blueman wrote:

One of the wood structural beams (4x8) of our porch serves dual use
as a "step". However, over the many (~100) years, part of it has
work down so that it is no longer flat with the amount of wear
varying between 1/4 and 1/2" For many reasons, I do not want to
replace the beam but I would
like to level it off and restore it to its original height.

The 3 ideas I am considering a
1. Sand it down to an even level and then fill it with a uniform
thickness board. My concern is that it could be a fair bit of
work and that I would prefer not to take off more wood.

2. Fill and level off with an expoy-type mixture. Not sure though
what would be the best materials to use and how strong/durable
it would be.

3. Hybrid approach. First fill to get the surface level and then
cover with final uniform 1/4" piece of material (though not sure
what would be best to use that would weather well and stand up
to some abuse)

Any thoughts on whether this or other approaches would be
recommended?

Having built a boat, have used more than my fair share of epoxy
fairing compound; however, advice is worth what you pay for it.grin

Assuming you will paint the repaired beam to protect it from the sun
as well as the elements, the following will do the job:

Usre a small right angle grander equipped with a 24-36 grit sanding
disc and remove any damaged/worn wood.

The idea is to get back to fresh wood leaving a coarse surface for the
epoxy to bond with so it doesn't need to be level, only clean and
fresh.

Coat surface with epoxy using a throw away chip brush.

Mix up some fairing putty using some Cab-O-Sil and microballoons,
nothing magic about the recipe, just a little of both.

Apply putty to wood about 1/2" thick max.

Allow to cure for at least 48 hours, then scuff with 24-36 grit and
repeat filling, if required.

Final application of putty should be done with a plastic spreader and
left proud by about 1/16".

Allow to cure for at least a week to achieve some strength.

Now it is belt sander time.

Level out patch finishing with 100 grit, remembering to break front
edge of patch by say 1/8"@45degrees.

(Use a straight edge as a fairing batten check that patch is flat and
level)

When fairing patch is finished, apply a final coat of epoxy with a
chip brush and allow to cure for a week, then paint after washing
patch surface with soap and water to remove any blush.

Lot of work, but you already knew that.

Lew