Laying tile over old thinset

[Matt Tallent]

Can I lay new tile over old thinset? I took up the tile in my kitchen and want to replace it with new tile. There is a lot of thinset stuck to the cement board. Will the thinset I put down create a level surface and a good floor? Is this common? Or should I put down new mason board and lay over that. It would be a lot more work but if it’s really bad to go over old thinset I’ll do it. Thanks!