GAC 400: Fabric and Paper Stiffener

GAC 400 is used to stiffen fabric or paper made from natural fibers. It is a water-borne acrylic that dries to a hard, stiff film. One good coat that soaks in well should be enough to stiffen the material. It can be used to replace rabbit skin glue for stiffening linen and canvas in preparation for oil painting. If you would like to build larger scaled, free-standing structures, it will need the help of an internal or external rigid structure.

GAC 400 should soak into the fibers of the fabric or paper so it is functioning throughout the material. It should not be applied thickly and will function best if not diluted. Depending on your specific application, you may opt to heat-set GAC 400 to decrease water sensitivity, and increase the stiffening properties to some degree.

Care should be taken not to roll, stretch or bend any fabric or paper stiffened with GAC 400 as micro cracks will form that will eventually decrease the stiffness of the material. One ounce of GAC 400 should cover about 1 square foot. The soaking method will use more product.

Two Most Common Uses for GAC 400

1. Fabric, Textile and Paper Stiffening Applications

Brush apply GAC 400 to the paper or fabric liberally, allowing it to soak into the material. Thicker natural fabrics like cotton canvas work best. Excess product sitting unevenly is fine, as it will become translucent and much less visible when dry. Expect some gloss on the surface and a slight darkening of the fabric. For even more stiffness, you can soak the fabric or paper in GAC 400 that has been poured into a shallow container. Wipe off the excess and drape or position for drying. Again, you do not need to be so concerned about removing all the excess medium. Latex or vinyl gloves are recommended for this technique.

Soaking fabric in GAC 400.

Soaking fabric in GAC 400.

Dried and stiffened canvas.

Dried and stiffened canvas.

Polyethylene plastic sheeting works well as a non-stick surface for the wet fabric pieces and you should be able to peel the fabric off when dry, but paper may be more of a challenge as it can tear easily if stuck to the plastic. Some heavier weight papers may work better. It is always best to use acid free paper for any fine art application.

For sculptural uses, GAC 400 is best used on small scale paper or fabric pieces, as it may be difficult for heavy or very large objects to retain their shape. It can be helpful to drape the wet material over a form to keep its shape as it dries, but the form should be made of HDPE plastic or covered with polyethylene plastic sheeting to prevent sticking. Smaller pieces of fabric can be stiffened and assembled by gluing the pieces together in an architectural fashion, using thicker Gel Mediums like our High Solid Gels. Think post and lintel construction. This method works quite well as you can see in the photo. It will still be a somewhat delicate structure and should be handled carefully.

Sculpture made of stiffened cotton duck canvas "glued" together using High Solid Gel (Gloss).

Sculpture made of stiffened cotton duck canvas “glued” together using High Solid Gel (Gloss).

Bas relief paper collage made with thin notebook paper stiffened with GAC 400.

Bas relief paper collage made with thin notebook paper stiffened with GAC 400.

Various types of bas relief paper collage can be done using GAC 400 soaked paper adhered to an appropriate substrate and manipulated to create raised and textured surfaces. Rigid panels are best. The paper or fabric can be painted once dry.

2. Rabbit Skin Glue Replacement

Materials like Rabbit Skin Glue are extremely hygroscopic, which means literally ‘water loving’, and will respond rapidly to changes in relative humidity, dramatically tightening and growing slack in the process. As a safer alternative, GAC 400 can be used as a size on canvas or linen, stiffening them in a similar way as rabbit skin glue, but without the same amount of sensitivity to humidity. This allows it to retain its stiffness over a much wider range of ambient conditions, although it remains vulnerable to prolonged contact with water. To lessen that sensitivity, please see the following section on Heat Setting.

Please note, unlike Rabbit Skin Glue, GAC 400 will not block oil penetration so additional steps are needed before painting with oils. Please see the following for our recommendations:

Preparing a Canvas for Oil Painting:

Here is a link to descriptions of our special purpose mediums, including GAC 400:

Special Purpose Mediums:

Heat-Setting Option and Recommendations:

While GAC 400 is rarely heat-set, and will work to stiffen materials without it, heat-setting does provide some benefits such as much less water sensitivity and some increase in stiffness. If heat-setting is not done, pieces with GAC 400 should not have prolonged contact with water, nor ever be immersed, as the medium could soften or possibly liquefy.

To heat-set, allow GAC 400 to dry overnight. Using a hair dryer set on high, heat-set GAC 400 for 5 or 10 minutes. This heat-setting is based on temperature and duration; the hotter the setting, the faster the process will be. Do not scorch the surface. The temperatures in hair driers can vary greatly so it is best to select one which seems to offer the hottest settings.

Please note that heat-setting GAC 400 releases trace amounts of formaldehyde, which may be of concern to those with chemical sensitivities. We recommend providing fresh-air ventilation when using heat-set products.



15 Responses to GAC 400: Fabric and Paper Stiffener

  1. Wilma April 20, 2016 at 6:44 pm #

    Very interesting! I work on lots of collages and have made many papier mache’ figures & painted sculptures. I will give this a try. Thanks for the information.

  2. Tina Clark March 15, 2017 at 4:16 pm #

    Can you tell me the differences between GAC 400 and the textile hardener called Paverpol?

