The past tense of lay it on with a trowel is laid it on with a trowel.

The third-person singular simple present indicative form of lay it on with a trowel is lays it on with a trowel.

The present participle of lay it on with a trowel is laying it on with a trowel.

The past participle of lay it on with a trowel is laid it on with a trowel.