I'm still agonizing over what finish to use on an exterior
blackbutt handrail which will get full exposure to the weather
all the time.

I experimented on an offcut with Sikkens products. I applied 3
coats of "HLS" plus 3 coats of "Filter-7", and left it outside
about 4 months ago. I'm disappointed to see the grain lines
gradually darkening towards black (presumably because the sun
is drawing up the resins?). I can also detect the first signs
of cracking along the timber.

Recently, someone suggested I should be using marine grade
products. E.g: International's "Everdure" 2-part sealer (which
has to be applied as 4 coats, wet-on-tacky), and then 6-10 coats
of either "Schooner Tropical" or "Goldspar Original" high-gloss
varnishes. I also thought about "Perfection" 2-part varnish,
but was told that although it lasts longer, it's a bitch to
maintain when it does eventually start to crack up.

My problem with the International range is that they're
essentially clear, but I want to put a deeper colour into the
blackbutt - which I can do easily with Sikkens. A technical guy
at International expressed reservations about whether some sort of
stain (eg Feast-Watson prooftint) applied underneath the Everdure
would be ok. There doesn't seem to be any officially-sanctioned
additive for the varnish that would allow me to build up the
desired colour gradually.

Anyway... even using Everdure+Varnish, I'm told that I'll still
get maybe 1 year or so before I need to re-coat with varnish.
If I leave it longer than that between re-coats, the varnish is
likely to go off too much, requiring more severe maintenance.

So now I don't know which way to go. I could probably get
a year from Sikkens before re-coating (if I prepare/clean the
surface better, and apply more coats initially). Then I'll have
to re-coat. So what would be the benefit of Everdure+Varnish
compared to HLS+Filter7? I presume the 2-part Everdure would
be a much better sealer coat than HLS - but will it stop the resins
rising and darkening the timber surface underneath the finish?