Hi
1. One way is to change the material.
2. Another way is to remodel the Planks using " Curtain Wall "
3. you can even use a wall, Edit profile .. something like this... this will solve the material issue.
One wall, edit profile... needs to manually copy the profile ( not arrayed ) but it takes few clicks when you double up... 2, 4, 8, 16, 32, 64 .. few copy commands will get you enough numbers.
Corsten
Building Designer