Concrete floor levelling & build-up questions

Hi All,

I am looking to refresh the flooring as part of a bungalow reno, and following some of your advice in another thread, my current plan is to:

- Strip & prep (leaving remains of current old bitumen tiles in situ). Tiles are likely to be ACM so I don't want to dusturb them if I don't have to;

- Pour self-levelling compound compatible with bitumen tiles & old adhesive (e.g. ardex NA). Apply liquid DPM;

- Build up some insulation (thinking that 20mm XPS is better than nothing) and a structural deck that will take laminte or LVT.

Your further advice is very welcome - I haven't done house renovation work that involved this amount of stripping back before, so would be great to double check I'm on the right track.

Step 1: Prep for levelling.

1) I believe the floor is suspended concrete. And I appear to have a hole in the floor. 

Poking it with a screwdriver reveals a completely rotten wooden batten running 12" from a wall, embedded in concrete. 

Would anyone have any idea why somebody placed a wooden batten into concrete? 

Grounds for nailing wooden flooring?

Plan: My kneejerk reaction is to patch the hole with mortar and forget about it, as I'm screeding and building up the floor above it anyway.

2) Rip out old wooden skirting grounds and install new ones.

Original grounds looked just like rough-sawn untreated softwood.

Any reason not to make my own grounds and rip a few 2x3 pine CLS lengths to size on a bandsaw, then pass through a thickness sander? Works out about 4 times cheaper than buying sized planed & squared strips. Not a big difference for 1 room, but for the whole house the costs will add up.

Will install the new grounds by screwing into masonry 400mm apart.

3) I've got very old plumbing chased through the floor. The channels were patched up with mortar, but one of them appears cracked & bits are loose. Old pipes must be steel or cast iron and removing them would be a bugger of a job.

Plan: break up the old chasing and patch with fresh mortar. Any issues with pipes rusting inside the concrete over the years to come?

3) Seal the room perimeter under the skirting grounds. Prevent any unwanted air gaps and prevent self-levelling compound from leaking out.

Low-expansion PU foam under the grounds, then cut back in line with the wall. 

Silicon dam in front of the doorway.

Q: Do I need closed-cell perimeter strips? Or would foam be sufficient to prevent the screed from escaping?

Thank you.