Weatherproofing exterior wooden staircase

[douglasgrant]

Hi

I have a wooden staircase that leads from the top of my lean-to garage,, down into my garden. As it's wooden, it used to get quite green and slippery near the bottom. I've painted it all with the usual garden shed type weatherproofing and have stuck special 3M non-slip tape onto the treads.
My problem is with the stringers. Over the years, the top surface that of each stringer has expanded and contracted with the changed in weather and has opened the grain, for want of a better expression. I'm worried that this is going to let water in and rot them. I've carefully filled them, using normal wood filler, but that doesn't seem to be flexible enough. I'm wondering if there's any kind of flexible filler, or even rubberised paint, which I could use to do the job? I guess an alternative would be to attach a long thin strip of wood to the top of each stringer.

Any advice would be gratefully received.

 

[petewood]

I don't think you could easily weatherproof open grain like this, but before anything else you should get some clear preservative and brush it on liberally, as this will help to prevent any rot.