[pyper33]

I heard that you can thin down water based paint with water and use it as a primer on drywall prior to painting. If true, what is the paint - water ratio?

[21boat]

I would not recommend using a latex "paint" as a primer at all. I don't know what or how much you are painting.
On the job sites we buy a "primer sealer"and at the paint store we get it tinted to the color we are going to paint the wall. Then its only two coats One primer and one finish
What I feel you are trying to do is the old fashion "I can save some money" and I will use this paint to "seal" the wall. All paint will evenly seal a wall. The equation is how many coats and how much time and paint. A primes sealer stops the many coats it takes to prime and seal a wall. Just because you male runner paint to suck into the wall isn't;t going to seal.
"prime" Is applying a liquid. That another liquid will stick to.
"seal" is creating a barrier so the next liquid will not pass through that barrier IE primer sealer paint.
If this is new drywall I would never try to thin down a reg latex and try to make that out of a sealer.
After 30+ years on construction its not a good rick and short cut. The other problem is the more paint that pass into the watered down non sealer paint is a VERY high risk that you will not achieve the color and depth of that color because it again sucked into the wall because there is NO SEALER in what you are suggestion SO do it right and you will SAVE putting on a third coat and spending the extra time and money to buy more paint

Signed 21 Boat

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