Polytab Technique
(written by Chris Cart)
The Hallowell mural was created using what is called the Polytab Technique. This is mural process developed by the Philadelphia Mural Arts Program so that large exterior murals could be painted inside and then adhered to masonry walls when complete.
Summary of the process:
The Polytab fabric is first primed, and cut into manageable sized pieces. Then the artist or artists, (in this case just me, the artist Chris Cart) paint the mural on the primed canvas. When the art is completed the finished canvas pieces are glued to the exterior masonry wall and smoothed in, abutting the edges of the various pieces to complete the mural. Then the final is varnished for permanence.
Note: This method is sometimes called the Parachute Cloth technique. However this is a misnomer as the Polytab “canvas is not at all like traditional cloth used ror parachutes.
Polytab
THE MATERIAL:
Polytab is a non-woven (no warp or weft) synthetic fabric (sometimes called Parachute Cloth.) The material is very light, lighter than canvas and is traditionally used in the garment industry as an interfacing fabric.
The fabric is tough but thin and when adhered to a wall it takes on the texture of the substrate—for example, when glued to a brick wall the mural takes on the appearance of having been painted directly on the brick. For several decades Polytab has been widely used for large public mural art projects like the Hallowell Mural.
It is distributed by QST and STC-QST out of Los Angeles.
Product name is Polytab20 Style # 320 and is available in 46” width or 60” width. Each roll contains 250 yards. Inquire with the vendor about pricing.
A 250 yard roll of Polytab material.
priming the canvas
The Polytab material needs to be primed prior to painting. The non-woven fabric is very absorbent and would be very difficult to paint on without filling the fabric “threads” with primer. For the Hallowell Mural I used Sherwin Williams best primer. Other artists have used a 50/50 mix of acrylic medium and acrylic gesso.
We ended up priming both sides of the canvas to even out the paint tension on the material to avoid curling, but I think this may have been overkill. In any case I ended up with a very nice surface to paint on.
Priming 700 square feet of canvas was a several day project—letting each batch of canvas squares dry before storing.
NOTE: For the Hallowell Mural I cut the canvas into 24-five by 5 and a half foot “squares”—six rows of 4 canvas pieces per row, to make up the full 28 x 24 foot mural. The top and bottom canvas rows were a tad shorter than the full 5 foot wide of the Polytab off the roll.
The five foot square-ish pieces were a manageable size for later in the gluing on the wall process. Anything bigger might have been a real problem, juggling glue, mural fabric and any wind blowing by. As it was installation was fine.
However, for my next large mural I will plan on leaving the canvas in larger pieces while I am painting the mural, so I have less edges, and then cutting into smaller pieces for the installation day.
It turned out to be a bit of a task to line up the various edges of the canvas pieces as I was painting the mural. It would have been okay had I worked methodically from top to bottom, finishing each section as I went.
However, this did not work as planned. Mid way through painting of the mural, several of our local historians brought up key pieces of Hallowell history I felt I could not leave out. This necessitated a fairly major redesign of the mural to fit in the new chapters of history. So there was a lot of juggling of mural canvas sections. Lining up the painted edges of faces and such was important.
firehouse studio
The City of Hallowell kindly offered the second floor of the old Hallowell Firehouse, on the corner of Second Street and Perley’s Lane as my mural studio for the duration of the time I worked on the mural.
Jen and I built a temporary, freestanding plywood wall in the large room to use as my large mural easel.
The mural began as tons of sketches in my drawing pads and lots and lots of research deciding what to include. You can see some of the many drawings here.
Once I began painting, though I did not work full time it was certainly a solid chunk of each week. This turned into a huge project, weaving all the chapters of Hallowell’s story together.
Most of my many murals have been months long projects. This Hallowell mural took much longer, partly due to some interruptions of COVID and a major redesign part way through the project to add new parts of the Hallowell history, but also because there was jsut so much to include.
The brick wall section where the mural is installed was skimcoated to provide a smooth surface as a substrate for the mural. The mural was to be installed in September of 2022 but concrete skim coat took longer to cure than anticipated and the weather got too cold for the mural adhesive.
So the mural was rolled and stored until June of 2023 when Jen and I went up in the aerial lift and glued the canvas to the wall. You can read a detailed account if the installation here.
mural adhesive
We used Golden Acrylics mural adhesive for the installation on the wall. This is a thick paste glue used much like wall paper paste to stick the mural to the wall.
The adhesive is an acrylic medium that contracts as it dries and suck the canvas into the wall texture.
We used large brushes to apply the adhesive from teh 5 gallon buckets to the rough concrete wall. It took 18 gallons of glue to mount the entire mural.
Then we stuck the canvas pieces to glued area of wall, being careful to abut the edges to line up the paint. And then we smoothed the canvas to get rid of air bubbles and lumps of glue. Smoothing out the air pockets is very important to ensure proper adhesion of the mural to the wall.
varnish
Prior to installation the finished canvas was first top coated with an isolation barrier acrylic varnish to protect the paint layer during the installation…This is just a layer of clear soft acrylic medium. This adds a layer of protection to the paint during the installation process.
Once the mural was installed I spent an afternoon on the lift doing a few touch-ups.
The we applied a thick coat of Golden Acrylics’ MSA (mineral spirit acrylic) mural varnish.
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