yes you will need to thin especially if you are using a paint gun. The paint is usually too think on house pants and will clog the gun i would add a cap full to the paint and lift the stick to see how fast it drips down if it drips the whole glob of paint within 7 sec you should be fine under any circumstances do not add any watter to the paint it will ruin or get too thin then you would have to buy more paint. and if you are painting outside of the house i would suggest you power wash the whole exterior of the house let it dry then prime it with waterproof primer and then let that dry put two coats of primer. then i would paint the outside of the house the inside you would not need primer unless you are painting bare drywall. Note do not use lacquer thinner in a paint gun for home use it will ruin the seals. Use only mild paint thinner. Or the specific pain thinner that the gun says to use. When you are painting use fluid motions to paint the walls becareful not to let it run if it does you put too much.