Timber wall water proof

[hopper]

Building a retaining wall from 6x6 timber for parking pad. 3-4' high. I want to water proof the back side. Should I coat it? Or staple a membrane sheet to it? Or both. If anyone has suggestions please post em. The last one started to rot after 5-6 yrs. I will lay a drain pipe at base and back fill about a ft wide with gravel.

 

[earlthegoat2]

Sprayed on tar would be the best option.

Any layer that is not actually sealed and adhered to the wall will get moisture behind it.

Coating it in used motor oil would buy a few more years also.

Buying saltwater rated marine Timbers with 2.5% CCA would be a bombproof choice for material as well. Probably wouldn’t pass a DPH inspection but I assume no permits will be pulled.

You might be able to find 0.6% CCA Timbers used for pole barns. They might be more readily available.

 

[Pig Predator]

Put some of this on the backside before putting drain and fill back so mud won't constantly seep through the cracks between the timbers.