Go to your local Home Depot and buy this Quartz infrared heater http://www.thethingsiwant.com/item/1354218/ It's $30 bucks and works great for spot heating in a cold garage. Put it about a foot away from the block for 30 minutes then switch it to the other side for 30 minutes. Block should then be nice and toasty. Spray away, let the paint flash and put the heater back on. This time keep it a little farther away, rotate to the other side, keep this up until the paint is dry.