Back when I was a full-time remodeler (1983 – 1991), one of my older brothers, Izzy, taught me how to lay ceramic tile. I really liked the combination of physical work and craft, and the beautiful finished result. My brother and I agreed that it seemed out of whack to lay color-fast, durable, water-impermeable tiles and then surround each one with porous, easily-stained, grout. Yeah, the latex-based cement grouts are easier to work with and can be sealed once they have cured, but it seemed like most of our work with this product—and everyone else’s—had dirty, cracked, grout lines down the road, especially in high stress areas like mudrooms, kitchen counters, and showers.So we tried epoxy grout from Mapei. Anyone who has used two-part epoxy grout, even the newer versions with detergents in the formula, knows how difficult they can be to work with: the short pot-life means you have to really keep to a pace and you do not want to have to try to remove grout film that has even partially set on the surface of tiles. Epoxy grout is a pain for installers. The tradeoff is that it is way better for your clients. It is strong, nearly stain-proof, and yet it remains flexible.A 2003 tile counter with epoxy groutWith that knowledge and experience in mind, when we remodeled our kitchen, I used epoxy grout for the two tile counters and backsplashes at the sink and side cabinets.The author’s kitchen remodel is nearly done with tiled kitchen counter and backsplash tile.Here is a photo taken Saturday, Sept 28 2019, 16 years after installation, of the sink countertop, which sees a lot of water and food waste:This is the kitchen sink’s tiled counter about 16 years after installation.And of the side counter that sees little to no water or contaminants:The side counter with tile and grout is exposed to little or no stress from water, food waste, or cleaners.And here is a close-up of the right hand side of the sink:The grout just to the right of the kitchen sink shows some discoloration.If you look carefully and compare the grout lines just to the right of the metal sink, especially compared to the grout lines in the backsplash, there is some darker discoloration right along the sink and some light almost white spots in the grout just to the right of the 2nd full course of tiles. There’s more on this in the closing section of this blog.A 2011 experiment with polyurethane groutIn part because of the epoxy grout staining around our kitchen sink, I went looking for a different grout to use when I tiled our downstairs shower stall and floor in 2011. Here’s a shot of the shower stall:This is the author’s downstair 3/4 bath with a tiled shower stall and floor, both grouted with Bostik Quartzlock2, a polyurethane grout.The owner of a local flooring store who was doing a lot of ceramic tile work in his own home strongly recommended a polyurethane grout, Bostik Quartzlock2. He swore that this grout had all of the advantages of epoxy grout (durability, color-fastness, stain-resistance) without the installation challenges: polyurethane grout is a one-part mix and has really long pot-life and does not bond to the tile surface if you leave any grout film for an extended period of time.I like the way that polyurethane sealants perform, so I decided to give the Bostik grout a try. I carefully read and followed the installation directions, in no small part because the flooring store owner warned me that the polyurethane grout works and tools differently than either standard latex-modified cement or epoxy grout.Here are current pictures of the polyurethane grout in our downstairs shower:The author’s downstairs bathroom shower stall photo is taken Fall 2019.And the downstairs bath floor:The author’s downstairs 3/4-bath tile floor installed was installed in Fall 2011. This photo was taken in Fall 2019.For me, the polyurethane grout was much easier to install than epoxy grout and seems to be just as durable and stain-resistant.So why isn’t polyurethane grout more popular?I went to three local flooring retailers looking for information for this blog and not one of them could tell me of a single tile job that used polyurethane grout. Two stated that they can’t even get local installers to use the better-known epoxy grout, much less polyurethane. One retailer told me, “It’s just too much harder to install than latex-modified cement grouts and too expensive. The only time our installers use it—and not without a lot of groaning—is when it’s specced on commercial jobs.”When I told both retailers how and why we got clients to use epoxy grout—we told our clients that if they could afford ceramic tile, they could afford epoxy grout. And we asked, “You know how ugly the grout is on your current tile floors?” This stuff is durable and does not stain, we told them. The retailers both said: “Hey, that’s a great way to sell it!”Cleaning epoxy and polyurethane groutBack to my kitchen and downstairs bathroom grout…neither has proven to be completely stain-proof, despite performing