Hi, Mary Anne. I would hesitate since the hypertulfa contains peat moss. In quantity, peat moss stains the water and would stain anything under it. It also breaks down over time and exposure which would weaken the repaired spot. I would look for repair products that would closely match the present coating. There are plastic and poly products that contain fiberglass and are waterproof. You can get them in small quantities at most building supply stores. Color can be matched with paint or stain.