T-molding is a transition piece that is needed to adjoin laminate to another type of hardsurface flooring. It is used to meet up to tile, wood or other types of laminate. Here are the basics of how t-molding works and what it does for you.
Expansion
One of the main purposes for t-molding is to allow laminate to expand and contract. As temperature and humidity changes occur, laminate will expand and contract accordingly. Around the outside of the room, you have to leave an expansion gap to accommodate this. When you meet another floor, you cannot leave a gap to walk over. Therefore, putting a t-molding in the gap, will help cover it up and allow the floor to expand.
Professional Finish
T-molding also provides you with a professional-looking finish to the floor. If you do not install a t-molding, you will have an unfinished edge to walk over. Laminate is a floating floor and does not actually attach to the sub floor. Therefore, if you do not put a t-mold in where it meets where one flooring type meets another, there will be nothing there to hold the edge of the laminate down. A t-molding helps hold the laminate in place and keep it from coming up.
Source: www.DoItYourself.com