Wood rot can cause major structural damage.  To defeat wood rot, you must destroy it's source. Wood rot is the result of a fungus, which must be eliminated before any repair can be made. A homemade solution of 10% bleach and water will do the trick nicely. Apply the solution generously and let it stand for 10 to 15 minutes before rinsing. This solution kills the wood rot causing fungus that causes wood rot and prevents it from spreading to adjacent wood.