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Articles by Chris A. Paschke, CPF GCF CMG

 

 

 

"Adhesive for Dry Mounting"

  July 1994

 

Once the decision has been made to eliminate all conservation procedures and enter the world of mounting or gluing onto a substrate, the need for a better understanding of mounting adhesives becomes imperative.

 

Mounting is probably the least glamorous and most frustrating of all aspects of custom framing. There are so many options, adhesives and procedures that knowing what to do and when to do it can be frightening. A successful framer should strive to understand basic procedures, as well as attempt to keep up with new product development, industry updates and technical advances.

 

Adhesives include wet, spray, pressure-sensitive or heat activated materials. The chemical base or make-up of an adhesive will often categorize and in turn determine its adaptability or appropriateness for any given type of mounting.  Some adhesives best adapt to mass production, where speed and permanence is desired, while others allow for specialized attention during a slower mounting process and are removable.

 

ADHESIVE BASES AND OVERVIEW

Water-based adhesives include, vegetable starch and PVA, and may be found as both wet and spray glues.  Removable vegetable starch glues remain removable with distilled water even after long term mounting. Non-removable polyvinyl acetate glues (PVA) are water soluble when wet, but like any acrylic are permanent once dry. 

 

Rubber or acrylic based solvent adhesives are found as both pressure-sensitive and spray glues. These are often considered permanent depending upon the mounting application and technique used.

 

Then there are the dry mount adhesives. As little as five years ago production of commercially available dry mount tissues was held to a small cluster of major manufacturers, while today numerous generic and private label brands have been introduced into the market. Often the only differences we consumers detect involve price, but like any competitive product, a closer look might reflect thinner core tissues, variations in adhesive colors and perhaps time/temperature adjustments. 

 

HEAT ACTIVATED ADHESIVES

Dry mounting adhesives are easiest to understand when broken into specific categories. By taking the time to analyze the various available tissues, you will be better prepared to select the proper adhesive to fit your needs. 

 

All heat activated adhesives are identified by: 1) type of bond (permanent or removable); 2) degree of porosity (breathable or non-breathable); and 3) physical composition (tissue-core or film). Acidity levels need to be mentioned but don't require a separate category.

 

1) TYPE OF BOND

One of the keys to successful dry mounting is remembering where the bonding actually occurs. A permanent adhesive bonds within the press. All layers of the mounting package must reach the required bonding temperature and remain there during the required time allotment of time to set the adhesives. 

 

A removable adhesive bonds at the conclusion of the mounting process, once removed from the press, while it is cooling under a weight. It becomes removable through the reapplication of heat which reactivates the adhesive, making the art separable from the mounting substrate. Once again, permanent adhesives bond inside the press once they reach bonding temperature, while removable adhesives bond outside of the press as they cool.

 

Weighting all dry mounted items is an extremely good "habit" to get into, whether using permanent or removable adhesives. It establishes correct mounting technique regardless of selected adhesive, expedites the actual cooling process, and will help reflatten any newly mounted items during cooling.

 

Whether an adhesive has a permanent or removable bond will also determine its appropriate applications. This brings me to the issue of porosity. 

 

2) DEGREE OF POROSITY

Porosity is the level of which an item, in this case an adhesive, is permeable by moisture or air. This is an extremely important designation when selecting a tissue for compatibility with all selected mounting materials. 

 

If a non-porous/non-breathable material, such as a photograph or heavily lacquered print is to be mounted, the adhesive must remain breathable to allow for air to be forced out and/or through the mounting layers. By using a non-breathable adhesive with a non-breathable photo, there is much greater potential for air to be trapped between the two non-porous items creating bubbles in the completed mounting.

 

If a breathable piece of art is to be mounted however, essentially any tissue or film may be used regardless of its porosity factor, simply because air will always be able to be compressed out through and around the porous art.

 

3) PHYSICAL COMPOSITION

Dry mount adhesives are available in both roll and pre-cut sheets, and come in two basic compositions, tissue-core and film. Tissues have a center core or carrier of either breathable tissue (ColorMount, TM-2, TriMount) or non-breathable glassine (Seal MT-5, TM-1), with adhesive applied to either side of the carrier for mounting. 

 

Since both sides are identical there is no top or bottom. They are clean, dry, non-tacky, relatively opaque white in color, and are also extremely time effective when considering production use. Tissues adapt extremely well to oversized mountings, float mounting or multiple bite procedures.

 

Pure film adhesives (ie: Fusion 4000, TM-3, Flobond) are a 100% adhesive with no carrier or tissue in the center. This makes them translucent when unmounted and clear when mounted. Films may also be pieced or overlapped because of the lack of central carrier paper, which allows for greater creativity and less waste. 

 

They are perfect for mounting fabrics, wrapping mats, embossing, controlling color ghosting, tiered matting and numerous other creative layering techniques where maximum bonding, flexibility and lack of color is important. Since they are removable, they bond as they cool under a weight so never attempt to check the mounting by peeling apart the items until they are cooled.

 

4) ACIDITY LEVEL

Nearly all dry mount adhesives are inert, meaning they contain no harmful acids capable of damage. It is actually the carrier sheet which needs to be checked for pH levels.  Many manufacturers have developed tissues using acid-free or archival carrier papers in conjunction with dry mounting adhesives (ArcivalMount, TM-4, Drichival). These tissues mount at lower temperatures, are breathable, removable and neutral pH. They are considered more delicate but do not meet conservation standards.

 

Using heat activated adhesives can never be considered archival because the very act of dry mounting art to a substrate breaks all conservation guidelines. Adhesives travel toward the heat as they are mounted and the very act of dry mounting encourages a certain percentage of non-reversible adhesive to penetrate the back of the artwork, even with a removable tissue. This is NEVER ARCHIVAL regardless of the name of the tissue!

 

ADHESIVE SELECTION

So what does all this mean? With dozens of dry mounting tissues alone on the market how does one ever select the correct adhesive for his/her specific needs? By researching the basic components or classifications of assorted tissues and comparing them to the items most generally mounted in your shop you can determine the best adhesive for your applications.

 

Target your specific market by types of art, porosity factor, sizes, creativity etc., then select two basic adhesives. The first you will use 80% of the time, the second 20% of the time. No doubt you will also maintain a repertory of assorted mounting procedures, for those one-of-a-kind situations. And lest us never forget Japanese hinging.

 

Always consider the basic factors of removability, porosity, and composition.  By simply paying closer attention to the items being mounted, their desired appearance and the substrate selected, each project will tell you which adhesive you should be using. 

 

So perhaps that paper embossed mat should be mounted by hand with a water soluble wet glue this time and not a heat activated adhesive after all!

END