Traders say they are furious with the district council because they were not told about resurfacing work which took place on the Greenwoods Row car park this week.
Workmen spent Monday and Tuesday resurfacing half of the car park and repainting lines.
But Ged McKnight, who runs Fellows cafe on Westgate, and Grantham Computer Centre owner David Charles say they have lost custom because it was shut.
Mr McKnight said: “This was totally out of the blue. If I had known I would not have brought any staff in.”
He also said it did not make economic sense to only resurface half the car park so that equipment would have to be brought back again to compete the work.
Mr Charles said customers were down 40 per cent on Monday compared to the previous Monday and down 30 per cent on Tuesday compared to the previous week.
He said: ““We weren’t told about the closure. It would have been nice to have been made aware of it in advance, then we could have made our customers aware of it.
“It comes down to a lack of communication. If we can get the Independent Retailers Association going we can communicate these things between the council and independent retailers.”
Workmen finished resurfacing work on Tuesday. While they only tarmaced half the car park they did re-line all the parking spaces and created seven new spaces for disabled drivers.
SKDC’s head of property development, Neil Cucksey said: “We deliberately assigned the work to Mondays and Tuesdays in the summer holidays when we know car park usage is lower. The work on the Guildhall Street carpark completed on schedule on Tuesday.
“Notices were placed in the car park one month before work took place and the remaining five council pay and display carparks were fully open to the public on those days. We apologise however for any inconvenience the works may have caused.
“All SKDC car parks have to meet certain standards which include the number of disabled parking spaces, the quality of the surface and the clarity of the lines. We have completed resurfacing and re-lining works to about half of the carpark this time around due to phasing the works for operational reasons and budgetary constraints, the remaining work will take place at a later date.”