If exposed to water, and not allowed to dry, it will soak the water into the core of the wood, in the same manner that it did, while growing, and eventually rot.

If kept dry, by the use of primer and paint, or proper ventilation, it will continue to harden.

The problem, when used with windows, is that paint will cake up and interfere with the proper movement of the window.

For this reason, it is best to avoid or limit the paint that is used on the sides, top and bottom of the sash, and allow the air to circulate.

Savy homeowners refer to this as allowing the wood to "breathe".

For this reason, if you have elected to caulk or paint your windows shut, due to the lack of air flow, they will eventually begin to rot.