how do i mount these on watercolor board properly?

Question

I am creating a two part painting that will need to have both parts parallel and it is best if none of the image is hidden and there is no border. The images are on watercolor board in acrylic.

If these were on canvases, it would be easy to hang them. But this part is complicated. i need to draw both images before painting, but i would like to cut off the border to do that.

Answer 1

By the choices you have made, you are almost certainly going to have to accept some sort of a shadow line. If you have not painted them yet, then keeping some of the material outside the painting would allow to "mount" them by cutting windows in a "mat" of paper or very thin plastic or velum and laying that on top of the paintings. Double sided tape or a more artistic substitute would hold the paintings and paper to the wall and have the images floating.
Otherwise, you are going to have to hang them by sticking them to the wall and it becomes your border. The eye is going to give them a border.
An alternative is to paint them in exactly the right location for your desired relationship on a single board perhaps using masking tape for a crisp edge (and to draw on) and then use gesso to make the non-painting part of the board exactly the color and texture you want.

Answer 2

i ought to correct the board with acrylic gesso so as that the board isn't too absorbent. also, if the board starts warping, coat the opposite facet with gesso (i imagine board needs an extraordinary kind of coats, or some thing like that.