Thinning latex paint is the process of adding a liquid to the paint in order to make it easier to apply. This can be necessary for a variety of reasons, such as to make the paint easier to brush or roll on, to reduce the appearance of brushstrokes, or to make the paint more suitable for spraying. There are a number of different liquids that can be used to thin latex paint, including water, paint thinner, and Floetrol.
The most common liquid to use for thinning latex paint is water. Water is inexpensive and readily available, and it does not alter the color or finish of the paint. However, water can weaken the paint film, so it is important to not add too much water. A good rule of thumb is to add no more than 10% water to the paint.