Types of Mortar Joints
Mortar is placed between bricks or stone when building to bind them together. A mortar joint is the exposed mortar. There are several different styles of mortar joint, each created by using a different finishing technique. When you are deciding the appropriate joint type for the application, first consider the amount of moisture to which the mortar will be exposed. Joints that are made with the assistance of tools are recommended for exterior walls. The tool compresses the mortar, making the joint more resistant to deterioration from moisture. Second, look at the design of each joint type. They each have a unique appearance to offer to the design of your work.
The concave joint is made by using a curved tool that pushes the mortar inward. This is an ideal choice for exterior walls, because the formation of the joint compacts the mortar. Combine this with the half-circle shape, and you have a joint that is highly resistant to water penetration. This joint is also forgiving; it hides many irregularities in the mortar and stone edges that come from the laying process.
To create a V-joint, use a V-shaped tool or trowel. This produces an indentation in the center of the joint, which is considered to be very ornamental. The mortar is compacted from the tool used to make this joint, making it durable against water. The shape also directs water away from the joint, making this a great choice for an exterior wall.
Mortar is angled from the bottom to make a weather joint. The top is recessed about 3/8-inch into the wall. This joint is suitable for exterior building walls because of its shape, even though the mortar is not as compact as other styles.
The struck joint is similar to the weathered joint. The difference is the struck joint is angled from the top and the bottom is recessed. It is a poor insulator against water, as water collects on its bottom ledge.
The grapevine joint is created with a grapevine jointer tool, which is a metal blade with a raised bead that creates an indented line in the center of the mortar joint. These lines tend to be rough and wavy, similar in appearance to a grapevine. This joint is a common choice for antique-style brickwork.
Extruded (Squeezed) Joint
The extruded or squeezed joint uses no tools to create. It is the natural formation as excess mortar pushes out from between the bricks as they are laid. The joint has a very natural, rustic appearance and is often chosen for garden applications. It is not recommended for outside building walls, as the edges of the mortar tend to break away.
The beaded joint is rounded, bead-shaped mortar. It is considered to be a formal design and an old-fashioned style. It is not recommended for exterior use, though, due to the exposed ledges.
The raked joint takes the mortar and removes it from the joints at an even depth. It is not very water resistant unless it is compacted, but other options still repel water better, as these joints leave open ledges for water to collect on. Pressure or acid cleaning to remove mortar residue from the ledges also compromises the water resistance of this joint.
The flush joint is when mortar is flat and level with the brick. This joint is chosen for use on walls that will be further finished with plaster or paint. The mortar is not compressed; thus this joint is not intended for exterior use.