I haven't been posting regularly about my progress and work with casting reliefs, screen painting and photo fresco works as I keep testing new materials and until now I have been too caught up in the work to report to headquarters. As a result I will post a bunch of material in short burst with some accompanying photos, not in any particular order. My latest experiments have been with using cheaper materials like Portland Cement based mortar, stucco and cements to try increase the waterproof character of my pieces.
Water resistant, water proof and ultimate durability go hand in hand. The most toxic element in regular outside exposure is water, through mist, fog, rain, and basic humidity. Temperature change is also an invisible factor that changes the shape of items throughout a day. Strength within an item may resist the shape-shifting, but the porosity of an item also allows saturation which in turn may cause materials to breakdown. Sealing a piece is also a way to stop water from getting into an item, but my understanding is the if an item is completely sealed temperature changes will still make the materials that are used increase and decrease in size throughout a range and this is what can cause materials to crack and break away from each other.
I have been using Epoxy instead of Polyester resins in many situations when it comes to sealing the top side of my photo fresco pieces. The epoxy may expand and contract more easily than the stiffer polyester resins, although the resins may bond and seep into spaces better. The setting time for the polyester is shorter, but the smells are more annoying. I prefer the polyester resins to the epoxy when it comes to casting detail and strength, but I think when it comes to sealing an outside piece the epoxy, without any layers of resin works best. The thickness of the clear epoxy layer also seems to work like a clear plywood that bonds the exterior edges.
It takes a long time for the epoxy to set up and the air bubbles are problematic, as well as, bugs, debris of any kind and paint brush hairs. Everything will show up in the end. However, with the epoxy I can use the final layer as a part of the structure and reduce the depth that is required for strength. However, the protection against Ultra Violet radiation, UV, is limited with Epoxy and I have gotten yellowing very quickly once I have exposed my pieces to daylight.
I found that the epoxy seems to bond well to portland based cement products and gypsum based plaster products, considering that both of these are porous on the surface and the epoxy has a long set time that allow is to migrate into any crevice that may help with bonding. By using epoxy on the cement and plaster castings I have now had to put a final varnish cost to protect from UV exposure. To me this is the weakest link and requires additional work with drying time, blurring and the basic problems that come with varnishing. I have heard that there may be some kicker that can be added to epoxy to increase or add UV protection to epoxy, but I haven't work with spending more money on that yet.
Assuming that epoxy and clear coating varnishes don't add anything other than new layers of invisible protection and exterior strength to a piece I have gone backwards to find more durable products that don't require coating to exist for a long time outside. This brings me to my next issue about Gypsum Plaster versus Portland Cement.
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