Ideally, you’ll need 3-4 continuous days without rain if you are doing this outside. It can be done in three days, but you’ll have to stay on top of your timing.
You’ll need to figure in drying times after washing the blocks, then priming, flipping the blocks, painting, flipping and then repeating for one more coat.
Why Paint The Cinder Blocks?
The reason you should paint the cinder blocks is that it will help preserve the wood posts. By painting the blocks, you are waterproofing them.
If they aren’t painted, they are absorbing water, so the wood will be sitting in holes that are constantly wet when it rains.
Even though the posts will be stained and coated with urethane, they will be much more likely to rot. Painted cinder blocks will dry much more quickly and wick away much of the water.
How to Make a Cinder Block Bench Step by Step Tutorial
Step 1. Wash The Cinder Blocks