COMPARING GLASS, PLASTIC AND RESIN: INTRODUCTION
The properties and constraints of glass, plastic and resin are frequently misunderstood and as a result, these materials are frequently misapplied. In this series of articles I try to clear up the confusion.
Evidence of the misapplication of materials abounds in “resin” surfaces which have prematurely faded and chipped, peeling backpainted glass with adhesive showing through the colour layer, curved glass railings surrounded by blobby caulking, irregular gaps, shattered glass paneling, etc.
A&D professionals have a range of motivations for selecting these materials, most often because they transmit light, as in windows, or because they do not block light, as in glass railings. But this family of materials is also chosen for reasons that are merely byproducts of their transparency, such as the unique “modern” appearance of a resin countertop with a glowing edge. Likewise glass is very hard and has fantastic longevity, so it is used in applications such as the ongoing replacement of 72 stories of stone facings on the BMO Tower in Toronto, or as wall covering in airports.
Though it may seem odd to discuss glass, plastic and resin together, this article does so because the apparent interchangeability of these three materials is often what results in misapplication. Additionally, resins and plastics are used in decorative and laminated glass fabrication, so the applications of resins and glass are intertwined.
Please note that the emphasis of this article is glass, plastic and resin as used in decorative architectural applications, both interior and exterior, such as canopies, cladding, work surfaces, railings, screens, etc. I will explore envelope applications such as cable-stayed, unitized and stick glazing systems in another article.
Debunking, demystification and detailing tips
Resin is plastic
The marketing gods must have been smiling when the first ad-man used the term “Resin” instead of “Plastic” to describe a sheet of lightly-pigmented cast plastic used as a screen in a trendy café. This is because plastics are no longer celebrated as the next great thing, in the way they were when Mr. McGuire delivered the word from on high to Dustin Hoffman’s character in “The Graduate”. Light and time are not kind to plastics used architecturally, so unfortunately the word “plastic” brings to mind sagging vinyl siding, crazed Plexiglas windows and ghastly pseudo-classical doors. The reality is that resin is plastic and presents all the application challenges that plastic does: It is soft, it fades, it sags, it expands and contracts more than most materials and it melts and / or burns.
This is not to say that plastics have no legitimate uses, far from it. I have used plastics many times and in many cases it was the only viable option. The point is that plastics work in some situations and they don’t work in others and detailers have to know the difference.
The taxonomic trickery is rooted in the technical definition of plastics, which are broken down in to two families: Thermoplastics and thermosetting polymers. While there are subsets and exceptions, most commonly used plastics fall neatly in to one category or the other. Thermoplastics are shaped by melting, molding and cooling. Notionally the same material can be formed over and over with minimal degradation in a process called remelting. Examples of thermoplastics are polypropylene (used in cheap, rope), vinyl (records, blinds). Polytetrafluoroethylene (Teflon) is a high strength, high melting-point thermoplastic polymer. By contrast, Delrin and Epoxy are thermosets, which cannot be melted and re-used.
Plastics recycling is largely based on the fact that thermo plastics can be re-melted. Thermosets are composed of two or more compounds which are mixed prior to molding and which then undergo a chemical change after which they no longer respond well to melting. For this reason, most thermosets are banned from the blue bin. As always there are exceptions, as explained in this article: http://www.iom3.org/news/recycling-thermosetting-plastics
For both families of plastics the precursor chemicals, or the plastics themselves, are referred to as “resins”, hence the source of the term used in the very effective re-branding of these materials. So in this article, for the sake of brevity, resins and plastics are referred to collectively as the less romantic but non-the-less accurate “Plastics”.
The most common misapplication of “Resin”
I believe that the biggest misapplication for “resin” is in horizontal surfaces, especially high traffic ones such as transaction tops and tables. The vast majority of these tops are produced by casting catalyzed (often tinted) liquid plastic in to a mold, then sanding and polishing the slab that results. Some parts are cut from full-sized, stock sheets, but because of the high cost of the material, if the part size isn’t close to 4’ x 8’, too much material is wasted.
Except for some epoxies (which are very expensive, so seldom used), most plastics which can be cast are simply too soft and / or brittle for use in high traffic horizontal applications, so the surfaces become chipped and scratched. So while these glowing-edged slabs look great on day one, plastics sag over time, so they degrade due to the effects of cleaning fluids and sunlight and the pigments fade, leading to a tired look. On the other hand well-thought-out vertical applications can be quite successful, as with the cast supergraphic floor numbering used in the offices Bloomberg’s Manhattan HQ.
Taking all this in to account, the worst possible use for resin would be a window sill next to the coffee station. My advice: Consider using backpainted or coloured laminated glass instead of resin. Just note that while the glass surface is tough, backpainting is fragile, so it must be protected.
Copyright Julian Bowron and Vector Praxis, June 2022