The undercoat acts as a preparatory coating on the guttering surface increasing the stickiness and durability.
How to paint gutters with a brush.
You can also apply a thin layer of top coat with a paint sprayer if you d prefer.
For more see how to clean the outside of gutters.
Apply primer after cleaning your gutters and leaving them dry for an entire day you can start applying a coat of primer.
Apply a thin layer of top coat with a paintbrush or a sprayer.
If the gutters are not clean before you paint them the paint will not stick.
Use a small amount of top coat on the paintbrush so it spreads thinly on the gutters.
Correct any runs in the paint using the brush.