Perhaps standing water, or subsurface water ingress? I am not sure, but I can tell you that I've never seen it being a problem. Also, I know a number of the formwork tie systems are actually "rust-proof" alloys, such as Zamac. That would address the issue directly, and do bear in mind that concrete itself is a very good rust inhibiting environment (at least until carbonation sets into any depth to speak of).
The ACI position on tie hole patching is: "Tie holes should be plugged or the exposed metal portion of the tie sealed to prevent corrosion or possible staining of the surface, except where stainless steel form ties or fiberglass ties are used."
See paragraph 10.2 of Cast-In-Place Architectural Concrete Practice (ACI 303R-04):
I don't permit or use ferric metal chairs. The noncorrosive options are too cheap and plentiful to allow a potential corrosion source to be unnecessarily added to the job.
Current practice is to patch or plug form tie holes in order to prevent ingress of moisture and corrosion of remaining tie components. While the ties are not necessarily connected to reinforcement, the tie itself can corrode and expand, resulting unsightly if not deleterious spalling. Is it really needed? I guess it depends upon exposure and the owner's reference.
ACI 301-10, section 2 on formwork says:
2.3.2.6 After ends or end fasteners of form ties have been
removed, repair tie holes in accordance with 5.3.7.2.
and section 5:
5.3.7.2 Repair of tie holes—Plug tie holes except where
stainless steel ties, noncorroding ties, or acceptably coated ties
are used. When portland-cement patching mortar conforming to
5.3.7.4 is used for plugging, clean and dampen tie holes before
applying the mortar. When other materials are used, apply them
in accordance with manufacturer’s recommendations.
As to the use of wire bar supports, supports should be selected as needed for the purpose and exposure expected. CRSI RB4.1 outlines the requirements (this is the updated, ANSI version of chapter 3 from the CRSI Manual Of Standard Practice.)
I have never seen any project where tie holes were cleaned, moistened and patched. They seem to be describing an SSD condition in preparation for repair. If not handled seriously, this is only going to make the condition worse. This appears to be a change for change's sake and not of value. It is certainly not in keeping with international practice. Sounds like the kind of wording I would expect if an engineer from the manufacturer of a form tie system sat on the ACI 301 committee.
Most tie systems are noncorrosive, and ferric metal ties usually cost more than their noncorrosive equivalent. A solution in search of a problem and a problem incredibly easily avoided.
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