The Bishop Mill was visited by a former Russian spy, Sergei Skripal and his daughter Yulia, who were poisoned by the nerve agent last year.
On the first anniversary of the Salisbury Novichok attack, Dawn Sturgess's son makes plea to Putin.
The deep clean and construction work is expected to take up to four months. Sergei and Yulia Skripal were poisoned with Novichok in March.
Specialist teams removed them from behind shops in Catherine Street in Salisbury at around 11am on Thursday for testing.
A murder inquiry is underway in Wiltshire after the death of Dawn Sturgess who was exposed to the deadly nerve agent Novichok.