I described my problem in this question here
This is the outcome of that project. There ended up a bit of gap in some area like 1/8" - 3/16". It's the one on the left here:
The reason is that when I cut 2 boards using the table saw, it's not straight all the times. Plus the bottom beam is not flat so it's impossible to join two boards like that without any noticable gap when looking closely.
At the end, the gap is a bit larger but not bad. You can see the beam directly below:
My question is: how to fill the gap to prevent water from sipping in and rot the lumber below over the years? If there is no lumber below, it's easier. But this is always a target for rotting.
I am thinking about filling in the PL 400 completely and wipe it off at the surface using thinner or gas to clean it. Making it like some sort of filling / grout.
What are some options?