Ideas on how to fill a hollow gap between substrate and engineered wood floor

Hi,

I've got a customer who had a floor laid over some uneven screed. There are a couple of hollow spots where the adhesive wasn't thick enough, mostly at the edges. Is there a bonding product that could be poured to fill the gap(s) to create a solid bond so there isn't that horrible hollow noise when it's walked on?

Thanks,

Dan

 

Bona make a gap injection kit

 

Thank you.

Dan