Replies

1. 
   SteveSchoene | Nov 09, 2005 04:37am | #1

   I've not used them, but according to my published sources, these materials cure similarly to varnish, with a chemical reaction, while NC lacquer, like shellac dries by evaporation. This gives them superior resistance to chemicals.  As far as rubbing out, it is supposed to be more difficult than NC lacquer which is the easiest, along with shellac, out there.  These sources also suggest that having to add catalyst increase the chance of error, and also gives a smaller window to complete the work. 

   Hopefully, someone with more direct experience will chime in. 

2. 
   Tao | Nov 09, 2005 07:44am | #2

   I've used pre- and post catalyzed finishes a lot over the years.  There's a lot of variation in durablity and color with various products, but they pretty much all spray pretty much like lacquer, are ready to sand / recoat in about an hour, and ready to package overnight.  The big difference is in durability and chemical resistance, which generally far exceeds non-cat products.

   Precat lacquers are on the low end of the scale. They are lacquers with cross-linking resins added with a level of resin and catalyst that is low enough to give extended shelf life.  Post-cat lacquers are next up the scale.  They have more cross-linking resins in them, and get the catalyst added just before application.  Both of these products amber or yellow just like NC lacquer, and tend to be sensitive to too much film build -- they crack if you build them up too thick.

   Conversion varnishes using straight amino-alkyd resins or something similar stay pretty much water white and have higher wear and chemical resistance than most post cat lacquers.  The ones I have used spray nice, sand easy and dry fast

   Catalyzed urethanes are very much like automiotive clear coats, with similar clarity and durability.  I find them very easy and satisfactory to use on commercial work. They also are comparatively safe.  The one I use most (ICA) has a better health rating than regular lacquer, if memory serves.

   Polyesters are the king of high-build, high durability, but they can be tricky to apply and rub out, and generally have a very short pot life. Unlike the other finishes, I don't believe it is available in different gloss levels, and it's fairly common practice to build depth with polyester and then topcoat with cat. urethane to get a given off the gun sheen.

   That's a pretty sketchy overview, but I hope it helps a little. New product variations keep coming along, and I can't cover them all here.

    

    

   Michael R

   Sometimes it's the artist's task to find out how much music you can still make with what you have left.  Itzak Perlman, upon playing a concert on three strings at Lincoln Center after breaking a string.

1. 
   KesslerCraftsman | Nov 10, 2005 05:50am | #5

   An excellent quick overview, Michael.

   I do have a couple of questions as follows:

   When you speak of pre- and post-cat lacquers being 'ready to package overnight" you mean you don't have to let them cure like one does NT lacquer or Shellac, correct?

    

   Secondly, when you speak to conversion varnishes you say they spray well and dry fast.  I'm used to thick, slow-drying poly varnish, etc....  How fast is "fast" compared to lacquer?  I'm not using a spray booth...not a pristine environment, but not bad either.

   I ask the two dissimilar questions from two different perspectives.  I make studio furniture, but also frames to customer/frame shop measurements. 

   For the furniture, "packaging" time is not an issue...quality, clarity, sheen, etc is. 

   For the frames, these things ship all over the country and have to ship FAST to meet customer demand...nothing like finishing a frame, putting in the packaging and having something "stick" in transit...although it's only happened once, it's still a fear...  For the latter, would the post-cat stuff do the trick...in your opinion?Thanks again!lp

    

1. 
   Tao | Nov 10, 2005 07:06am | #6

   A typical finish would consist of one coat of vinyl sealer or self sealing with the topcoat itself, depending on what kind of stain and glazes you might be using, followed by two top coats applied about 4 mils wet at package consistency, or with very little thinning.  Such an application is usually cured out well enough to package overnight.  If you apply too many coats, or don't allow enough drying time between coats (typically an hour), or apply the material too heavy or if the work area is cold, your finish won't cure out as fast. Most finishes take considerably longer to cure fully, but they are OK to stack or package overnight.

   Most conversion varnishes I have used handle just the same as lacquer, and dry and cure just as fast.   They are called varnishes because they crosslink and don't have any nitrocellulose in them, not because they dry slow.  I occasionally brush traditional alkyd varnish, but never use oil based poly, since there are so many better alternatives available.

