2 questions

[Mmll]

Hi Rip,
2 questions.
1. On page 635 of the Starting Strength ebook you said the rack should be fitted with a heavy plywood floor, 'reinforced with a welded crossmember under the wood'.
What does crossmember mean? Can you please explain exactly what it means to reinforce plywood with a welded crossmember? I know nothing about tools, building etc.

2. I havent got the space to build the rack as it is in your instructions. So I just put 3 sheets of 1200mm×2400mm×19mm plywood on top of each other and screwed them together, and put 15mm gym mats on top. Anyway it doesnt feel as good as a flat gym floor, because the plywood is slightly bowed. Builders here have told me all plywood in Sydney is slightly bowed...its not much but its enough to make me feel off balance. The concrete garage floor however is flat. So i was wondering if you think just putting 2 or 3 layers of 15mm gym mats on the garage floor, along with using bumper plates, would be enough to prevent the floor from getting damaged doing deadlifts of 180kg? And are they likely to bounce up a lot?
Thanks a lot.

[Mark Rippetoe]

1. A "crossmember" is a structural component that spans the distance between other structural components to reinforce the whole structure. In our rack, the crossmember is another piece of the C-channel the frame is composed of. You're actually standing on the crossmember when you stand in the middle of the rack floor.

2. The plywood is absorbing moisture, and it will "dish" where particle board will not. Flip the platform over every couple of months, and it will be flatter.