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I'm spraying SW ProClassic Hybrid with a big air compressor (20 CFM @ 90) and an auto gun. To get proper atomization I'm thinning it a lot maybe 30%.

My theory is this:

I don't think you can overthin water based paint. It may take more coats to achieve the desired mils (and associated performance) but thinning shouldn't affect the chemistry itself.

Why? Because paint is pigment + binder (what holds the pigment to the painted surface) + carrier (water). The carrier evaporates off any way so it shouldn't matter how much carrier is present. All we care about is what is left after the carrier evaporates.

Any one have a different idea?
 

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Thinning 30% seems a bit much. Not sure why you would think more coats would be better. Maybe adjusting your spray pattern and air would be easier. What kind of gun do you have?
 

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It sounds to me your spray nozzle is too small. 20 cfm is plenty of volume but 90 psi is a bit high. When I spray WB with convention air spray I thin about 10% use 50 psi.

I use a nozzle for WB material. Too much reduction in my experience changes the sheen. Semi Gloss to Satin, Satin to Flat.

Your results may vary but I would check out my work a few days later and see how well the coating is holding up.
 

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I'm spraying SW ProClassic Hybrid with a big air compressor (20 CFM @ 90) and an auto gun. To get proper atomization I'm thinning it a lot maybe 30%.

My theory is this:

I don't think you can overthin water based paint. It may take more coats to achieve the desired mils (and associated performance) but thinning shouldn't affect the chemistry itself.

Why? Because paint is pigment + binder (what holds the pigment to the painted surface) + carrier (water). The carrier evaporates off any way so it shouldn't matter how much carrier is present. All we care about is what is left after the carrier evaporates.

Any one have a different idea?
Ok Im revising my position. You also have less pigments when you thin with water.

As long as you dont thin with solvent (floetrol?) you should be good...
 

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Ok Im revising my position. You also have less pigments when you thin with water.

As long as you dont thin with solvent (floetrol?) you should be good...
At some point, thinning will leave to a film lacking in both cohesion and adhesion.

This isn't an issue with products like lacquer and shellac, since each application dissolves the previous ones, "melting" together.
 

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To be more specific (if anyone cares), when waterborne paint dries it forms a crystalline lattice that gives it its strength. If you over-thin it, the molecules will be too dispersed and it won't have enough of the binder to form a film when it dries. Putting on more coats won't help, because each coat has to stand on its own merit. If you put more coats on, it will simply create more stress on each layer, increasing the likelihood of failure.

To put it in a simple example for those not interested in the science, it would be like trying to put wallpaper on by only dabbing glue (just kidding, it's paste ;)) in one little spot every 2 feet on the wall. Your wallpaper is going to bubble and fall off (or just chalk and flake more likely).
 

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To put it in a simple example for those not interested in the science, it would be like trying to put wallpaper on by only dabbing glue (just kidding, it's paste ;)) in one little spot every 2 feet on the wall. Your wallpaper is going to bubble and fall off (or just chalk and flake more likely).
That would however make it easier for removal when the decision to convert to paint is made. :whistling2:
 

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I honestly only remember thinning two paints since I started painting.

One was Aura when I first started using it and it was driving me insane with the super fast dry time. Once I got used to it after a few jobs I never did that again.

The other was oil floor paint where the instructions called for the first coat to be thinned 10%. Wow, did that smell.

I just don't see the point in thinning paint when the goal is to get two solid coats on whatever surface your doing, but then again I've never sprayed anything in my life.
 

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Yeh, much more of an issue when you're spraying. I've never thinned anything to lay out with a brush or roller; but then again, I'm not a painter ;)
 

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I would argue that over thinning can compromise the thermodynamics occuring during the vehicle evaporation and subsequent coalescense critical to film formation.

Using my pale porpoise like body as an example, dousing myself with large amounts of water will not cool me down any more then the controlled beads of evaporating persperation will. In fact, the excess water retards the thermodynamics that result in heat transfer through vapor release.

It is important not to exceed the allowable ratio of vehicle solvents for similar reasons.
 

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I would argue that over thinning can compromise the thermodynamics occuring during the vehicle evaporation and subsequent coalescense critical to film formation.

Using my pale porpoise like body as an example, dousing myself with large amounts of water will not cool me down any more then the controlled beads of evaporating persperation will. In fact, the excess water retards the thermodynamics that result in heat transfer through vapor release.

It is important not to exceed the allowable ratio of vehicle solvents for similar reasons.
Sorry, John, while your point about excess vehicle/solvent is valid, your analogy is both bad and incorrect. Heat can leave your body by other routes besides evaporative cooling. In this case, conduction.
 

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Sorry, John, while your point about excess vehicle/solvent is valid, your analogy is both bad and incorrect. Heat can leave your body by other routes besides evaporative cooling. In this case, conduction.
But its more efficient when evaporated...winner!
 

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pH IS IMPORTANT!!!

Just to add another reason why you can and shouldn't overthin water based/borne paint;

They have a specific pH range that they function in. Too far below that range and you can have the resin or other raw materials settle out and be extremely difficult to reincorporate.

Floetrol or BM's extender would probably be a better option for extensive thinning as they have a proper pH and also contain some resins/binders to keep from weakening the paint.
 
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