Regrooving an old teak deck to accept new caulk.

[lustyd]

These are designed for the job.
https://www.amazon.co.uk/Bosch-Professional-compounds-Accessories-Multi-Cutters/dp/B075VLTY18

YouTube Cadoha showed it in use on one of their refit videos. It’s much less likely to damage anything than a router and very quick.