You don't need to steam the cloth. Your biggest mistake was not sealing the fibers before you applied color. Use PVA to seal the fibers. It should be a mixture of 4 parts water and 1 part PVA. If you don't know what PVA is, its the same thing as elmers glue. I usually mix a gallon of Elmers glue with 3 parts water in a 5 gallon bucket. Make sure the canvas is completely dry before adding your colors. This allows your colors to stay wet longer and sit on top. It makes blending with other colors much easier. Trust me. You will love the results. Oh and use a big brush to apply the PVA. not a roller. That way you can work the wrinkle out as you go. When dry you will have a perfectly flat canvas to paint on. Oh and I don't use rollers to apply paint. I find that brushes and a mop work the best.
James I have to put undercoat on a 5 metre x 2.5 metre canvas. I cannot staple the canvas on the floor. So I taped the canvas down. I am using BondCrete 50/50 with water (as advised by an experienced artist) and I just tested the undercoat on a 1 metre x 2 metre sheet and the canvas has puckered - with fist sized circles here and there. Does that mean that the water and bondcrete (1 cup quantity) was not mixed well? Should I use a different sealer? www.bondall.com/concrete-additives/bondcrete/ I have a seamed edge and will not be sealing the edges. After thought - I think the puckering after sealing has occurred because the plastic I laid down first is very thick and has creases in it when I unrolled it. I just bought very thin plastic and will test again. Although the puckering (non-stiffness in some areas) may have occurred because the water and bondcrete in the 1 cup was not mixed properly (although I mixed for 1 minutes).
I mix my elmers glue 1 part elmers to 3 parts water. They say to mix 4 parts water but, you will get the puckering with 4 parts water. You can buy the elmers in the gallon.
I used PVA as my base too. @James Strength, I found that after applying the PVA the canvas is hard when it's touched. Is this normal? Also, what kind of paint is appropriate for painting, Matt Emulsion or Acrylic Paint? Which one did you use @YvensB Photo? This comment has really encouraged me to continue. Thanks @YvensB Photo | @James Strength.