Possible Clues:

• Thin wood strip supporting plaster
• Strip of wood machine cut short
• A thin strip of wood as for making furniture
• Plaster's backing
• Leveling strip
• Foundation for plaster
• Latticework
• You can't say it's a bit thick to make it with soap on 'er
• The thin way to get ''er soapy
• _____ and plaster