Conversion varnish flow
Getting conversion varnish to lay smooth. April 11, 2001
Q.
How do you make conversion varnish lay like glass without buffing it? My experiments with temperature and reducing tell me that it will not lie like lacquer. I tend to get a bit of a ripple effect in it. Not orange peel, but not the flow I would like.
I am using either Duravar or Krystal (ML Campbell). Ambient temperatures seem to be a key factor, as it likes to be warm. Also, I have found that in the cold Midwest, the extremely low humidity causes it to flash off too quickly, so I use plenty of retarder. My reduction formula is fairly straightforward--10% cat, 10% retarder, and 10% thinner. This is to be applied to tabletops with a sheen of approximately 70. I have no problems with lower sheens, as the light is not so harshly reflected.
Forum Responses
What types of reducer are you using? I have had good luck using Sherwin Williams CV with high-flash naptha as a reducer and also using toluene with a little MAK (methyl amyl ketone). The MAK acts as a retarder and also as a solvent. It will work with Sherwin Williams products. Check with the chemist from ML Campbell to see if it will be compatible with their product.
10% sounds like too little reducer. Do you have a Zahn cup? Also, you don't say what type of equipment you are spraying this with or what air and/or fluid pressures you are using. These are the big three that make a gloss finish without orange-peel--viscosity of material, proper solvents, and correct gun setup for the material being sprayed.
This stuff goes on like butter if you reduce it right. I use the S-W water white and reduce it with 15% xylene as recommended by S-W. You worried me with what you listed as your reducer. You don't add catalyst to the reducer. You take the C-V right out of the can. Catalyze it as directed on the can and then add reducer. Xylene works good. MAK should be great.
You are right about temperature. You should not use C-V under 68 degrees F, as the catalyst will not activate. Here in Arizona, I use pre-cat lacquer during the winter (about 50 degrees F) and C-V the rest of the year (100+ degrees F). C-V loves hot weather.
The problem is the temperature at which you are spraying. If you spray the catalyzed coatings at below the recommended temperature (I believe MLC recommends 70 or above), your coatings may not crosslink.
Also, if you use MLC, you can buy the premixed Slow Reducer to go with Duravar or Krystal. You need to slow down the drying, but the temperatures need to be right, too.
You need to make sure you apply about 4 mil wet coat. Get a mil gauge--they are free!
The reduction should only be made after the finish and catalyst are mixed properly. Then reduction within the 5-10% range should be sufficient.
From the original questioner:
I spray with a Binks mach 1 and use a Binks 2.5 gallon stainless pressure pot. Also, let me clarify my reduction. I use the prescribed MLC care catalyst at the 10:1 ratio. I always mix this first, then add 10% retarder, finally 10% c-160 MLC lacquer thinner.
Temperature seems to be one of our main trouble spots, as I am required to turn the thermostat in the finish room down to a chilly 50 degrees at night.
I have discussed a Zahn cup with the owner and always spray to a 4 mil wet coat. What piece of equipment would anyone recommend to heat my mixtures to the proper temperatures?
Experimentation has brought me to using a 91 fluid tip (.039) and 34 lbs fluid pressure and about 36 air. Basically, I have found that the higher my air at the tip, the better it atomizes, which also seems to help tremendously.
If you use the slow reducer after catalyzing (I believe the c160 is a slow reducer), you should not have a problem with the 5-10 percent reduction. Don't use the lacquer thinner.
The finish room needs to be around 70 degrees for 4-6 hours after finish application.
I spray mostly Duravar. Reduction after catalyst is around 6 percent in the winter and 10 percent in the summer. I use Slow Reducer #2.
We use an Accuspray turbine (HVLP). It tends to warm the finish a little, which is good most of the time, except the hot summer.
I've used the Mach 1 gun. 36 lbs. air pressure sounds real low to me. We had a salesman bring in a gauge to check the atomizing air at the cap and it took close to 90 lbs. to achieve the 10 lbs. of atomizing air we were allowed in southern California at the time. Also, those guns are very sensitive to viscosity. Anything over 19-20 sec in a #2 Zahn cup is going to have orange peel.
