Percival P. Cassidy wrote:
We have some retaining walls built using railroad ties. I don't know how
long they've been there, since they were already in place when we moved
in, but they are beginning to look as though it's time to replace them.
If we replace them with new (actually old) railroad ties, how long are
the new ones likely to last? What kind of timber is used for railroad
ties? Anything we can do to make them last longer? -- creosote? The
bottom course is actuually below ground level.

We are thinking seriously about using interlocking concrete blocks
instead. Any thoughts on those?

Perce

There are RR ties and then there are RR ties. They are made from all
kinds of lumber. I have 300 ft of retaining wall built from basically
cull RR ties that is still standing after 20 years but I am surprised.
I have posts that I just pulled after about 20 years in the ground. 3
of 5 were too rotted to reuse (one fell over, rotted at ground level).
2 would still grade #1.

Harry K