Glues and Adhesives
Many kinds of glue and related chemical adhesives are used in model railroading. I cover some of the issues with these on my Material Safety page, but this page is to discuss their performance.
Note that a number of glues come in different variations, and these can have very different properties. It isn’t enough to refer to a glue by brand or general type. You may need a specific part number.
Layout Structural Adhesives
This section describes glues used for building a layout.
PVA (White Glue / Wood Glue)
PVA (or Polyvinyl Acetate) is the basic of many glues, including ordinary “white glue” or “wood glue”. Both forms are water-based and cleanup using a damp rag is very easy (they’re also both very safe). The difference is that white glue remains water-soluble after it sets, while yellow “wood glue” does not.
Both work best on porus materials, seeping into tiny cracks before setting to tightly bind two materials together. A non-porous material such as insulation foam or painted wood won’t bond very strongly to white glue, and if you bump it the foam may break loose (experience speaking here). On the other hand, if the material isn’t going to be expose to bumps (i.e., it’s within the borders of the layout and protected by other materials or a front-of-layout fascia) then this glue will work very reliably. If greater structural strength is needed for non-porous materials, specialty glues like Liquid Nails will be preferable.
PVA works very well for attaching cork roadbed to a wood subroadbed, or joining two pieces of unpainted wood. It’s also useful for attaching scenic materials, even to non-porous materials (as these usually aren’t under mechanical stress). It’s not a good choice for attaching vinyl roadbed or when used with painted or otherwise sealed wood.
Many branded adhesives are variants of PVA formulations, but their characteristics can be quite different.
Foam Tack Glue
Woodland Scenics makes this for attaching scenic foam. It appears to be a PVA type of glue, but there is no Material Safety sheet or other ingredients list I could find that would confirm it. It appears to be water-based and can be loosened with either water or denatured alcohol.
Mod Podge comes in several forms. The standard form is definitely a PVA, but the formulation of the others is less clear. This is a low-tack glue suitable for attaching paper to a variety of materials. When working with photographs (and possibly anything intended for long-term use), the acid-free Photo Mod Podge form is preferable to the standard kind.
I use this for attaching photographic backdrops to painted particle board.
Caulking materials are a thick form of adhesive, usually used to seal large gaps. The name refers to the application, and the individual formulas can vary significantly.
Silicone-based caulking is often used to attach roadbed (cork or vinyl) to subroadbed (wood or other materials). Aside from the pungent smell when it cures, this generally works very well. Howeve, it’s important to note that the solvents may damage foam scenic or structural materals. There are versions designed for use with insulation foam that are safe for this.
This title is something of a misnomer, as there are glues involved, but they’re attached to something (like tape).
Velcro is a brand-name for hook-and-loop closures. Equivalent closures are available under other brand names. Hook-and-loop closures work by having two different kinds of material, both made of plastic. One has small loops, while the other has fishhook-shaped structures that connect to the loops, but bend and disengage with the two are pulled apart. Because the hooks and loops can be shaped differently (to avoid patent issues), it’s best to use the same brand for both sides of a connection. The gripping strength of hook-and-loop closures can vary by model based on the size and rigidity of the two structures, as well as their shapes (which may vary to avoid patent conflicts).
This is very useful for attaching things that can’t easily be screwed in place to the underside of the layout, while still allowing removal for maintenance (unlike double-sided tape). Some people use them to attach servo-motors for turnout control, and they can also be used to attach circuit boards if the board is in a case or similar.
Although normal hook-and-loop material is described as non-conductive, this doesn’t necessarily apply to the adhesive. Do not attach self-adhesive backings directly to a circuit board: over time even the non-conductive ones can become conductive due to chemical changes that happen as they age, and they could also potentially pull small components or metal traces right off the board.
Typically the back of a piece of hook-and-loop material has some kind of glue on it, usually activated when a protective paper cover is removed, exposing it to air and the backing is then pressed against something (it’s described as pressure-sensitive, so air exposure may not matter).
There are two broad classes of such adhesive: rubber and acrylic. In Velcro-branded closures, “B” marked on the backing signifies rubber, while an “R” signifies acrylic (which seems likely to be confusing). Acrylic adhesive costs more, and most of its benefits aren’t applicable to layout uses (it’s more stable under high temperatures or exposure to UV light). But acrylic forms a stronger bond with wood and is less subject to damage from solvents, either of which may make it appropriate in some cases. Rubber-based adhesives work well with plastic.