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Picture Framing Magazine

"Solid Sheet Backer" for a stretched canvas

Cathy Coggins

Cathy Coggins

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Kissimmee, Florida
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Needle Craft World
So, studying for my CPF. And taking on bigger jobs. And educating my customers as to products and their uses keeps pushing my brain and my abilities. So a customer that I have framed many and item for brought me a painting. She is a preservation believer. Understands cost/benefits of good frames, great mats, and Museum Glass. So, she picks up the latest giant poster I framed for her and unrolls a canvas she wants stretched and framed. And asks, "wouldn't it be better to have this under Museum Glass?" And since I have been reading a bunch on this topic, here on the G, in the CPF study material.

I have been framing for over 8 years, mostly needlework, I can stretch a canvas pretty well, in fact this one stretched so nicely it is sexy. I have liner, I have Museum Glass, I have turn-buttons and offsets, and this gorgeous piece of business on my table. I want the back to be just as useful, well done, and the product used to complete the package just as sexy. Remember 99% needlework when I ask, what is best to back this with to make a great finished package?

Page 49 of the "PPFA Guidelines for Framing Paintings on Canvas" Under topic 4:"Supplemental Frame Support", halfway down the page the topic is SOLID SHEET BACKER. "A solid sheeting material, such as acrylic, matboard, Masonite, Plywood, or plastic, attached to the back of the frame by screws or staples". And then it mentions "Fluted Polypropylene Board", is that this Coroplast that I have heard about but never used?
Which is better?

The frame is fairly deep, a GORGEOUS mother of pearl frame, and the glass and liner fit within the depth of the rabbet of the frame, the stretched painting hangs out a wee bit. Do I attach the backing board (which ever is appropriate) to the stretcher bars? With offsets from the frame but over the painting? Or to a built out back of the painting making everything rather flush?

Give me linen or aida, or a mono canvas and I am a ninja. This other stuff is cool, but I don't wanna do it wrong. Especially for this customer who values wise choices.
 
Cathy, Yes Coroplast is the brand name of fluted polypropylene. It is probably the most sturdy backing since it is firm but puncture-resistant, partly because it "gives" a bit when you push on it, but not so much that something hitting the back will allow it to come in contact with the back of a normal canvas. If you haven't worked with it, you might want to get some to work with, but I don't know if it warrants getting it just for this job.

What I choose depends on what the future risks to the painting might be. Low-risk & foam board is probably more than enough, especially for smaller paintings. Sometimes even 4 ply matboard is enough. For a rigid back, I prefer 8-ply rag and like to use it on larger paintings. I cut it out on the CMC & this makes a nice bevel for finishing the back.

Coroplast is always great, but I don't always use it. I would stay away from masonite because of its uncertain chemical make-up.

Hope this is helpful.
 
Thanks Greg. The answers in the book seemed broad. It is the intuitive information I am looking for. And I did not fancy getting a 48" by 96" Coroplast for JUST this job. Wouldn't mind getting some and futzing around with it. And masonite and plywood seemed like added weight and or corrosives.

The book did NOT say 8 ply, I like that answer, it may have implied it though. Tougher than foam core. And the bevel cut will look spiffy too.

Exactly the info I was after my dear Mr Norris, between you and my phone a framer to Sondra Quatraro, MCPF and the lovely Andy the warehouse dood at Complete Framers Supply I feel good about finishing this job up.

THANKS! :thumb:
 
Cathy, you can get coroplast from LJ in sheets smaller than 4'x8'. There's is supposedly higher grade but most sign shops can supply you with either a full or cut sheet also. As for getting in a vehicle most of the time it will roll slightly with the direction of the flutes.
 
Fluted Polypropylene is a very useful product to have in the frame shop.
It's moisture resistance makes it a bit better for backing canvas than some of the other boards IMO.
Not only is it an inert filler board and rigid, but it can be used to anchor custom bent rods for some shadowbox mounting.

For canvas backing, the board should be screwed to the back with washers and the holes in the board should be large enough to allow for some expansion/contraction.

I actually prefer to velcro the backing board to the back of the stretchers. This gives much less restriction while keeping the board with the painting if the frame is removed in the future.
 
Cathy, you need Jim Millers shadowbox book. It explains exactly how to do it. (If your chapter doesn't have a library, it would be a great place to start right after acquiring the Guidelines series). And he can probably explain it with words and a simple drawing, but it is beyond my technical writing skills!:sour:

But basically you are inserting bent rods (think piano wire) into the flutes and anchoring them with epoxy or hot melt, passing them through your back board, bending them into shape, covering the ends with heat shrink tubing, painting the tubing to match and VIOLA'. In practice, you might be beginning at the front and working to the back. I found it required a little practice.
 
Greg, I have the whole series of CPF books. I had a bunch from my journeys, took my CPF over a year ago. Flunked it. Found out I was missing like half the books, and some lovely human (still don't know who) gifted me the books I was missing. Thank you again whoever you are!:love:

I read the books, but as a very tactile learner, working the stuff out makes the lesson come alive, as I make problems that then cause the BEST questions to come about. One of my favorite proverbs (Chinese Proverb) "when the student is ready, the teacher appears". The teachers are dropping out all over the place for me these days. :smile-new:

Thanks for making it come alive boys.
 
Hi Cathy:


Yes, 4 mm fluted polypropylene sheet (aka polyflute, and by brand names such as Coroplast, Coreflute, Matraplast) would make a good backing for stretched canvas. Here are some attributes:

- Lightweight

- Rigid (in one direction, anyway)

- Easy to cut with beveled edges (cover with plastic Framers' Tape to keep insects out of air spaces)

- Readily available 48x96 sheets in several colors from local sign-making suppliers.

- The "archival" milky-translucent type is also available from Bainbridge distributors in framing-board sizes.

I agree with Cliff that you should try at least a full sheet, and I suggest you cover a work table with it. White polyflute is my favorite table-topper because white shows dirt/debris and reflects light; the surface is smoother and less abrasive than cardboard, paper, or most carpets; it cleans easily; wears well; and it's cheap enough to replace every few months, after it gets cut and scuffed enough to notice.
 
The problem with using rag or cotton board as a backing is, that it absorbs moisture more, than conservation-board does. This means, that a framed item with rag backing hung against a damp outside wall can develop fungus.

Rag 8 ply is thicker than conservation 8 ply, cuts less easily, costs more and creates small dust-particles, like foamboard, then can sit behind the glass, just when all the nails are put in.
 
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