Tree help please

Morning

We have a massive huge great big bugger of a horse chestnut tree in our back garden.

We have to get it trimmed every couple of years and last year the man kindly trimmed off all the new leaves/branches that are starting to get lower and lower down the trunk. He said we could paint something on the trunk to stop the regrowth and for the life of me I can't remember what it was. We can't get hold of said man for one reason or another and was wondering if anyone might have any idea of the stuff he spoke of?