I haven’t used it for a few years because I no longer have a boat with wood trim, but as I recall, the instructions on Cetol products directly states that thinning the product is not recommended, even on the first coat. I am inclined to believe that the people who make a product know more about its use than anyone else. The slowness of the drying is also planned into the product. That’s how the different layers are able to bond with each other, and why sanding between coats is discouraged. I always followed the instructions to the letter and was highly satisfied with the results. I doubt if YMMV. Terry, ex-Tamarack