Assuming a single stage paint is properly mixed, with the recommended amount of reducer and hardener and is spraying correctly, what is the effect of adding additional reducer? Does it make it thinner with possible runs, or does the additional reducer evaporate faster and cause it not to lay down as smoothly?

My first thought was with more reducer, thinner, smoother application, but after some recent minor touch up and small parts painting, I'm not so sure. I was mixing 4:1:1, and wanted it to lay down a little smoother. Additional reducer seemed to go more toward a rougher finish, requiring more aggressive wet sanding.

 

Additional reducer will cause a condition called "dieback". You lose depth and shine. Also, in a single stage, will cause it to be more transparent. Also, the more reducer you add, the thinner the film build will be....more material needs to evaporate(reducer). Reducer is a medium to allow you to transfer paint from gun to surface. It gives you a thinner viscosity, which can also be achieved by raising the temp of the product......and yes, you will lose some vertical stability, resulting in possible runs or sags....

 

Lots of good paint info at autobody101.com

 

And more thinner increases the chance of lifting the undercoats.
getting a smooth lay down is more a matter of gun cleanliness and adjustment which is harder with a hvlp if that is what you are using i finally gave up on them and went with the sata rp for my clear coats which shoots more like the pre hvlps and lays down smooth without waiting for flowout with the hvlp. i use a hvlp for the base as it saves material has less overspray but the rp in my hands is far superior to the straight hvlp. others will have different opinions but i started when binks was the only gun to have and just could'nt feel confident with the new tech. until i found the rp series

 

If you are spraying acrylic single stage enamel, you need to use the hardner which slows down the drying time and allows the paint to flow smoother. Acrylic enamel drys very quickly almost like laquer.

 

Sorry, but I have to disagree. Hardner has nothing to do with the drying time of the paint but rather it causes a chemical reaction in the paint. And acrylic enamel certainly does not dry as quickly as lacquer. A coat of lacquer that is sprayed on a panel will be dry to the touch usually with 15 minutes give or take a little based on temperature. Enamel will be hours before you can touch it without leaving any marks.

The first thing is to always follow the recommended mixing ratios stated by the manufacturer. They developed them for a reason. The other factor related to how well the paint will "flow out" or lay down is the reducer used. All companies offer different reducers for different temperatures. Using too fast of a reducer (evaporates quickly) will result in a rougher finish. Too slow can result in a longer drying time and less vertical stability (love that term Erik) resulting in runs. Painting is not easy and it requires a "feel" for laying on the paint and you need to understand how the products are used.

Quality single stage paints today will be urethane and the solid colors can be wet sanded and buffed to achieve a beautiful finish.

Brian

 

You must be a painter. I am not. All I have gone on is the people that have sprayed several cars over the years and what they told me. They would not spray without the hardner and got very nice results. I did not use a stopwatch to time the drying time but I have sprayed door jams and wheels with acrylic enamel and it dried pretty fast.

Thanks for the expert opinion.

 

So far I have only been doing small jobs with a small disposable gun and the paint in bulk, not rattle cans...lower rockers, mirrors, top radiator plate, some underhood brackets and parts, but I was just trying to improve those paint applications.

Thanks for the input.

 

Always use the hardner but keep in mind it's not for drying. If you were speaking about rattle can enamel paint, that's a different animal and shouldn't be compared to the PPG, DuPont, Sikkens etc type auto body paints.

For a smoother finish, make sure the prep is correct. You'll want to usually finish sand the primer with 800 grit to have a nice smooth surface and one that won't show sanding scratches. Mix the paint per instructions, use the correct temp reducer and type turning up the air pressure at the gun. If you have it too low the paint will come out heavy which could lead to a rougher finish. Higher pressure will make the paint come out of the gun a little finer. Check the size of the tip and nozzle in the gun you are using For finish painting, you'll want a tip and nozzle around 1.3mm. Some of those little guns may be sold for primer work and could have a 1.8mm setup.