Financial Times 13,444 – Flimsy

Quite probably the most anodyne set of grid-entry words I’ve ever encountered (21A is the only answer that could even remotely be considered specialist or unfamiliar).  But that by no means necessitates a similarly low-falutin set of clues.  Simple words can still be clued with well-disguised definitions (10A, 8D) or via entertaining surfaces (22A, 20D).

Across
1 CONSTRUCTS – con + (c in strut) + s.
7 EATS – {b)eat + s(on).
9 ISLE – is L + {Cruso}e.  A very laissez faire construction in a couple of regards, but some rigour was probably sacrificed at the altar of including the various Castaway elements.
10 GUARANTEES – (guest near a)*.  ‘Stranger’ being a somewhat superlative anagrind.
11 CRISPS – crisp + S.  My last entry, due to mid-atlantic interference (“potato/potahto”) when trying to think of a six-letter snack.
12 ACROBATS – (a bar + cost)*.
13 MERRIEST – me + (r in tries*).
15 ICES – hidden.
17 ASIA – Si in aa (=’volcanic rock’).  A rare venture outside of the realms of barred cryptic puzzles for this setter-friendly lava deposit.
19 REACHING – {p}reaching.  ‘Pastor’= p was new to me.
22 CURTAINS – c + (train* in us).
23 DETAIL – de-tail.  This pun is more usually found within a clue’s wordplay itself, rather than as an answer in its own right.
25 ACCOMPLISH – (MP + colic has)*.
26 PLOT – l in pot.
27 USES – E(nergy) in USS.
28 NOSY PARKER – (a pryer knows)* – w.  ‘Gossip’ here is the agent, rather than content, of the tittle-tattle.

Down
2 OBSERVE – (verbose)*.
3 SPECS – {poseur}s + pecs.
4 REGISTER – double def’n.  The roll-call in British schools – as exemplified here.
5 CHARACTERISTICS – (each is + strict care)* – E.  I enjoyed the use of ‘half cut’ (i.e. one-and-a-half sheets to the wind) as an anagrind.  And the ‘logs’ in question are logarithms.
6 STAIRS – {Conservative}s + (a stir)*.
7 ESTABLISH – a in (his belt’s)*.
8 THEATRE – (a t{reat}) in there.  This one hinges upon unpicking the near-invisible seam within ‘ham sandwich’.
14 REACTIONS– (I can store)*.
16 HARDSHIP – hard + ship.
18 SOURCES – homophone of “sauce” + s{on}.
20 NOISOME – (o + M) in noise.
21 PIPPIN – pip + pin.
24 TAPIR – I in (trap)*.