If other materials or fillers are desired, such as quartz or glass fibers, or a reaction product of potassium bicarbonate and urea (i.e., a carbamic product), these may now be added. -It may be desirable to reduce the amount of glass microspheres which are added in lieu of the weight of the filler material which is to substitute for the glass microspheres, binder resin, fiexibilizer resin and curi