My main preference for a surface is a linen canvas. This comes in different grades. The one I am using at the moment is a fairly fine linen, which I bought on a roll of 10 metres from Ken Bromely. You can buy stretchers for your canvas but as I work outside a lot I prefer the portability of boards.
I buy a whole sheet of 3-5mm MDF (8' x 4') which my local woodyard cut into 8, 24" squares.
The next step is to seal the boards front AND back. This is especially important as MDF is porous and will absorb moisture. If, in the future, your painting were to be hanging on a damp wall or in a damp atmosphere, then, water absorbed through the back could potentially ruin your masterpiece.
Paint is applied with a roller for an even coverage
Cut the canvas to size
While the boards are drying I cut the canvas cut to size. It does shrink so I allow approx 1cm extra all round.
A good quality PVA is poured on the board. You could use the roller again but cleaning up is a sticky business so I spread the glue with a piece of stiff card
Spreading glue with card
PVA poured on board
I ensure that there is a good even coverage of glue before carefully laying the canvas on top.
A quick note here - the canvas comes ready primed, I have known people to used the unprimed side thinking that the linen colour was the side to use.
Use a clean piece of card
Starting from the middle of the board, use a clean piece of card as a squeegee and work towards the edges. Wipe off any surplus glue that squeezes out. When I am happy that there are no lumps of excess glue under the canvas, I repeat the whole procedure with all the other boards. I lay them face down on top of each other with some weight on top. When they are dry, trim any surplus canvas from the edges with a craft knife on a cutting mat canvas side down.
Trim surplus canvas
Now they are completely dry I can decide on the sizes I want to work on.
I do like to work my still life paintings in a square format so I might cut one board into nine 8" x 8" squares. Another into sixteen 6" x 6" squares and another into four 12" squares. Alternatively you can mix the sizes. For example two 10" squares and two 14" x 12". This does mean a bit of wastage but it is minimal.
Mark out canvas side up
Mark out the sizes you require using a 'T' square, canvas side up. It is important to use a sharp knife and cut down through the canvas side. If you were to cut through the back of the board you wouldn't get such a clean cut.
Use a fresh blade in craft knife
I use a metal ruler with a safety edge cut down through the board. It does take several strokes to get through. I usually get husband Frank to do it for me if he's around.
Now we have a neat stack of boards all ready to paint on. If I am going to use them for taking out to work plein air, I glue matchsticks onto the back so that I can stack wet paintings together. I wish I could claim this as my idea but it was a tip from Ken Howard. I keep a clean board for 'the lid' and use masking tape to keep the pictures together
Matchsticks glued on
Ready to go out painting
Doing a whole sheet at a time is time consuming but well worth the effort, not just because of the stash of boards you have to paint on but, just think of all the money you've saved and the convenience.
If you would rather not go to the trouble of gluing canvas on then you can always cover the boards with gesso. Do use a good quality one though and give the boards at least two coats and don't forget to seal the back of the board. You can use household emulsion, PVA or gesso to do this.
Another tip - try and work to standard sizes, it is much easier if you have standard size frames. This way you can swap you work around.
Good luck and do let me know how you get on