Epoxy Tricks

[LennieG]

Howard I thought it was a great question you raised and it was very useful to me. I don't generally weigh in with advice as my skills are not there unless it will save one of the experts time and something I feel I know well and can knock it off quickly for everyone.

I had just capped the leading edge of CB with 10oz and goo, and had sanded one side with a random orbital sander. Norman weighed in and suggested a longboard at that very time. So, that is what I used (my 80 grit longboard) for sanding the second one. It was a piece of cake! The longboard worked great. I know much of the discussion is on inside of boat, but believe it applies whenever there is a self edge. I worked on a couple coats of thick goo and some sanding and it was done. Very helpful!

[Fishman38]

Speaking of "longboards" will someone tell me exactly what that is?  Can one buy them and if so where?  And what does one ask for?  If the image I have of what it is and what they're used for, it seems it would be pretty easy to make one out of scrap plywood, say 1/4 inch, (but how wide and how long?) and stick on whatever grit sandpaper you want with a spray on adhesive.  Maybe add something on each end to hold onto................?  My guess is you'd find them at an auto body paint store?

[LennieG]

Piece of cake to make, or see Jamestown Dist website

Start with longest belt sanding belt you can find at big box store, build from there. Knobs at Lowes.

Great tool!

[Tom Lathrop]

Speaking of "longboards" will someone tell me exactly what that is? 

 

Longboard is a misnomer.  They are more properly called a "torture board" as using one is much like torture if you have any arthritis.  My best use of one is in marking the bottom with carbon and using it to highight areas that need to be worked on with a power sander or hand plane. 

[Chick Ludwig]

Here is what us lazy people use whenever we can get away with it.

 

http://www.harborfreight.com/2-3-4-quarter-inch-x-15-3-4-quarter-inch-air-inline-sander-91773.html

[LennieG]

To expand, 1/2" ply scrap works great, and what I did was cut length of ply so there was an 1 1/2 " overlap of paper on both ends. And then stapled on a small board to hold paper on top. Didn't even need adhesive. The big knobs designed as dresser knobs work best for me. They talk about a stiff one and a flexible one but I just did an 80 and. 120 with the ply I had available.

[LennieG]

Tom-

If you are struggling using the longboard it is probably a technique issue. You want to make sure when using one that your tongue sticks out of your mouth and points right and you kind of squint your eyes. That's what the guys in my wooden boat class were doing so that is what I do.

[PAR]

Long boards come in various shapes, lengths and sizes, usually geared to match the job. A 1/2" plywood board is too stiff for most boats, except in large expanses of relatively flat areas. I've got a number of boards, one of my favorites is made from 1/8" Lexan. It's 4" wide, about 20" long and fairly flexible, so I can work compound curves. I have ones that are 1/8" and 1/4" plywood too and even one made from 14 gauge aluminum sheet. I buy paper on rolls and cut to length, using a spray adhesive to mount them, though you can just as easily use a clip or slot at each end, to hold the paper to the board.

 

Technique is key with a boogie board (board-'o-pain). Typically you work from one end of the area (or hull side) in a single direction, across it's full length. You select an appropriate angle, which often seems to be about 30 degrees to the centerline and stroke the board at this angle the full length of the area. All strokes are at this angle, leaving a series of angled scratches. You then come back at the opposite angle, in the other direction, netting a cross hatched pattern of scratches. The low spots will be clearly visible, not having scratches in them and the high spots will be knocked down a touch. At this point, you mark the low spots and apply a little filler in these areas. The next pass with the torture board is focused on the now filled low spots, so you can knock them down to surrounding areas. I often use a very light dusting of primer at this point to fine tune the surface and help see what needs what. Again, working a common angle, you run from one end, to the other, placing a new diagonal scratch pattern and come back on the reciprocal angle for the cross hatch pattern. Each pass will continue to knock down the high spots and reveal the lows you've missed on previous passes.

 

A pro will make three passes with the cross hatched, long board pattern. The first to find the lows, the second to knock the lows back once filled and the final pass, to even everything up. The backyard fairer, can make a career out of this process, with many passes and filling sessions. The more you work this set of steps, the fairer and smoother the hull will be. The same process is used with paint, if you want a baby's butt surface, just with finer grits, usually wet. It helps a lot to have the right lighting for this process. You can have too much light, particularly if it's directly over head. You want a low angle of light, so you can see the shadows in the low spots.

 

The biggest mistakes novices make are not using a long board, thinking a palm sander or orbital will do and over working the surface. The Harbor Freight "in line sander" linked above shouldn't be used. It will remove material at an alarming rate and it's not flexible enough to conform to curved surfaces. That particular Harbor Fright tool is a single piston design and you'll be in serious pain, with just a 1/2 hour of use. It's a real piece of crap and if you want one, get a duel action/piston design so it doesn't tear your elbows off. Try not to get aggressive with material removal, just lightly scratch the surface, so you can see what's high and what needs to be filled. On plywood hulls you'll bring the lows up to the highs for the most part, so skim coat the lows with some filler and knock these filled areas back locally at first, then with the long board passes. A jitter bug (palm sander), DA or orbital sander will not fair a surface, just smooth it. Fairing and smoothing operations are wholly different. The long board fairs. Once the surface is fair, then you can move onto smoothing operations. Fair is what you can see, while smooth is what you feel. A surface can be smooth, but quite unfair. A dent in a car door is a classic example of this. The dent can be polished and really smooth, but the light reflection will clearly show it's not fair.

