ᐅ Metal Window Sill – Correct Installation in External Wall Insulation Systems

Hello everyone,

I have an EIFS (Exterior Insulation and Finish System) facade on rigid foam insulation boards.
I have now noticed that my aluminum window sills bend upwards in hot temperatures because the facade contractor installed the sills with a solid plaster application, without leaving a joint. The sills have a simple end cap, unfortunately not ones with expansion joints. The problem is that after a few months, one or two of the sills have warped so much that the slope has been lost and after rain, water remains standing inside (which I only realized after sealing the gap between the sill and facade). (see photos)

My question is, is the rigid, tight plastering of an aluminum window sill (without expansion joints) and without an elastic joint (e.g., compressible tape or at least a polymer sealant) considered a defect? To my knowledge, this was often done in the past but should no longer be standard practice, even though there are no specific standards for it. The facade contractor was the last trade on the job, so shouldn’t they at least have raised concerns?
Another question is what to do next? Remove all the sills and partially restore the facade? Is there a less extensive option? For example, cutting out the facade around the end caps and filling with a permanently elastic hybrid polymer sealant, then carefully re-plastering? Any other ideas?
Thanks for all your suggestions!

Best regards

dirkthomas schrieb:
(see photos).

Which photos?

sorry forgot...