Question
I HAVE PLACED AN UPLAND RETENTION WALL ON MY PROPERTY. IT IS MADE OF RAILROAD TIES WITH (CRESOL?). THERE ARE SPACES, HOLES THAT NEED TO BE FILLED IN BEFORE I CAN PLACE DIRT BEHIND IT. WHAT WOULD BE THE BEST AND MOST DURABLE COMPOUND TO FILL IN THE HOLES.I WOULD LIKE THE WALL TO BE STANDING A LONG TIME. I WOULD LIKE TO COAT IT WITH SOMETHING TO HELP INSURE A GOOD AGE FOR THE WALL  THANK YOU    BOB

Answer
If you want the wall to be standing a long time don't use railroad ties. They can last up to 20 years but often fail much quicker. If rebuilding the wall is not an option then make sure you back fill the wall with at least 6" of gravel all the way up to the top and be sure you put a drain at the bottom. Ground contact with water and soil are what speed the decay of wood walls. The gravel will ensure the water moves down and away and does not set into the wall and keep it soaked. You may also want to place a 10mil  poly plastic sheet against the side of the wall between the gravel and wood as an additional precaution.
If there are holes fill them with concrete and stain it to match the ties when it becomes visible.

Good Luck


Sean J Murphy, LA,ISA, LEED AP
Please check out my blogs and articles on landscape topics like this on my websites.
http://www.seanjmurphy.com
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