There are so many ways I’ve seen people stretch paper, from simply wetting the back of a sheet and gum taping it down to a board, soaking the paper in the tub for a few minutes and attaching it to a specially made stretcher board, or again gum taping it down to a board then stapling around the edges so it dries drum tight. I have tried all of these methods not always successfully!
One thing to remember is that if your paper is 140lb weight sized or less and you intend on using a lot of wet in wet techniques, it will need stretching to help prevent warping issues.
Unfortunately this is something which I have never had much success with! You are supposed to wet the tape by dipping pre-cut lengths into a bowl of water then laying at least an inch over the edge of the already soaked watercolour paper. I have found however that the tape can start to lift when dry. Should you be using an old board for stretching paper you can add heavy duty staples to go around the edge of the wet paper to ensure it dries nice and flat.
This method does work well but you are then left with the need to remove all the staples after you have completed your painting, so quite time consuming…….plus I don’t like damaging my boards with staples!
Wetting the back of watercolour paper
This is a quick method to stretch paper and it does work ….. well sort of. Use a wet sponge to go over the back of a sheet of paper a few times, don’t rub the water in or you risk damaging the paper. Once soaked you then move the wet sheet to a dry board, placing it wet side down. Attach your masking tape to the dry side and this will hold the paper down flat whilst it dries.
This does work but you may need a bit of trial and error to have success every time!
That said, lightly wetting the back of a painting that has warped (cockled) and sticking it to a board as detailed above, can be a good way of flattening out a bendy painting.
I would personally try this out on an old painting or test sheet first just to make sure I am confident with the method before I ruin things!
Shop bought stretcher boards work well but you do have to work with pre-made sizes. I have made my own using three thin sheets of plywood with one sheet smaller than the other two. Glue all three together with the smaller one in the middle, allowing an even gap for the sandwich.
Seal the wood with a couple of coats of exterior varnish and all is ready for wetting the paper in the bath tub for a few minutes!
This is ideal for those different paper sizes you want. I find it particularly useful for A3 and A2 size paintings.
Prepare a solid surface to work on covered in an old cloth. Lay the wet watercolour paper onto the surface and place the stretcher board centrally on the paper. Lift one edge of the board upwards and gently ease the paper into the gap between the boards, I found an old paintbrush helped with this. With the paper partially in the gap hold it in place with some climbing rope or plastic tubing cut to size. Repeat the process but keep an eye out for any air bubbles and use a wet sponge to gently ease these out before finishing with the fourth side.
Pre-stretched block pads
For speed and complete ease of use my preferred choice for the majority of my paintings is to use a block pad of watercolour paper. This is literally all ready to go! The paper is pre-stretched and is glued around all four edges with just a small gap at the top of the sheet. You will get very minimal cockling with this type of paper and when your painting is finished simply slide a palette knife or guitar pick into the gap and around the pad to remove the sheet of paper. Definitely my preferred choice for a non hassle way of painting without the need to mess about stretching paper!
Hope this helps a little,
PS “Keep them brushes wet!”