A Muslim accused of involvement in a plot to target London's transport network said he was buying chemicals to strip wallpaper
A hair product supplier told Woolwich Crown Court that Manfo Asiedu said the liquid hydrogen peroxide was to be used in the course of flat decorations.
Prosecutors say 443 litres were bought from three shops ahead of 21 July 2005.
Mr Asiedu, 33, and five other men deny conspiracy to murder and conspiracy to cause explosions.
The other men on trial are: Muktar Ibrahim, Hussein Osman, Yassin Omar, Ramzi Mohammed and Adel Yahya.
Christopher Diaper, director of the Hairways in Tottenham, north London said Mr Asiedu bought the shop's entire stock of the high-strength peroxide on 19 May 2005.
"When I asked what the product was going to be used for, I was told it would be for the stripping of wallpaper, that they were doing some flats up and that this was a quick and efficient way of doing it," he told the court.
"When I suggested that this was a dangerous product to use, I was told it was no problem, that they had done it many times before and this was the best product for doing the job."
Mr Diaper said he decided to question Mr Asiedu because it was unusual for someone to buy so much liquid hydrogen peroxide, generally used to bleach hair.
But he said he was not aware it could be used to make explosives.
The bombs were allegedly made at Mr Omar's flat in New Southgate, north London, using a mix of the liquid hydrogen peroxide, chapatti flour, acetone and acid.
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