Water Repellent Masonry

What is an Integral Water Repellent? 

Integral water repellents are polymer based chemical admixtures added to Concrete Masonry units (CMU) during the manufacturing process. The water repellent is incorporated into the concrete mix at the plant to ensure that each block has water repellent distributed throughout the concrete matrix. 

Untreated masonry units readily absorb water through a process called capillary suction or wicking action. RainBloc anti-wicking action ensures that even if rainwater penetrates past the exterior face of the wall, RainBloc system water repellent properties minimize the amount of water that is absorbed into the concrete, causing any water inside the wall to flow to properly designed flashing and weep holes.

*Integral water repellents do not change the appearance of the units.

Will RainBloc prevent any moisture from entering a masonry building?

RainBloc is typically used in single-wythe masonry construction for additional protection to water ingress. Single-wythe masonry walls can provide the performance of cavity wall construction in a cost-effective manner. 

RainBloc is not a replacement for proper single-wythe wall design and construction.  A complete water repellent system emphasizes proper masonry design, details and implementation. Use of the RainBloc system provides an effective barrier to water intrusion and water wicking into  CMU by allowing any intruded moisture to fall down the interior of the cores and exit at the flashing weeps.  

However, even with the additional protection, designers of masonry walls must still expect and prepare for moisture to penetrate into the walls through defects, cracks or other means and incorporate water collection and draining details into the design. Proper flashing, weeps and movement joints designed and located appropriately to control cracking are essential. Of course it is also important for the mason contractor to follow the design specifications and drawings and apply good construction practices to their work.

View the RainBloc Product Data Sheet.


Concrete Masonry Structure Exposed to Wind-Driven Rain

Untreated Concrete Masonry Unit

  • Moisture can penetrate through concrete surface
  • Untreated concrete matrix has excess voids that moisture can penetrate into
  • Wicking action pulls moisture through excess coils and capillaries deeper into the concrete

RainBloc Treated Concrete Masonry Unit

  • Water repellent blocks moisture from entering at the surface
  • High quality concrete matrix reduces voids that moisture can penetrate into
  • Anti-wicking action reduces water movement in voids and capillaries

Can a post applied sealer or water repellent be applied to RainBloc treated masonry?

Yes, there are no incompatibilities between RainBloc and post applied sealers which are often used to provide additional protection in a “belt and suspenders” approach. 

Topical (surface) treatments are applied to the weather exposed side of the wall after the wall is in service.

Can paint be applied to RainBloc treated masonry?

RainBloc typically does not change the “paintability” characteristics of CMU, and therefore if untreated masonry units can be painted, the same will apply to RainBloc treated units.  Latex, acrylic latex, cementitious coatings and waterborne epoxies may all be used. Note that oil based paints (alkyls) are not recommended for any exterior applications and should be carefully tested before application in any masonry construction.


Is there a RainBloc treatment for mortar?

Yes, RainBloc for Mortar is specifically designed for mortar applications, and contains additives to improve the workability and water repellency of the mortar. RainBloc for Mortar does not affect the bond strength between the CMU and the mortar.

Can RainBloc for CMU and RainBloc for Mortar be interchanged with each other?

No, their formulations are different and they cannot be interchanged.

Can an accelerator be added to RainBloc for Mortar if needed during colder weather?

Non-chloride accelerator integral admixtures may be used during winter months when faster set times are desired.  Chloride accelerators are not recommended, as they can react with steel reinforcement and cause corrosion of the steel. 

To use an accelerator admixture, simply replace a portion of the mix water with the recommended dosage rate of non-chloride accelerator.

View the RainBloc for Mortar Product Data Sheet.


What does it mean to be RainBloc Certified?

RainBloc certified producers go through a rigorous certification process to ensure that performance of their CMU conforms to RainBloc standards for physical properties and water repellency. Certification must be renewed each year to ensure continued compliance. 

Is Masonry treated with RainBloc breathable?

RainBloc is not impervious to moisture and it does not form a film on the masonry surface. RainBloc is not a vapor barrier, and the masonry units remain breathable. 

What is the life expectancy of RainBloc?

RainBloc is designed to perform for the life of the masonry building. 


Contact Us for help finding a RainBloc producer.