A substrate is a board or other media to mount to, and selecting the right substrate is as important as selecting the correct adhesive and technique and method to mount. Whether used for mounting or as a filler board, rigidity is the main purpose for substrates. Almost any rigid surface may be used as a mounting substrate, including glass, foamboard, ACM (aluminum composite material), Masonite, or paper ply boards. Higher acidic levels are found in chipboard, greyboard, MDF (medium density fiberboard), hardboard, Masonite and plywood. (photo 1)
Photo 1
(L top to bottom) Encaustic original art on Tycore and 8-ply rag as substrates; (R top to bottom) ¾" Tycore, ½" Hexamount Conservation Board, 8-ply rag, ¼" and ½" Baltic Birch plywood; (back L-R) Birch panels, cradled boxes, and ⅜" primed hardboard.
Europeans continue to favor MDF and hardboard for framing, though as a wood product, thinner MDF is rather soft and prone to bowing under surface stress like other substrates may be. In order to best eliminate warping, the weight, thickness, and rigidity of a mount board should accommodate the size and weight of the item being mounted. To prevent as much bowing as possible, select thicker, harder boards for larger artwork, to compensate for greater surface tension.
It is important to be consistent with material selection throughout the entire job. If acid free mats are chosen, then acid free mounting substrates and neutral pH adhesives should also be used. An acid free or inert adhesive on an acidic substrate still equates to potential acid burn, just as any non-neutral pH tissue on acid free backing is cancelled out.
Matboard
Matboard is a multi-ply paper based product available in 4-, 6-, 8-, 10- and 12-ply thicknesses used as the natural spacer between glazing and artwork. Though most often used for matting, 8-ply or thicker rag is also used by artists as a substrate for drawing, painting, pastel, encaustic and mixed media. True ragboard originates from cotton linters broken down to fibers then molded into board. Museum ragboard is a market phrase designed to acknowledge the board is a permanent, durable, stable product that may be used to safely house valuable collectibles.
Warping of large mounted pieces is a common problem when selecting 4-ply matboard as a substrate, and should not be used as a mounting surface if the print is any larger than 16 x 20". Using too thin a substrate for too large a mounting will encourage warping of the mountboard. Though countermounting helps compensate for warpage it is better to select a thicker board for larger pieces.
Unbuffered Museum Solids—previously known as photo boards—are unbuffered, solid color, 100% cotton for photographs and textiles requiring a low alkaline environment, naturally acid- and lignin-free, fade and bleed resistant, without the benefit of added calcium carbonate levels. Available as neutral colors of black, cream, antique white and white. The white boards have a slight color variation from buffered white cotton boards because of the lack of calcium carbonate.
Foamboard
Foam center boards are extruded polystyrene with assorted clay coated, acid free (2% calcium carbonate buffer), colored, or 100% cotton rag surface paper. Lightness, rigidity, and ease of cutting are the primary benefits of foamboard, and since 2001 International Standards Organization—ISO 18902—acknowledges paper-covered polystyrene as an approved substrate for use in enclosures. Boards are available white or black core with white and black surface papers in ⅛", ³⁄₁₆" and ½" thicknesses, and are used more than any other board for mounting in the United States. Adhesives already applied to foamboards are found as both pressure-sensitive and heat activated types which will be covered in another article.
Foamboards undergo the highest degree of prolonged heat and pressure when dry mounted, making them more susceptible to edge crushing. They will physically melt as they reach internal temperatures of 230˚F, but will compress around the outer edges from the pressure exerted during standard mounting, especially in a hot vacuum press. Compressed outer edges of foam in no way effects the actual bond and is a natural end product of using a vacuum press. If uncrushed square edges are required, it is necessary to mount on a slightly oversized board then trim down to the desired dimensions after mounting.
Acid free (AF) foamboards may be used as filler or backing behind hinged 4-ply museum board preservation applications. Use of AF foam maintains a more consistent use of neutral materials in a framing package when all other boards are acid free and/or buffered. Also, 100% cotton rag covered foam meets surface paper preservation quality backing requirements for hinging or mounting. Black surfaced foam works well for control of ghosting and color tinting, or to create a contrast bevel for an unframed poster edge.
High Density Foamboard
Heavy-duty foamboards offer a high-density foam center with double-thick surface liners. The biggest difference between heavy duty foam is the toughness of the inner core and the outer coating. High density (HD) boards are becoming more popular with wide format printing and roller demand for larger substrates.
HD products include Ryno Board® HD—Gilman Brothers—a high-compressive foam resistant to crushing, warping and denting, with extra-thick coated surface paper; Ultra Board™—United Industries—a heavy-duty, all-plastic foamboard with high-impact litho-grade polystyrene surface and extruded polystyrene core; Jetmount® Board—3A Composites—is an extruded polystyrene foam laminated between 11-point clay-coated paper liners, resisting dents, with exceptional durability, ¼" thickness increases strength and warp resistance; and Gatorfoam®—3A Composites—an extruded polystyrene bonded between two layers of wood fiber veneer, making it stronger and more durable than other foam products. Though more difficult to cut, it is extremely smooth, rigid and resistant to warping, perfect for oversized mountings, even with tinner sheets.
