Drying up an oily wall

Q: I have an 88-year-old home that I bought after it was "flipped." I noticed some moisture areas on parts of the interior outside walls, which seem to be oil. One area drips and, when I rub my hand across the wood trim, it is oily. I have been told to just wash my walls with mild soap. It has helped with the dripping, but what would you recommend? Also, I am getting ready to repair a couple small cracks and was told I should put on a special glue before I patch with plaster. Any suggestions?

A: The main reason moisture forms on the interior portion of an exterior wall is the lack of insulation in the wall cavity. The moisture can dilute the latex wall paint and cause streaking. The oily substance is caused by the surfactants (wetting agents) that are part of all latex paints. When the moisture levels are high, the paint does not have a chance to cure properly and an amber-colored oily streak appears.

There are three things you need to do to repair the plaster and to prevent future streaking.

1. Have the exterior walls of the home insulated with low-expanding foam insulation. On older homes, small holes are drilled at three different heights on the interior side of the exterior walls, and liquid foam is pumped into the wall cavities through a small nozzle. Not only will the insulation provide protection from the outside temperatures; the foam also prevents airflow through the walls, which will save hundreds of dollars a year on your energy use.

2. Where the plaster is cracked or loose, an adhesive such as Plaster Magic (www.plastermagic.com) is used to secure the plaster to the wood lath behind the plaster. Several small holes are drilled where the walls are damaged, and the adhesive is forced through the holes using a standard caulking gun. Wood screws with large washers are then used to secure the plaster until the adhesive has dried. The screws are then removed and the holes are filled with a plaster spackling before painting.

3. Before painting, wash the walls with a TSP (trisodium phosphate) solution, rinse thoroughly, allow the walls to dry and apply an oil-based primer to seal any of the surfactants not removed by the washing. Finally, the walls can be painted with no fear of oil bleeding.

Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home-improvement questions at d.Barnett@insightbb.com. Sorry, no personal replies.