If you were to be asked “What is the most inportant ingreidient of you mortar mix?” what would your answer be? Everyone knows its the portland. But what about sand? Others will say water changes the whole mix.

But what about air? It’s free, available everywhere and is just as important. Just put a shovel full in and you are good to go.

I wish it was that easy. So lets take a look at what function air plays in the mixing process of our mortar and what its function is.

During the mixing phase of masonry mortar, entrained air refers to the incorporation of tiny air bubbles into the mortar mix. This is achieved by introducing air-entraining agents or by mechanically agitating the mix. Entrained air is intentionally introduced into the mortar to improve its properties and enhance its performance in masonry construction. Here’s how entrained air plays a part in masonry mortar:

1. Workability and Consistency: Entrained air improves the workability and consistency of the mortar. The tiny air bubbles act as lubricants, making the mortar easier to mix, spread, and work with. It helps reduce friction between the mortar and the masonry units, making it more manageable for the masons during construction.
2. Water Retention: Entrained air in mortar helps in retaining water. The air bubbles create a network of small voids within the mortar, which traps water. This property is beneficial because the mortar gradually releases the trapped water, keeping it hydrated over an extended period. Adequate water retention prevents excessive drying of the mortar and allows it to properly bond with the masonry units.
3. Freeze-Thaw Resistance: Entrained air in mortar significantly improves its resistance to freeze-thaw cycles. When water trapped in the mortar freezes, it expands, and without entrained air, this expansion can cause cracking and damage to the mortar. However, entrained air provides space for the expansion of freezing water, reducing the potential for damage. It helps the mortar withstand freeze-thaw cycles without significant deterioration.
4. Durability and Strength: The presence of entrained air in mortar enhances its durability and strength. The air voids act as internal cushions or shock absorbers, absorbing stress and preventing the propagation of cracks. This property improves the mortar’s resistance to external forces, such as wind, thermal expansion and contraction, and vibrations, thus enhancing the overall performance and longevity of the masonry structure.
5. Bonding and Adhesion: Entrained air can improve the bond between the mortar and the masonry units. The air voids create a textured surface within the mortar, increasing its surface area and providing better contact with the masonry units. This improved bond helps to distribute loads more evenly, reducing the risk of mortar failure and improving the overall structural integrity of the masonry.

It’s worth noting that while entrained air provides numerous benefits to masonry mortar, excessive air content can be detrimental. Excessive air can reduce the compressive strength of the mortar and compromise its load-bearing capacity. Therefore, it’s important to carefully control and balance the air content during the mixing phase to achieve optimal results.