How Much To Sand?

[paul oman]

Hi guys:

Today I'm looking for tips on tricks on 'how much to sand." I'm trying to do an older wooden
hull right and I keep sanding away. It there a better way then just closing one's eyes and rubbing
one's hand over the surface to feel if all the flaws, paint drips, sags, etc are completely sanded
away? Experience tells me that when it feels smooth to me, I'll be disappointed with the surface
when I paint it. This time instead of slapping on some oil based stuff or latex, I'm using 2 part pricey
Parker Poly so I want it nice. All suggestions (well almost all!) welcome.

paul oman
progressive epoxy polymers

[JimD]

What kind of wood is it? View it with directional lighting such as a flashlight at a very low angle?

[brent stella]

One of the things I like to do is draw light lines about 3" apart on the boat and then sand them out. When I'm done I draw more lines on and moved to the next grit sandpaper.

[gaffman]

If you want it perfecto, hand sanding is not the answer. Get yourself a longboard and sand at 45 degree diagnonals to the planking, sanding 2 or three planks at the same time. The longboard of course has to be flexible. You'll like the result better than hand sanding will give you. This is tough work. An air longboard working off a compressor is living good.

[pipefitter]

There is no substitute for the long board.A semi flexible one for boats because of the curves.The last step can be to block it with an off color so that the color left after sanding shows the low spots.I wet mine and look at a low angle.Also,with a wooden boat,as you repaint it over the years and you resand the old paint with the long board the boat's finish gets better every time you paint it.The long board I am using is 2ft long. On the first initial pass when everything is still shiny it immediately shows the trouble spots.If you use primer you can use white primer under gray primer or vice versa.Power sanders are your finish worst enemies.

[paul oman]

FYI: This is a molded wood firefly sailboat with some lasting 'extra curves' from sitting too many years on a trailer. Looks like it had white LPU that was peeling in places, seams openning up etc. I covered with drippy white epoxy primer, now sanding the drips, sags, areas around the peeling with a random orbital sander.
Would a long board even work on such a curvy 12 ft hull?

Pls keep the comments comming! I'm eating up all your suggestions!

paul oman
progessive epoxy

[Bruce Hooke]

I'm not so sure that longboarding is right when you are sanding a previously painted surface. However, I will add the caveat that this assumes the underlying hull is fair, or at least that it is as fair as you want it to be. Refairing the hull is a different realm from simply sanding paint.

Some sort of backing pad behind the sandpaper is, however, a good thing because it helps you take off the high points, which is what you want to do. It's a question of finding the right backer so that you have something soft enough to follow the overall curve of the hull but not so soft that it follows the small ripples that you want to remove.

As to when you have sanded enough, here are a few thoughts:

1. You have removed any paint that is peeling or otherwise no longer sound. This, of course, is the first essential stage.

2. There are no shiny areas left (or at least if there are they are pinhead size or smaller).

3. From here it gets more subjective...to find small problems your hand is a good guide. Low angle light can help identifiy larger problems, but remember, unless you want to get into fairing the hull, not just the paint, most of what you will be dealing with will be quite small.

Remember, too, that you will likely be putting on at least two coats of the finish paint. After the first coat you have a chance to see pretty well how the finished product will look and this is your chance to look for any areas that are not smooth enough for your taste.

[Andrew Craig-Bennett]

Yiles! You didn't say she was a Firefly!
Hold Everything!!!

PUT THAT LONGBOARD AWAY!

NOW!!

As the very happy owner of Firefly no F3000, let me hasten to assure you that the hull you are proposing to sand is 3/16" in total thickness, comprised of three skins each of which is structurally essential!

Furthermore, this is an Uffa Fox classic, designed in 1936, used as the Olympic singlehander in 1948. Often called the smallest most affordable true classic.

Shame she was painted but there we are.

Hand sand, very carefully, using a cork block, please!

[Andrew Craig-Bennett]

Should add; ours is still varnished, 12 coats of Epifanes, most of which got sanded out, in order to get a finish.

here's a bit of background (http://www.ybw.com/cb/firefly.html)

With these boats, you build up to get a finish; you don't sand down to one without building up first.

