Concrete concerns are common.

A contractor's decision to pour slumpy concrete at Donald Trump's Riverside South development, despite requests not to from the-engineer and construction manager, could cost the company more than a million dollars to rectify and would not be covered by insurance, attorneys say. And those familiar with construction practices say pouring below-par concrete is common, but it usually comes in small doses.

What was different about this incident, as project engineer Ysrael A. Seinuk agreed, was the extent of the bad concrete.

It is not unusual to reject one truckload, he said, but here the contents of five were not up to snuff.

"It happens on many jobs that I work on, and in other jobs. It's not unusual that some of the concrete is low strength. The difference in this case is that it's a lot," said Seinuk, a partner with the Cantor Seinuk Group, one of the most prominent and respected engineering firms in the world.

Seinuk is the licensed professional engineer for Trump's condominium project at 300 Riverside South who tried to turn the trucks away but was overruled by the concrete contractor, Laquila, as is its option.

Trump is 50/50 partners with a group of Hong Kong businesses to develop the 1.8 million square-foot mixed project along the Hudson River between 72nd Street and 61st Street. When it is complete, Riverside South will house another 5,000 residents in 16 buildings.

The first condominium building and the site of the poor concrete is being erected by HRH Construction. HRH has worked on many of Trump's jobs, and they have a long relationship. The company is owned by Starrett Corp., which is in the middle of a friendly buy-out that should close in the next week.

Just to the south, Lehrer McGovern Boris is constructing the first of Riverside South's rental buildings for Trump, and the two construction companies are in what has been termed a "friendly competition" which could result in further work on the next 14 buildings.

One concrete consultant, who asked to remain anonymous, as did other engineers interviewed for this report, said that the concrete contractor, Laquila, is know for its high strength concrete and is often called on for quality work and for repairs.

Still, Laquila Contracting has been barred from working on city jobs for not disclosing information about earlier accusations of bribery and illegal dumping in New Jersey. There are reports that this past April company and its operations manager pied guilty to filing false documents in connection with a job at Elmhurst Hospital, in which they subbed out the work for less money than they bid - and then didn't pay the sub. Its principals were just arrested in October for operating an illegal refuse transfer station next to their Brooklyn headquarters.

The concrete at Riverside South was apparently poured into spaces between 40 and 60 of the 80-column site between the fourth and fifth floors of the tower portion of the condominium, where work continued until October 29, resulting in another 15 stories of construction.

The bad concrete will also have to be jackhammered away and replaced with even stronger concrete, said Seinuk, referring to what is known in the industry as grout. "It will achieve a higher strength," he explained, expected to be as much as 8,000 pounds per square inch (psi).

For this particular area of the job, the concrete was specified as being able to hold up 5,000 psi. Despite the regulated oversight from the lab, TestWell Craig of Ossining, the concrete just didn't look right when "slump" tests were done.

The first of Mayor Rudolph Giuliani's Building Commissioners, Frank Luzi, was from TestWell. He resigned after just a few months when company officials were investigated by another state. They declined to comment on the event.

The slump test is conducted at the construction site, explained Sing Chu, P.E., president of the Concrete Industry Board and an engineer with the engineering firm of Weiskopf & Pickworth.

The concrete is poured in a specific way into a short conical cylinder and inverted. If the top isn't firm and "slumps" too much, the concrete is most often rejected by the engineer and the truck is sent away.

According to Chu, the Concrete Board is an association of engineers architects and suppliers that distribute information on how to make quality concrete and foster the placement of good concrete.

Concrete is comprised of cement, which is usually manufactured from limestone mixed with shale, clay or marl that is pulverized and baked at about 2700 degrees fahrenheit. This material is transformed into what is known as a "clinker." This clinker is then ground into the very fine dust found in bags of cement. There are five grades of cement that are commonly used in construction.

The plant where the concrete is to be hatched is typically visited and inspected by either the engineer or someone designated as "controlled inspector." The machines are then calibrated and tests are made to verify the quality and correctness of the batches, and then they come up with an approved design mix.

When construction starts, the concrete is ordered and batched. At the cement batching site, the correct cement grade would be mixed in specific, computer directed proportions, with sand, gravel and water, and sometimes other chemicals, to reach a certain consistency.

Concrete is placed in the truck and to keep from setting, is continuously mixed during the journey to the site and while waiting to be poured.

The engineer's concrete specifications also designate a time limit, and if the truck is not completely used before the elapsed time, one engineer explained, the truck should not be emptied.

The on-site lab is supposed to check the ticket on each truck to confirm that what is being delivered is as specified by the mix. Then there are tests the lab will make as the concrete is taken from the truck.

As a rule, the experts say, the major factor controlling strength is the amount of water used per bag of cement. But the cement needs to have a minimum amount of water to keep it workable until it is poured, and to conduct the chemical reactions needed for setting.

Concrete usually gains strength as the chemical reactions between the cement and water take place over time, and in favorable conditions of temperatures and moisture. So if the cement dries too quickly, for instance, it will never gain full strength, nor would it if too much water were used or the wrong proportion of other elements.

