Do Concrete Block Walls Need to Be Sealed Before the Brick Veneer Is Laid?

Sealed Concrete

• Concrete sealer is a chemical applied to concrete blocks to prevent water from penetrating the surface of the concrete. Sometimes concrete sealer is applied to already water-damaged concrete block walls to prevent further water damage. However, it is not necessary to apply sealer to an already sound concrete wall. In fact, if you plan to seal the concrete wall before you lay veneer, you will need to take additional steps to apply the veneer to ensure that the veneer will adhere to the wall.

Brick Veneer on Unsealed Concrete

• Brick veneer can be glued to the unsealed concrete blocks using a layer of mortar, or mortar mixed with a little thinset. Use a trowel to apply a layer of mortar to the back of the brick veneer, then press the veneer directly into the wall. The mortar will squeeze out over the sides of the brick, and can be used as grout visible between bricks.

Brick Veneer on Sealed Concrete

• Mortar will not properly adhere to a concrete wall that has already been sealed. In this case, you will need to install a moisture barrier and a scratch coat over the concrete wall. Line the sealed concrete with breathable grade D paper, then install a rain screen over the paper. To form the scratch coat, attach metal lath to the concrete wall with metal fasteners. Next, use a trowel to place mortar on the metal lath, so the mortar fills all the holes in the lath. This is your scratch coat. Wait for it to dry according to the manufacturer's instructions before installing the veneer on the scratch coat.

Repellent, Not Sealant

• After the veneer has been secured to the wall, do not coat the wall with sealant to prevent moisture from leaking in. Your brick veneer wall will need to breathe. Use a water repellent instead. Water repellents, while they do not offer as much protection as sealants, allow moisture to exit the brick once it has entered. This feature will prevent your home from becoming water damaged in the future.

Painted Versus Sealed Concrete

• If your concrete has been painted but not sealed, the effect is the same. Mortar cannot bond with the concrete blocks beneath if it only touches the layer of paint on top of the concrete. In this case, you will need to add a moisture barrier and scratch coat.