Thinning latex paint

[Craig Zettle]

I was just reading the responses to the "considering a spray gun" thread, and was wondering why you could not just thin latex enough to get it to go through a small tip nozzel? My Wagner finecoat does not reccomend using it with heavier latex paint, but what would it hurt? I know you would need more coats, but for small projects maybe? I need to spray a bookcase and did not want to invest in another gun just for this project.

[Steve Schoene]

The way I understand it, the small "bundles" of solvent based latexes that are emulified into the water to make the paint, have to come together when the water evaporates to coalesce into the paint film. If there is too much water, they can't link together properly and the film will be weak or not adhere.

Whether the above is a precisely accurate discription I'm not sure, but I do know that when I tried what you propose some years ago, I got paint that just flaked off in sheets from a well sanded substrate.

[Jim Becker]

Latex paint does not like to be thinned. Adding some Flotrol or similar helps, but you really should use the correct projector set for the material you are spraying if you want nice results. When I sprayed my shop doors (conventional cheap gun), I used the Flotrol and had good results. That gun has a nozzle you can practically drive a small truck through, however... ;)

[David Eisenhauer]

There is some stuff called a "conditioner" that is added to latex which helps with getting better performance when spraying. One brand name is "Floetrol". I have used it and immediately noticed improvement in the ease of spraying latex. There is a finite amount that can be added, maybe 20-25%?, but it definitely helps. Best of luck.

[Howard Acheson]

Steve basically has the answer. Waterborne finishes are a pretty high tech product. The chemicals that make them up kept apart by being suspended in the water. When the water evaporates, it allows the chemicals to come into direct contact and a process called coelescing occurs. Coelescing is the sort of "melting together" of the chemicals into a film which forms the finish.

If you add water, you may end up moving these chemicals so far apart that they do not come into contact when the water evaporates. Therefore the coelescing process does not occur properly--or at all--and you will have a finish failure.

The answer is not to add water to any greater extent than called for on the label. If the label does not state any thinning instruction, don't add water unless you contact the manufacturer.