We have a client withholding final payment because they believe there was a deficiency in our design that is causing cracking on the surface of their deck. We requested additional info: pictures, location of the cracking, info from the contractor on what they believe caused the cracking, as this could have been caused at many points throughout construction. They have not furnished the additional info. How should we proceed?
How you should proceed depends on a lot of factors and information that isn't available from your question. Assuming you're a contractor and you're talking about the mix design, if the project is private, you may have some lien rights you can assert. You could also some breach of contract rights, but someone would want to read your contract to determine that. You might be entitled to interest on the breach of contract damages.
If you're an architect/engineering and you're talking about the design of the deck rather than just the mix design, that's a whole different set of issues. But, you'd still have some breach of contract damages.
An experienced construction attorney can help you with these issues, but will need to talk to you to know what you options you have and which option is best.