This we have quite successfully treated with vinegar. Since it is a very mühseelige work, we thought that we still resort to chemical means to speed up the process.
The hardware store has been recommended us this product.
We have sprayed it and even leave for the maximum time (overnight). Unfortunately, the result was worse than our previous vinegar treatment.
Therefore I can only recommend: Let it take ... Mr. Vinegar is .. cheaper and more effective.
