I’ve been refinishing fir posts: no stain, clear coat only, southern exposure, beachfront. The side of the post that is facing out was very damaged and so required full clear coat removal (sanded down to bare wood using 80, 120 grit). The other 3 sides were in very good condition and only required a light sanding and recoat. Sounds good right? Only problem is this… the newly sanded side is turning quite a dark amber when I apply the product, while the sides that did not require sanding are as beautiful and light in colour as before, and perfectly match all the other wood work on the house. As it happens, any little bits of clear coat that accidentally got left behind (in those tight spots where the post meets the ceiling or deck) are also maintaining their light colour. Oh, and yes, I’m using the same product as was originally used: Sikkens Cetol door and window clear satin finish. Is it possible that this could be really deep sun damage that is actually below the surface that was completely sanded off? I’m confused! Usually the opposite is true… sanding off wood that has darkened due to UV from the sun generally goes lighter in colour and is more true to what it looked like the day it was installed.
It is quite likely the fir wood has gotten darker with the age the sun caused.
I try to relate this line of thought to my customers. If you stood out in the sun for 3 or 5 or 10 years what would your skin do?
To rid the deeper color from the wood you will probably need to sand as much as 3/8 of an inch from the original surface.
I'm also trying to redo my fir post and beams exterior, originally varnished with a natural finish of boiled linseed mixed with Timberlox oil based penetrating finish. Sun exposed portions are fading, etc. Some of what I'm learning indicates that sanding or pressure washing damages surface cell structure, causing discolouration. My test patches are showing that to occur as well. I am leaning toward chemical stripper, possibly reconditioner, then re clear coat (I love the natural finish).
it's been very hard to find advice on line for exterior fir refinishing. have you resolved it?