I have an old (1920’s) home constructed out of Rock Face block (Cinder). They are very porous, irregular and stained (rust, etc). They have never been painted and I would like to spray the paint on the home. What is the best product to use on this surface?
You will need to spray a heavy coat of acrylic block fill primer and then <a href="https://www.house-painting-info.com/back-rolling.html">back roll</a> with a 1 inch or thicker lamb's skin roller. This will fill most of the pores. Now you can spray your paint. I recommend also back rolling the paint to help fill any remaining pores.
It is a good idea to pressure wash the block first to remove dust, dirt and possibly some stains.