How do you evaluate if a new elastomeric coating applied over a 12 year old elastomeric coating will be durable? The old elastomeric coating will be pressure washed before applying new coating. Where do you find competent technical adviser to evaluate?
You shouldn't have any problems with durability as long as the old painted surfaces are prepared properly. This includes a good washing to remove any chalky residue, removing any peeling paint, priming and caulking.
The chalky residue is oxidation and is normal. It needs to be removed so the new coating can stick. You might have
to use some house wash or Simple Green, usually scrubbing isn't necessary. Some loose old elastomeric might be removed as well. This depends on the condition of the coating and type of surface.
For good technical advice as to your specific needs you should talk to the contractors sales rep at your local paint store. He/she will have knowledge of the specific products you will need as well as their use.
The real key to any lasting quality paint job is the prep. This alone can make or break any paint job. Pay special attention to all of the requirements of your building.