What’s in That Bag of Grout?
By Frederick M. Hueston
Getting to Know Your Grout
If you’ve been in the stone or tile business for more than a week, you’ve handled your fair share of grout. You’ve probably recommended one type over another, fought with it on the jobsite, and maybe even cursed at it when it didn’t behave. But have you ever stopped to think about what’s actually in that bag (or bucket) of grout?
Whether you’re working with sanded, unsanded, or epoxy grout, every ingredient is there for a reason. Understanding what each component does can help you choose the right product for the job, troubleshoot problems, and explain to customers why you’re using what you’re using.
Let’s open the bag and break it down.
1. Sanded Cement-Based Grout
This is the go-to for most floor installations and wider joints (typically 1/8 inch or more).
Main Ingredients:
- Portland Cement – The binder that hardens when mixed with water, locking everything else together.
- Silica Sand – The filler that prevents shrinkage and adds durability.
- Lime – Improves workability and water retention.
- Water Retention Agents – Cellulose-based additives that keep moisture in for proper curing.
- Pigments – Mineral-based colors that resist fading.
- Polymer Additives – Improve flexibility, adhesion, and water resistance.
2. Unsanded Cement-Based Grout
Used for narrow joints under 1/8 inch, vertical applications, and scratch-prone surfaces like polished marble or glass tile.
Main Ingredients:
- Portland Cement – The binder.
- Finer Fillers – Very fine silica or mineral powders that allow tight packing without scratching.
- Lime – Improves workability and water retention.
- Water Retention Agents – Keep moisture in for curing.
- Pigments – Mineral-based colors.
- Polymer Additives – Improve adhesion, flexibility, and stain resistance.
3. Epoxy Grout
A completely different system, not cement-based. Mixed right before use.
Main Ingredients:
- Epoxy Resin – Base binder that creates a dense, chemical-resistant solid.
- Hardener – Amine-based compound that reacts with the resin to cure.
- Filler – Silica sand or mineral fillers for body and wear resistance.
- Pigments – Color agents compatible with resin.
- Additives – Flow agents, thickeners, and UV inhibitors.
Why This Matters to You
Knowing what’s in your grout helps you:
- Choose the right type for the job.
- Troubleshoot failures.
- Educate customers.
- Work more efficiently.
Grout is more than “the stuff that goes between the tiles.” It’s a carefully engineered mix of binders, fillers, pigments, and performance boosters.
Grout Ingredient Comparison Chart
| Ingredient | Sanded Cement-Based | Unsanded Cement-Based | Epoxy |
| Portland Cement | Yes – main binder | Yes – main binder | No |
| Silica Sand / Fillers | Yes – coarse sand | Yes – fine powder | Yes – graded mineral filler |
| Lime | Yes – improves workability | Yes – improves workability | No |
| Water Retention Agents | Yes | Yes | No |
| Pigments | Yes – mineral based | Yes – mineral based | Yes – chemical resistant |
| Polymer Additives | Yes – often included | Yes – often included | No (different resin system) |
| Epoxy Resin | No | No | Yes – base binder |
| Hardener | No | No | Yes – cures resin |
| Additives | Possibly | Possibly | Yes – flow agents, UV inhibitors |
