You need spackle, a putty knife, a comb and something to put it all on (canvas, acrylic, etc.).

Using the putty knife spread spackle all over your acrylic in a thin layer.

Once you have it all spread use the comb to  create the design of your choice.  It shouldn't be perfect so don't try to make it.

The spackle goes on pink then dries white. Here is the finished DIY Spackle Wall Art. 

DIY Spackle Wall Art

For more DIY Art Projects go to At Lane and High.