There seems to be a lot of confusion out there, especially online forums. Experts seem to be quick to advise all glass installations require unsanded grout. Why is that? The quick answer is that glass scratches easily, and sanded grout will cause permanent damage.
However, if you were take those experts opinions who often refer to "industry standards", you would also think that epoxy grout should not be used because it's "too strong" and could crack glass under movement.
So now we have 2 issues to deal with so how do figure out what works and what doesn't?
It is always a good idea to contact the glass manufacturer directly as they will stand behind their product with in-house testing and can offer the best advice. Following "industry standards" by the book is NOT your answer. You have to understand that it takes time, sometimes a long period of time before an outdated standard is "revised and published". Manufacturers are the trailblazers who stay current, especially with their own products. It just makes sense.
I personally have been using Super Grout Additive sanded grout for glass installations for years. If the joint is 1/8" or larger, sanded grout will be tested on a sample piece for scratching with the grout float application and wiping process using sponge. I use little pressure and try not to overwork the grouting process. Too much pressure could scratch the glass for sure so you do have to be careful.
I have also used sanded grout for smaller grout joints, such as 1/16" using Super Grout Additive.
Question: Why and aren't you supposed to use unsanded or nonsanded grout? Industry standards says those are the rules, so why are you against their opinions?
Answer: Those rules are based on grout mixed with water not epoxy. Regular grout gets it's strength from surrounding the adjacent tiles and the full depth of the grout joint. Once the grout has dried, it has "locked itself" around the tiles resulting in an "mechanical bond". Super Grout Additive is a glue and will stick to tile, grout, metal, some types of plastic, and just about anything it touches. That means it is getting it's strength from the epoxy, not the "mechanical bond". You don't need a grout joint for silicone to bond because it's an sealant or type of glue too. Do you ever see unsanded, nonsanded, or sanded 100% silicone? Problem with silicone is the fungus problems associated with wet areas like shower floors. I will use Super Grout Additive® for corners even when the tiles are touching each other because I know it works, even with sanded grout. I use sanded grout for all repairs because it's easier to work with and produces a stronger repair vs unsanded, nonsanded grout.
If it's a glass backsplash, I will use Super Grout Additive where the counter meets splash. I do not, and have not used silicone caulk for many years. I have found that most movement or "change of plain" is not enough to damage glass. Most movement inside a house is more cosmetic than structural. Houses are made to move, expand, contract, to a certain degree without causing damage. If you have substantial movement in your house, you will have more worries than grout cracking issues. Exteriors are a different story and change of plain, expansion, contraction, should be considered more seriously.
jim in arizona - October 08, 2017
how much apoxy bond do I need for 12 sq. feet of river rock shower floor installation