Abstract: The present invention relates to a filler injector for applying a filler to crevices in concrete surfaces. The injector has a transparent outer tube having scale markings thereon to indicate the pressure of any filler backing up from the surface and an adaptor connectable to a pressurized source of filler and screwed onto the outer tube. The injector also includes a check valve mounted in the adapter, an inner tube mounted inside a closed top of the outer tube and having a bore therein which can convey the filler from the adaptor to the surface, and a piston slidably mounted inside the outer tube and on the inner tube. The filler injector thus will not result in unwanted explosion, implosion, or skipping of a seam joint because of the pressure of the filler, and will provide a reading of the filling pressure on the concrete surface as the filler is being applied.