Generally, water repellents are only an interim solution to any water penetrating a brick wall since they loose their ability to repel water after 1 to 10 years. However, in cases where all other options have been exhausted, it may be considered as long as one is aware of the inherent nature of water repellents.
There are basically two t ypes of water repellents: films and penetrants. Films such as acrylics, stearates, mineral gum waxes, urethanes and silicone resins form a thin membrane over the brick. Penetrants such as silanes, siloxanes and blends actually penetrate the brick surface. Films are good at repelling water but poor at permitting water vapor transmission which allow the wall to breathe. Penetrants, on the other hand, are good at both. They will usually have a matte finish while films may produce a higher sheen. Penetrants are more acceptable since they allow any water present in the brick to exit the wall. However, penetrants will not provide graffiti-resistance to a wall while some films will.
Application of a water repellent does not negate proper brick construction and detailing procedures. Any deficiencies in a brick wall such as inadequate flashing, weep holes, mortar joints or broken brick should be corrected prior to the application of a water repellent. The wall should also be cleaned and allowed to th oroughly dry before administering a water repellent.
For additional information on water repellents, see Technical Notes 6A.