(last updated 6/24/2010)

What Grout do you use? Cementitious (often called exterior grade), polymer modified, sanded. All three parts of that description are important.

There are 2 main types of grout: Cementitious and Epoxy. Each comes in sanded, for use in cracks wider than 1/8 inch, and unsanded, for narrower cracks. Sanded grout is stronger than unsanded. There is some concern among tile installers that sanded grout will scratch the surface of glass tiles. I use my hands rather than machinery for polishing and have had no problems on stained glass applique.

Epoxy grout is stain resistant and I recommend it on indoor tilework. Glass is another matter: epoxy's different coefficient of expansion and general stiffness often results in pressure fractures or scallops along the edges of glass pieces. These appear several months down the line so even if the piece looks good when you make it, you may find fractures later. Some of the newer brands say they have fixed this. Several tile shops have told me they recommend epoxy grout for mosaic but not for 4" glass tiles or the larger size glass pieces used in glass applique. I am still testing and will post my results soon.

Cementitious grout in this application needs to be polymer modified to add a bit more flexibility and frost resistance. I use Custom Polyblend brand from Home Depot as well as Laticrete brand sanded grout. Other artists I know use Super-Tek grout with good results. I add the Laticrete polymer admixture to both brands of grout powder rather than water. Since I primarily use gray grout, I do not have the color stability problems some folks have run into with adding Laticrete polymer to Polyblend..

Laticrete Sanded Grout (#1500) is usually sold in commercial tile stores (contact me if you have trouble getting a little bit to do a table). You need to use the admixture rather than just water. The formula I use is 1 cup dry grout to 2 oz. admixture (#1776). This covers a 20" round table. If your table is larger, mix another batch after applying the first rather than mixing a larger batch. Apply the second batch to both sides of the first batch and so on so that the next batch contacts the most recent batch, not batch one.

Choose your grout color with care. Dark grout makes the dark pieces merge and accentuates the lines between the light pieces. Using a light colored grout reverses the effect. I usually prefer medium gray grout in my designs but other artists use colored grout to great effect.

Sealer: Cementitious grout also needs to be sealed after it cures to make it stain resistant. Follow the directions on the bottle: usually this means wiping the liquid off after 10 minutes. If you allow it to dry, you have a major scraping job. The plastics used in the sealer break down in sunlight so you need to repeat the application every year or two to keep the stain resistance at its peak. I know the bottle says "lasts 20 years": I think it means 20 years in the bottle.

Regrouting: (you did keep your extra grout in a cool dry place?)
Gently remove the crumbly grout with a small screw driver, leaving the stable grout. Thouroughly wet the remaining grout or it will suck the water out of the new grout before it cures. Wipe out the trough where you will put the new grout. Mix and apply the new grout according to the manufacturer's instructions (it's just like grouting tile). Keep it moist and out of the sun for at least 3 days to give it a chance to cure. Seal it with a penetrating grout sealer.