Broke slates with proper roof ladder.

[Restoration man]

Last year I had to have a lead Valley replaced. My plumber did the lead but I did the slating work very satisfactory as it was near the ridge and managed to number them and put it back like a jigsaw job done.

But where the ladder had been there were about 3 cracked slates I had to replace at the end of the job.

I need access on another part of the roof but I'm scared slates crack again where the ladder sits.

I'm using a proffesional roof ladder from a well known company in the midlands. I tried covering the supports in dense pipe insulation to provide some cushioning in the past. This helped but didn't stop it.

I think I've heard slates become brittle with age so is it just tough? My house has heather welsh and is nearly 90 years old.

Any ideas?

Thanks