I hope this is the right forum for this. I have a wood retaining wall made of creosoted timbers, about 5 feet high and 60 feet long. A few of the timbers have rotted and curled outward; I was able to get them roughly back in place with lag screws and washers, but there are some voids that can collect water. What would be a good product to fill these cavities--mortar mix, Sacrete, or...?

(Replacing the wall at $24,000 is out of the question.)