   Any finish I use is based on looks, durability, cost, speed, and ease of application, pretty much in that order.  Depending on the application, it could be anything from shellac (a particular favorite) to catalyzed urethane. I have had good luck rubbing out most of the catalyzed finishes I have tried.  CAtalyzed urethane has a definite window of a few days, after which it gets a lot harder to polish out, especially if you are after a wet look.

   You might want to try one of the high performance precat lacquers like Magna-Max for your frames.  No mixing, very good durablity, easy to spray, and not too expensive.  Mixing post cats can take up more time than you think, and pot life is typically only a few hours, so you probably don't want to bother with it unless you really need the extra performance.

    Michael

   Sometimes it's the artist's task to find out how much music you can still make with what you have left.  Itzak Perlman, upon playing a concert on three strings at Lincoln Center after breaking a string.

1. 
   KesslerCraftsman | Nov 10, 2005 07:35am | #7

   Thanks!

    

   lp

3. 
   beachfarm | Nov 10, 2005 01:53am | #3

   My shop finish is M. L. Campbell "Duravar Plus" - a post catalyzed lacquer. If you're comfortable spraying "traditional" lacquers and/or varnishes, then you'd be comfortable with Duravar.

   Some points:

   • Mixing the catalyst is a no-brainer. Campbell supplies quart cups with clear markings for the catalyst to lacquer ratio. Once you're comfortable with the product and the ratio, you can eyeball the mixture (using the marked cups) with confidence.
   • Duravar takes toners well - either Campbell's Woodsong brand or, in my case, Mohawk finishes.
   • Once mixed, the pot life is rated at 8 hours. That's the factory message. I've used two-day old mixtures on cabinet interiors and shelves with perfect success. For exterior and other surfaces (those that you care about), mixing a fresh pot is always best.
   • Thinning the product (if necessary) is done with Campbells higher grade of thinner.
   • Clean up is with economy lacquer thinner. Measuring cups can be dumped and left to dry upside down - the resulting dry lacquer film inside the cup just pops out. I clean my gravity feed gun with the same thinner.
   • I wear the very same mask and filters that I've worn for every finish I've sprayed.
   • I prefer to let my first coat - which also acts as a sealer coat - dry overnight. Two coats is best, but if I need three, I can sand between the first and third at 1/2 hour intervals.

   As a product, Duravar (and other post cat lacquers) offer superior protection from water, chemicals and abrasion. There are pre-catalyzed lacquers, too. Frankly, I can't see the point in spraying a film with inferior durability, so I don't spray pre-cats. For jobsite touch-ups, Campbell's Magnalac is a pre-cat that dries quick with a finish to match their product line.

   As far as rubbing out the finish - that depends. I don't rub out commercial work. I don't feel that I need to. Duravar comes in several finishes (satin to semi to gloss). If your spray room is clean, the final coat goes down like glass. I have rubbed the finish on personal work and found that, given the right amout of cure, post cats rub out just fine. (All through the sanding stages, it easily sands to a talc.)

   You can find the answer to just about every product and process question on their website. I only use Campbell as an example.

   Regards.

   http://www.mlcampbell.com/

1. 
   DougU | Nov 10, 2005 05:09am | #4

   Beachfarm

   Have you ever used the UltraStar water borne finish? If so what did you think of it?

   I have a dilemma in  that I have to spray some cabinets on site and I don't want the neighborhood police coming after me for stinking the place up with lacquer. Homeowners wont care because they will be gone but I'm afraid the smell will be to much of a nuisance.

   Doug

1. 
   beachfarm | Nov 10, 2005 03:29pm | #8

   Sorry, but I haven't used UltraStar. Haven't sprayed other water base, either.I've only sprayed on-site once, with pre cat lacquer - and that was the last time. My concern then and what might be yours now is not the smell but the hazard of spraying a volatile lacquer in a dwelling. I had the luxury of spraying in a house that was under a serious renovation (no concern for overspray) vacant (no concern for the health of others) and had no powered ON appliances or furnace (no concern for life ending explosions).I'd say brush the boxes and spray the drawfronts and doors off-site.

1. 
   DougU | Nov 11, 2005 03:07am | #9

   I'd say brush the boxes and spray the drawfronts and doors off-site.

   Funny you should mention that, we just talked about doing that today!

   Thanks

   Doug