Before trying my hand at canvas printing and stretching, I did lots of reading on the web and found lots of conflicting advice regarding canvas shrinkage. Decided to do my own experiment to get answers to my combination of ink, canvas and coating. So, FYI, here is what I found.
I printed with a Canon ipf6400 using custom profiles and PS contrast curves on rolls of both BC's Lyve Canvas (ipf's Cotton Matte2 Media Type) and Epson's Exhibition Natural-Matte Canvas (ipf's Fine Art HW Photo media type) with a sprayed over-coat of Premier Art's Glossy Eco Print Shield (3 coats). Both canvases are poly-cotton blends. When I sprayed the printed canvas, the entire length of all 4 sides were attached to a backing (over-spray) board using painters tape. That's lots of tape, but that's the cheapest part of the process. I took shrinkage measurements on the largest prints of 22"x48" and 12"x36". I only observed shrinkage in the long dimension of the canvas on the roll.
Shrinkage when printed: Lyve 0.29%; Exhibition 0.55%
Additional Shrinkage when Coated: Lyve 0.0%; Exhibition 0.0%
D-Max when printed: Lyve 1.61; Exhibition 1.55
D-Max when coated: Lyve 1.65; Exhibition 1.75
There's lots of comments on the web that shrinkage occurs when coating the canvas, not when printing. This is certainly not what I observed with my experiment, though results could change with a different combo of materials. It's also possible that, by taping the entire perimeter of the print when spraying, I eliminated any additional shrinkage from that process.
I've questions on the effects of humidity changes on the tightness of the stretched canvas, but again I found lots of conflicting advice. However, I did find a FAQ on the Masterpiece Arts site (An art canvas manufacturing/sales company) stating that stretching a canvas in a humid climate and moving it to a dry climate will make the canvas loose. I figure they are pretty authoritative on questions concerning canvas. I find their comment comforting as I'm stretching high in the Rockies where it's very dry, hoping that my first efforts at stretching will only improve as I ship it elsewhere. The 36" wrap is going to my son in Charleston SC to see how it holds up in that very different environment. You can ask me how it went after next summer. The 48" print is going to a paying customer near Dallas, so I'll keep my fingers crossed in the hopes I won't have to replace or fix due to sagging. Cost of OTJ education, if there are issues.
I previously had wraps done by Simply Color. They used Epson inks on poly-cotton canvas and included instructions to lightly spray the back of the canvas with water if the canvas becomes loose. Again, I've found lots of conflicting advice on the web ("Never spray the back of a glicee/ink-jet canvas...", "Poly-cotton canvas will not tighten by spraying the back..." etc, etc). Well, I sprayed the back of my smallest wrap (11"x14") and have not seen any damage to the print, but I can't answer the question about whether it tightened simply because I can't remember from one day to the next how tight it sounded. Suppose when a wrap sags, I'll see if this works. It's interesting that one of my letter-sized test prints (Exhibition) mistakenly fell in a bucket of water between coats of Print Shield, soaking portions of the canvas and there was no apparent harm done. In this instance the tape fell off, thus my use of tons of tape on the more important prints.