hi this david and we are buiding a 2400 sq ft yoga floor in costa rica. the joist system is metal and the floor is 1x4 teak boards. there is a lot of humidty. the roof is metal and there are no walls. we are concerned with the humidty and it's affect on the life of the teak. are there any moisture barriers recommended ? david

Teak is a very dense tropical wood, and very tolerant of moisture- even liquid water, which is what made it the classic material of choice for boat decking before synthetic materials became available, which are cheaper, but not necessarily better. Teak is still a common decking material on luxury boats.

Ipe would be another durable moisture tolerant wood for your application.

Treating the teak with a mold-resistant finish on both sides can keep it looking a bit cleaner, but as long as it's protected from chronic direct wetting from and has free air movement underneath mold is unlikely to become a serious problem.

I know people with that design in similar countries. No problems with the good woods. Termites can be a problem with cheaper woods. Add a sealer only if you prefer the color.

Before you install it, let it equilibrate and have them verify it is at the right moisture content. I would then put on several coats of teak oil. You want the penetrating oil, not the stuff with varnish in it. After the floor is installed, treat it with another coat of teak oil about once per year and enjoy. If you need the shiny varnish look, I would find a local boat painter to spray it with clear Awl-Grip That stuff is ~200$ a gallon and is dangerous to spray, but it is the hardest finish for tough conditions. Cheers, Eric