Many of the rights under the Party Wall Act are very wide-ranging, and have the potential to catch many building owners unaware. For example, the right under section 2(2)(a) to “thicken” a party wall might well include plastering the wall becuase it increases the width of the wall, or the right under section 2(2)(f) to “…cut into a party structure for any purpose…” might well include cutting in chasings, or even drilling into the wall to insert screws.
Historically it was thought that the legal doctrine “De Minimus Non Curat Lex” (that is, the law does not concern itself with trifling matters) applied to this type of works; that is, the works were so small and trifling that the Party Wall Act did not apply.
In the case of Grand v Gill  EWCA Civ 554 the Court of Appeal held that:-
“…plasterwork generally, including that applied to external walls, as being ordinarily in the nature of a smooth constructional finish to walls and ceilings, to which the decoration can be applied, rather than a decorative finish in itself. I would therefore hold that it is part of the ‘structure’…”
If the plaster is part of the “structure” of the wall, does this mean that work that involve the plaster are notifiable? No necessarily.
First, that case concerns housing disrepair, and not the Party Wall Act, and the Court may distinguish it on that ground alone.
Further, it does not automatically follow that, just because the plaster is a party of the structure of the wall, the works are notifiable.
Whether the works are De Minimis or not depends on the nature of the works, which is a question of fact and degree in each case. Drilling a 8mm hole half an inch into a 9 inch brick wall may well be De Minimis. Contrast this with, say, cutting a 3 inch chase into a 6 inch wall, which could not be described as trifling.
There will, of course, be many cases where it will be unclear; in those situations the most sensible course of action would be to discuss the matters with your neighbour, and getting them to agree to the works. If there is any risk of causing damage to the neighbouring property then it would be sensible to have a surveyor produce a schedule of condition of the next door property, so you have a record of the condition of the wall against which any alleged new damage can be compared
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