The slump test used to check the consistency of the concrete is performed right out of the truck and is used as a standard site test by the industry, but further lab tests are always conducted to watch the concrete's strength over time. In this case, those later tests revealed the concrete never came up to what should have been its full strength.

Seinuk says he was called to the job, and after seeing the slump tests on the five trucks, rejected the concrete, as did the construction manager for HRH Construction.

In New York City, it is still the unions that rule. Laquila has the right to place concrete despite what the construction manager or the engineer or the controlled inspector think. Laquila would therefore basically ensure the strength of the concrete by agreeing to replace it if it failed later strength tests. Those in the industry say that most often, the rejected concrete does come up to full strength as it cures and hardens.

But sometimes it doesn't, and one engineer described finding a floor in another project that was two different colors - and two different strength concretes.

To keep a scientific eye on the curing, additional sample cylinders are therefore poured, as they were in this instance, for hardening hack at the lab.

At least six such test cylinders would have been transported to the lab for curing and storage until testing. Chu says initial tests are generally conducted on two of the cylinders after seven days, when the concrete is supposed to reach 70 percent of design strength. Then, at 28 days, two more cylinders are broken and tested.

"At that point, we look for full strength," Chu explained.

But here, at seven and 28 days, the lab found the concrete to be only half the specified strength.

Ilyse Fink, a spokesperson for the Buildings Department, said the city's design guidelines are usually specified to be stronger than needed, but there was no question this concrete would not have been able to support the expected size of the structure because "it was half the strength, not even three-quarters."

When the 28-day tests came back, Seinuk had some of the work halted and decided to allow the construction to only bring the building to 21 stories while a fix was designed. When a Buildings Department inspector came by on a routine stop, some of the workers complained they were idled because of bad concrete on the fifth floor. That led to the decision by the Chief Inspector of the Buildings Department Enforcement Safety Team, Pat Ferrante, to direct an immediate stop work order be issued until an engineering report was submitted.

Seinuk submitted a letter the following day assuring safety would not be affected as long as construction did not proceed above the 21st floor. To ensure a greater margin of safety, Buildings Commissioner Gaston Silva, however, limited construction to 20 stories.

At a meeting held at the Buildings Department last Wednesday, Seinuk outlined plans that he described as being similar to what a dentist would do to fill a cavity.

First, each of the columns will have to be reinforced from the cellar to at least the 15th floor before jackhammering out the bad concrete. Then the stronger mix will be used to fill in the columns. Several columns could be shored up at a time.

Seinuk will be submitting a plan to the Buildings Department and a Buildings inspector will be on hand to watch at least the first column being fixed.

Commissioner Silva said the concrete needs to be replaced with material of the proper density before the columns, currently holding 20 stories, can support the weight of the additional 26 stories planned for the full 46-story condominium tower.

Since the situation was not dangerous, Seinuk, the engineer, was not required to notify the Department of Buildings.

Former Buildings Commissioner Rudolph Rinaldi, who is now an executive vice president with Santa Fe Construction, explained that there are often mistakes during construction, which are usually resolved after a lot of "posturing," but the main concern on everyone's mind is liability.

Should the engineer insist on not allowing the concrete to be poured, for instance, there would be liability costs, perhaps for the rejected truckload of concrete, which another engineer says could cost as much as $50,000.

"In the world of lawyers and litigation, to some degree it's the easy way out to let someone fail, and reject [the concrete and let them pour it] and let them pick up the liability," said Rinaldi. "It becomes a litigation and liability issue rather than a business issue."

Attorney C. Jaye Berger, who handles real estate contracting and hazardous substance issues, said Trump would probably have a definite completion date and a liquidated damage clause in his contract with the general contractor, HRH Construction.

"That would be for damages calculated in advance that the contractor would have to pay the developer for each day the project is late," Berger said, suggesting that those costs would undoubtedly be passed along in any contracts with the concrete provider. But she noted, "This is not an insurable event - just bad workmanship."

Michael Zetlin, a partner with Zetlin & De Chiara, agreed that while there would be liability insurance to cover actual property damage if the building fell, "paying to rip out concrete is not an insurable risk." Zetlin expects there could be performance bonds to cover some of the costs.

"Laquila is a sizable contractor and should be able to cover the cost of the repairs," he said. "There may be disputes over the delays and the impact, but the underlying costs for the error will be picked up."

Another potential problem for the future would be if the grout doesn't really fix the problem and there is later shifting.

"If it causes cracks in the condominium it could come back to haunt him," Berger said of Trump.

Berger, who is currently litigating a similar problem, will be discussing "Renovation Disasters and How to Avoid Them" at the Council of New York Cooperative's Housing Conference at Hunter College on November 16th.

Developer Trump was unfazed at the construction blip and fix, which he says will be paid for by the contractor.

"We'll chop and fill," he said last week.

"It will be stronger than before."