A Primer on Mortar Joints


A Primer on Mortar Joints

In masonry, the term ‘mortar joint’ refers to the area filled with mortar or grout in between the brick, concrete, or other materials used in your project. Aside from acting as an adhesive for masonry, mortar joints play a significant role in protecting your structure from water penetration.  Since Abbot is primarily involved in outdoor masonry projects, we will focus here on mortar joints best suited for outdoor applications.

Outdoor mortar joints need to be especially equipped to withstand water penetration as they will be directly exposed to the elements.

Concave Joint

This popular type of joint is formed in mortar through the use of a curved steel jointing tool. It is very effective at resisting water penetration due to its recessed profile and the tight seal formed by compacted mortar. Patterns are emphasized on a dense, smooth surface, and small irregularities are hidden.


V Joint

This type of joint can be made with a V-shaped jointer or a trowel soon after the bricks are laid. Ornamental and highly visible, the V joints conceal small irregularities and are highly attractive. Like the concave joint, the V-joint is water-resistant because its formation compacts the mortar and its shape directs water away from the seal. However, the geometry of V joints may allow water and ice to accumulate if the mortar is not adequately tooled.

Weathered Joint

The straight, inclined surfaces of weathered horizontal joints tend to catch the light and give the brickwork a neat, ordered appearance. Less compacted than concave and V-joints, weathered joints are still suitable for exterior building walls. Although weathered joints are designed to allow water to run off the masonry, they can allow water to follow along the bottom of the masonry. Should this water settle and freeze, your project may begin to crack or erode.

Flush Joint

Flush joints are best used when the wall is intended to be plastered over or the joints are to be hidden under paint.  Because the mortar is not compressed, it is less water-resistant than some other designs. Water can also sit on top of these joints if the joints are exposed to the elements.


No matter which of the mortar joints you are working with, proper tooling is a key to extending weather resistance and lifespan. For more information on masonry and mortar joints, contact Abbot Building Restoration at 617-445-0274 or email us at

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