Either through advertising, or some other method your client called you to furnish them with a quote, you obviously convinced them that you knew what you were doing, and that you had the knowledge and expertise required to clean their building to the required standard.
Your last post mentions that previously, they had relied on in house cleaners, who failed to do the job to the required standard.
During your survey, you will have noticed ALL the materials that require your attention, you should have ensured that you correctly identified the materials present, and have the required knowledge and expertise to clean and maintain these materials.
Your statement "I thinks its Altro" calls into question your knowledge.
Within your written quotation, you should have specified that the flooring would need maintenance/deep cleaning at certain frequencies throughout the year( depending on traffic/use etc) and that this service would be an extra £XXX per clean.
The client has now complained about the state of the flooring, it is not your clients fault that you failed to mention the specialised care that Altro requires, it is I am afraid, yours! My advice is to do whatever it takes to get the floor cleaned, if it costs you time and money, suck it up, put it down to experience and make sure you dont make the same mistake again.
What has happened to the in house staff? Have you taken them on under TUPE?
If this really becomes a sticking point for your client, could they cancel the contract ?
If they did cancel, what would your liabilities be ?
Redundancy?
Breach of contract?
Constructive dismissal of staff?
Unless you are very sure of positive answers to the above, clean the floor properly, take the hit and hope that your client forgets all about this, raise the price each year a little until, the maintenance cleaning is covered. Telling them what is required after they have accepted your quote will just make them dig their heels in and make you look foolish.
Once that point has been reached, the contract will become a chain around your neck, and will cause all parties concerned, nothing but grief!
Regards,
Rob