How to flatten a large water color painting

To flatten a large watercolor painting, you will need several things,

Spray bottle with water
Foam core, cardboard, or a large piece of mat board.
Books or other heavy items
Paper towels (no prints or printing)

First thing you need to do is turn the painting over onto a flat surface such as a glass tabletop or a piece of foam core slightly larger than the painting.
Spray the back lightly with water, do not allow this water to seep around to the front of the painting.
Put paper towels over the wet surface and lay another piece of foam core or mat board on top of the paper towels.
Place books or other types of weights on top of the foam core and allow to sit 24 hours (depending on temperature and humidity it could be less)
Take the books or weights off and take a look at the painting. It should be totally flat. And dry. If it is still damp it may warp again so replace everything and allow it to sit a while longer.

 

The painting right side up and also turned over ready for spraying with water.

 

The painting covered with paper towels after being sprayed lightly with water,   The books which I used as a weight

The painting lying flat under the foam core and the books for 3 to 24 hours.

The finished painting  ready to frame!