Before painting mildewed wall, a good cleaning

The inside concrete-block walls of our house are mildewed, although a dehumidifier has helped to retard its growth. In repainting, what is the proper procedure to avoid the mildew problem?

Elaine Williams Ormond Beach, Fla.

A Wash the mildewed masonry walls with a mixture of one quart of household bleach, a half pound of tri-sodium phosphate (TSP), and a gallon of warm water.

Second, scrub the walls, using a medium-bristle scrub brush. Allow the mixture to stand on the surface for 15 minutes. Then rinse with clear water. When the wall is thoroughly dry, apply paint.

Add the maximum allowable quantity of mildewcide to each gallon of paint. In California the amount is three ounces per gallon. Ask your paint dealer for the recipe.

Home-built insulation blower

To the real estate editor:

In response to Mr. Holly's Ask a Builder column of April 15, ''Rigging Up a Device for Insulating Walls,'' here is how I insulated the walls of my house all by myself:

During the past five years the electric rates to cool and heat my frame house have doubled. Insulating the attic and crawl space was conventional, but the walls presented a different problem.

I investigated all the products on the market and found the only one I could easily blow in myself was W. R. Grace Zonolite Masonry Insulation (a lightweight , free-flowing, granular vermiculite) which is specially treated for water repellency.

It is inorganic, will not rot, emit odors, or support combustion.

Zonolite is primarily used in new concrete-block construction, but is suitable for wooden-wall cavities. To inject the Zonolite into the walls I had to build my own blowing machine.

I bought a used 55-gallon drum with a removable lid. I cut two 2-inch round holes in the lid and over one hole mounted a used 11/4-hp. home and shop vacuum cleaner motor. Fasten the motor with a gasket on the outside of the lid, blowing into the drum.

In the other hole, mount a 2-inch PVC (polyvinyl chloride) fitting which can be capped or uncapped. Use this fitting with a funnel to pour Zonolite into the drum. I used a friction-fit PVC elbow for the cap. I epoxyed one end shut with plywood.

Cut two holes in the drum - a quarter-inch hole at the top for the electric motor cord and a 1 1/2-inch hole at the bottom side for a male 1 1/2-inch PVC hose fitting. I bought 13 feet of wire-bound rubber hose and attached it to the 1 1/2-inch fitting with a clamp. At the other end, fasten a 1 1/2-inch plastic fire-hose nozzle, tapering down to a one-half-inch outlet.

Attach the lid to the drum, using the rubber gasket and clamping ring supplied with the top.

Fill the barrel with one bag of Zonolite at a time (20 pounds, 4 cubic feet, about $5). For a funnel I used a paper paint bucket with a 2-inch hole in the bottom. Center the funnel over the 2-inch PVC fitting. When blowing, remove the funnel and cap the fitting.

Drill 5/8-inch holes through the outside siding centered between the studs 2 inches below the ceilings and windows. Drop a plumb into the holes and check for fire breaks. Drill another hole below the breaks and drop a plumb until you reach the floor.

Before blowing insulation into the walls, seal all cracks around the electric outlet boxes, etc. Blow Zonolite into each hole for 15 seconds. Then go under the house and stop up any leaks with loose fiber glass. Fill all wall cavities completely.

I filled one 8-foot by 16-inch by 3 1/2-inch section in two minutes, using about 1 bag per section (70 bags for a 2,000-square-foot house). Plug each hole with a 5/8-inch wood dowel. Spackle, sand, and paint each dowel.

I spent 40 hours on my project and $50 for my machine. The R-value, including the siding, is R-11.

Montgomery L. Young Miami