O. Grant Roofing
"If your roof is indeed a natural or man made slate covered roof, then you will need to re-fix the slates using aluminium nails to the roof batten. There should be nail holes where the old existing nails would have been prior to the slate coming loose. You may also need to use a "Tingle" which is a strip of narrow lead, nailed to the under batten, this will permit you to slide the slate back in place and simply curl the lip of the lead strip over the bottom edge of the slate to keep it in place.
Answered on 10th Jun 2019 - Member since Mar 2018 - report
You might also need a "Slate Rip" which is a long handled tool used for removing the existing nails that might well be left protruding from the under batten. These protruding nails will prevent you sliding the slate back into place. These nails must be removed prior to attempting to replace the slate.
Alternatively, you can use a good quality silicone based product to effectively glue the slate back into place, but this is not as good a method as fixing the slate back in correctly using nails and or a lead strip.
You can also look up "Replacing a slate on a roof" on You tube, this would show you exactly how the job is carried out. I hope this has been of some help to you."