The question of whether plaster on a wall is part of the “structure” (and therefore part of the landlords duty to keep in repair under section 11 Landlord and Tenant Act 1985) has been a long running one.
Background to the question of whether plaster is part of the structure
In Quick v. Taff Ely Borough Council  QB 809 the landlord council conceded for the purposes of the appeal that the plaster in the house was part of its structure and so that decision provided no authority on the point. In Staves & Staves v. Leeds City Council (1991) 23 HLR 107, a decision of the court of appeal, a like concession was also made by the landlord council. Given the concession, that case also cannot be regarded as authority on the point. In Niazi Services Ltd v. van der Loo  1 WLR 1254 an issue came before the court of appeal as to whether plasterwork forms part of ‘the structure’ of a dwelling-house within the meaning of section 11 of the 1985 Act. Having recognised it as a difficult question, the court decided not to answer it.
The point was, however, the subject of decision by Mr Recorder Thayne Forbes QC in Irvine v. Moran (1992) 24 HLR 1;  1 EGLR 261. The lease there in question was one to which section 32 of the Housing Act 1961 applied, but section 11(1) of the 1985 Act is, so far as material, in identical terms. Before the judge were preliminary issues as to which of several items – including ‘internal wall plaster’ – were part of ‘the structure and exterior of the dwellinghouse’ and so within the landlord’s repairing covenants imposed by section 32 [now section 11 L&T 1985]. Mr Recorder Thayne Forbes was guided to some extent by and followed the approach suggested by Lord Justice Megaw in Campden Hill Towers Limited v. Gardner  1 QB 823, and said this:
‘… As I have said, section 32(1)(a) and the words “structure of the dwellinghouse” mean something less than the dwellinghouse overall and limited to the essential material elements that go to make up the structure of the dwellinghouse. It seems to me that internal wall plaster is more in the nature of a decorative finish and is not part of the essential material elements which go to make up the structure of the dwellinghouse. I therefore hold that internal wall plaster and, for the same reasons, the door furniture do not form part of the structure of the dwellinghouse, bearing in mind I have held that those words mean something less than the overall construction.’
Until now therefore this was the general consensus namely that plaster was not part of the structure and was “more in the nature of a decorative finish”.