I have heard that some people have coated brick with silicone in the past to improve their IRA. This sounds like a good idea and I wondered why it wasn't done more often. Are there any problems with coating brick with silicone?
There have been some studies on the treatment of brick with silicone, including one reported years ago by the National Research Council in Ottawa, Canada. They found a potential increase in bond strength, a reduction in efflorescence, and better resistance to water penetration in walls built with treated brick compared to those built with untreated brick. Treating the bedding surfaces of high-IRA brick with silicone is an alternative to wetting the brick to improve bond. However, it's important that the treatment be confined to the bedding surfaces only, and that the silicone coating be applied uniformly. Silicone on the brick faces may trap water within the units in use, leading to deterioration from freeze/thaw cycles or salt crystallization. If the treatment is not uniform, some bricks may have reduced bond due to overtreatment or undertreatment.