Portable apparatus for treating surfaces

In an abrasive throwing machine comprising an enclosure having an opening therein, sealing means around the periphery of said opening in said enclosure to contact a surface to be treated and to retard the escape of spent abrasive from said enclosure, means within said enclosure for projecting abrasive particles along an incident path through said opening to a blast zone on said surface and from the blast zone along an upward rebound path, said projecting means being oriented to establish both said incident path and said rebound path at acute angles relative to said surface, and means for returning spent abrasive along a spent abrasive recycle path to said projecting means, the improvement wherein said return means comprises a substantially unobstructed, elongated, recirculating chamber means connecting said blast zone with said projecting means for returning spent abrasive from the blast zone to the projecting means for re-use, said chamber means diminishing in cross-section from said blast zone to said projecting means, and means for providing a stream of fluid into said blast zone, wherein the energy of said rebounding particles and the force exerted on said particles by said fluid are together sufficient to carry said spent abrasive along said recycle path to said projecting means.