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Fine Surface Cracks
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=29607		 Page 1 of 1
Author:  bill stewart [ Fri Oct 22, 2010 1:43 pm ]
Post subject:  Fine Surface Cracks
I'm mystified by three very fine surface cracks appearing under the nitro finish I'm doing at present on my Colombian rosewood, (dalbergia tucurensis), concert parlor build. After three coats of Z-poxy I had a wonderful smooth finish but since I've started spraying the the finish these fine surface cracks, two about 1 1/2 " long, and the third is running partly down the center seam. There are no signs of cracks on the inside.... which has me baffled! I'm just wondering could temperature changes be the cause of this? I've been spraying just outside the door of my shed and then hanging it inside (with the heater on low) to dry between coats. I've only done three coats. I would add that the weather is dampish and windy just now. Someone please tell me this is not serious and can be rectified!

Bill S. gaah
Author:  ChuckG [ Fri Oct 22, 2010 3:47 pm ]
Post subject:  Re: Fine Surface Cracks
Are the cracks in the wood or in the Z-poxy filler?

Chuck
Author:  TonyKarol [ Fri Oct 22, 2010 6:13 pm ]
Post subject:  Re: Fine Surface Cracks
I am guessing, bit I think the heater is the problem .. its curing the finish too fast (its warm and dry heat ) and causing it to shrink (catalize) too fast ....

OR ..

it could be you have hairline gaps at the centre seam ... lacquer is extremely thin and will not bridge gaps - it looks fine when you spray, as its wet, but after it flashes off, the gap will be evident. You will need to drop fill these as you build the coats ... then flat sand them
Author:  bill stewart [ Fri Oct 22, 2010 6:29 pm ]
Post subject:  Re: Fine Surface Cracks
I'm not sure Chuck, after the second coat of nitro the first two "cracks" just seem to have magically appeared. After the third coat was applied the fine line showed about 4 or 5 inches down the center seam of the back. Nothing has appeared on the sides so far.

Bill
Author:  bill stewart [ Fri Oct 22, 2010 6:43 pm ]
Post subject:  Re: Fine Surface Cracks
I think your answer could be the right one Tony, the sudden temperature change from spraying in the cold outside to the warm shed causing it to flash off too fast. I'll try the drop fill and see how I get on.

Thanks Guys

Bill
Author:  bill stewart [ Sat Oct 23, 2010 6:56 am ]
Post subject:  Re: Fine Surface Cracks
Hey thanks Todd, I followed your videos on epoxy pore filling to the letter. Even got myself the same 6" squeegee and the stuff spread like a dream. On previous guitars I used used an old credit card. The results weren't as good and I had to do a fair bit of leveling prior to shooting the finish.

Bill
Author:  Darryl Young [ Sat Oct 23, 2010 7:38 am ]
Post subject:  Re: Fine Surface Cracks
Bill/Todd, where did you find the 6" squeege? The smallest they had at Lowes was a 12" model. I finally found a 5" one at Bed Bath & Beyond (wifes suggestion) but I don't think the quality is as good as the one Todd uses in the video. I tried the one from BB&B last night on luan plywood and it did ok, but not great. Will see how it sands out today.
Author:  ChuckG [ Sat Oct 23, 2010 7:49 am ]
Post subject:  Re: Fine Surface Cracks
I agree with Tony and Todd. I had this happen on a Ziricote guitar not long ago and drop filling the "cracks" and then leveling did the trick.

I buy the longer squeegees and cut 2 inch ones from it on the bandsaw. I spread the Z-poxy initially with these small ones and then go back over each area with a single edge razor blade. The reslust is a very thin coating that's easy to sand. You have to work pretty quickly, though.

Good luck!

Chuck
Author:  bill stewart [ Sat Oct 23, 2010 9:19 am ]
Post subject:  Re: Fine Surface Cracks
I got a 10" one locally from a market stall in my home town in Scotland and like Chuck I cut a couple of inches off each end with a junior hacksaw to give me a six.

Bill
Author:  bill stewart [ Sat Oct 23, 2010 12:54 pm ]
Post subject:  Re: Fine Surface Cracks
I'll bear that in mind next time Todd..thanks again.

Bill
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