Basecoat Coverage, What, How and Why

[crashtech]

I want to start a post here that is sure to generate some (hopefully respectful) disagreement. Basecoat or color coat coverage is an issue that affects almost everyone who paints anything other than black. Knowing how to achieve full coverage with a minimum of material use is an important skill to learn when refinishing! Here are some quotes from another thread, asking the question and receiving various answers on the subject, can we discuss it further?

Rusty,
Do you feel the white underneath gives the red more "pop" than say a gray or black?
I am curious as to how much the color of the undercoat effects the base color. Not just with Red but any color other than a Candy. My thinking would be that full coverage would produce the same results regardless of the undercoat color but I have been wrong many times before.
Thanks,
Jim

i can put 2 maybe 3 coats of red over white and have an even color that pops . or you can put 4 or 5 coats over gray or black and have a red car. there is a difference when trying to hide white ( lighter color ) or black ( darker color ) dark is harder to hide. just like a primer spot in the middle of a door.

When Barry says to spray red over white that's what I do.

Forgive me as I don't want to highjack this thread but the reason I am asking is because I have a gallon of SPI Red stashed away for a future project. I normally only buy the Black epoxy and planned to use it but if the white is what makes the "look" then I will use that.
So what I am reading into this is that white with 2-3 coats of Red base will produce a different result than black with 2-3 coats of Red base. Am I correct in assuming then that Red is more transparent and 2-3 coats would not be full coverage?

The way to answer that question definitively is to get a sprayout card that has black and white printed on it. Spray it with a some of your red, counting coats. Coverage has been achieved once you can't see the printing under the paint when viewing in bright sunlight.

What is being discussed in regards to using a white primer or groundcoat is the technique of purposely failing to achieve full coverage to achieve "pop." This turns the job into a three-stage paint system, where the red is effectively a translucent midcoat.

The main problem with such a job is that it makes subsequent repairs more difficult, as applying more coats of red, even from the same can, will cause the vehicle to appear darker in the repaired area. Special procedures must be used that would resemble the repair of a three stage paint system.

I agree... full coverage is full coverage-the true color. A sprayout would tell the story and a let down panel would show if there's any differences on the white undercoat on coat 4, 5, 6 when the black reaches full coverage.

It seems that Bob and I might be swimming against the tide, since Barry (through Rusty) recommends white under red, and Chad (not quoted above) also agrees with this procedure. I can't say that it won't produce a fantastic looking, uniform finish, because it will. My argument against it is more from a technical and repair perspective.

My suggestion, if the amount of basecoat color must be limited, or coverage is poor, is to find the right color primer that will give a very convincing illusion of full coverage under strong sunlight. The way this can be done is to first create a sprayout card that has full coverage of the color just by itself, no matter if it takes 8 coats, then clear the panel. Mark this as your reference sample.

Next, begin creating several more sprayout cards with various colors of primer. The current palette of SPI epoxy includes black, gray, white, and now oxide red. The oxide red in particular might present an interesting option under a red basecoat, especially when mixed with white. All of the SPI epoxy primers are intermixable, so you can create custom shades to suit the job.

Once these cards are made, make sure to label them as to what mix of primer they were shot with. Then apply equal amounts of basecoat to each one, however many coats you believe should be necessary to do the job, say 2 to 4, enough to look good but a number you know is short of true coverage. Clear all these panels, and examine them along with the reference sample in strong sunlight. If you have one that appears identical to the reference, you win! Otherwise, take the closest one, and decide how to re-create another test panel with a slightly different shade of primer, or one more coat of base.

If a perfect match to the reference sample can be achieved, you not only know the paint job will look the way it is supposed to, you also know what shade of primer to put over any future repair, and how many coats it will take to cover it!

 

[Barry]

First let me say I agree, Full coverage is full coverage like said.

Now why white under SPI red, orange or yellow.
The red as well as the other colors that SPI made does not have fillers or excessive amounts of whites or blacks to make the color cover better, so the color although will look like full coverage may still be transparent in certain light and the white will offer a nice extra pop but that pop would go away with excessive coats, so if instead you did three coats as a rule of thumb the white will or may play into the pop but with full coverage say 5-8 coats (I really don't know the number) the white will or may not be a factor.

Same reason all the companies want white under their orange and yellows, too keep down the number of coats needed.

So you and Bob are right but there are a few exceptions.

 

[Bondoskimmer]

I like Mar-Hyde Ultimate 2K Urethane buff primer (basically yellow) for my yellow tints. I can cover in 1 coat. I still go 2 coats.

 

[danp76]

If "full coverage" isn't achieved, would you have a problem applying additional base coat when it comes to a repair in the future? The white will be less noticable, as the repair area will contain more layers of color, possably creating panel miss-match?

 

[Bob Hollinshead]

If "full coverage" isn't achieved, would you have a problem applying additional base coat when it comes to a repair in the future? The white will be less noticable, as the repair area will contain more layers of color, possably creating panel miss-match?

Bingo, that's the scenerio I avoid by making sure true full coverage is achieved on the important jobs. I've seen the halo when repairing jobs that didn't get enough paint applied and it can make for a difficult repair.
On stuff that isn't real critical you can cheat it a little by using a similar tone undercoat or spray a ground coat color that is very close to the base that's being used but make sure the difference isn't noticeable-test cards are a good idea like Crash outlined. I sometimes burn up old paint by using it as a ground coat to help with coverage-example: the budget repaint I'm doing on my Daughter's 06 police impala. We picked out a cleaner white than the 8554 that came on the car, I'm using white epoxy for the final prime and sealer-this helps, I also will shoot a ground coat of some Ford Performance White I had on the shelf which is very close to the white we picked out. This enables me to get the the job done with two quarts of actual color instead of buying 3 or 4 and although I verified full coverage isn't achieved with this color untill three coats is applied there won't be any noticeable difference with using the white undercoats.