Green’s Dictionary of Slang

plaister of warm guts n.

sexual intercourse.

c.1698		B.E. Dict. Canting Crew n.p.: Plaister of hot Gutts, one warm Belly clapt to another.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Plaister of warm guts. One warm belly clapped to another; a receipt frequently prescribed for different disorders.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1988		J. McDonald Dict. of Obscenity etc. 67: As far back as the eighteenth century we have [...] plaster of warm guts.

In phrases

do a plaster of warm guts (v.) (also get a...)

to have sexual intercourse.

c.1698		B.E. Dict. Canting Crew.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1896		Farmer Vocabula Amatoria (1966) 16: Appliquer un homme sur l’estomac (s’) = to receive a man; ‘to get a plaster of warm guts’.