[Fishman38]

My favorite uncle always said "you gotta hold your mouth right."   No matter what you were working on.

 

Thanks everyone for the explanations!  Sounds like I'm in for a lot of fun. Not!.  A bit of arthritis but only in the left thumb so maybe it won't be too bad.

 

Especially thanks to PAR for the comprehensive primer on the process!

[Chick Ludwig]

You're right about the Harbor Freight "in line sander". I threw mine away and got a good one. I use it on fairly flat areas only, and not on compound curves. Use with finer grit paper so that it won't " remove material at an alarming rate". I build plywood boats which are fair to begin with. The sander mostly knocks down the filler used to fill the cloth weave and over-laps. With careful use, this tool can save time and wear and tear on an old body. All that said, the "torture board" is the better way to go for the best job.

[Howard]

The auto body world refers to the "long board" sanding technique Paul (PAR) describes as "block sanding". In addition to "block sanding", they also use the terms "body file",  "file board" and "file paper".

 

Google "auto body block sanders" and a world of information will turn up in the form of YouTube videos and supplies.

[Hirilonde]

Start with longest belt sanding belt you can find at big box store, build from there. Knobs at Lowes.

Belt sanding belts are the most expensive way to buy sand paper for a long board.  You can buy sticky back paper in rolls that allow you to build a long board of any length you like and re-paper for far less.  Just one example of the paper I am talking about can be bought on line at: http://www.onlineindustrialsupply.com/loboab.html

 

You can also buy the knobs and plywood for your long boards (or use scraps from your boat) at any full service lumber yard.  I think you will find the prices are as good as the big box stores and the employees actually know something about their products and can provide you some service.  If people keep going to the big box stores soon we will no longer have the quality materials we boat builders demand.  They are the Walmarts of the woodworking trades.  Every dollar you spend is a vote for where you want to buy things.  I choose to support the businesses that support their employees and the community they are located in.

[Miyot]

I've found that some sanding belts will often leave some deeper scratches here and there.   I have used them for long boarding.  I no longer do so.

[PAR]

Typically, sandpaper can be had in 2" to 5" widths in 150 rolls. Available in sticky or hook and loop backs. I like sticky or plain backed paper, as it's cheaper and isn't "squishy" like hook and loop can be.

[Lynn Watson]

Thanks, Paul and Dave, for the very useful info on longboarding. I can feel the upper body burn already :-)  It sparks a couple of questions, though:

 

---  What range of grits do you run through in the fairing/shaping process, before moving into the smoothing phase?

 

--- and more generally, what stage of the boat's assembly do you start thinking about fairing? It seems that with something as inherently floppy as 1/4" plywood, the hull is bound to change shape some as interior pieces get installed. Alternately, how do you set the right shape for the hull panels initially and then maintain it while you're crawling around inside measuring and scribing for bulkheads and bunkflats and other furniture?

 

Lynn

 

btw, I absoutely concur with your views regarding HomeWalDepotMart.

[Fishman38]

Long before Walmart came along most of the groceries were sold by chains such as Safeway, Kroger and so on.  Ditto for much of the other stuff that walmart sells.  J.C.Penny, Sears & Roebuck, Montgomery Ward and so on.  The difference?  Walmart treats their employees such that most don't feel the need to unionize, thus no union wages (or dues), thus no subsidizing of fatcat union thugs, thus lower prices.  I've known a lot of Walmart employees and customers, most of whom are happy with their lot.  Check out their parking lots.  Lots of small towns in the USA have access to goods within a couple of miles that would otherwise mean a round trip of 50-60 miles. 

 

BTW,  If you want to see what unions (the UAW in this case)  does to a company and city, look no further than Detroit.

 

All that being said, I do occasionally miss being able to talk to someone in a store who knows a thing or two.

 

Sorry, I know this is no place for editorializing. Just felt a couple of comments above needed a rebuttal. And sometimes I just have to stand up for Wal-mart. 

[Hirilonde]

Lynn, I virtually never use sand paper more course than 80 grit.  80 is a nice compromise between speed of removal, control over what is removed and ease of smoothing out the scratches later.  So for longboarding I would do most of the work with 80 and maybe go to 120.  After that I figure I have the surfaces fair and go to my DA aka RO sander and work from 120 to 320 to prep for paint.  Then 400 between coats.

[Fishman38]

This may be a big "no,no" but I have tried this and it seems to work ok:  I get about done with a gluing procedure and find that I'm going to be a bit short of mixture and that what is left in the container is starting to stiffen (kick, maybe?).  I add a pump stroke of A & B into the same container, stir and add thickener and proceed and it seems to work just fine.  Will I "pay later"?

[Miyot]

That is a not a good idea.  At least in most cases.  Once it starts to kick, it no longer has the penetrating qualities.  So it is not good if you are wetting out.  It can also make the new batch kick faster.  You could get a lump or a  really thick spot.  Not allowing the parts to come together completely.  I would not do it.  If you get caught at the wrong time, you could end up having to tear it apart and re do.  Epoxy is expensive, but I would avoid doing that. 

[Fishman38]

Advice well taken Miyot.  I'm pretty sure it's worked ok so far but I'll not take that chance again.