Abstract: A handtool for the application of sheet materials to surfaces, specifically the application of wall coverings to walls, is of obtuse angle triangle shape, with a knife blade at each base apex, the tip apex being rounded for folding the sheet into a corner and the edges adjacent the tip constituting guides for the respective knife blades. One blade may be circular and rotary with the guide edge tangential thereto, while the other blade is triangular with the guide edge colinear with the cutting edge. The circular blade may be toothed with a recessed cutting edge, while the triangular blade may be equilateral to provide six cutting edges by transposition and reversal. Two similar guides are provided on opposite sides of the body slidable in guideways between a retracted position and extended positions in which they lie alongside the knives to guide their cutting with respect to a surface engaged by the guide.