Hi.
I am a business coach and mentor and I also own a building business doing renovations and conversions.
My question to you is; What is he actually doing that benefits the business or project and what is the value of that?
I would then ask; If you were to bring in outside help to do what he is doing, what would be the cost?
Having said that I don't understand why, if you are partners, this hasn't been discussed and agreed before hand. I have seen a number of good businesses get into trouble due to lack of communication between partners.
The best advice I would give at this stage, bearing in mind I don't know any more than is in your question, is for you both to sit down together over a coffee and discuss the situation and come to an agreement that is win/win for you both.
Feel free to contact me if you wish to discuss getting further help. Regards. Rick 07415984455. I'm back at work on Tuesday if you wish to call then.