how to smooth lapstrake seams

I'm a first time builder, and while I was successful in getting the lapstrake seams of my eastport pram filled with thickened epoxy, the joint is lumpy in places with high and low spots, and there are marks in the hardened glue where the copper wires ran across the seam.

I'd like for these seams to be smooth the length of the boat before finishing the hull.  I've had success grinding down some of the lumps with a dremel using a quarter inch sanding drum, but the surface is still uneven.

It was suggested that I lay a "final fillet" along the length of the seams to smooth things out.  I can see this working, but in places, the existing glue is right up to the surface of the "gutter" created by the seam, and I'm concerned that this approach will only work if the entire length of the seam is concave (allowing for the new fillet to fill the void).

Has anyone else confronted this?  Any advice for tools, techniques and solutions?  My inner perfectionist is going crazy with this stuff.

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RE: how to smooth lapstrake seams

   Shinto saw rasp. Get the one that has the handle on top. It will lay on top of the lap and you can take off as much as you want. Just don't put to much pressure on it 

RE: how to smooth lapstrake seams

I used a wood dowel of the correct diameter for the shape you're looking for, wrap with sandpaper and go to town.  Also, don't forget the trick about smoothing epoxy fillets before it gets too hard with a gloved finger wetted with denatured alcohol.  Save a ton of sanding, works great, and leaves a nice, slick surface.

RE: how to smooth lapstrake seams

   I used a combination of a tapered rat tail file or a chainsaw file on my lap strake joints to smooth out bumps and generally make the seams consistant.

These files work great for the first cuts on drips or runs rather than trying to sand it all.

Use a wire 'tooth brush' to keep the files clean.

RE: how to smooth lapstrake seams

   Thanks all.

Based on a recommendation from CLC, I opted to lay a thin fillet over each seam and that did the trick.  A light sanding should neaten everything up nicely.

RE: how to smooth lapstrake seams

I use an Oregon at work to sharpen customers’ chains... makes a tedious job (done w/file, guide or no guide) a piece’o’cake. (Pricey though, but if your time’s valuable it might be worth the investment.)

Unless customer’s been doing it themselves w/file & teeth aren’t at all even anymore. Still better than the file way but teeth get real short real quick even if it take three, four laps around each chain.

And if you’re cutting lapstrakes with a chainsaw, I want to see the boat you’re building!! 

RE: how to smooth lapstrake seams

CLC sells these:

...which would help.  I didn't know of them until after our project (Passagemaker) was finished, but I have them now.  Handy for all sorts of shaping jobs.  The next CLC kit (it's addictive, somehow) will be easier that way.


RE: how to smooth lapstrake seams

   The rasp set is pretty cool. But doesn't it appear that you might end up rasping the palm of your hand as well as that pesky nook in the boat?

RE: how to smooth lapstrake seams

   And the lesson learned might be obvious for "next time..."

I have found that these steps help with a prettier - and much less labor intensive - lapstitch lapstrake joint:

Achieve seams as well aligned and as tight as possible by adjusting wires.

Tack weld well with CA glue.  Use packing tape backing to prenent glue spots from running through to back side of joint if necessary.

Pull your wires.  If desired, you can achieve nearly invisilbe stictch holes by filling these with epoxy/wood flour paste at this point.  Use a scraper after pressing paste into each hole so that you don't leave any lumps to sand.

Back any remaining gaps that might leak-thru to the oposite side with blue or packing tape, pressed down deep into the gap.

Consider rotating your boat so that only a couple of seams are done at a time.  Rotate so that the epoxy filling the seam will create the fill-angle you desire between the two planks.  This will prevent some seems from being near 90 degrees (hard-step) fill angles, while others are at less aggressive angles. I think about 10-20 degrees is about right.

Mix your epoxy cell-o-fill paste - and because you've ensured you don't have leaky gaps, you might keep it a little more runny than otherwise specified - that will allow it to flow a bit for a nice smooth filet-seam.

Get two turkey basters for the outer-hull side seams.  Use a partner to fill one while you empty the other into the seam.  Create a nice constant fill level in the seam by moving smoothly, trying to avoid over-fill drips.

When the seam fill is partially set up to the right consistency (keep your eye on it) use the rubber glove and alcohol trick to furhter smooth the filet-seam as necessary.

When all seams are completed from the outside, remove any tape you put on the inside of the seams. 

Here is something not in the book: I had great success putting a smaller fillet-seam of epoxy on the inside of all seams.  There won't be any chance of run through - and the relatively smaller seam gap means that you can usse two large plastic syringes instead of turkey basters.  Use the same process as for the outside, including the alcohol smoothing when the time is right.  This really works well to hide and harden that inner edge of plywood.  

If done well you can create some very nice lapstitch joints this way, requiring very little sanding.  The time and effort put into this process is much less than sanding after the fact.

Good luck!  And if testing this out means you need to build another boat, well then - build another boat!


RE: how to smooth lapstrake seams

This is funny - a bogus spammer with a BS story to get you to click on a spam link reinvigorated a 3 year old thread.



RE: how to smooth lapstrake seams

I did wonder about the chainsaw business--never clicked on the link--but didn't notice the date gap.  Should have looked more closely.  Well, heck, it was a good discussion, anyway!  Might have learned a new trick or two, though I do wonder these days whether it is even possible to reteach an old dog his old tricks, never mind any new ones.  <;-)


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