Rooftop deck repair questions

Question

I'm in the process of restaining rooftop deck. I first washed it with a deck cleaner product. I'm now in the process of sanding. I was hoping to ask a few questions:

1. I noticed a few areas where dryrot had set in. I'm hoping these are small enough that they can be repaired with a wood filler or bondo product. They're on the top edge of the 2x4s. The largest measures approximately 14x1 and is maybe a half inch deep (the affected area slopes). Is that possible? Is there any product recommendations?

2. After sanding the deck, I still noticed some very small areas where algae existed. Is it safe to paint over those or should I wash the deck a second time? Does washing the deck require me to resand? Each time that takes a few days and being in a rainy climate, my window to complete the staining isn't very long.

3. If there are very small cracks running the length of the wood, should those be filled before applying new stain?

Answer 1

Judging from the pictures you attached I would say that yes, you can extend the life of those boards a bit and no, you cannot save those boards- they will continue to deteriorate. What you are doing is good (and necessary) but in a perfect world it should have been done sooner before the wood was actually damaged.

As far as preserving/ filling the damaged areas- I am not sure where in the world you are, but here where I am (US) I have used Elmers Rotten Wood Preservative. It comes in a plastic bottle and is basically a clear glue-like thick liquid which seals and hardens the damaged areas. As for filling those areas I expect that would be difficult to form very well because they are on the edge of the boards. You could try with Bondo, wood filler would be more difficult to work there. The checks (surface cracks) could be filled with Bondo or wood filler and sanded easily. Filling in those surface checks will help keep water out of the wood and assist in prolonging its life. Whatever you can do will help both longevity wise and looks wise.

For the remaining algae perhaps a spot treatment of bleach ? Again, everything you can do (within reason) will make the deck look better and hold up a bit longer.