[ 04-18-2005, 11:37 AM: Message edited by: Andrew Craig-Bennett ]

[paul oman]

Andrew:

it's just painted on the outside and still bright on the inside.

it reminds me a lot of a Thistle. As a teenager I sailed and raced Thistle #154 - an old Lady even then. I even won Yachting Magazine's Jr. Article Writing contest in 1976 about a cruise on Long Island Sound with it.

regards
paul oman
progressive epoxy

[John Meachen]

You may as well continue with the power sander until all the runs,sags and other nasty bits are removed.As clearly stated above,you ought not to remove any of the veneer. Your description of the distortion may mean the you need to fill the low spots,perhaps an epoxy/microballoon mix and then prime the surface to match the rest of the hull.If it feels reasonably fair,give the hull a very,very light coating of dark car touch up paint.Not a coat of paint as such but just a liberal sprinkling of spots on the surface.If you then find a piece of Styrofoam about 15 inches long and a couple of inches wide and wrap it with 180 grit paper you can start to seek out the imperfections.
Hold the foam parallel to the keel and rub at a 45 degree angle for a couple of minutes,then change to an angle at 90 degrees to the one you had been using for a little while.Concentrate on a section around two feet long,from keel to gunwale before moving along the boat.If you have no bare wood visible and no dark paint spots you can confidently apply a perfect top coat.If you have my sort of luck in these matters,you can go back the next day and chisel off the dead insects at their ankles the rest of them won't be visible in normal use.

[Wild Wassa]

Paul, To pick up my act, I painted the ceiling in my paintery a flat Mars Violet (a purple black). I found that a lot of the problem in being able to assess the true quality of the surface happens because of too much extraneous light. Doing this has made the process more accurate it has stopped me from sanding off work.

I find that no matter how perfect one finishes a small boat (which means the hull, topsides can finish themselves) just give it three months with the poly's shrink wrapping and you will wonder if you actually did anything at all, I find. I stop painting and polishing hulls when the boats stop fighting me.

Warren.

[ 04-20-2005, 03:12 AM: Message edited by: Wild Wassa ]

[paladin]

start from the outside but stop before you get to the inside....

[preston]

CWB has a Firefly for sale. See http://www.cwb.org/BoatsForSale.htm
Seems a little expensive; we'll see.
I also wondered about the "racing pram."
Buchan was a big name in Seattle racing, but I'm not sure of his relationship to this pram.

Preston

[ 04-18-2005, 07:49 PM: Message edited by: preston ]

[Wild Wassa]

There is a flexible sanding block called a Wonder Block (about $20 in Oz). WB's (or similar, there are a few) are used by the automotive guys when they colour cut and when they are taking real care, if they are not wanting to reduce the paint too much.

Automotive painters use long boards and not so long long boards on their curves. The one I use the most on curves is only about 10" long. Using long boards save a lot of time compared to using small blocks. Plus you don't get the rippling affect that one can get using blocks, if you keep the shorter long board as flat as possible on curves and stroke in the direction that allows the board to remain flat.

Very rarely will I use the maximum length of a long board with the direction of the stroke, parallel to keel, gunwales or strakes ... without paying good attention to not cutting tramlines.

I also use glass bubbles (5 micron hollow glass) in paint, when I need to fix poly's shrink wrapping. It often gets to this level close to finishing poly over old ply. The glass bubbles makes sanding easier, ready for the final touchup if needed.

Warren.

[ 04-18-2005, 11:25 PM: Message edited by: Wild Wassa ]

[pipefitter]

If someone doesn't know what they are doing with short files they will tend to spot rub sags and divots out which gets rid of the eyesore spots but creates harder to see ripples that show up when you put gloss on.You have to really match the curve areas with the proper length files if you can.Or turn the longer ones on an angle so it isnt as long on contact.
Ok,yeah,what Wassa said.
Also,if you are trying to feel it with your hands it helps if it is totally dust free and cold smooth to touch.Or to walk away from it for awhile and come back to it and run your hands over it again.
Most of my sanding experience comes from classic cars and the hardest one I can remember is the faint body line behind the rear wheel on a 69 Buick GS. The long file on my simmons is a home made 14" but the boat is mostly fair convex from fore to aft. I roughed it in with a 24" Flex board because it bridged more than one frame per stroke and I had epoxy/glass butts joining the planks.All the butts on the boat are invisible now but thats fairing,not painting.
I knew when I put the primer on, stuff was going to jump out at me but to my surprise my paranoia paid off and I didnt find a speck.But I admit,when I started to get to this stage I did read what the paint guys on here said and adhered to it because it made sense with what I had experienced with cars.

