I currently have a retaining wall made from PT Mini Ties and it will need to be replaced. I am wondering if I replace it with PT 6x6 if I can put a PT fence directly on top of it to get a clean finished look?
That's very vague, Tom, so I'm going to say no you can't. Based on the fact of the existing mini ties tells me it's a low retaining wall. That fence will create problems when the wind blows. How high will your fence be? You won't have any support for a proper 4 ft or higher fence. Because you gave no other information, I suggest drilling the holes for the fence posts, then laying the 6x6's between the post, then build your fence. And to make it look good, use 6x6 fence posts, too.
I tend to agree with Mike. More information is needed but regardless, you need some posts penetrating the ground to support the fence. The height of the fence and the style both make a difference as well. Wind and the weight of the material contribute to stability of the finished product. Do it properly and get basic plans on line. Just Google building a fence.
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