I'm creating a world opposite of [Les Visiteurs](https://en.wikipedia.org/wiki/Les_Visiteurs), where modern age structural engineer accidentally time travels to 13th century. When guards of the local lord arrest him on suspicion of being a spy, due to his weird clothing and the way he talks, he claims that he's mason from abroad looking for work. The lord is just starting a new castle and needs skilled workers, so he hires him but feels deeply suspicious of him, so he tells the [Master Mason](http://www.historylearningsite.co.uk/medieval-england/medieval-masons/) to keep an eye on the newcomer.

Would the Master Mason have any use of modern structural engineer knowledge or their level of technology is too low for any of it to be practical?