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| precat nitro v straight nitro http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50824 |
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| Author: | roby [ Thu Jul 19, 2018 5:50 am ] |
| Post subject: | precat nitro v straight nitro |
Whats the pros and cons of each one. |
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| Author: | jshelton [ Thu Jul 19, 2018 8:50 am ] |
| Post subject: | Re: precat nitro v straight nitro |
roby wrote: Whats the pros and cons of each one. I tried pre-cat nitro a few years ago. You must be very careful about thickness or it will craze. I had to refinish three guitars and will never use it again. |
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| Author: | DannyV [ Thu Jul 19, 2018 9:59 am ] |
| Post subject: | Re: precat nitro v straight nitro |
Enlighten me please. Isn't the likes of Mohawk or Behlens pre cat? That would be speaking in terms of pre or post cat. Thanks! |
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| Author: | Clay S. [ Thu Jul 19, 2018 12:41 pm ] |
| Post subject: | Re: precat nitro v straight nitro |
The difference between pre cat and post cat lacquers is that with pre cat the catalyst is in the lacquer when you buy it. With post cat you add the catalyst just before spraying. Pre cat is more convenient but because the catalyst is in the lacquer it has a shelf life. I'm pretty sure Mohawk instrument lacquer and Behlin's are non catalysed lacquers - just old fashioned nitrocellulose lacquers with some plasticizers added, but I could be wrong. |
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| Author: | jshelton [ Thu Jul 19, 2018 1:10 pm ] |
| Post subject: | Re: precat nitro v straight nitro |
Clay is correct. |
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| Author: | DannyV [ Thu Jul 19, 2018 3:48 pm ] |
| Post subject: | Re: precat nitro v straight nitro |
jshelton wrote: roby wrote: Whats the pros and cons of each one. I tried pre-cat nitro a few years ago. You must be very careful about thickness or it will craze. I had to refinish three guitars and will never use it again. Any thoughts on the cause of it crazing John? The products would likely be formulate for woodwork. A little more dimensionally substantial than our work, but nonetheless.... |
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| Author: | Ken Lewis [ Thu Jul 19, 2018 4:36 pm ] |
| Post subject: | Re: precat nitro v straight nitro |
Most pre-cat lacquers recommend max of two-three coats. Any more, you can and likely will run into problems. Also I'm thinking that "nitro" as is being referred to here is never available as catalyzed, pre or post. Maybe being confused to lacquer in general? I'm not entirely sure about this though. Perhaps Brian H. can clear things up for us. |
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| Author: | Glen H [ Thu Jul 19, 2018 4:49 pm ] |
| Post subject: | Re: precat nitro v straight nitro |
I believe Mohawk sells all three. This article helps a bit https://www.thewoodwhisperer.com/articles/different-types-of-lacquer/ |
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| Author: | jshelton [ Thu Jul 19, 2018 6:09 pm ] |
| Post subject: | Re: precat nitro v straight nitro |
DannyV wrote: Any thoughts on the cause of it crazing John? The products would likely be formulate for woodwork. A little more dimensionally substantial than our work, but nonetheless.... When I bought the nitro I specifically asked for nitrocellulose lacquer and the moron assumed I meant pre-cat lacquer. It said nitrocellulose on the can so I used it just I've always used nitro for the past 50 years. I like to spray many very thin coats, sanding in between so that the finish doesn't get too thick. I discovered by this unfortunate episode that you can't do that with pre-cat nitro. It's not unusual for me to spray 15 or more coats including the color coat and finishing clear wash coats and have the grains in the top wood show through the finish in just a few days. That's how I know it's not too thick. I can't tell you how annoying it is to have to refinish a brand new guitar that is already sold. I am now very careful to only order nitro from people I trust, sadly the nitro available today is nothing like the wonderful stuff we used to be able to buy. |
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| Author: | B. Howard [ Fri Jul 20, 2018 5:51 am ] |
| Post subject: | Re: precat nitro v straight nitro |
All catalyzed wood finishes I have worked with have functional limits of right around 5 mils. Dry films any thicker will craze, pop or peel in some fashion at some point. This is true of pre and post systems. Catalyzed systems have the benefit of an initiated crosslinker in the chemistry which uses a chemical reaction to help form the coating reducing dry times considerably. A pre cat system behaves a bit like an air dry polyurethane inside as it dries while a post cat is more like a 2K system in how it crosslinks and dries. These additional resins and cross linking components of course change the make up of the final film. This from an article of mine a few years back. You can read the entirety here https://howardguitars.blogspot.com/2015/02/air-dry-lacquers.html "This discourse would not be complete if we did not touch on pre-catalyzed lacquers. This is a basically an air dry type of acrylic lacquer and is not really catalyzed in the same sense as a two part urethane or acid cure amino alkyd. It has a cross-linker and some catalyst added to it. The reaction is triggered when enough solvent evaporates and the ppm of the catalyst reaches a point where the linking reaction begins spontaneously. These coatings do not really have a set pot life per say but do have a definite shelf life. Most industrial pre cat is 90 days. I have seen some consumer grade stuff labeled at 1 year. While it has no set pot life, you can't simply leave it in the gun for days like an air dry. It will usually solidify in the fluid passages and require a break down and clean of your equipment. Pre cat lacquers that I have used were all water white clears. They can be re-dissolved like an air dry so they are still very repairable. That is a main difference between them and their post cat cousins. They are fast dry, generally considered 12-14 hours to stack and pack which makes them popular in a production setting." In fact I believe Martin has been using catalyzed lacquer since the 90's at least..... |
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| Author: | Clay S. [ Fri Jul 20, 2018 9:05 am ] |
| Post subject: | Re: precat nitro v straight nitro |
Hi Brian, What problems may you run into using pre cat lacquer that is a year or more out of date? Someone told me it just doesn't cross link and there may be some lose of clarity. What are your thoughts on this? |
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| Author: | roby [ Fri Jul 20, 2018 12:19 pm ] |
| Post subject: | Re: precat nitro v straight nitro |
Thanks for all the responses, so am i right in thinking that a pre cat or post cat would be more durable and scratch resistant than straight nitro? Here's a couple i'm looking at one pre one post, anyone tried this, not sure if you can get this in the US. https://www.wood-finishes-direct.com/product/morrells-440-acid-cat-laquer https://www.wood-finishes-direct.com/product/morrells-280-pre-cat-lacquer Now a stupid question, when they refer to the number of coats how many passes of the gun roughly would you say is a coat.Thanks Rob. |
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| Author: | Glen H [ Fri Jul 20, 2018 9:42 pm ] |
| Post subject: | Re: precat nitro v straight nitro |
When the passes overlap and flow together it is one coat. |
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| Author: | B. Howard [ Sat Jul 21, 2018 4:23 am ] |
| Post subject: | Re: precat nitro v straight nitro |
Clay S. wrote: Hi Brian, What problems may you run into using pre cat lacquer that is a year or more out of date? Someone told me it just doesn't cross link and there may be some lose of clarity. What are your thoughts on this? It will lack good adhesion and will be softer. The final film simply will not form as designed. Application gets tougher too because that unused catalyst becomes seed crystals that form odd little pock marks in the finish that will repel the next coat unless completely and I mean completely sanded away. |
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| Author: | Clay S. [ Sat Jul 21, 2018 5:01 pm ] |
| Post subject: | Re: precat nitro v straight nitro |
Thank you Brian, That is good to know. There is always the desire to use up out of date materials and usually a good reason not to. |
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