The original Mach 1 was a complete air hog and needed a lot of air pressure and air volume. The new series is much better, but if you have the original (5 years old or older) you need much more air pressure.
When I use the Binks two-gauge pot, I normally set around 10-12 psi on the fluid side. Is this what everyone else is using? 34 psi seems a little high for me.
That's right about the feed pressure. This should never go above 15 psi. I've seldom needed to exceed 5 on a pressure pot unless I'm spraying very thick materials.
Maybe we can help if your DOI is atomization related. Binks has had various MACH-1 guns and air caps available over the years. Listed below are the gun inlet air pressure and CFM for their possible air caps. HVLP guns' primary atomization comes from "volume of air (CFM)", not so much compressor pressure. It is important that the air cap is sized to the compressor CFM output, with 3/8 I.D. air line and no cheater valve at the gun to restrict CFM. Take a look at your compressor CFM rating.
Air Cap #'s 95P, 95AP, 97P, 97AP need 22.5 CFM at 50 psi gun inlet pressure to produce 10 psi at the air cap.
Air Cap # 94P 13 CFM at 33 psi gun inlet pressure to produce 10 psi at the air cap.
Air Cap # 93P 10 CFM at 18 psi gun inlet pressure to produce 10 psi at the air cap.
90P and 92P air caps 6 and 8 CFM at 15 and 19 psi gun inlet pressure to produce 10 psi at the air cap.
The above data is extremely useful. If you notice, the original aircaps required more air than most 7 HP compressors can produce. These used so much air it was like you had an open end on your air hose.
From the original questioner:
I will try turning the fluid pressure down some. My mach 1 is a new gun with a 94p air cap. We run 3/8 line and I will have to check how much CFM the compressor puts out. I believe we have it up around 110 psi.
c160 is MLC lacquer thinner. You are perhaps confusing it with c161 care retarder, which we also use.
If I run the air pressure up past the 40-45 range, I seem to get a lot of "bounce back" and it tends to dry out the previous pass of material, causing "dry spots" in the sheen.
Another way to check if your fluid pressure is correct (I never did completely trust gauges) is to turn your atomizing air off completely and spray fluid into a 5 gallon pail. You should have about a 3' arc coming out of the gun. If the fluid comes out like a bullet, and can punch a hole in a wall 25' away, that's too much fluid. You need to find the balance of fluid and air that creates the best atomization.
Regarding Duravar, Krystal and room temperature, these finishes require at least 60 degrees F for a full 48 hours after spraying them, so that they cure and crosslink properly. You can weaken your finish otherwise, wreaking havoc on its ability to perform and be durable.
The tech sheets say to lay down a 5 wet mil film coating. Do this regardless of how much the coating is reduced.
These coatings are formulated to spray best at 20 seconds in a Ford #4 cup (that's close enough to the Zahn #2, isn't it?).
When spraying the insides of corners, etc., reduce the air pressure considerably. A friend suggests blocking the air holes on the horns of the air cap when spraying these difficult corners and insides (I have not tried this).
Duravar is a catalyzed lacquer. It reduces with lacquer thinner (preferably theirs so that you do not create recoat window issues) and it has nitrocellulose in it. Krystal is non-yellowing and contains no nitrocellulose.
When spraying the MLC line, it has been my experience that thinning of the material depends on your equipment. When I move it through my Kremlin, I go full strength and it lays down excellently. For smaller jobs, if I need to use cup or HVLP, I reduce 10-15%. Stay within the guidelines when using retarders on post cats.
You asked about heating your material because of your cool finish room temperature. Depending on the volume of finishing you're doing, you may want to look into an AirMix system with a circulating heater. During those cold winter months it's a huge help, but a big investment. It puts your material directly on the surface, so you're saving on your material plus there is very little over-spray and it's pretty clean when operating. Talk to your coating supplier regarding operating temperature, as CAT coatings are sensitive to heating.
