Solvent Vs. No Solvents
Coatings that contain solvents or water are inherently more porous than coatings that are truly 100% solids. With solvent or water in a coating system, the formulator must allow for that solvent or water to evaporate through the coating. By design, the formulator must plan for enough space between the polymer threads of the coating to allow the solvent or water molecules to escape through the coating itself while it is drying or curing.
However, if there is enough space to allow the molecules to pass out, you should be concerned that there is also enough space for those same molecules to come back in. That coating may be unable to stop water or other contaminants from passing through the coating. The way the polymer threads are woven together and the density or packing of those threads is called cross-link density. The higher the cross-link density, the better the barrier-type properties of a coating system.
When you apply a coating that has 50% solids and 50% water or solvent, you are paying for materials that will not help protect your surface. This is because the solvents and/or water volatilize, or evaporate, out through the coating surface, leaving you with only half of the coating thickness that you have brushed or sprayed on. Possessing only half of the thickness in applications that involve abrasion or wearing away of the coating means that you have only half of the protection, or half of the service life, possible with a coating that contains no solvents or water.
One additional benefit of having a 100% solids, no solvent or water coatings is that it can typically be applied at virtually any coating thickness. Additionally, a coating containing any solvent and/or water has significant limitations in its application thickness. The coating formulator knows that the solvent and/or water must escape the coating film as the coating dries or cures, or it will bubble, blister, and peel. So, if the applicator paints the coating on too thick and the solvent/water does not get through the coating film before the top of the coating sets up, the coating will fail. Unfortunately, since coatings wear away through atmospheric abrasion, UV exposure, and other effects at a certain rate per year, a thin coating means that the coating will likely fail earlier than a thicker coating. This leads to having to apply multiple coats to try to get longer service life.