Wow. That is a mess. You have your work cut out for you. If you were going to use a semi transparent sealer of a different color you would positively have to strip that deck with something much stronger than RAD. If yu are okay with blotchiness (it may not even be too bad if you use a Cabot's decking stain). Back to the prep.. There is so much mold and it is so deeply ingrained you are going to have to let the RAD dwell for about 45 minutes and keep the wood saturated with cleaner the entire time. This will remove a decent portion of the sealer that is on there and make sure the mold spores are gone. Make sure you neutralize/brighten right away while the deck is still wet. Re-rinse. Let dry and apply Cabot's oil based penetrating deckin stain. It is a semi-transparent but it is opaque. Seacoast gray should cover the deck well and make it look pretty sweet.

David, As John said, you shouldn't overthink a pressure treated deck, as it won't look good for very long anyway. That said, you can still build it well and be proud of it when you're finished. I build higher end, using Ipe for decking, and this is how I frame for butt joints. I stagger the joints, and create a repetitive pattern. I sister joists wherever a joint happens, so each board lands on it's own joist. Butt joints are always problematic...I work with a caliper and a table saw to make sure that I butt 2 boards that have exactly the same width. You'll find out that 5/4x6 really means 1"x5 3/8 or maybe 1"x5 1/2". I rip the wider board to the same width of the smaller. Then there's the cut...the 2 boards need to meet at a tight joint. It's not easy, so I round over the tops of both cuts. It's more forgiving. If there's a slight gap, you won't notice it. Anyway, there is a lot to deck building that you can obsess about, but do you want to? I do, because I like to...I need to. Back to your question...I sister the joists together...no 1/2 gap. steve

Yes, it's pretty easy. Are the existing boards nailed or screwed down? If nails, pry the boards up; if screws, get a power drill and back them all out. Lay the new boards down, screw them in, maintaining a 1/8" gap, and you're good to go. There are some tips and tricks, but that's the gist of it. Composite boards often need closer joist spacing than wood (i.e., 12" on center instead of 16"). How far apart are your joists? If you post some photos, that might bring up other recommendations to share that apply to your specific deck.

We live on St.John in the Virgin Islands. Our average daily temperature is 84 degrees and never lower than 70 at night. It showers frequently and the deck outside of the short term rental apartment needs replaced. We added a treated wood deck to the rental apartment on the lower level of our home about five years ago. We are now having to replace deck boards and the surface was just painted with "Restore" by rustoleum to give it a few more months of life. We would like to use a non wood product to support and rebuild the frame then cover with Durarock as an underlayment to Travertine marble or a porcelain tile. Any advice appreciated. Thanks in advance. AlyceUSVI