What is the highest/lowest relative humidity the rust sealer can be used in?

The lowest would be about 30% and the highest would be 80%. We strongly recommend waiting for a day that is closer to 50% relative humidity, as this is ideal for working with these products. However we understand that some customers live in climates that are always very high humidity. In this case, you can apply the rust sealer in 80% humidity, but please understand this is still quite a bit of moisture for these materials and they may not behave as they would in 50% relative humidity. If the humidity is higher, do NOT apply thick coats--apply multiple thin coats, waiting until each coat is dry to the touch. Even if it is dry to the touch in 2 hours, it is best to still wait 3-3.5 hours before recoating.