Okay, here goes a stab at this.
First, consider carefully the plan to power wash. People do a lot of things to wood to get an old finish off- sandblasting, shell blasting, scraping, heat guns, grinding, wire brushing, and power washing, for examples. Each can cause big problems. Blasting, grinding, and wire brushing will rapidly eat away at softwoods like cedar. Heat guns work, but you have to be very judicious in application to prevent burning of the wood. Scraping also works, wield the scraper careully- as with blasting, grinding etc., you can quickly create a topographic landscape that will require a compass to navigate. So, now to power washing- if you've never done it, give it a whirl, but wear shoes or boots because you can easily cut right to the bone. In fact, it's pretty easy to remove a layer of concrete with a power washer. So what will it do to soft thin cedar planks attached attached to cedar ribs by thin brass tacks? To borrow a poetic line from MC 900-Foot Jesus, "Somethin's gonna happen and it's probably not good!"
Oh, the TSP- why even begin with a detergent when power washing will go right through the finish and the wood?
About sandpaper, 100 grit isn't fine enough for a quality finish. On the other end of the abrasive spectrum, you can over-sand wood to the point of polishing it with very high grit numbers. Polishing interferes with finish adhesion, but 220 will not polish, and does leave a surface that takes varish well.
Finally, the finish itself... Your aquantance recommends 3 different products it seems, when only one is really necessary. Thinned varnish makes an excellent first coat, and is an effective (and often used) sealer. As a sealer under varnish, there can be none better because subsequent coats of varnish are going to adhere best to earlier coats of the same material. Any good marine spar varnish is great for finishing. The advocacy of a Hi-Build-type product comes from the desire to build a thick coat fast, but most high quality restoration is done with multiple coats of good spar varnish rather than searching out a product that goes on thick and fast like the top coat and the talk at a Hooters bar.
You didn't mention stain, which in this humble opinion is a good thing (not mentioning it, that is). Stains often get slathered over beautiful wooden boats, muddying what otherwise would be a beautiful study in the natural richness of wood. Don't even get me started on those filler stains- yuk! These are the heavy colored fillers often globbed onto runabouts and other boats to reduce the tedium of filling pores in open-grained woods like mahogany. If not done VERY well, it is very obvious. I just scoured this pigmented nightmare out of some old mahogany to find absolutely exquisite wood underneath. It seems near blasphemy to treat wood so. The horror!
So, one working formula:
- strip, clean with TSP, treat w/2-part teak cleaner/brightener
- apply thinned high-quality spar varnish, working from more to less thinned through subsequent coats (start 50/50, gradually work to more concentrated, sanding lightly between coats).
- 3-4 coats serviceable, 8-10 or more coats for fine work
More details if desired.
For an excellent treatment of wood finishing by a true expert, see Rebecca Whitman's book entitled "Brightwork". Reviews:
Classic Boating : ``Everyone who does varnishing should have this book!--Wittman does an outstanding job of educating in all there is to know about this critical stage of boat restoration--A superb book I highly recommend.''
Sail : ``It's elegant--elegant as the work it describes so successfully, elegant in its writing, elegant in its photography.''
Sailing : ``Packed with useful information for both amateur and professional refinsishes alike--A first class and highly readable text that should be mandatory reading for anyone who owns or is contemplating owning a wood-trimmed vessel--The book's only drawback is that it's so beautiflly illustrated that you'll need to buy a second copy to replace the one assigned to your cofee table.''
