Essentials of
Masonry

MIXING THE MORTAR

Mortar is usually mixed on the job site in portable, mechanical mixers. However, on some small jobs, you can mix mortar by hand.

1-15. Mortar Packaging. The proportions for mortar types are based on volume measurements, and mortar ingredients are packaged by volume. Portland cement is packaged and delivered in 94-pound bags containing 1 cubic foot. Hydrated lime is packaged in 50-pound bags that each contain approximately 1 cubic ft. Sand is delivered by the cubic foot or the cubic yard. A 1:1:6 mortar mix would call for one bag of cement, one bag of lime, and 6 cubic feet of sand. This mixture will equal 6 cubic feet of mortar.

1-16. Machine Mixing. Use the following steps when mixing by machine:

Step 1. Add a small amount of water to the drum. This will prevent the mixture from caking on the machine paddles.

Step 2. Add one-third of the sand.

Step 3. Add all of the lime and the cement.

Step 4. Start the machine and mix for approximately one minute before adding water.

Step 5. Add the remaining sand and water to obtain the desired consistency.

Step 6. Continue mixing for at least three or more minutes after all ingredients are in the machine.

1-17. Hand Mixing. A mortar box is used to mix mortar by hand. It is approximately 5 by 10 feet and can be constructed with 2-inch material (Figure 1-2). The box should be as watertight as possible. Use the following steps when mixing by hand:

Step 1. Place half of sand in the mortar box.

Step 2. Spread the specified amount of lime and cement over the sand.

Step 3. Add the remaining half of the sand. This sandwich operation permits a more thorough mixing with less effort. Turn the mixture twice with a hoe, and then pull it to the end of the box.

Step 4. Add the water and cut the dry mixture back into it. Continue adding water to obtain the desired consistency.

 
Figure 1-2. Mortar box

1-18. Retempering. If the mortar has become stiff on the mortarboard because of the evaporation of water, you must add water and retemper the mortar to restore its plasticity. Remember the following:

• Mortar should be used within 2 1/2 hours after original mixing when the temperature is 80 degrees Fahrenheit or higher.
• Mortar should be used within 3 1/2 hours when the temperature is below 80 degrees Fahrenheit.

1-19. Discarding. It is sometimes difficult to determine if the mortar should be remixed and used. If in doubt, discard the mortar. Ensure you comply with all environmental laws and regulations when discarding waste. Never use mortar after it has been dropped on the ground or contaminated in any way.

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