You will need to create a relationship from the field that you enter in the IDs for the finish fkWallFinishID to a table occurence of the 'wall finish' table if you havent already.
Then you have couple of options. You could use a portal to display the related wall finish info or you could create a calc in your parent table ( you didnt specify the name ) of: Substitute ( List ( WalFinishTableOccurence ); "¶"; ", " ) ). This will create it on one line with commas.
Showing it in a portal worked just fine for me.