Texture and three-dimensional elements make two-dimensional art much more interesting. Having thicker pieces and pieces that stick out make people want to reach out an touch your mosaic. Why would you want to cover that up with a material that scratches easily, can’t be repaired and turns yellow with age and sunlight?
Even if you do need to cover the mosaic somehow to provide a level surface, there are usually other means of doing so that don’t involve permanently coating the mosaic with these relatively short-lived materials.
My Mosaic Is A Table Top
Most mid-sized towns and cities have a glass shop where you can have a sheet of glass cut to a custom size and have the edges beveled (smoothed and rounded) with a torch. This same shop will also have small rubber pads for sitting under sheets of glass, and you may be able to use these for holding the sheet above your mosaic. If the surface of your mosaic is fairly rough and irregular in height, then you can use larger rubber stoppers and other means of holding the glass above the surface of the mosaic (such as a rim around the table).
I have seen some wonderful mosaic tabletops that were made from all sorts of found stones, shells and artifacts and then covered with a sheet of glass that rested on rubber stoppers. The overall look and feel of the table was like one of those curio coffee tables that have the glass tops over artifact collections, only the artifacts were closer to the glass cover, more visible and seemed to be part of the surface, which they were.
One important caveat: Make sure that the mosaic is evenly supported in multiple places and that no one piece of the mosaic can make contact with the glass if heavy objects are placed on the table. Otherwise you could possibly crack the glass.
My Mosaic Is A Floor
In general, I do not recommend making floor mosaics from materials with different thicknesses due to the potential for them to be a trip hazard and to be damaged by shoes and wheels and vacuums. If you do want to use material of variable thickness in a floor mosaic, make sure you do something that results in a level surface.
Consider Using Mortar Instead
One option is to press these pieces into a bed of thinset mortar similar to how crafters press tile into wet concrete to make garden stepping stones. However, be aware that mortar thins as it cures, so there is only so much height difference that can made up for by mortar when a tile is much thinner than the tile around it. In our studio, we solve this problem by mixing small pea gravel into the mortar underneath the particularly thin tile. We also have thin pieces of stone tile that we coat on both sides with thinset mortar and use as shims under thin pieces. Note that these methods aren’t really practical for large areas or commercial jobs.
Clear Epoxies For Floors
There are epoxy products that will last a long time by standards of flooring and architectural products, but I tend to think in terms of archival standards for fine art and making things as intrinsically durable as the Roman aqueducts. If you put a epoxy clear coat over the top of the mosaic, then you need to carefully review the manufacturer literature on the packaging and Internet. You want to look for information concerning scratch resistance and hardness and durability. You will also want to review the manufacturer’s recommendation for maximum recommended thickness.
Epoxy Not Polyurethane
If you do use a clear coat to make a level surface over a mosaic made from irregular pieces, then make sure you use an epoxy and not a polyurethane. Polyurethanes are not as hard and scratch-resistant as epoxies. They also do not bond securely to glass the way epoxies can.
How To Find Epoxy Clear Coats
These will not be in the tile aisle of the building material store. They are sometimes in the flooring department, but they are more often in the paint department. The important point is that they aren’t specific for mosaic or tiling, so don’t expect them to be sold for that purpose. Also, you should not expect professional installers to know how epoxy clear coats might be used to cover tiled surfaces, at least not in a thickness significant enough to compensate for differences in tile height.
Problems With Clear Coats For Mosaic
- They cannot be removed or repaired by practical methods.
- Installation is not very forgiving. You may have bubbles and haze that cannot be fixed.
- They are not inexpensive and usually cost more than the mosaic tile.
- They are not commonly used on mosaics, so professional installers don’t have experience with them as far as mosaics are concerned.
- They scratch easily compared to porcelain, glass and most stone.
- They turn yellow in ultraviolet sunlight, some much faster than others.
- They won’t last the millennia that glass and stone mosaics are capable of lasting.