Our roof doesn't have felt underneath the tiles. The 'cement' that was put onto the underside of the tiles is old and crumbly, thus covering everything in the loft space with muck. The roof will be redone in a few years, but in the meantime I'd like to staple something on the underside of the roof beams - removing all the loose cement would take absolutely ages. What would be best?..I thought of either roofing felt or heavy duty plastic