quite well. Wondering how they would clean up, I did some experimenting.The epoxy grout discoloration to the right of our kitchen sink is quite different than spots on our shower stall polyurethane grout. And I think I might know why after reading this tech sheet on tile in commercial kitchens from Mapei. The oleic acid in fats along with sustained contact with the grout is especially challenging, and something we were not aware of.In any event, I decided to do a bit of testing, treating both the kitchen sink epoxy grout discoloration and polyurethane black spots with two different cleaners—Soft Scrub, as recommended by Bostik—and my own idea—OxyClean MaxForce stain remover. I know that this cleaner is targeted for fabrics, but it has worked really well for us in removing stains without damaging the substrate on more than just clothes.In each case, I applied the Soft Scrub and OxyClean generously to three different places as shown below, leaving the cleaners to sit for 15 minutes before scrubbing each with a toothbrush, wiping clear, cleaning and rinsing with water, and then drying with a hair dryer.Here are the sequence photos, in each case the two cleaners were separated by green masking tape, which also meant there was a spot between the two cleaners that did not get any treatment.Kitchen sink cleaners applied:To the right of the green tape, the cleaner applied is OxyClean; to the left, Soft Scrub.Kitchen sink cleaners scrubbed, wiped, rinsed, and dried:I have moved the green tape to expose the strip of grout between the two cleaners that did not get any treatment.Shower floor showing black spots:Shower floor with cleaners applied:Tile grout cleaners applied; Soft Scrub to the left of the green tape and OxyClean to the right of the tape.Shower floor scrubbed, wiped, rinsed, and dried:The green tape has been moved down to expose the strip with black dots remaining between the areas of the two cleaners. But the left hand Soft Scrub area is more clear of the black dots than the OxyClean area.Polyurethane grout, all the wayI think the staining around the sink showed little improvement after each cleaner was used. The staining is modest and is somewhat better with either cleaner but probably permanently stained by food waste and water left too long in contact with the epoxy grout. On the other hand, one final look at the right side of the sink after scrubbing the whole counter with Soft Scrub shows pretty good results—not perfect, but certainly acceptable after more than 18 years in place. It could be that more “elbow grease” is as important if not more so than the type of cleaner used.After Soft Scrub was used on the entire kitchen sink counter, and thoroughly dried, the discoloration right next to the sink is more slight, than modest.In the shower, the Soft Scrub on the polyurethane grout pretty much eliminated the black spots, doing a much better job than the OxyClean. And in general, after now more than 8 years, our polyurethane grout is in really good shape.If I had to do any of this over again, I would use the Bostik QuartzLock2 polyurethane grout without hesitation. I wish I knew two more things:Why I found it so hard to find users of polyurethane tile grout.How other polyurethane grouts performed in comparison to Bostik’s.Anyone tile setters out there care to weigh in?-Peter Yost is GBA’s technical director. He is also the founder of a consulting company in Brattleboro, Vermont, called Building-Wright. He routinely consults on the design and construction of both new homes and retrofit projects. He has been building, researching, teaching, writing, and consulting on high-performance homes for more than twenty years, and he’s been recognized as NAHB Educator of the Year. Do you have a building science puzzle? Contact Pete here. Photos courtesy of the author.AUTHOR’S UPDATE: Thursday, October 3For nearly two weeks prior to posting this blog, I worked hard to engage Bostik technical support with questions I had about their polyurethane grout. I wish their technical support was as good as their grout, frankly. Here are the questions I emailed to two different technicians at Bostik that remain unanswered, but I am still working on it:1. how are PU and epoxy grout different, chemically? I want to better understand the chemistry involved (and this in no small part because I do some consulting on product selection with chemically sensitive clients)?2. whom do you consider to be your competitors making PU grout and what do you consider to be QuartzLock2 advantages over competing PU tile grouts?3. Why is your PU tile grout not GreenGuard certified, as say, Laticrete’s epoxy grout is?https://www.greenbuildingsupply.com/All-Products/StarQuartz-QuartzLock2-Urethane-Grouthttps://laticrete.com/en/tile-and-stone-installation/grouts/epoxy-grouts/spectralock-pro-premium-grout4. Very narrow grout lines are challenging with both PU and epoxy grout; what sort of guidance can you offer on the best grout for very narrow grout lines?