1
general::
Also, lay it on with a trowel. Exaggerate, overstate; also, flatter effusively. For example, Jane laid it on thick when she said this was the greatest book she'd ever read, or Tom thought he'd get the senator to waive the speaker's fee if he just laid it on with a trowel. This idiom alludes to applying a thick coat of paint or plaster. [c. 1600]
American Heritage Idioms
2
general::
Phrase(s): lay it on thick [and] lay it on with a trowel; pour it on thick; spread it on thick
Fig. to exaggerate or overstate praise, excuses, or blame. • Sally was laying it on thick when she said that Tom was the best singer she had ever heard. • After Bob finished making his excuses, Sally said that he was pouring it on thick. • Bob always spreads it on thick.
McGrawhill's American Idioms And Phrasal Verbs