For Lasting Paint. Polymatrx is an elastomeric paint additive that can make an exterior paint job last 20 years or more, says maker Gulf Synthetics. It’s designed to keep the paint coating flexible through many years of temperature variations, minimizing cracking and chipping. One quart of the product treats one gallon of any exterior latex paint and costs $36. Gulf Synthetics, 678/584-9309, gulfsynthetics.com.