The Ash Grove Cement plant in South Seattle is humming these days. Barge-loads of rocks and minerals are crushed, then heated in a huge...

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The Ash Grove Cement plant in South Seattle is humming these days. Barge-loads of rocks and minerals are crushed, then heated in a huge rotating kiln, creating the fine gray powder that’s the lifeblood of construction.

Cement supplies are tight across much of the country, and plants like Ash Grove’s are churning to keep up with demand. The shortage has driven the price of cement, one of the primary ingredients in concrete, up about 12 percent nationwide in the last year, estimates the U.S. Department of Labor.

In Spokane, shortages forced hardware stores to ration bagged cement this spring, and some builders had to lay off workers for lack of raw material. In the Puget Sound region, supplies are in better shape, but higher prices are making construction more expensive.

“Definitely, the cement supply in the Northwest is tight,” said Tom Whiteman, general sales manager for Cadman, one of the area’s biggest suppliers of ready-mixed concrete and a big buyer of cement. “This may not go away any time soon.”

The shortage, along with the tight supply of structural steel, has contributed to sharply rising construction costs.

Walt Miles, president of Miles Sand and Gravel in Auburn, another concrete mixer, says his cement supplier has put customers on limited allocations based on their past consumption. It hasn’t affected his operations yet, but he’s concerned.

Cement vs. concrete

Cement Made from lime and other minerals ground into a fine powder and baked at 2,700 degrees. When water is added, crystals form, and the substance hardens. Cement is the binding agent in concrete.

Ready-mix concrete Precise proportions of cement, sand, gravel, stones and water, mixed and poured to become sidewalks, roads and foundations.

Source: Portland Cement Association

“We haven’t seen cement-supply issues like this since the late ’70s,” Miles said.

It could get worse. After a deep recession followed by three years of slow recovery, the Northwest economy appears to be accelerating. The residential housing market has been hot, and commercial construction is awakening after several slow years.

Several concrete-hungry public projects, such as Sound Transit’s light-rail line, are in their construction phase, and state highway building is likely to pick up later this year.

Getting more cement will be a challenge.

U.S. plants are running at capacity, and inventories are at historic lows, says Ed Sullivan, economist for the Portland Cement Association. A May survey by the Illinois-based cement-industry group found short supplies of cement in 23 states at the start of the peak construction season.

Washington wasn’t listed among those states, but that could change this summer, Sullivan said.

“It does not take much of an imbalance between supply and demand to generate a regional shortage,” he said. “I expect the entire West Coast will be hit as the building season heats up.”

Cement from Asia, which the Northwest relies on heavily, is harder to come by because China, the world’s biggest cement producer, is consuming a lot more than it used to.

“This is not cyclical,” Sullivan said. “This is structural. We’ve taken our infrastructure for granted for so long.”

Few new cement plants have been built in the United States in recent years because of flat prices and lengthy environmental-permitting processes. U.S. builders have grown to rely on imports — largely from Mexico, Asia and Canada — for nearly a quarter of the cement they use.

Several new and upgraded domestic plants are in the works now, but the new production capacity will take years to come on line.

The Ash Grove plant in Seattle was built in 1928 and upgraded in the 1990s to more energy-efficient and environmentally friendly production, spokesman Lance Latham said.

The coal-fired plant on the Duwamish consumes 1.2 million discarded tires a year as it produces 750,000 tons of cement. The tire remains and coal ash are combined into the final product.

Because of the boom in trans-Pacific trade, Sullivan said, there has been a shortage of barges to bring cement from Asian producers.

Spokane’s cement problems this spring were aggravated by another shortage — rail cars. Mark Murphy, president of Central Pre-Mix Concrete, said Spokane relies on railways to bring cement, but cars that used to be available for cement are now busy with other cargo.

Murphy said a mild winter also played a role, allowing construction crews to keep working during the normal off-season.

That kept cement suppliers from replenishing their inventories.

“I hope Seattle doesn’t have to go through what we went through,” Murphy said. “We just kept a boom pace on housing and commercial construction and basically got out ahead of our suppliers, and they could never catch up with us.”

Another factor has been U.S. anti-dumping duties placed on cement imported from Mexico.

Commerce Department officials have recently said they hope an agreement will be reached that would allow Mexican cement to flow more freely, which would ease supplies in some places.

Tom Boyer: 206-464-2923 or Times researcher Gene Balk contributed to this report.