We're getting ready to paint the exterior plaster detailing and trim on our 1934 Spanish Revival house in Los Angeles. Should we use a wire brush to loosen the old paint as we prep the plaster? The existing paint is in good shape - I think the previous owners did a quick paint job before they sold last year. My concern is that the wire will leave "scratches" on the surface of the plaster. Would sanding it be a better choice? We're in an historic home and I don't want to do anything irreversible.