One of the joists under my bathroom floor has been damaged by water leakage. When i first seen it it was wet after soggy chipboard sitting on it i let it dry out then a building firm came and said it was ok and painted some green stuff on it. I am now putting down a new plywood floor so the joist has been exposed again, i was doing work in the area with a chisel and a top layer of the joist was just flaking of. I seemed to get rid of this loose top layer which in parts could be around a 1/4inch deep and the damage is about a foot in length. Is there any treatment i can apply to the joist to stop any further deteriation and is the a suitable filler i can use to level the top of the joist after treatment. The joists are substantial things 7 1/2inch deep and this damaged joist has a second joist butted up to it and the two have the partition wall resting on them.