In the November 2003 issue of the Painting Clinic (www.pfonline.com/articles/clinics/1103cl_paint5.html), you replied to B.B. regarding the addition of a heat insulating additive to his paint material. I had two further thoughts. One is that the pigment to binder ratio must be considered. As you pointed out, gloss will probably be affected and we both know what happens to film integrity when there is too much pigment. The coating can powder and/or just flake off. Also, I wonder if the heat insulating properties of the additive is a function of the particle size. If these particles are ground finer, will this property be minimized? S.B.
You raised some important issues, S. B. The pigment volume concentration or pigment-to-binder ratio are extremely important in organic coatings for all of the aforementioned reasons. Although it didn’t occur to me at the time, I believe that B. B. is referring to a cementitious paint used as a thermal barrier to protect structural steel. Unfortunately, I don’t know the material used and don’t know the reaction mechanism. Therefore, I can’t comment on the effect particle size reduction will have on the heat resistance of the final product. On the other hand, I am aware of the reaction mechanism of intumescent paints that release gasses that expand the coating film to form a foam carbonaceous char that thermally protects a substrate. But that doesn’t help here.