Handyman on call

JULIE

A. If you can afford to add to the thickness of the floor, put a new layer of concrete on the old, 4 inches thick. If you can’t do that, you will have to have the old concrete broken up and carted away, and 6 inches of concrete poured in its place, flat and level, with steel reinforcing bars called rebar.

Q. My black wrought iron railing needs painting, but it has several rust areas. Do I have to get rid of the rust before painting? How can I do that?

JEANNE PERRY, Lexington

A. Yes, you have to remove as much rust as possible. For the remaining rust, treat it with Rust Reformer, one of several treatments containing phosphoric acid that will turn the rust black and make it paintable. Finally, paint it with a Krylon wrought iron paint that needs no primer.

Q. My oil man said he will charge $5,000 for me to switch to gas. Isn’t that a lot of money for a conversion?

SURPRISED

A. No, that is not too much, because he will have to take out the oil burner, put in a new gas unit, take out the oil tank, and perhaps install a stainless steel chimney liner, which is required by law for gas burners.

Q. I have two big cracks in my driveway, one 1 to 2 inches wide, the other 2 to 3 inches wide. What is the right way to fill them?

HELEN YOUNG, Weston

A. There are several ways, but which is right is to find out which one works. Here are three:

1. Buy blacktop patch, sold in hardware and big box stores. Insert this patching material in one crack, about halfway full. Then tamp it down very compactly. I’d use a board, inserting it in the crack and whacking it with a sledge hammer. Then fill the rest of the crack, with a bit mounded up over the crack. Then put a piece of plywood on the crack and drive your car over it several times.

2. Buy crack filler, which is a little softer patching material, and fill the crack, then sprinkle sand on top to prevent feet and tires from picking up the sticky material.

3. Fill the crack with stone dust, and keep filling it as the sands settles. It will get quite hard. The reason you want to fill them is to keep water out. Water will freeze and expand, making the crack even bigger.

Q. The rollers on the bottom of my slider screen have broken. How can I get new wheels or have the screen repaired? I need a new front door, but only the front door; no frame or any other part of the structure. What is the best material?

BARBARA McSURL, Belmont

A. If you can find a brand name, the company should offer new wheels, even for a price. Or, find a large hardware store that repairs screens. Ace Hardware has a good reputation.

As for the door, wood and fiberglass are the leaders. Both are expensive, but both can be stained with a semitransparent stain, which I suggest, because most of my exterior doors and storm doors are stained. I think wood still serves well, and wood can be trimmed to fit odd size openings, while fiberglass I don’t think can. The Brosco Catalog, carried by the big box stores and independents, has lots of pages full of both types of doors and of styles, too. Both are insulated well enough that a storm door is not required, mainly because buildup of heat between door and storm can damage the door and any finish (paint, stain, and other coating it might have). If the door is in constant shade, then the storm door will cause no harm. Take your pick.

Steel makes a good door and is insulated, too, but it must be kept well painted to prevent it from rusting. Once rust starts it is costly to sand, treat, and repaint.

Globe Handyman on Call Peter Hotton also appears in the Sunday Real Estate Section. He is available 1-6 p.m. Tuesdays to answer questions on house repair. Call 617-929-2930. Hotton (photton@globe.com) also chats online about house matters 2-3 p.m. Thursdays. Go to www.boston.com.