Functions of mortar in concrete block masonry

The Masonry is built with blocks and mortar. The primary function of a masonry is to withstand load & transfer it safely. Stability and strength of a masonry depends on following factors,

1. Quality of materials (Blocks & Mortar)

2. Laying pattern of blocks

3. Workmanship

When it comes to the quality of materials, we often give higher importance for blocks than mortar. The main reason is that the blocks are procured from outside and mortar is prepared in-house. So here we want to discuss about mortar. Only one thing generally understood by every one is its ratio - 1:5 or 1:6.

In our training programs, we ask our people to list out the functions of mortar and its strength requirement. Usual answers are as follows,

Functions: Binding the blocks, transferring load, cushion for blocks

Strength: _________________

Somehow we understand the functions of mortar and have no idea about the strength. Strength of the blocks are mostly known which is around 3.5 N/mm2. Now for the discussion, how much should be the strength of the mortar compared with blocks; choose the correct option from below,

1. Mortar strength > Block strength

2. Mortar strength = Block strength

3. Mortar strength < Block strength

Before jumping to answer, lets discuss about the function. The primary role of blocks and mortar is to be fulfilling primary function of the masonry, that is withstand & transfer load effectively. At this point we need to discuss about the laying pattern of the blocks. The blocks are placed always with staggered vertical joint. We don't stack them with continuous vertical joints. If we place the blocks with continuous vertical joints, it will work like a column and not like a masonry.

Vertical joints

Now going back to strength comparison,

1. Mortar strength > Block strength - in this case, if any cracks to be appeared because thermal expansion and contraction, blocks will fail first; and will leads in failure of masonry.

2. Mortar strength = Block strength - in this case, there are equal chances of block as well as mortar to fail. So there is possibility for masonry to fail

3. Mortar strength < Block strength - in this case, mortar fails first, cracks appears in stepped shape, before block fails. so here we can taken corrective measures before masonry fails. Because even without the mortar, primary function of mortar will be fulfilled by blocks alone with proper staggered vertical joints layout.

So strength of mortar should be slightly lower than the block.

From above discussion, the primary function of mortar can also be derived as,

1. Keeping the blocks in its position

2. Works as cushion, so that blocks can be leveled

3. Not the load transfer.