Hardener either 205 or 206 which will give you more working time. Brush the holes with the liquid epoxy
before mixing the colloidal silica in until it is about as thick as peanut butter. Place tape like duct tape over the holes on one side. Fill the holes with the thickened epoxy
and tape over the remaining side until it is set. This will prevent sagging. I sometimes tape a piece of plastic over holes as the epoxy
doesn't stick to it and when set it will leave a finish that requires little sanding.