Why is the white-bottom deck on my job covered with red streaks across the bottom?

Why is the white-bottom deck on my job covered with red streaks across the bottom? Exposure to the atmosphere for your composite steel deck has caused the uncoated panel ends and edges to rust and moisture has carried that rust-staining to the interior of the bundle.

 

How does this happen?
Red Rust on White Bottom DeckIt is important to understand that when a metal deck is ordered with a white bottom and no other qualifiers, that means the deck will be supplied with a white primer over bare steel. When the white primer is applied to the deck coil, it does not coat the edges of the coil, nor does any paint cover and protect the cut ends. A bundle of tightly-nested deck sheets draws water inside and traps it, bringing rust stain from the ends and edges into the bundle. As we discussed last month, it does not even have to rain on the bundle for moisture to get inside. Condensation can also spread rust stains and trap moisture inside a bundle of deck.

 

Can I repair it and still use the deck?

Probably not. It’s like spilling ketchup on your white shirt. How can I prevent this in the future?

1. The BEST way to prevent red stains on white bottom deck is to order galvanized AND painted white deck. The ends and edges of the deck will not rust, nor will scratches in the paint. Yes, it is more expensive than deck with white primer only, but it will quickly become more economical if you’re trying to figure out how to get red stains out of 1,000 SQs of roof deck!

2. If for some reason option 1 is simply not an option, at the very least you should:

a. Spray paint the ends and edges of the deck with a white primer.

b. Follow the SDI guidelines for proper jobsite storage (see below).

c. Install the deck as fast as humanly possible.

Steel Deck Institute Guidelines for proper jobsite storage (re-printed from last month for your convenience):

1. Store the deck off the ground.

2. Elevate one end of the bundle to provide drainage.

3. Cover the bundle with a waterproof covering, but allow ventilation at each end of the bundle to avoid condensation.

Recommendation for Protecting Deck Bundles at Job Site