From the Floor Up, a Blog for the Flooring Professional From the Floor Up, a Blog for the Flooring Professional

Tips of the Trade: River Rock Tile / Urethane Grout Installation

Friday, September 23, 2011
River rock, also known as pebble stone, tile installations can be difficult and requires special grouting techniques depending on the river rock material selected. The challenge is the grout joints in river rock applications often fall outside the widths/depths recommended for many types of grout, including Urethane Grout. Failure to recognize and account for this fact can lead to grout failure if proper installation techniques and the appropriate precautions are not taken.

Urethane Grouting Tips—

Before spreading grout: Stir each bucket from the bottom up just enough to mix in the skim of urethane that may be on top (by hand – preferred; drill mixer – low speed for 30 seconds; no drill mixer for glass filled grout). Do not add anything to the bucket. Stir grout periodically during installation.

Remember to seal and/or enhance any natural stone depending on your requirement. Some kind of sealing is required prior to grouting. Be sure to follow the sealer manufacturer’s cure time instructions before grouting. A good rule of thumb is to wait at least 24 hours after sealing before grouting.

While spreading grout:

Use a sponge and clean water to lightly dampen 3-5 square feet of River Rock Tile (generally not necessary on vertical surfaces).
• Float grout in using a softer-edged stone float, ensuring that all joints and spaces are tightly filled. Do not overfill as this may make grout cleanup very difficult. Grout joints must be 1/16” - 1/2” in width and at least 1/8” in depth. Joints that are deeper than 3/8” will require more cure time than typically recommended. Spread only in an area that you can reach (3-5 square foot sections typically for River Rock tile) to apply and clean urethane grout. Remove excess grout from the tile surface.
• Use a whisk broom or a block brush to knock grout from the face of the tile/stone and to smooth the areas between the stones.
• For best results, remove grout haze as you work, particularly in warm or dry climates. If working alone, only grout as far as you can reach (arm’s length) before initial cleaning. If working as a team, one person should grout, with the other(s) cleaning immediately behind the first person.
Rinse sponge in water and wring out completely. Since urethane grout requires very little water during cleanup, make sure that the sponge is wrung nearly dry. Wipe lightly, leaving sponge flat on the tile surface to prevent grout removal from joints. Excessive water during cleanup can dilute the urethane binder and cause curing issues that may lead to grout failure. Change rinse water every 100 square feet or less.

After installation:
Allow cleaned tile areas to dry, then inspect the surface. If additional haze removal is necessary, we recommend the use of Bostik® Blaze™ Urethane Grout Haze and General Purpose Cleaner. Wait 3 hours in low humidity/warm temperature (< 50% RH and > 70°F) environments and 6 hours in high humidity environments/cool temperature (> 50%RH and < 70°F) environments before using Bostik Blaze. Make sure the grout is cured enough to withstand light
finger pressure without losing form. Spray Bostik Blaze on a scrub pad designed for delicate surfaces such as the 3M™ Doodlebug™ white cleaning pad. Rub the cleaning pad lightly over the urethane haze on the tile being careful not to touch the grout joints. Note that excessive haze may require direct spray on surface, more dwell time or repeated cleaning. Do not flood the surface with cleaner. Allow Bostik Blaze to rest on the tile/stone surface for at least 60 seconds to ensure sufficient penetration. Use a damp sponge and clean water to remove the film and cleaner. Finish by drying the tile surface with a clean towel or cloth. Allow urethane grout products to cure sufficiently as follows: Light foot traffic – 24 hours; heavy foot traffic and normal cleaning – 3 days; wet areas such as showers – 7 days.


1. Use an approved waterproofing membrane such as Bostik® GoldPlus™ for mud bed applications. Be sure to follow the manufacturer’s recommendations for membrane installation. Apply to within 1” of any drains to prevent weep hole blockage. The use of pre-sloped, waterproof trays (instead of mud beds) is highly recommended.
2. Do not use urethane grout to re-grout commercial and wet areas such as showers, steam showers, and outdoor applications. On traditional shower floors apply a waterproof membrane such as Bostik GoldPlus over sand/mud bed to keep hydration from slowing or stopping full grout cure.
3. Protect outdoor applications by tenting the grouted area at least 1 foot above surface for 7 days.
4. It is not recommended to grout or clean tile if the tile surface temperature is above 90°F (32°C). If this is the case, wait for the tile surface to cool prior to grouting or cleaning. You may accelerate the tile cooling process by wiping with a damp sponge. Be careful not to add excessive water during the tile cooling process.

Need more help? Contact our Technical Service group at 1-800-7/BOSTIK.


shobanaa said...

This post is very nice and the subject is very useful to everyone. Thanks for sharing a nice post.

flooring Houston said...

Once you see the finished product, you will not realize the difficulty your construction crew has gone through to ensure that it is indeed waterproof. Handling concrete is not easy and this requires skills especially when drilling holes to prevent cracks. When you have a radiant heating flooring, it would be nice to have an even distribution of heat but if you are not sure exactly what to do, ask the assistance of a professional and read helpful blogs such as this. Once again, thanks again for the tips.

flooring Houston said...

What a very helpful post. River rock tiles can really give a different look on floors however installation can be quite a task. However with the information provided, homeowners that are into do-it-yourself projects can really enjoy doing the task.