What is the best way to join 2 pieces of MFC together to increase the length and minimising the joint line when making a face frame for built in wardrobes?
Use 2800x2070 commercial size sheets so you don't need so many joints :wink:
I take it you are using strips of MFC for the faceframe :?: , the only way is a butt joint reinforced with a small biscuit or two, joint line will depend on how cleanly you can cut the mating ends.
I would usually only do the carcases in MFC, with the faceframe in solid wood.
i'm with jason, but it might be worth considering a scarf joint like you would with a skirting board, but unless you make a feature of it, you will see it anyway. :?