The joint profiles in brickwork make up approximately 17% of the overall wall area and different joint profiles can affect both the aesthetics and weathering properties of the wall.

• Raked joints increase the risk of water penetration.
• A concave joint reduces water penetration through the joints. ( Tobermore recommend a concave joint )

Industry guidance for mortar joint specification in masonry.

RAKED JOINT – This joint strongly emphasizes horizontal joints. It is however a very poor weather joint and is not recommended if exposed to weather. This mortar joint incorporates the ledge of the block to create the horizontal lines that are so desirable with this joint. The ledge is however a collector of rain water as it pours down the wall. Eventually the water will find its way around the mortar joint into the interior of the wall and building.

CONCAVE JOINT– This is the most common joint used in masonry construction. The tooling works the mortar tight into the joint to produce a more consistent weather joint. The pattern is emphasized and small irregularities in laying are concealed.

Further guidance can be found here https://nhbc-standards.co.uk/6-superstructure-excluding-roofs/6-1-external-masonry-walls/