Q: The walls of our 1938 San Francisco home are lath and plaster, with a canvas-like fabric over the plaster. There are cracks in the plaster, which can be seen through the paint as raised creases in the canvas.

 We've been told that the best solution is to replace the plaster with drywall, but we are put off by the cost and the huge mess we'll no doubt have. When we investigated less costly alternatives, we got conflicting advice.

One repair technique involves laying mesh over the cracks, applying a skim coat and smoothing out the edges. The other solution is to remove the plaster in areas larger than the cracks, then fill with new plaster.

Are these variations of the same method or different methods? The guy who recommended the "cut" method said a skim coat would hide the cracks for only a year or two.

A: Yes, it's expensive and messy, but your first thought is your best. To do the job properly you should strip all the plaster from the walls, leave the lath in place and cover it with 3/8 -inch drywall.

Tape the joints with fiberglass mesh tape, and cover that with a quick-drying joint compound such as Durabond 90. Finish the taping with regular joint compound to a smooth (also known as a No. 5) finish.

The negatives are the cost, which is mostly labor, and the mess. The positives are that the job will last for decades, and you'll have the opportunity to update the electrical system by adding receptacles, light fixtures and ground wires. This is also a great time to add insulation to exterior walls.

Of the other two fixes you mention, the best by far is cutting out the damaged plaster and replastering the cracks. A mesh-and-skim-coat job will fail in a New York minute.

Your walls were constructed by nailing wood lath over the wall studs leaving a 1/4-to- 3/8 -inch gap between each piece of lath. Then, three coats of plaster were applied to the lath. The first two coats were composed of sand, lime and Portland cement.

The first coat, called the scratch coat, was troweled onto the lath with sufficient pressure to force the plaster though the gaps between the pieces of lath. When the scratch coat dried the plaster formed keys on the outside of the lath that held the plaster on the wall.

A second coat, called the brown coat, was then applied. A third coat of unsanded plaster made for a smooth finish. In your case, "plaster paper" was applied between the brown and finish coat. This was meant to stop any cracking.

What's happening now is that as the earth moved over the years, the walls moved with it. When this happened the underlying plaster cracked and the muslin paper wrinkled.

If new drywall just isn't in the budget and if there isn't too much cracking, the best way to do a quick fix is to score the paper along the crack with a utility knife. Then, with a teardrop-shaped scraper or a 5-in-1 painter's tool, dig out the cracked plaster all the way to the wooden lath. Widen the crack as much as possible. With the crack exposed, vacuum out any loose plaster or dust. Fill the crack about halfway with patching plaster and let dry. Put a second coat on, filling the crack. Sand lightly. Then put on a final coat if necessary and sand smooth.

Then get out the paintbrush.

The Burnett brothers are freelance writers. E-mail: sweatequity@sfchronicle.com