bowed/ concave board canvas

[Gillthepainter]

I was at an art class, and was asked by a fellow painter if she should paint a picture on a used board canvas, the grey board covered in white canvas type.
She'd painted on it 2 times before, and it had bowed badly (concave).
My answer was to get rid. The inner grey board had warped, and no matter how many weights you put on the other side, it would be warped.

But a framer can fix that surely.
I just said the picture when framed would look worse, as the arrow straight lines of a frame would accentuate the warping, and also bowing would be in the shade from the frame. Also the painting perspective would be distorted.
It's hard enough to do a decent painting, let alone setting yourself up with difficulties because you are being cheap.

I ended up giving her one of my canvases to make her picture.

So, you must get artists coming in with warped boards, how do you fix it for them?

[JFeig]

Not knowing what your labor rate is vs the cost of a new 16x20 canvas board being in the £5 range ($6) you have to tell them the facts of life. It is just cheaper for them to purchase new boards.

[Jon_Brooke]

If you have a painting that's warped like that then you can just add a sheet of plywood behind it when you frame it to hold it flat.

[prospero]

The thing is with that sort of prepared board is that they are not really intended for 'finished' paintings
that are going to be framed. More a quick'n'easy thing for preliminary oil sketches, especially those done 'in the field'.
Small ones generally don't warp much. I've framed 100s. Bigger ones 20x16+ can go a tad wappy but fortunately they
tend to warp the right way so a good beefy backing board will persuade them flat.

[Gillthepainter]

I hadn't thought of the backing board fix, thank you.
I do know why it's so useful to paint on boards, they are portable, and your canvas will never ding. Storage is easier too. But for me, their problems outweigh their advantages.

I just avoid them I guess.

JFeig, I'm going to tell her to buy a stash of new canvases.
She has been coming to art classes every wednesday for over a decade. And has nothing to show for it, as she reuses a canvas to death. We have exhibitions, and she declares I don't have anything good (which sadly is true). But only because you can see eyes from a previous portrait, or an elephant for example.

But I was curious how a framer would handle this inferior piece of board, as you say. And the good ones don't distort.