Decks, Patios, Porches and Docks - what's the difference btw waterproof sealant & polyurethane?

I have a nice piece of hardwood maple that will need to remain outside and the manufacturer told me to apply a few coats of polyurethane.

would a water sealant like Thompsons be better or should I go with the poly?

thks,

-MC

If the manufacture said to use polyurathane I would. Since it will be outside use a marine/spar urathane. Minwax sells this in their Helmsan label.

Waterproofers like Thompsons are a water repellent and often have a short life span. Polyurathane is a coating [much heavier film] which goes on heavier and gives better protection.

Polys don't hold up well when subjected to UV rays [rain don't help either] so be prepared to sand and recoat yearly - depends a lot on the amount of exposure.

I can throw a tarp over it to block out UV rays when not in use. I'll put several coats of poly on it

thanks,

-MC

You are subjecting a very fine wood to exterior conditions, so you can expect a short life of the coating and possibly the wood.

You can cover whenever remember to, there are always situations (wind, memory, accidents) that will cause exposure that cannot be cured just by covering it up again.

Also, be perpared to have the wood take on moisture (humidity) from the surrounding area. When subjected to heat, the moisture will want to come out and could destroy the coating, especially in the hot humid summer conditions and variable winter conditions you have in the summer.

The key operatives in your question are "maple" and "need to remain outside". I doubt any coating is designed for fine wood under these conditions, but there are some that are adequate for other types of wood under adverse conditions.

You can apply it, but be prepared for continued maintenance.

Dick