I tried to paint over a logo on a T shirt last week and labelled it as a Pinterest fail, which isn’t quite fair because it was a trial run of my acrylic textile medium. (I’m not sponsored by that shop).
The medium works, but isn’t opaque enough to hide a bulky printed logo. It did however provide a nice surface to apply more paint to and reduced the contrast between the white print and black T shirt.
I disguised the logo by incorporating it into a design, a bit like a cover up tattoo.
If you want to paint on a T-shirt with acrylic paint and textile medium, definitely put cardboard inside the shirt, because paint soaks through and can stick the front and back of your shirt together. Yes, I used cardboard 😛
Before:
After:
I’ll have to see how well it survives the laundry to decide whether it’s a big win, or just a fun experiment 🙂
3rd September 2019 update: after 2 washes it’s looking really bad. There isn’t an obvious reason why some bits have peeled and others haven’t. Some pure textile medium bits are fine, others are really bad. It’s the same story with the bits painted over the logo, so I don’t think the medium or original print are the problem. Next time I’ll either accept an unwanted logo, or use appliqué. 
1artplease 