How do I seal and repair a composite wood porch

Sure looks like wood planks not composite, and part of the problem looks like they didn't space the boards with room to drain. I would start by scrubbing it clean with either a power washer, or using a real stiff brush and a deck cleaner. I used really hot water, detergent and bleach as I have just sand around and under the deck with a real stiff brush. This is the stuff I used, and it works great, be sure to use the stiff brush after rolling it on as it preserves the wood look.... http://defywoodstain.com/clean-seal-composite-decking/

This looks like plywood to me. I am not sure about it being out in the weather...but, hey I spray painted my bath tub. I love unusal stuff. Get a water proof stain and put on it. Clean it good first. What the heck it should last another year or two. :)

Actually looks like OSB (Oriented Strand Board). Usually use as roof or house sheeting. Not the proper product for a wood floor. Especially outdoors. It will swell and shred from moisture. Replace it with outdoor plywood, decking, etc.

I agree with the others, just a word of caution...the Rustoleum deck product has actually led to a class action lawsuit. It's awful. I used it. It peels up in sheets in some places, next to impossible to get off in others. Lots about this on the internet. You should replace your decking.

William is correct. That is OSB. It is never used for exterior decking....period. Do not waste your money trying to seal it etc. It needs to be removed before somebody falls through it!!! It will never be a solid surface. Replace it with proper decking. Home Depot or Lowes can help you find the most budget friendly solution.

Jeannie Atlanta, Ga

I agree with others this is OSB (oriented strand board). and replacing with proper deck product would be best. However, if you cannot afford it at this time, Give it a sanding to get rid of most of the black weathering and printing, then use an oil based semi transparent stain, this will at least soak into the board and provide some protection. We did this as a temporary (haha) solution on our untreated plywood deck and it lasted for more than 10 years, I think I recoated it once. Do not use waterbase stain or any paint as it lays on top and will just flake and peel. Good luck let us know what you do.

That's not composite. That's OSB and you shouldn't be walking on it. It's not proper decking. You don't want to repair and seal that garbage! Rip it out before someone gets hurt.