When applying stain to an exterior surface, it can be a battle with Mother Nature to find an adequate weather window. With TWP Wood Preservative it should not rain within 12 hours after applying. The stain may not be affected by a little rain especially if it has soaked into the wood already. But in the case of significant rain, it can have an effect on the stain’s appearance.
If it rained on your TWP and you want to know how to fix it here are some tips. After getting rained on still allow the surface to dry for at least 24 hours. Only then will you be able to see the extent of the damage. Because water and oil do not mix, the rain may not affect the appearance as badly as you think.