You need to get a rub brick for any type of ledge except marble or granite, you need to use the rub brick on the ledge, you need to blow or beat the dust off and you probably need to repeat those steps, then you need to spraypaint a think layer of clearcoat on the ledge and you need to wait for that to dry, then you need to wax the hell out of it. If you do all this, the ledge might as well have angle iron on it for how smooth it will grind.