When do I reapply Aerospace Protectant to my Vinyl Spa Cover
Use 303 Aerospace Protectant's cosmetic properties and water repellency as a guide. A surface treated with 303 Aerospace Protectant is water repellent (beads water). When the water repellency begins to diminish, reapply.
Or (our preferred method) if you think it may be time to reapply but don't know for sure, do a small spot with 303 Aerospace Protectant. If any of the color or luster comes back, reapply.
Vinyl spa covers are one of the few constant exposure situations for vinyl. Even RV vinyl awnings, vinyl convertible and soft tops, tonneau covers and car bras are not constantly exposed all day, every day. It depends on the time of year and where you are, but typically with a spa cover reapplying every 30-45 days is sufficient to maintain a maximum level of UV protection.