Help! My grout is cracking as it dries!

Old 11-13-02, 07:59 AM
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Exclamation Help! My grout is cracking as it dries!

Sorry, I have a lot of questions here.....I am new at this:

I am using tumbled marble on the fireplace hearth. The tile looks like small multi-colored stones that are arranged onto a rectangular backer. I bought them at home depot. Therefore, there were a LOT of big holes to fill with grout in between the small stones. Now that the grout has dried it looks like it is sort of cracking in the larger spaces between the stones. Why is it doing this?

Plus, it looks like i didn't put enough grout down - i wanted it level with the stones, but its not. Can I add more grout even after it has completely dried? Grout over top the dried grout to fill the holes?

And lastly what consistency should the grout be? Can it have lumps? What is the best way to mix it? I was having a hard time getting using a paint stirrer.
Old 11-13-02, 04:20 PM
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You mixed too much water in the mix!
Grout must be mixed precisely.

Grout gullies need to be deep enough to hold the grout. When the water leaves the grout, and you had a lot of water it sounds like, the grout will shrink.

A mixing paddle on a reversible drill is the only way to mix grout to the consistency of toothpaste, going in both directions of the drill. Then you let it sit for about 5-10 minutes in the mixing bucket to "steep". Then remix both directions again. Now it is time to spread grout and get muddy!
Old 11-13-02, 04:33 PM
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Cracking grout

Cracking. Cracks in grout joints are most obvious even to a casual observer. Such cracks may result from any of a variety of causes. Among the most common causes is shrinkage of the grout due to excess water in the mix - in other words, the product was improperly blended. The cracks occur due to the loss of the excess water in the grout through evaporation which, in turn, reduces the grout's mass.

Some cracks in grout can be attributed to the use of dry, absorbent tile that absorbs the water in the mix, stops the hydration needed for strength and reduces the mass of the grout. If you know you are dealing with dry and very absorbent tile, you can avoid this situation by dampening the joint before grouting. Use of a latex-modified grout is also helpful in resisting this type of cracking.

Deflection in the structure, either by racking or substrate deflection, will also cause grout to crack. Again, the use of a latex-modified grout might help in such instances.

Anytime the curing process is thwarted by environmental conditions, meaning hydration has been curtailed, the likely result will be weak grout that is susceptible to cracking. ANSI specifies damp curing to prevent the hydration process (curing) from being interrupted. Curing is critical to obtaining strong, crack-resistant grout. Therefore, it's vital that the proper blending of the mix be obtained. Do not over water, do not speed mix (to avoid air bubbles), and do not add water to your mix - even if it is becoming stiff.

It is important to use the proper tools for finishing your joints. Avoid using too much water in the joints, as it will definitely cause crazing.
Posted on: 12/04/2001

Preventing Unacceptable Grout Joints
By Joe Grady
Retrieved 13 November 2002.,68338,00.html

Grouting is quick and easy, but requires a little forethought.

Before mixing, we recommend dampening your tile with a sponge.

When mixing grout, add enough water to create a toothpaste like consistency. Allow this mixture to slake (set) for aproximately 10 minutes. Remix the grout at this time and add water as needed to re-establish a toothpaste consistency.

note: grout that can be poured from a bucket is too thin.

Scoop a manageable quantity of the grout mixture onto the surface and begin spreading it with a grout float at a 30 angle moving the float left to right and back working the grout into the joint.

After grout has had an opportunity to partially set (between 10 and 15 minutes depending on temperature), remove the excess grout with the grout float held at a 90 angle.

Note: We recommend grouting a small area in order to evaluate how quickly the grout will set up. You will avoid a difficult clean up by knowing how quickly or slowly your grout will set up and you will minimize the amount of time and effort required to finish the job.

Tile and Grout Cleanup
Cleanup the Excess

After grout has set for the 10 to 15 minutes, you are ready to wipe the surface clean with a sponge and water. Make sure you make multiple passes with a wet sponge until the excess grout is removed.

We recommend running the sponge at a 45 angle to clean the grout joint.

Rinse sponge often to remove loose particles of grout from the sponge.

Clean water in bucket often as to not to contaminate grout with dirty water and loose particles.

The grout joints should be of the same consistent shape and depth.

After grout has been allowed to harden there will be a haze left by the grout residue that will need to be removed.

Remove this residue by wiping over the tile with a piece of cheesecloth until film is removed. If grout film is difficult to remove you may have to use something a little stronger

Grouting Procedure. Tile Education. Retrieved 13 November 2002.

It is not recommended that new grout be installed over cracked grout. The defective grout should be removed before regrouting.z

Mixing grout by hand can lead to very inconsistant color and strength. Most of the installers I have observed used a five gallon plastic bucket and a drill with a slurry mixer bit. Water goes in the bucket first and dry grout gradually added while mixer is running. Grout should not be soupy or lumpy. If you can take your finger and run across the top of the grout mixture in the bucket and make a groove and see the grout slowly move back to fill in the groove, then you have a good mix.

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