I tint paint as well as being a painter. I will say that the gray primer works! Even though I work part time at the local Lowe's paint counter for bennies, I am quite knowledgeable. You will not achieve any reduction in the total number of coats for tough colors by tinting the primer to a % of the desired color whether it be reds, deep vibrant blues, bright green, orange, yellow, etc. You DO need the proper color gray primer.
I will say there is a flaw in the g1-g5 tinting system for grayscale. For lots of reds commonly used for say a front door, there is a large gap between the g4 and g5 gray. I care enough, even when very busy to do a test of the topcoat color over a sample of the gray primer. I start with a p? and adjust it as I see fit until I am satisfied. Lots of times a g3 or g4 is too light and a g5 is way too dark. With just 1 or 2 trips back to the tinter aqnd a quick test, they leave with the proper gray to do the job in 2 topcoats. (That is if they had any clue how to paint haha)
The unfortunate part is that most employees that tint your paint at the SW's and the like have never really painted. They have no real field experience so they have no clue if the gray they are mixing will actually work as well as it could.
Why does the gray primer work better than just tinting the primer to a % of the original color you ask? Simple really. The colors that have coverage problems have a large amount of synthetic colorants in them as opposed to natural ones. Natural ones are fairly opaque while synthetic ones are very translucent. The large amount of synthetic colorant will produce a translucent topcoat.
Most likely you are planning to paint these translucent colors over a white substrate. White is the most reflective color. When the translucent topcoat sits atop a highly reflective substrate, light will pass through the topcoat, reflect off the substrate, and beam back out some silly looking crap that looks nothing like the desired color. This is usually a much lighter blotchy version of the desired. Black is the least reflective color, while gray varies. Applying the proper gray base-coat allows one to control the amount of reflectivity which best suits the translucence of the color you are trying to get.
Again, it REALLY REALLY works, but ONLY if you have the correct shade of gray that does not always fall in the 5 common choices. The fix for this is to remember this, and when getting the primer tinted, make sure they do a sample of the topcoat over white, then a sample over the gray primer. If there is too much of the gray that shows through, it means it is probably too light, so have them add a little more black. It will be very obvious when it is too dark, trust me. Also, and this is VERY IMPORTANT - - make sure they lay the topcoat samples very and equally thin over the white and gray primer, NO CHEATING. None of this 3 drop mountain crap over the gray.
StefanC has the right idea by carrying some white and black in the field so he can adjust in the field and on the fly as needed. Don't trust a tint person that you don't know and don't be afraid to ask them for another 5 minutes to adjust the gray if it is not working. If they screw it up or go to dark, make em' eat it and start again. Life is to freakin short to have to paint a door or a room with 4-5 coats!
Alton
arty:.
