Yes he did. Floetrol is for latex paints, Penetrol is for oil based paints. An easy way to remember which one is for what is to remember the phrase "penetrating oil". Penetrol is used for thinning OIL based paints.

Robert:

Use a Dixie cup (or other paper or styrofoam cup) to fill a clean empty soup can about half full with the paint you're having trouble with. Thin the paint in that can by adding 10 percent of the paint volume in water (Distilled water is best.) and stirring it into your paint with your brush. I believe that thinning the paint will make a big difference.

You see, when you have liquid paint in a gallon can, it will self level perfectly by itself. But, once you spread that paint into a film that's only a fraction of a millimeter thick, it needs to be much less viscous to flow and self level by itself. So, you'll find that you might need to thin your paint with 20 to 30 percent water, and put on two coats instead of only one.

So, thin the paint in your soup can with up to 30 percent water (try 10, 20 and 30 percent, but stop when you're getting much better results) and you should find that you can spread the paint on a horizontal surface, and it will still be thin enough to self level, thereby eliminating the brush strokes.

That's really the trick to getting a good paint job on horizontal surfaces with a brush.

When you're painting vertical surfaces, the problem is that the more you thin the paint, the slower it dries, and the greater the likelihood that it will "sag" on vertical surfaces. Floetrol is a paint conditioner made for latex paints that has higher viscosity than water, so thinning with Floetrol won't reduce the paint's viscosity nearly as much as thinning with water, and that helps to prevent the wet paint film for "sagging" on vertical surfaces as it dries.

So, when painting horizontal surfaces, thin small amounts of your paint in an empty tin can until you get a good feel for how much to thin it. When painting vertical surfaces, do the same, but use Floetrol instead of water.