If you are not designing the site, I highly suggest not using a grid or any other tools that would alter the design (proportionately or otherwise). Leave the design to the designer, and handle development, trying to get your finished design as close as possible to the finished mockup from the designer.
Nother irritates me more than when I have handed off a design to a developer, and he "adjusts" it because of some improvement he thought relevant.
If your designer doesn't use a grid, talk to him about it. If he prefers to continue without a grid, then don't force a grid on his design.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…