Barry Hunt, who said he was a geologist, called in to the Jeremy Vine show to say the Pee-Back scheme could cause more damage to the historic ramparts.
Cheshire West and Chester Council have covered some walls across the city in the translucent paint which repels liquids.
It is hoped it will cause those inconsiderate enough to wee on the walls to get a soaking.
But not everyone approves of the campaign.
Mr Hunt said: “What they’ve done in Chester is almost a criminal event.
“They will cause the stone to decay more rapidly in thinking they are protecting it.
“It will be saved in the short term, but cause catastrophic damage in the medium to long term.”
He explained that while water would not be able to get into the rock, it also cannot escape and could cause lasting damage if it froze within the brick in a process known as ‘freeze-thaw erosion’.
Vine carried out a demonstration of the paint in his studio alongside its manufacturer Essence Ltd director Matt Cooper.
He squirted water at a coated brick and produced an excited reaction when the liquid fired ‘off at every angle’.
CWaC cabinet member for environment Karen Shore responded to the claims.
She said: “Preserving the integrity of our historic structures is our priority.
"The corrosion caused by the acidic nature of urine presents a serious risk to these structures.
“We have taken the advice of conservation experts when planning this campaign. Because the paint has been applied in localised areas and does not cover entire surfaces, it will cause no short-term or long-term damage.”
The Pee-Back initiative is a collaboration between Streetscene, Regulatory Services, Community Safety and CH1 ChesterBID and has the support of Chester’s Pubwatch scheme.
It has been created in-house by the council’s design team and was officially launched earlier this week. The campaign will continue through 2017, with heightened promotion at key times like during Chester races.
Urinating in public is a criminal offence and the council will prosecute individuals caught in the act.
CCTV operators can direct police officers to offenders in seconds. In September this year, three offenders were taken to court and received fines totalling more than £1,000 between them.
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