Plaster-type products in your undercoat paint give your walls texture and hide flaws. All-purpose joint compound is the best product to use for this purpose. It is similar to plaster of Paris, but it will not shrink, crumble or crack the way true plaster can. Mixing your paint with joint compound lightens your paint colour. But this is an undercoat, so it is less important because the finish coat is the colour that shows. However, you should choose a finish coat that is close to the colour of the undercoat in case a scratch goes through to the undercoat.
Stir your latex paint thoroughly, and pour it into a large mixing tub.
Add a 2.25 litres (1/2 gallon) of joint compound for every gallon of paint in your mixing tub. Use only the premixed all-purpose form of joint compound. Other types do not mix well with paint and can dry too quickly or too slowly.
Add 1/2 litre (1 pint) of white glue for every half gallon of joint compound in your mix. The glue helps bind the paint and joint compound to each other and your walls.
Secure a paint paddle drill attachment to a drill. These paddles are wide, often wave-shaped blades with openings along the blades. Many look similar to ice cream maker paddles.
Put on safety goggles and latex gloves. Sink the paddle into the paint without immersing the drill itself, and turn the drill on its lowest setting.
Stir the paint as thoroughly as you can with the drill attachment, then reach into the mixing tub with your gloved hands and feel for any clumps of joint compound.
Break up any clumps you find with your fingers, and then mix the paint again with the drill attachment until it is smooth. At this point, it is ready to apply to your walls with a roller, brush, sponge or putty knife.