Here it is Sir, in black and white, it should help:
From current
BS 6891:2005
Installation of low pressure gas pipework of up to 35 mm (R1¼) in domestic premises
(2nd family gas) — Specification
8.8 Pipes buried in concrete ground floors
8.8.1 Installation pipework shall not be buried in concrete slabs.
8.8.2 Rigid stainless steel pipework shall not be buried in concrete screeds.
Pipe buried in concrete screed shall be installed in accordance with Figure 5.
Where a pipe is buried in a concrete screed there shall be a minimum of 25 mm of cover above the pipe.
8.8.3 Pipes buried in concrete ground floors shall be protected against failure caused by movement. Joints shall be kept to a minimum. Compression fittings shall not be buried in concrete screeds or concrete slab.
COMMENTARY AND RECOMMENDATIONS ON 8.8.3
Suitable methods of protection are as follows.
a) Pipe laid on top of base concrete and subsequently covered by a screed (see also 9.2.1).
b) Steel or copper pipe installed into preformed ducts with protective covers.
c) Steel or copper pipe fitted with additional soft, non-permeable covering material. The coverings should be soft and thick enough to provide movement yet resilient enough to support the concrete cover while it is setting.
The covering should be at least 5 mm thick and resistant to concrete ingress which would negate its ability to allow movement.
Reference should also be made to 9.2.1 for the application of adequate corrosion protection.
9.2 Buried pipework
9.2.1 Internal environment
9.2.1.1 Pipework that is buried in a solid floor or wall shall be factory sheathed, or protected on site by wrapping or with suitable bituminous paint protection.
The entire section of pipe and fittings to be buried shall be protected. Any sheathing or wrapping shall be examined for cuts or other defects and made good prior to use. Joints and fittings shall be cleaned, and wrapped or painted with bituminous paint after the satisfactory completion of a gas tightness test.
Galvanized or painted pipes shall not be buried without additional protection as specified in the previous paragraph.
COMMENTARY AND RECOMMENDATIONS ON 9.2.1.1
Protective measures are applied as a precaution against electrolytic and/or chemical corrosion. The use of factory bonded wrapping or sheathing is recommended.
9.2.1.2 Where installation pipes are to be buried in magnesium-oxy-chloride cement or magnesite flooring, they shall be of copper with a factory bonded sheath and jointed with copper capillary fittings.
Bends and joints shall be further protected by wrapping with a suitable plastic tape. All surfaces shall be clean and dry before the additional protection is applied with a minimum 50 % overlap to provide at least a layer of double thickness.
