyed just like epoxy. One application generally does the trick unless you have reall wide deep pores. Fumes are the only hassel
Author:  paul h [ Mon Oct 27, 2008 4:57 pm ]
Post subject:  Re: Back finishing problem
Michael - do you sand the CA back and just leave it in the pores, or leave it on the surface the way most people use zpoxy?

Thanks, Paul
Author:  vandenboom [ Fri Oct 31, 2008 6:00 am ]
Post subject:  Re: Back finishing problem
Well, over the past week, I scraped the lacquer off the back again - a bit drastic you might think but this has become a learning thing for me - I found some Zpoxy finishing resin in Melbourne, put it on, sprayed on 4 coats and had a good look tonight after a light sand. No holes or slits at all - just the more familiar shiny low spots that are easily sanded out!!!! So in conclusion...
1. Hesh - I think I can now say that I have had my ah-ha moment re pore filling
2. Howard - for this wood, water based filler definitely sucks. Never again.

Thanks everyone for your interest and help.
Frank
Author:  Michael Dale Payne [ Fri Oct 31, 2008 1:00 pm ]
Post subject:  Re: Back finishing problem
paul h wrote:
Michael - do you sand the CA back and just leave it in the pores, or leave it on the surface the way most people use zpoxy?

Thanks, Paul


Paul sorry for the delay. I have done it both ways leaving a ultra thin film of CA or sanding back to wood. I prefer to sand to wood and seal with shellac to get color but it is a bit more work to be sure all the CA is off the wood except in the pores. Either method works equally well but is sometimes hard to not sand through if you try to leave a fine film. but that is the same with epoxy
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