It's a way to see India, Mexico, Korea and Zambia, and to have a few mojitos with new friends.

It's tourism. It's a family activity. It's an addiction.

"It's an unbelievable feeling when you do it. I started last year, and I can't stop," said Mary Lou Johnson, 53, who traveled to the District from Florida last week to get her fix. "I'm up to about once a week now. Yeah, I've got to do it once a week."

Power tools, chop saws, miter saws, hammers and two-by-fours make Johnson happy. So she volunteers for Habitat for Humanity International, which on Friday launched a project on the Mall to frame 51 homes for victims of Hurricane Katrina.

The buzz of power saws and the rhythmic sound of hammer thwacks against fragrant lumber fill the city air every morning near the Washington Monument. The symphony is created by volunteers such as Johnson, who pays her own plane fare and books hotels for her and her husband, Bill, to travel wherever homes are being built.

"We've done Detroit, we've done Vera Cruz, Mexico. We're going to India next," said the retired marriage counselor, who said this is the best way to get her husband out of the Sunshine State. "He really doesn't like to travel, but this way, I get some travel and we have an adventure. And it feels so good doing this."

The Johnsons have become friends with other volunteers, and together, they travel the country, build homes and tell stories over drinks after work.

She takes instructions from Doris Meyer, 59, a volunteer from Tampa.

"I've built in Korea, South Africa, Mexico," Meyer said before filling in a volunteer on lumber placement. "One of the biggest mistakes the new ones make is not putting their boards flush with one another," she said. "They've got to be flush so your drywall isn't lumpy."

Meyer, a nurse and mother of four who wears dainty jewelry and wrestles lumber like a pro, built her home with her husband in Tampa 25 years ago and loved the project. So after hearing about Habitat for Humanity, they decided to volunteer when they became empty nesters. The last of their four children left about eight years ago, and they've been swinging hammers ever since.

"My husband has been to Zambia, even," she said.

Meyer and some of the other experienced builders helped guide the volunteers who came yesterday, spurred by the spirit, or in some cases their bosses, to help.

"Seriously, hammering is so much harder than it looks," said Sarah Harvey, 29, health legislative assistant for Rep. Marion Berry (D-Ark.).

Her boss asked the staff to help build the house representing Arkansas, which was done yesterday.

"I'm going to be so sore tomorrow," Harvey lamented, removing her hard hat and work gloves.

By the end of the week, one home for each of the nation's 50 states and the District will have been framed on one of the assembly pads set up on the Mall.

Each is designed for three bedrooms and about 1,100 square feet. The Bayou models are going to Louisiana; the Jackson models, a bit different, will go to Mississippi.

Once built and checked for precision and stability, the frame panels will be taken apart, loaded into containers and trucked south, where other volunteers will help reassemble them for families left homeless by hurricanes.

The homeowners will repay mortgages -- limited to the cost of materials -- for the 51 units, according to Freddie Mac, which donated the materials.

The building will continue through Friday at Constitution Avenue and 14th Street NW. Volunteers are welcome, and Habitat staff members -- including Kat Russell, 27, famous for once guiding a blind volunteer to help complete a roofing project -- are ready to help teach.

"Whatever your comfort level is, I'll work with you. There was a guy who wanted nothing more than to use the chop saw. Oh, man, he wanted to use that chop saw. So I showed him," she said.

But she's also good at teaching the uninitiated how to hold a hammer.

Jillian Gross, top, urges her crew to raise a truss higher. Fifty-one houses -- representing each state and the District -- are being framed on the Mall.