Thanks everyone, for the responses. I have been off the forum for a couple of days because we set the tub and repaired the hole yesterday, and last night I was exhausted. So I am just seeing some of these responses today. I am happy to announce that at Bill and Mongo's strong suggestion, and my own gut feelings and common sense, I had decided by yesterday morning to definitely go with the concrete. It just seemed to me that if concrete was there originally, it should go back in. The plumber's viewpoint was once the slab had been broken into, its former strength could not be restored by using concrete. Another guy said that mortar would 'adhere' better to the old concrete and was more supple... so if there was any 'movement' under the slab, the mortar would have more 'give' and be less likely to crack. The plumber seemed convinced of his viewpoint, but he was flexible. I told the plumber that I preferred concrete. He said OK. He got the concrete to set up quickly by 'layerin' it. It worked very well. I hope that's a good thing. Ventupete, the 'rebar' idea is brilliant, and you're right, he would have thought it was overkill. The plumber thought it was overkill to have my exterminator over there to treat the soil in the open hole. You asked about the hole? It was kind of centered under the tub, with part of it extending out past the surround, in order to rework the plumbing. So the greater part of the tub was always resting on existing slab. BTW, does everyone know that exterminators recommend treating ANY infraction in a slab? They say that termite (subterranean insects that they are) will come up through even the tiniest hole in a slab and will be 'pigging out' on the studs in your home...you won't know a thing! If you are adding on to your home, treat the soil in the piers of your addition, BEFORE it is poured. True story. It happened to friends with their add-on. Thanks again for the input. We successfully have a tub in place. I would call that a small miracle. :)

Thanks, brickeyee. There are other factors, which is why I'd like to know if there was a preference from a plumbing perspective. The ceiling is popcorn in an open floor plan, not conducive to spot repair. It might be better to cover the whole ceiling with 1/4" to get rid of the popcorn, rather than just a repair. Then I could put in can lights at the same time ... another plus, but also another expense. I've done drywall ceilings myself before, but that was 15 years ago. Hiring someone would be necessary this time cause I'm so old. The ceiling isn't damaged right now, just stained a little, so priming and painting would probably fix it. It's about 700 sq. ft. I have no idea what it would cost to have it covered with 1/4" and mudded, but that would probably be the way to go. The bathroom floor is original sheet vinyl, in need of replacement. Plus, the geniuses who put it in used nails rather than screws to attach the plywood subfloor. The nail heads have poked through in a couple of places. If I pulled up the floor, I could replace the nails with screws, and put down new vinyl or tile. I did my kitchen with TrafficMaster Allure a few years ago and love it. No problems, and it still looks like new several years later. It's about 100 sq. ft. I could fix the floor of the bath myself. That makes three checks in the floor column. It's a tossup as to which would be the better upgrade. Both are on the "eventually" list.

Hi Sophie, I have seen the "wrap" you link above. This is not a option for me. It would cover the window. And it is very flimsy. But the replacing the plumbing is a great idea when I do the other walls. But I can only focus on the back wall right now due to budgeting issues. Safety first, looks laters. BTW the laminate on the wall was put in by the original builder did remolding in the late 60's. I have alway used a back shower curtain to protect the back wall, The whole bathroom walls are covered from floor to 4 ft with this same color laminate/Formica. I know ---I need to get you guys better pictures. Also the original builder was a farmer who built it for his son- in- law. Not a professional. He cut corners and did not spend any money to do things correctly. I have over the years correct some major mistakes, but now I can not. All I can do is simple stuff.

What kind of primer would you use? I removed the shower floor tile and thinset today. Under the thinset which was about 1-1 1/2" was a ~1/4" thick liquid rubber barrier. Below the rubber was very wet and weak mortar/cement of some sort which was again separated from the actual slab by another layer of that rubber. Is this normal? I haven't removed the bathroom floor tile or the buildup that is underneath it yet. the second photo shows how thick the thickest part of the mortar bed was...