Re: what can mix in2 acrylic paint in order to apply with knives and scrappers any1???
I just re-read this post and I am wondering if you might have better results by using acrylic ink and a sponge brush or roller. As you mentioned you would need to work flat. You could also try acrylic gouache, which has already been suggested, like Pebeo Mat Pub, or ordinary gouache or casein paint.
"I am not yet born; provide me, with water to dandle me, grass to grow for me, trees to talk to me, sky to sing to me, birds and a white light in the back of my mind to guide me."
From Prayer Before Birth by Louis Macneice.