Castle Cement closed its kiln at the end of June, putting the decision down to the "current economic climate".
The firm says it plans to eventually reopen the indust-rial oven but can not say when it will happen.
In the meantime, the company is reviewing its practice and looking at the organisation of staff.
General manager Gareth Price said it was normal practice to close the kiln for part of the summer but usually it would be for a shorter period of time.
He said: "We normally have a summer shutdown of the kiln but because of market conditions we decided to bring the date forward this year.
"It's still to be determined when it will be reopened.
"It's a case of balancing stock - we need room in stock for the kiln to be continuous, we can't keep stopping and starting it."
He added: "Everybody is continuing to work as normal.
"If it's off for longer we may well look at re-organising staff.
"We're reviewing the situation and considering all options available to us."
The Ketton works date back to 1928, when the Ketton Portland Cement Company was incorporated and construction of the plant began.
Now, Castle Cement produces some 1.4m tons of cement a year and currently provides about 360 jobs.