MEMPHIS, Tenn. -- Jimmy Carter resumed his role as Habitat for Humanity's most prominent booster on Monday, donning a hard hat and a worn leather belt stocked with his tools to hammer and saw with other volunteers building a home.

"We haven't cut back on my schedule yet," Carter said, seeming invigorated during an interview. "I know it's going to come, particularly if my cancer progresses, but we don't yet know what the result will be from the treatments."

The former president celebrated his 91st birthday in October and is undergoing treatment on cancer found in his liver and brain. But he was sure-footed on the construction site as he moved from one task to another.

Arriving ahead of schedule, Carter installed a hammer, measuring tape and thick pencil on his tool belt. He helped place pre-framed walls, hammered nails into place and sawed boards into smaller pieces, occasionally shouting questions or suggestions at the rest of the crew.

His wife, Rosalynn Carter, 88, hammered brackets to secure the walls, pulling the nails from her leather tool belt. "Hard work," she said with a soft laugh.

Carter and the Atlanta-based charity have been synonymous for more than 30 years. His presidential museum even has his work boots and a hammer on display. Since leaving the White House, the Carters personally have been involved with 3,943 projects in 14 countries for the charity, which has helped 5 million people with home construction and repairs.

Each year since 1984, the couple has volunteered a week of their time to "Carter work projects," drawing thousands of volunteers. The streak seemed at risk in August when the former president revealed his illness, casting doubt on his ability to travel to Nepal this month.

Ultimately, doctors approved the trip, but it was cancelled because of concerns about civil unrest in the region, Carter said. He said Sunday he had been looking forward to the Nepal build, which would have involved making walls woven of bamboo.

"Back in August ... I didn't know if I would be physically able or if the doctors would let me go to Nepal, but they finally approved my going, and I was very happy and excited about that," Carter said. "To find out that we couldn't go because of civil disorder in Nepal was just a very serious blow to me, and I presume to the other 2,500 people who were going to join us down there."

Carter traveled to Memphis instead. By late morning, all the walls were framed and volunteers were placing wood planks around the exterior.

Arlicia Gilliams, a 25-year-old single mom, will soon move in with her 2-year-old daughter, Parisse, following a path her parents forged decades earlier when they moved into a Habitat home near the University of Memphis.

Gilliam put in the required 350 hours of "sweat equity," volunteering on other Habitat projects, and her mortgage payments will help build other Habitat homes.

Carter said Monday that Gilliams had been working so hard, he only had time for one quick joke, suggesting that she could always give back the house if she didn't like it.

"No way!" Gilliams said, grinning as she described what it was like to raise a wall with the Carters.

"It's been a long journey," she said. "This is the first time I've been able to touch down on my land."

Habitat's CEO Jonathan Reckford said Carter's jump-right-in attitude hasn't changed since his cancer diagnosis.

"He, to me, looks great, sounds great," Reckford said. "And he's very focused. You can tell when he's building; he's working on getting the job done."

Carter got a single dose of radiation, targeted at four tumors on his brain, in August, and four treatments since then of Keytruda, a newly approved drug that helps his immune system seek out cancer cells. He said he'll keep receiving the drug, and that it's still too early for doctors to determine the impact.

"I've reacted well to the treatments," he said. "I haven't been uncomfortable or ill after the treatments were over. So that part of it has been a relief to me and I think to the doctors. But the final result of how well the treatments are combating or controlling the cancer, we don't know yet."