I've just had a fireplace rebuilt for a new log burner and now have an issue installing a floating mantel on the wall. I've just drilled the first hole to fit the studs (onto which the mantel will slot) and have found that once drilled through there is no masonry behind the plaster.
I have gone through some photos my partner took of the guys doing the job and they used some sort of expanding foam when installing the new lintel which I suspect is what I've gone into.
Any help on what I should do here would be greatly appreciated.
Sorry, please see (poor quality) image of the fireplace during the build.