Acoustical tiles with thermoplastic covering sheets and interlocking tongue-and-groove edge connections

Claim 1

AN ACOUSTICAL TILE CONSTITUTED OF A RECTANGULAR POROUS BOARD WHICH IN THE DIRECTION OF ITS THICKNESS CONSISTS OF AN UPPER RECTANGULAR PORTION THE SURFACE OF WHICH IS DEFINED BY BEVELED SIDE EDGES AND IS INTENDED TO BE EXPOSED WHEN THE TILE IS LAID AND A BASE RECTANGULAR PORTION, SAID UPPER PORTION BEING OFFSET RELATIVE TO SAID BASE PORTION TO PROVIDE FLANGES INTEGRAL WITH AND ALONG TWO INTERSECTING SIDES OF SAID BASE PORTION, TONGUES INTEGRAL WITH AND ALONG TWO INTERSECTING SIDE EDGES OF SAID UPPER PORTION, WHICH SIDES ARE OPPOSITE THE RESPECTIVE SIDES OF THE BASE PORTION HAVING THE FLANGES THEREON, SAID TONGUES BEING POSITIONED JUST BELOW THE BEVELED SIDE EDGES, THE SIDE EDGES HAVING SAID FLANGES THEREON HAVING THEREIN GROOVES POSITIONED JUST ABOVE SAID FLANGES, WHICH GROOVES ARE EACH CONSTRUCTED AND ARRANGED TO RECEIVE A TONGUE OF AN ADJACENT TILE WHEN LAID, AND A THERMOPLASTIC SHEET COVERING THE FACE OF THE UPPER PORTION BONDED TO THE BEVELED SIDE EDGES THEREOF BUT NOT TO THE FACE, SAID THERMOPLASTIC SHEET BEING SHAPED TO CONFORM WITH THE SHAPE OF THE UPPER PORTION SO AS TO BE BONDED TO SAID BEVELED SIDE EDGES SMOOTHLY AND UNIFORMLY WITHOUT BULGES AT THE CORNERS OF SAID SIDE EDGES, SAID THERMOPLASTIC SHEET HAVING A NARROW OVERHANG EXTENDING OVER THE UPPER PORTION ONLY OF THE MOUTHS OF SAID GROOVES.