Should I Mix Paint from different machines for same room?

Question

I bought two gallons of Sherman Williams paint (White Shadow Cashmere - exact same productIds and barcodes) at two different locations and branches days apart. They are custom mixed colors, not stock colors.

1. Do you recommend mixing them half/half in a small tray when painting the room?
2. Another idea, is when doing two layers of paint, use the first bucket, and then second layer of paint, use the other gallon, would that work also?

I heard sometimes they can be slightly different from machine, minimal, but enough to see shadow differences in sunlights and tints. I would hate to see one part of the ceiling and wall, looking slightly different than the other. My friend says it doesn't really matter. Just curious what professional painters think.

If they were two different rooms, I would use different buckets, because you can't notice the difference between separate rooms, as easily as in same room.

Answer 1

Those paint dispensing machines have a mechanical tolerance. It's better than the old days with hand pumps (ie. better control of air bubbles in the metering), but they are by no means precise.

So anyone who wants to succeed at a project will shake ALL the paint cans (the ones used on the last coat), mix them together in a clean bucket, and pour them back into the cans. That is the only way to assure a match.

Even if you bought all cans from the same store from the same mixer on the same day!

In fact my suppliers (my local chandlery and Sherwin-Williams Industrial) do this for me. They mix my custom order in a large cauldron, and then pour off cans to give to me.

If you don't want to do that, then make sure you paint the entire wall from the same can. The way light works will tend to conceal paint differences at edges.

Answer 2

Most "professional" painters would probably say mix the two, since a lot of them do so to avoid issues like this even between two gallons bought at the same place at the same time.

You probably won't notice a difference, but since there is a risk of it, and you want to avoid it, go ahead and mix them.

Answer 3

I haven't used that particular brand of paint, but based on my experience with other paint+primer products, your option #2 will definitely work. The coverage on these is very good and you will never be able to tell if the coat below it is slightly different. (Though I would use primer below that as others have mentioned.)

The only thing I'd caution about is to make sure this final coat is cut all the way to every edge. If there's a line anywhere where the bottom coat is visible you may see the difference there.

Answer 4

If the concern is having 2 differing shades appearing together I would suggest: no need to mix if you are painting smaller rooms and likely to finish a room from a single tin. Reason is - the difference is only perceivable when the colors are beside each other. Different rooms don't allow that comparison. Mix the paint together if you feel you will end up partially using from one tin. In saying that - the accuracy of most paint dispensing machines is usually enough for the average person not to see the difference - however I would still try to avoid painting 1 wall from 2 tins from 2 batches.