Q. Five years ago we insulated the ceiling and outside walls of our kitchen. Wall-siding ''plugs'' provide humidity release from the insulated stud walls. Last summer the siding and the kitchen interior were repainted. Mildew now has appeared on the outside paint. Someone has told us we should have painted the inside walls with aluminum paint which would act as a moisture barrier. Is extra interior painting worthwhile? What do you suggest? Helen E. Payne Great Barrington, Mass.
A. The present mildew on the outside siding of your house may not be related to the insulation that was installed five years ago.
The repainting of the inside of the kitchen with enamel may have provided the recommended moisture barrier, of course. Besides, the ''plugs'' provide an escape for the humidity within the insulated stud cavities.
No one is quite sure why mildew chooses to grow on a given surface, albeit it is triggered by moisture or humidity.
To stop the mildew, add one cup of household bleach and one-half cup of trisodium phosphate (TSP) to a gallon of warm water. Scrub the mildew surface with a light-bristle brush. Allow the mixture to stand on the surface about 15 minutes and then rinse with clear water.
Quite often this treatment discourages mildew for some time and the process usually does not damage the paint film.
The next time you repaint the exterior siding, discuss with your paint dealer the suggestion that you add a mildewcide to the paint. A number of companies make such a product.