In the ravaged Brazilian valley where a giant mining waste dam burst, killing 19 people and spewing pollution, an incongruous sight pops up: billboards with a grinning workman and the slogan "communicate positively."

The boards stand in swirling dust raised by diggers and trucks repairing the damaged network of dams and dikes at the site of what's been called Brazil's worst environmental disaster.

But 12 months since the tragedy at the Samarco iron ore mine -- which belongs to two of the world's wealthiest mining companies Vale and BHP-Billiton -- there is little positive to communicate.

The sudden dam break on November 5, 2015 unleashed 32 million cubic meters (42 million cubic yards) of mineral waste -- a moving wall of red sludge big enough to fill 11 Dallas Cowboys stadiums and, according to the UN, containing dangerous contaminants.

The flood tore about 640 kilometers (400 miles) down the River Doce, killing mine workers and inhabitants of the nearby village Bento Rodrigues, and stripping thousands of their homes or jobs.

Samarco, located near the historic town of Mariana in Brazil's metals-rich Minas Gerais state, insists it is doing everything possible to draw a line under what it calls a tragic accident, denying that the spill was even toxic.

Victims and Brazilian prosecutors -- who have filed manslaughter charges against 21 executives, as well as billions of dollars in damages claims -- tell another story.

- Where are the houses? -

Samarco's highest profile commitment is to build new villages for the people of Bento Rodrigues and Paracatu, a second rural community wiped out in the mudslide, although no one was killed there.

To date, not a single brick has been laid. In fact, the sole physical sign of progress is a metal plaque reading "Novo Bento" in the middle of a forest that will become a building site but which for now is home only to tropical butterflies, birds and termite hills.

"A whole year and nothing has happened. They've done nothing apart from buying the land," an angry displaced villager, Antonio Geraldo Santos, 33, said last week after a meeting with former neighbors at a hall in Mariana.

BHP, the world's biggest mining company, and Vale, the world's biggest iron ore miner, say they and Samarco are committed to repairing the damaged communities, mine infrastructure and environment.

Alvaro Pereira from the Renova Foundation, a body set up to coordinate aid, said 8,000 families along the River Doce are receiving emergency compensation.

Many of these relied on fishing or tourism where the Rio Doce enters the Atlantic Ocean and have lost income. But the worst hit live near the dam and had only minutes to run for their lives when it broke, losing everything from cars to family photos.

Just in Bento Rodrigues there were 236 families forced to flee, Renova says. Another 108 families were displaced in Paracatu.

Pereira describes a "gigantic sense of responsibility" and attributes rebuilding delays to intensive consultations with villagers and authorities.

"Many question why it hasn't started yet," he said during a media tour where Samarco public affairs officers monitored every word said by employees to journalists. "But there is a lot of work that you don't see."

Construction will be complete by early 2019, he said.

- Justice and jobs -

By contrast, frantic work has gone into rebuilding a dam that holds back an even bigger waste reservoir after being badly damaged during the accident last year.

"We are working 24 hours a day, seven days a week," the head of the project, Eduardo Moreira, told journalists during the tour.

Huge trucks, earth movers and platoons of men in orange work jackets and hard hats dug and pushed earth and rocks to shore up the dam, centerpiece of a vast barren area gouged by Samarco from the green hills. Smaller dikes were being built lower down to ensure that waste left over from last year's broken dam doesn't go any further.

Asked if another dam could burst, Moreira said: "It's virtually impossible."

Samarco and its multinational owners face a barrage of lawsuits, with prosecutors notably demanding 155 billion reais ($49 billion) in damages, not to mention potentially lengthy prison sentences for the 21 executives and employees accused of qualified homicide.

Minas Gerais state prosecutor Guilherme de Sa Meneghin accuses Samarco of "using delaying tricks" at every step of compensation.

"They only meet their obligations after being forced to in court," he told AFP.

Yet despite this widely shared fury, victims want Samarco -- paralyzed since the disaster -- back in action.

Samarco employed 3,000 staff, about 1,000 of whom are now out of work. There were also 3,000 contractors and "many" have been laid off, a spokesman said.

"It really is a complex situation given that mining is the chief activity of Minas Gerais. The relationship with mining is very strong, so they want Samarco to reopen," Meneghin said.

"But they don't want them to be let off or to escape responsibility."