What a great way to re-purpose a useless bit @JustJim. For those unfamiliar with a marking knife, you might like to let us know what you are using ...

Welcome to the Bunnings Workshop community @desmo. It's sensational that you've joined us, and many thanks for jumping into the conversation. I'm ...

It'd be perfectly fine, I think. If anything it'd probably have a longer lifespan than interior paint due to its hardiness. The key difference is in ...