Thin water based paint?

[Norm.Mareeba]

Hi;
This may be the wrong forum but I can't think of another...

I'm painting my roof with a water based paint. My problem is that the paint dries too fast, gums up on the roof, and clogs (gums) up the brush.

OK, so I phoned the manufacturer and the suggested using a different sprayer (even though I said I was using a brush) and if I really needed to thin the paint - go to 10% water thinning.

OK, so my question is this: Why only 10%? Why not 25%? It's hot up there and windy (even in the mornings) and I'm thinking that 10% won't be enough..

I'm asking firstly to make my job easier but also to educate myself.

Thanks
Norm (in FNQ)

[MarthaLittle]

I do not have much idea about it. I would suggest you to talk to some local contractors in your area.