    • Mark Golden March 16, 2017 at 11:48 am #

      Tina, not sure the total properties of Paverpol but it appears to be a vinylacetate polymer. Not sure of the other constituents, but possibly including some type of plaster as well? Just a guess based on the uses and drying times. The GAC 400 is an acrylic polymer that was originally developed for the textile industry to create additional hardness to polyesters. It is not a great film former, but an excellent hardener, especially if heat set. The drying time is similar to other acrylics. Hope this helps. Best, Mark

  3. Anna Blom December 6, 2017 at 9:43 am #

    In traditional recipe for chalk ground you need rabbit skin glue so I’m wondering if I can use gac400 instead, as it’s suggested as the replacement for rsg. Thanks! Anna

    • Scott Bennett December 7, 2017 at 11:30 am #

      Hi Anna,

      We have recommended using our GAC 400 in place of Rabbit Skin Glue, but we do not recommend using it blended with chalk or any other solids to create a chalk ground. When used to stiffen canvas or linen in place of RSG, our recommendation is to apply the GAC 400 directly to the raw fabric so it soaks in well. Allow to dry overnight, then apply a coat of our GAC 100 to block oil absorption. Finally, apply a coat of our acrylic Gesso or an oil ground to the dry GAC 100 film.

      We also have a newer recommendation for using two coats of our GAC 200 to stiffen canvas and block oil absorption. Then, apply either our Gesso or an Oil Ground. Alternatively, we have seen that 3 to 5 coats of our Gesso will both stiffen the canvas and block oil absorption. Here is a link to an article from our Just Paint Newsletter where we outline these methods:

      Preparing a Canvas for Oil Painting:

  4. Niall June 22, 2019 at 1:04 pm #

    Can GAC400 be used as a glue? I looking for a way to make canvas covered panels. I’m wondering if I. Can apply gac400 to a board then stretch unprimed canvas over that and then cover the front with gac 400 too.

  5. Rebecca Lazenby July 15, 2019 at 3:56 am #

    Hi, in the photo, you’re showing a piece of painted canvas being dipped into GAC 400 but the text says it should be applied to bare, unprimed canvas. I read elsewhere that using gac 400 on a painted canvas will case the paint to flake off. I want to paint and make a relatively flat sculptural piece that is supported, but am a bit confused about whether I can paint first, mould after A’s is my preference, or if I need to paint after using the gac 400. Thank you for your guidance.

    • Scott Bennett July 15, 2019 at 12:50 pm #

      Hi Rebecca,…..You are right in that there is a photo that shows a piece of canvas with some acrylic color on it, and I can see how that could be confusing, and happy we can address this now. The color on that piece of canvas is very thin washes or stains; Fluid Acrylic thinned with a lot of water, so the canvas is still very porous. And of course, the other side is raw canvas, so the GAC 400 can still soak in very nicely to the canvas. So while using raw, unpainted canvas or other natural fabrics is best, if the acrylic paint is very thinned out, that can work as well. Where it would not work well is if the acrylic paint was a discreet thicker paint film that would block the absorption of the GAC 400 into the canvas. Generally speaking, I would say it would be best to paint after you have soaked, shaped and allowed the GAC 400 to dry thoroughly, but since the GAC 400 remains water sensitive unless heat set, we would suggest heat setting before painting.

      Depending on the exact kind of “flat sculptural” piece you are making, it might be possible to simply rely on some thicker applications of acrylic paints and mediums or gels or pastes to create your piece and not use GAC 400 at all. I have seen some pretty rugged sculptural canvas pieces ( large painted canvas collage ) that just use Gel fortified paint under and on the canvas to maintain enough rigidity for the crumpled canvas. I hope this answers your questions!

  6. Jenny August 15, 2019 at 8:58 am #

    Can I use GAC 400 on (primed, artist grade) polyester canvas? I want to stiffen it to make it easier to adhere to a panel. Without a stiffener it tends to be very difficult to adhere down smooothly as it’s quite light and tends to pop up in numerous places. Hoping you can help!

    • Scott Bennett August 15, 2019 at 12:21 pm #

      Hi Jenny,

      GAC 400 will not work very well on synthetic fabrics like Polyester. And I am not so sure stiffening the canvas would really help adhere it to a panel. If you are having trouble smoothing the canvas down onto a panel, it might be due to the particular acrylic medium you are using. Using a too thin medium can sometimes cause this “popping up” since it tends to spread out too thinly and not grab on the the fabric enough. We recommend using our Soft Gels or even our Regular Gels for this. You actually want the fabric to be soft and flexible rather than stiffer, so you can press it down easily into the wet Gel medium. Using a roller of some kind is a good idea. And, for larger areas, a tool called a notched trowel can be very helpful to quickly spread out the Gel onto the panel surface. Here is a link showing one related method adhering watercolor paper to a panel: Adhering Watercolor Paper to Panel:

      If you have further questions don’t hesitate to call or email us in Tech Support!

      • Jenny August 16, 2019 at 1:23 am #

        Thanks Scott!

  7. Shelly September 19, 2019 at 8:53 am #

    Can I use this on Acrylic skins to form rigid structures?

    • Scott Bennett September 27, 2019 at 1:25 pm #

      Hello Shelly,

      Our GAC 400 only works on porous fabrics and paper, although best with natural fabrics like canvas. It might stiffen the acrylic skin a bit, but we do not think it would be enough to create rigid structures. It must soak in the the material. You might want to consider using pieces of plexiglas that you attach the skins to, and then glue the plexiglas together using acrylic sheeting adhesive. Or, working on some kind of rigid structure that could hold the skins.


  1. Vegan and Animal-Free Paints & Art Materials | Just Paint - June 25, 2019

    […] does. Our GAC 400, an acrylic fabric stiffener, would be the closest match. See Just Paint article GAC 400: Fabric and Paper Stiffener for detailed usage […]

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