Green’s Dictionary of Slang

1. (Ulster) an untidy woman.

1910		P.W. Joyce Eng. As We Speak It In Ireland.
1928		L. Mackay My Oul’ Town 82: Don’t take the book by the cover. There’s many a swell of a girl has in her the makin’ of a ‘clart’.
1979		J. Morrow Confessions of Proinsias O’Toole 109: I just called her a dirty clart and shattered her eardrums with the loudest tongue-fart I could muster.
2015		I. Welsh Decent Ride 260: Oh God . . . thir comin fir us . . . they clarts fae Daft Kids ur comin fir us.

2. sticky excrement.

1997

Roger’s Profanisaurus in Viz 87 Dec. n.p.: clarts n. Tacky excrement, such as would cling to the lavatory bowl above the water level rather than slip into the water.