The laying of the track was supposed to begin in February but carnival holidays followed by unusually heavy rains have contributed to delaying the scheduled start.
"The material is there, it is all ready," Decio Chusid, the head of Playpiso Pisos Esportivos, the company that is laying the surface, told Reuters. "We are just waiting for the rains to stop and then we will get going, it shouldn't be long."
The rainy season in Rio usually ends around February or March.
Chusid said the concrete base was in place at the Olympic Stadium but needed to dry out before the track can be laid on top. If the concrete is humid there is a risk of bubbles developing on the newly laid surface.
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It takes around 35 days to lay the entire track and it is usable the day after, Chusid added.
The stadium will be the site of the most eagerly anticipated events during South America's first Olympic Games, and will play host to household names such as Usain Bolt and Mo Farah.
The athletics test event is scheduled for May 14-16 and Chusid said he is confident it will be ready in time.
"There is no alternative, it has to be ready and it will be ready," he said. "These things are often done at the last minute, the same thing happened with the Pan American games at the same stadium (in 2007). There were lots of problems but it was done in time. We are Brazilian, we are used to it."
Chusid's company is the Brazilian partner of Mondo, the Italian firm that has laid every Olympic athletic surface since 1976.
Together the two companies have laid more than 70 athletic tracks in Brazil, or more than 80 percent of those in the South American nation.
(Reporting by Andrew Downie; Editing by Alison Williams)
