A joint between core pieces is an internal construction detail. Its location and proposed treatment need to be defined before the skins close the panel. An uninterrupted outer face does not show whether the core underneath is one piece or several joined pieces.
Show the core layout
Identify each core piece, its material and the intended seam location. Include changes of thickness or material where they meet the joint. A skin drawing alone may not communicate those boundaries. If the supplier prepares a core kit, retain its layout reference with the panel definition.
Review the proposed joint treatment
Diab describes core finishing and preparation in relation to form and processing requirements. For the actual seam, ask the supplier to identify the proposed fit and any specified bonding or filling material. Do not treat an unspecified gap as harmless or select a universal filler from a generic sandwich sketch.
Keep the detail with the sample
The represented panel sample should retain the core layout and seam treatment alongside its skin construction. If the core is split differently to suit stock or tooling, record the revised proposal. Agree the required inspection while the detail can still be understood in its manufacturing context. The internal seam review is separate from the decision to join two completed panels in the final equipment.
Further reading: Diab: core finishing and construction review.