Wall and Floor Join still have solid line after joined

[Anonymous]

Hi everyone, 

Although I have join wall and slab but it still have the solid line between wall and floor. My wall and floor have the same material ( by category). I have check in default template of Autodesk, wall & floor are joined normally. I have attached the picture for your reference. Please help me solve this problem, thank you very much.

[artejon]

Check under Object Styles what these 'by category' materials for floors and walls are, I guess they are different while they should be the same to avoid lines at joins.