Preparing an External Wall for Painting

[timclyma]

Hello.

Before I apply some masonry paint to an external brick-wall I would appreciate some advice on how best to prepare the surface.

The bricks seem in good condition.

The mortar however is very powdery and crumbles to the touch in some places.

What are the steps I need to take to get the wall ready for applying the paint?

Thanks for your help,

Tim