Corrugated Materials
Ranging from basic inexpensive brown cardboard to heat resistant plastics, corrugated materials still remain popular. The blue-gray or white rag, corrugated acid and lignin free, buffered boards, are well suited as spacers or preservation backing. Coroplast—corrugated plastic or polyflute—is a rigid, chemically stable copolymer of polypropylene and polyethylene, and while similar to corrugated fiberboard it is easier to clean and repels moisture. They are not appropriate as a mounting substrate as they have ridges that may show, but are used as backing or filler boards.
notFOAM Kraft—Crescent Cardboard—features a ³⁄₁₆" thick white acid-free surface with Kraft core and backing that is 100% recyclable. It is recyclable, renewable, compostable and sustainable, composed of both E-flute for high quality printing with a thickness of ¹⁄₁₆″ and ⅛" of B-flute for rigidity.
Honeycomb Panels
Panels are the perfect rigid substrate for heavy textiles or stone artifacts, but the added thickness requires additional frame depth. They are lightweight, heat resistant to 300˚F, resist denting, cut easily, and are dimensional stabile. Hexacomb Falconboard® is made from reusable, renewable and 100% recyclable kraft paper honeycomb material. Eaglecell™ is eco-friendly, 100% recyclable paper core with lightweight warp resistance and triple-thick, bright white clay coated surface papers, available in both White and Kraft Core Options. Though all are hot and cold mountable, as with corrugates, excessive mounting pressure can leave unwanted surface patterns.
Hexamount Conservation board has a lignin-free core made from unbuffered certified virgin fiber alpha cellulose white wood pulp available as standard conservation with 100% cotton outer ply museum with black or white facing paper. Tycore, is favored by museums for mounting of valuable collectables because of its superior lightness and strength. The honeycomb interior has cell structure that are the source of the board's strength and rigidity which is made of chemical pulp and adhered to alpha cellulose conservation facing boards with a polyvinyl acetate (PVA) adhesive.
Hardboard
Flat mounting is the bonding of an image to the center of a larger substrate which is then used as the decorative area surrounding it. This technique has been popular for decades for traditional photos mounted to aluminum and poster images mounted to colored 4-ply mat board. The most common hardboard substrates are bamboo, ⅛" hardboard, untempered Masonite, ¼", ½" or ¾" plywood, pine, and MDF.
Acid content and porosity are always an issue so hardboards are not considered suitable as a preservation substrate, though that is not true for every discipline. Encaustic artists most often paint on wood as wax is a fragile material which needs to be adhered to a sturdy, rigid substrate with wood being most common. The substrate supports the ground, the surface on which paint is applied, and the ground must adhere well to the support while accepting the paint—or wax—with the right degree of absorbency.
With the advent of wide format printing and the ability to print an image to almost anything, hardboards have become more acceptable in the USA, though it is the renewable bamboo panel that has been most embraced.
Synthetic Boards
Sintra® Board is a durable, lightweight, UV and moisture resistant PVC board, that can be cut, routed, heat-formed, bonded, and screen printed. It is a plastic PVC rigid composite material for indoor and outdoor use usually used in signage, available in many colors up to 2" thick. Komatex expanded PVC sheets are lightweight closed-cell, rigid PVC with a matte finish available in 12 standard PVC colors, plus black and white. It is corrosion and moisture resistant, may be sawed, drilled, bent and fabricated, and is not harmful to the environment.
Aluminum Composite Material
Dibond® is a lightweight but rigid and durable aluminum composite material (ACM) made of two prepainted sheets of .012" aluminum bonded to a polyethylene core. They are available in numerous solid colors and assorted metallics, in 3mm thickness and in 4' x 8', sheet sizes. Originally designed for signage, it is best curt with a rotary saw, and is easily curved with a pyramid roller, hydraulic press or pipe clamp.
Follow Through
Substrates are the base to which a project is affixed. Whether Japanese hinging or dry mounting, the selection of the right substrate for the job is just as important as selection of the right adhesive and technique. Be consistent with material selection through the entire job. Spray mounting to a 100% cotton ragboard is as mismatched as a fully preservation framed package glazed without regular (non UV) glass. If AF mats are chosen, then AF mounting substrates and neutral pH adhesives and glazing must follow.
END
Copyright © 2022 Chris A Paschke
For more articles on mounting basics look under the mounting section in Articles by Subject.
Additional information on all types of mounting is found in:
The Mounting and Laminating Handbook, Second Edition, 2002,
The Mounting And Laminating Handbook, Third Edition, 2008 and
Creative Mounting, Wrapping, And Laminating, 2000 will teach you everything you need to know about getting the most from your dry mount equipment and materials as an innovative frame designer.
All books are available from Designs Ink Publishing through this website.
Chris A Paschke, CPF GCF
Designs Ink
Designs Ink Publishing
785 Tucker Road, Suite G-183
Tehachapi, CA 93561
P 661-821-2188
chris@designsinkart.com