Designing Kitchens and Bathrooms - After removing tile from concrete at back wall of tub HELP PLEASE

The tiles from the back wall came off easily and the concrete and mesh are in tact. After struggling with all the other walls to remove everything, my husband and I are looking for shortcuts.
The thin set is still attatched to the comcrete, we were wondering if we could re-tile over this portion of the wall, if so would we have to do a skim coat first? And how would this affect the tub, because of course the wall would be thicker?

If the wall in question is a concrete wall, thin set will adhere to it very well. The issue will be in getting the tile surface flat with all the old thin set on it since my guess is, it's pretty much like the surface of the moon right now. Chipping it as flat as you can get it is the best solution of course, but, provided non of the old is loose and the added thickness is not an issue, I suppose you could float it out. In a mud set, wire mesh is used for strength and to keep the mud in place as it sets up. If you're talking about a large amount of float, you may want to consider that. Perhaps getting the worst of it off and then floating would be a happy medium. If the section of wall being discussed is a mesh and mortar mud set and you decide to use that section of wall instead of replacing it, I'd recommend a waterproofing membrane coat over the entire shower before tiling it. There may be cracks in the existing that you can't see.

It is a mesh and concrete wall. we were thinking maybe we could put up a thinner durock over it, is that what you meant by a waterproofing membrane?
Thanks.

No. I'm referring to some thing like Red Guard which is a trowel on product that coats the whole shower with a water proof membrane. If you use it, there is one step not mentioned in the instructions I would recommend. The stuff is very thick and tends to sit on the surface rather than soak in and bond well. Dilute some three to one with water, the one being red guard, and paint it on. The diluted version will soak in and get a good bond. Let it set up and then trowel it on full strength, following the instructions. It goes on pink and drys bright red. When it's dry, it feels like plastic and is very water tight. There are other, less expensive versions on the market, but I haven't experimented with them. I know this stuff works well and, as Henry Blake said on Mash, "better the devil you know". It is also used as an anti fracture membrane and serves a dual purpose in a situation such as yours. As for the durock idea, I've never tried that and have no idea what the outcome would be. If I have to rebuild a shower, I rebuild it.

Have not viewed previous posts as to your project, but if you are tearing things out, go to the studs. I have never seen what you describe, apparently a previous DIY project, but tearing out to the studs gives you the oppertunity to insulate where there may be none. Green board is no longer something to put under anyhting that might get wet, it is a waste of time and money. Yes, there should be a moisture barrier on the studs, duroc or hardibacker should be the next layer, it you are doing tile. If it is a prefabricated shower/ tub enclosure, follow instructions. Some say greenboard, some go directly on the studs.

I am assuming that JUSt BILL is replying to my latest question regarding the Tar paper that was behind the mesh and concrete.
I have read elsewhere that people say to use plastic or thin roofing felt as a vapour barrier under the Durock.
Does thin roof felt look like black paper? Where I am from I think tar paper and roofing felt are one and the same.
thanks.

What you're describing is an old mesh and mortar mud set. They used tar paper behind the mesh and mud. There are still installers who know how to do them, they're the best way to go, but expensive and few want to pay for it. Concrete board was invented to get away from the expense and skill level required and still get a sort of similar installation. I know a couple old-school installers who still do mud sets exclusively. They were built to last and are a job to demo. You really do need to remove it all, but if you choose not to, you've got a few suggestions to consider.