I initially tried to strip the but was unsuccessful as the Behr semi-trans stain was like paint - just didn't want to come off. I used Defy stripper and a pressure washer (even agitated the stripper after 15 minutes before p/w and still not much was removed).

I am now in the process of sanding the entire deck with a 5" ROS and a palm sander using 60 grit paper and I think its going well, but I have a few questions on the current state of the boards:

1. There are some boards that look brand new (first pic), but there are a lot that have grooves in the wood where the old stain is sitting in and I cannot sand it off...
a. should I keep sanding these areas ​and (possibly go down to 40 grit) to try and smooth out the grooves and get the stain? Or will I be OK leaving these boards as is and will the new stain look good even when there is a small amount of old stain remaining like it currently it? See 2nd pic showing boards with minimal stain remaining in grooves. See 3rd pic of a closeup of the grooves in a lot of boards.
b. should I try to now strip again and really soak the stripper into these grooves to try and get rid of the difficult to reach stain? I used a garden sprayer before, maybe I can use a paint brush and really soak these boards. I'll let it sit for 30 mins and lightly mist it as it starts to dry, then p/w it off again to see if that works before really sanding it hard.
c. will the stain look different across boards that look brand new versus the ones that have grooves with a hint of stain on them? Does that give a random stain look across the deck? Is that alright, I see a lot of pics where the stain looks different across boards and its kind of cool looking.

2. I am using a solid white stain on the verticals, so instead of sanding these 100%, will the current state be perfectly OK for solid stain application? I gave it an easy sand but don't want to spend 10 more hours sanding the spindles and horizontal boards across the spindles if I don't have to.

 

What type and color stain do you intend to use on the decking? The railing is fine for applying solid stain.

 

I am going to use TWP 1500 cedartone, honeytone or pecan on the horizontals.

 

I've never used or seen any TWP [don't believe it's sold locally] although it's my understanding it's similar to Flood's CWF line of deck coatings. Are those colors semi-transparent? With the exception of the board next to the railing in the last pic, semi-transparent stains should look good with the prep you've done. While there will be differences in how the boards look, it should be minimal.

 

Ha, I'm not done prepping and last board is the outer I edge I haven't gotten to yet with my sander!

Yes, the TWP stains will be semi.

OK, so you don't think that the minimal remnants of the previous stain in the grooves of a lot of these boards will be visible or show badly?

Should I do a strip on everything once I am done sanding, just to see if any little spots come off, then follow up with cleaner/brightener before staining?

Also, is there a need to clean and brighten the verticals before staining solid white?

 

Your sanding seems to be doing a decent job, IMO going further would be a lot of effort for little gain. The railing looks clean enough for any solid stain including white.

 

So again, this sanding job on this board looks good to go for apply a semi over the top?

 

IMO it will be fine, not perfect but acceptable to most .... after all, how much time do you want to spend getting it perfect knowing that the decking receives the most weather and will need to be done again.

 

I put some elbow grease into it, bought some extra pads and went to town. I am now stripping it clean 100%.

Now, what about the side of the boards, you can clearly see the old stain - what is the best way to get rid of that?

 

It's next to impossible to remove the stain from the sides of the decking. As long as it is well adhered I wouldn't worry about it as it won't be overly noticeable once the new semi-transparent stain is applied.

 

You're being a perfectionist in area where it's just not worth the effort. Go ahead and apply your new stain.