If you absolutely want to use varnish for an outdoor table or other horizontal surfaces, it is recommended to choose a high-quality marine varnish. While many manufacturers offer exterior varnishes, they are not suitable for long-term resistance to UV rays and weather conditions. Marine varnishes are designed to last against the effects of water, snow, wind, and sand. They require similar preparation to other varnishes and require multiple applications, typically 6 to 7 coats, to offer optimal resistance. Quality marine varnishes contain UV filters to protect the wood over time. If you apply the varnish correctly by following the number of recommended coats by the manufacturer, it will last for many years and can be maintained with one or two applications as needed.