omission

The process is of non-migrating type i.e no further scope of levelling once cured, a care pre-treatment of fabric is a must to develop good and consistent wettability.

1) Are there a relative pronoun or any auxiliary verb omitted before 'once cured' in the given sentence?

2) What is the meaning of 'once cured' with respect to this given sentence?

3) In "is a must to develop good and ........" the article 'a' is placed before the word 'must'? Was it necessary to use this article in this case? If I omit this article, what differences of meaning of the sentence will appear?

Thanks for helping me.