This topic has come up a few times with limited resolution. In our case, both the sandblaster and a general contractor told us that we 'MUST' seal the block on our sandblasted house.
So...I went to Cohills (http://www.cohills.com/
) - a local company that sells a lot of concrete 'stuff' - coloring to mix in with cement, acid stain, sealers, you name it.
The professional opinion of Tim the cement guy is that a sandblasted home in AZ ‘should’ be sealed, but does not ‘have’ to be sealed.
Sealing will close up the pores of the block, making it more impervious to the elements (maybe it's me, but isn't concrete pretty dang impervious to the elements?), and less likely to accumulate dust (yeah, like we aren’t used to that after the dang blasting) as well as minimize the water migration into the home. If there was a bad monsoon or you have part of your house that gets a lot of water exposure when it rains, this is probably a good idea.
They had multiple products – ‘sealers’, ‘water repellent sealers’, and ‘waterproofers’. He suggested getting a water repellent sealer, which is about $25 a gallon – coverage of approx. 300 square feet per gallon if using an airless sprayer, 200 if using a garden sprayer (although they recommended airless).
So…there you have it. We’re going to do it as a preventative measure.