Switching to pre-cat or CV
Properties of these finishes and their applications. December 26, 2002
I am using regular lacquer now but thinking of trying pre-cat or conversion varnish. What do I need to know about these finishes before I use them?
I made the switch not too long ago and I'm relatively new to spraying. I use an Astro with a 1.5mm tip and I have had good results with Valspar PreCat. I think I have sprayed about 12 gallons so far and I'm satisfied with the finish. I believe the main advantage is that it is more durable than lacquer.
Durability is the main advantage. Spray technique and equipment used to spray is virtually the same and you'll not notice anything significant in the way they atomize, flow, dry, and sand. In other words, actually using pre-cats and CVs are not difficult at all. Pre-cats have a long shelf life (a year or more) and come pre-mixed for you. CVs will have to be mixed by you, in the quantity you need, just before you spray; their shelf life (pot life) is only a matter of hours, typically 8 hours. But 8 hours is not a magic number, as I've used mixed CV 10 or 12 hours later, even the next day after refrigerating it overnight if I have a significant amount left at the end of the day. I don't make this a habit but sometimes I can't finish what I started in one day and missed my guess on the amount to mix up. The shelf life of most CVs is basically indefinite, until mixed.
With pre-cats and CVs, you just add thinner and/or retarder as you would for a standard lacquer, in the same quantities to reach the same viscosity and flow properties that you like to shoot. With a CV, you need to add the catalyst before you add any thinner/retarder, as the catalyst is to be in direct proportion to the CV. I use MLC MagnaMax as a pre-cat and MLC Duravar for my CV. I'm completely happy with both. I use MLC's additives (thinners/retarders) for these finishes and I'd recommend that you stick with the same brand of additives that your pre-cat and CV is. Using off brands of thinner/retarder only invites problems and voids manufacturer warranties.
No need to hold off on using pre-cats and CVs. They are as easy to use as a standard lacquer. Once you mix the catalyst in the CV, you have a basic lacquer that you can further thin and shoot. The gun cleaning process is the same - use thinner as you would normally do with lacquer and just use a little more to thoroughly clean the equipment, especially with CV.
Almost forgot one significant difference. Pre-cats and CVs don't allow you to put on an infinite thickness of finish as does regular NC lacquer. Check the manufacturer's recommendation. You don't have to get scientific about it; I usually spray three coats of both. First coat is thinned about 30% for good penetration and adhesion and two full (or nearly full) coats to finish. I also treat pre-cats and CVs like varnish and lightly scuff sand between all coats, as I'm not confident of "burn-in" as you can be with NC Lacquer. That's not a big deal because I always scuff sanded after my first coat or two of NC lacquer, to de-nib and smooth/level the surface before applying the final coats.
From contributor D:
The main difference, as stated above, is that you must be careful not to build too thick of a film. Anything over three mils is a problem. Watching something you've taken great pride in have its finish crack is not very much fun.
Precat is easy. CV you have to mix but goes on good, as well. We've been using Chemcraft's Opticlear for years now and have always had good results. Find a distributor near you that caries a good line. They will be able to give you some advice on how to get started.
We just bought a new Kremlin system and I went the extra dollar for an agitator lid. We use pre-cat over CV because there is no worry about pot life. We turn on the agitator a few minutes before we spray, and then we spray. No mixing, no pouring, no stirring, no filling of silly cup guns. We leave the system pressurized overnight and often for days without using it, then when we need to we just turn it on again... and spray. It's just too easy! My point is that pre-cat will allow this type of use, while CV won't.
Do you use a sealer with pre-cat or do you just use 3 coats of finish?
Sealers are important when using pre-cat or CV (known as AC in Europe - AC = acid catalyzed) on certain timbers, particularly pines. The heartwood of P. sylvestrus is turned pink or red by the acid in the lacquer. Many companies don't, and you can see it in their finished product. My company sells an AC lacquer for flooring and failure to use the sealer has caused some unhappy bunnies in the past!
From contributor C:
Have you ever had to strip a piece of furniture that has been topcoated with CV or pre-cat? It is a job. If you are spraying cabinets, fine, but if you are spraying furniture, it's overkill. We only use pre-cat on tabletops. Everything else nitro. Touch up and repair takes on a new meaning with these cat topcoats.
From contributor D:
Contributor C, you have clearly never dealt with polyester. C-V and precats are jokes compared to that.
Contributor C, you must be in the business of refinishing instead of offering the highest quality coating.
Contributor C is exactly right; each coating has its place and application. Using the toughest coating you can find on a piece of furniture that is going to sit in a corner all day and collect dust is a waste of money and will give someone in the future a real fit if a new owner wants the piece to be refinished to change its appearance. For office furniture that gets daily abuse, using CV or polyester is inappropriate, as the work *will* need to be touched up or refinished, so using standard lacquer or pre-cat is going to save you time and effort. There are many different aspects to the quality of one's work and in some cases you want to be thinking about the job of the refinisher as he/she will educate the client on why your work was not done right - just a fact of life.
Russ Ramirez, forum technical advisor
I don't know what you guys are using for stripper, but I have stripped CV finishes many times with no problem.
From contributor D:
Here's a tip for C-V. Use a 60 or 80 grit disk on a Dyanbrade and do one pass over the finish. This scores the finish and will enable the stripper to penetrate and lift it. Works great every time and doesn't affect the wood at all unless to go nuts with the sander.