Deck recore fairing question

[galleywench]

Title is a bit misleading because I'm not really at the fairing stage yet, but my question will affect how the fairing will proceed when I get there.
I've recored all the decks and I should finish covering them up with the first 2 layers of 1708 biax cloth sometime next week. After that, the decks will obviously require some surface sanding to clean up any of the ragged edges from the first 2 layers so that the final layer lays flat. However there are a few spots (along the side decks) where the combination of the core and the first 2 layers of cloth are not flush with the original deck level. In some cases, the cored area is somewhat lower because the second layer of cloth rides up on the beveled flange that I ground in the original deck. None of it is too bad, but the way I see it is that I have 2 options (best explained in diagrams):
Option 1: Before I set the 3rd layer of cloth, do some 'pre-fairing' of the decks to build up the lower spots. Additional fairing will need to be completed after 3rd layer is applied.

Option 2: Prep the decks, add the 3rd layer of glass and then do all the fairing after all glass is in place.

I am leaning toward option 1, it seems if it will make the final fairing job easier, but I am looking for input. I don't want to miss something that may be obvious to those that have tackled this project before.

Comments? Recomendations?

[captphil416]

Dear Magic; Congratulations on a job well done. I would favor option one as the fairing compound unsupported might crack over time and might absorb water. One last suggestion would be to apply a cap layer of dynel, or xynole to guard against impact cracks from dropped tools etc. The open weave will be hard to fill, but will make a fine non skid where appropriate. Hopefully James Baldwin is out there as he did a better job on this project than I did. Best of Luck Phil

[galleywench]

Dear Magic; Congratulations on a job well done. Phil

Thanks for the kind words, but I think I'd rather take the compliment when I can sit on the boat in a harbor after a good day's sail drinking a 'Dark-n-Stormy'. I'm not even close to complete.

In any event, I should caveat the drawings with a 'These drawings are not to scale'. The most I would be 'pre-fairing' (underneath the 3rd and final layer of glass) would be approximately 1/8". The drawings are way out of scale in respect to the amount of fairing compound that needs to be applied.

With that in mind do you think I should go with option 1 or 2? The 3rd layer is all I am planning on doing. I would think that once I have that in place, it comes down to fairing, highbuild primer, then paint. Please correct me if I'm wrong, but I think the primer can go right over the faired glass?

[Zach]

Use #2 if the putty is an 1/8th inch. Use #1 when putty approaches 1/2 inch.

Your first drawing is how I prefer to do repairs that requires a lot of compound, but an 1/8th inch is practically nothing for putty thickness with epoxy putties. At least on custom cold molded wood and plywood boats... but that is just because builders don't often put the effort into construction with the mindset of achieving a 320 grit finish.

To put this another way, get out the battens and straight edges now before you do anything else and make your repairs straight, flat and true and don't think about the structural and fairing as two different topics. Start at the bow or the stern, and lay battens and mark the highs and lows. Otherwise your repairs that butt up to high spot turn into long humps, and repairs that are beside low spots end up as long low hollows.

The strongest way to fair out an 1/8th inch low across a wide panel is to cut 2 more pieces of 1708 to lay in while doing the glass work, all at one shot. (Slow or Tropical hardener, or coming back after the glass has cooled off and add more. Amine blush starts to show up within 5-6 hours of the glass work starting.)

I figure out where the glass goes with a stiff straight edge and a 1/16th and 1/8th inch thick pieces of wood. Slide it along the deck surface until the straight edge lifts, and mark where the wood where it does. What you end up with is a topographic map on the deck of the first and second layers. This works well, if the surface you are fairing is shaped properly already and just low. You can make life easier by putting brown butchers paper on deck before you do this, and lay the paper over the glass while you cut it out. (1 layer of 1708 is 1/16th, 2 layers is 1/8th.)

If the surface doesn't have shape, you can do it with fairing compound and use a stick of aluminum angle iron to bridge both ends of the repair, where hopefully you have shape... If you are dealing with an area that has sagged, you can make ramps on each end and connect them with your straight edge to shape areas that need large amounts of help. Epoxy and chopped glass fiber (if weight isn't much concern...) with a little cabosil to keep it together. Plywood sticks, and aluminum straight edges bow and make low and high spots. Angle iron stays flat and true and takes at least a few sanding cycles, of adding putty that a straight edge pulled out.

For your fairing, unless weight is a big concern use chopped glass fibers and cabosil. For one, chopped and milled glass adds strength, and it also screeds out better than microballoons and West systems 407 consistency products. Epoxy shrinks! The first 1/8th inch will be low tomorrow. If you let it sit a few days, your next coat will shrink less. Overfill the initial work.

Don't try to use high build primer to fair the surface, while it is a good product... it shrinks as the solvents escape. Think about high build primers as things that fill scratches left by 40 grit sandpaper, and let you go to 80 grit or 120 grit without going through the grits, more so than a tool in the arsenal for fairing. The heavier and thicker the coating goes on the more important overcoat and recoat instructions are, follow them to the to the letter, and if you are sanding and smell solvent you need to stop and come back another day. Overcoating while the solvent is still evaporating, means a chance of solvent popping through the next coat of primer or worse yet your top coat. You'll come back next month and have waves that were smooth!

Try to do whatever you can to get the surface fair and straight with long boards in 40 grit in the puttying stage. Use guide coats of spray paint, or rub aluminum straight edges all over to show black on the high spots. Load wooden battens with chalk and rub them around... Just try your best to get the surface free of high spots. High spots while sanding primer, mean you burn through your primer and hit fairing compound or worse fiberglass. If you are hitting either the compound, or the fiberglass you have to either sand the fiberglass and putty until they get lower, and recoat... or blast on ever thicker layers of primer.

Lastly, one of the cheapest things you can do to improve the finish is instead of priming when you think you should... roll on a few coats of neat epoxy to fill the 40 grit scratches. Sand with 80 grit, and if you still have shiny spots, your surface still isn't fair. Mark the shiny spots, sand them and apply either another coat of epoxy to those spots, or pull a real thin light coat of fairing compound.

30 inch long boards make the process easier, in time and results. Shorter boards are good for small parts of boats, but 16 1/2 boards fit in low spots. 3m Marine Hookit boards, with Mirca Abranet sandpaper are the best labor saving devices invented for saving your time in the fairing steps... second to having someone else do it. Much cheaper, are home made plywood boards with sticky backed 4 1/2 inch wide sandpaper glued to them, though nothing I have found cuts soft fairing compound as fast as abranet 40 grit abranet.


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[galleywench]

Excellent Zach, thanks for the detailed help. Once I finish glassing up the aft deck I'll do an initial pass to clean things up a bit and then set to getting things level before the final layer of glass (ie. option 1).