Scoring plaster to look like ceramic tile

Tool is made for scoring plaster.

Tool is made with a finish nail and a 2x4 block

Thanks to a reader from Iowa for a great question
Years ago, I worked with an old plasterer named Roland on an old hospital remodel in Richmond, Virginia.
More about Grace Hospital here...
Grace hospital was built right after the turn of the century when plaster scored to look like ceramic tile was popular. The finish plaster for most of this was Keene's cement. The reason I know this was from Roland, and also the evidence of a super hard water resisent plaster.
Roland showed me how to make a simple tool to score the tile that allowed us to match the old walls on the money.
A couple years later We worked on an old mansion remodel on Monument Ave. in Richmond. The old walls in the bathrooms were scored like ceramic tile. A cool thing was when the sink was removed, behind the sink someone had written with pencil "So and so name plastering 1903"
I am positive they used Keene's cement, because Roland told me he was sure it was Keene's. Keene's sets slow and allows large areas to be done. Keene's also is hard and water resistnt, as evidenced by how these bathroom walls were still in good condition after almost 80 years.
groove is adjusted by bending the nail

A one by four is used for a straight edge. The depth of the groove is adjusted by bending the nail.

Scoring plaster

Plaster is scored, dipping the nail in a water bucket every pass.

Sample board.

I made a sample board, because I haven't had a job doing this in 16 years. This really takes two people: one to hold the straight edge and one to score. The groover can also be made by cutting off the head of a nail, depending on the width desired.

I am glad to share this info I learned 40 years ago from someone who learned many years before.