[ 04-19-2005, 01:21 AM: Message edited by: pipefitter ]

[Andrew Craig-Bennett]

US$2,500 is a lot of money for a Firefly; not far short of the new price for a GRP one. The ones right at the top of the class change hands for that sort of price.

Slightly "tired" ones with all gear used to change hands at a standard £300, but they are coming back into fashion and I've seen one at twice that recently.

I'mm interested to learn that a Thistle has the same hot moulded hull construction. It is perhaps the best of all wood constructions for strength and durability.

Faireys had been building Mosquito parts in WW2 and had the idea of using the same technique to build dinghies, so Uffa Fox dusted off his "Cambridge University One-Design" and away they went. One of their charms is the excellent quality of the fittings, all of which were specially made. They were the first boats to have alloy masts - with a wooden top section as nobody knew how to taper alloy, back then.

[Andrew Craig-Bennett]

Another point about Fireflies. The C/B case lacks lateral support. A leak at the hog/case joint is normal! A recommended mod. is to add some sort of thwart-type crossbar at the fore end of the case. In the event of a total inversion, the plate can actually fall out of the case; recent boats have a plate with a hole, not a slot, for this reason.

They are tippy, but surprisingly good seaboats. A lady member of our local club singlehanded hers from Woodbridge to Calais (95 miles or so) in 27 hours - the last two hours were spent dodging ferries in the entrance - in the end she called up the harbour control on VHF and they held back a ferry so she could get in.

[Andrew Craig-Bennett]

I found the UK Firefly Association website:

here (http://www.fireflysailing.co.uk/)

[Chris Stewart]

Originally posted by Andrew Craig-Bennett:
With these boats, you build up to get a finish; you don't sand down to one without building up first.Here is a technique I have seen once in practice, but have not seen mentioned here, so it is either so common that it goes without saying, or is so far outside the box that only one fool has ever tried it.


Your hull is already painted and you have already sanded enough so that it feels smooth. Put on another coat of paint in a contrasting color and let it dry completely. Sand just enough to take off all of the new paint, trying not to take off any of the old. Your hull should now be perfectly smooth.

[pipefitter]

Thats what color blocking is. The high spots sand through to the under color and the low ones are left where the contrasting color cant be reached by the long board. It shows where it needs to be filled and sometimes the contrasted top coat is enough of a filler for minor flaws. Same with misting a light coat of dark primer over light.The little specks of misted paint stay in the lows and the higher areas sand clean. That is for a competition show quality finish.
We also used to longboard the color coats with wet/dry before clearcoat.One more step towards perfection. On repaint over sound paint we longfiled the existing color coat with wet/dry to expose shrink areas. Spot putties shrink over time as do primer/surfacers. Probably too much hassle for a boat since you can rarely see the whole surface from any one direction unless it is a small boat.This is just an opinion.There is others here that make their living from it so their word would probably get you the best results.I also tend to overdo everything.

[ 04-19-2005, 10:21 PM: Message edited by: pipefitter ]

[Wild Wassa]

posted by pipefitter:
"That is for a competition show quality finish."

... and you don't question if it's the skin that has let you down when racing.

"Probably too much hassle for a boat since you can rarely see the whole surface from any one direction unless it is a small boat.This is just an opinion."

You couldn't have said it better if you don't mind me saying. I painted my ceiling black ... Greg H said when he visited, "Was this room a darkroom?" More like a light baffle.

[ 04-19-2005, 10:34 PM: Message edited by: Wild Wassa ]

[pipefitter]

Ya know Wassa, In all my years of drywall hanging/finishing we used to always fight the buttjoints placement in rooms with large windows/sliding glass doors. Because if the light goes across them at any angle whatsoever they could show unless they were filled to about 2 ft or more on either side and with texture. So you would get them perfect,not see a thing.Later in the year the homeowner may have a complaint that a bump appeared in a wall in one of those rooms. What had happened is that the sun was now at a different place in the sky than when we did the finish work.Shines across the joints differently in summer than winter. So then we would hide them in the shadowed areas next to the windows running into the corners.That way it would be somewhat masked by the shadow year round. I guess this doesn't have a whole lot to do with Paul's question but to the notion that all my hobbies/jobs require this god forsaken task.Saddest thing,doesn't seem there is going to ever be a replacement technique for it in my lifetime.The best power sanders are really only good for the demolition stages of prior paint jobs and even then they will probably cause you more work in the end. The only thing we can hope for is permanent sand paper that never wears out.