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Dave and Anke
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Monday, August 8, 2016

More than One Way to Sheath a Boat

Better Living on the Milky Way
Borden's ELSIE

Hell has an entire level devoted to... wrapping.
- From the Internet, Somewhere

More Than One Way to Sheath a Boat

Once upon a time, before Epoxy was crowned King of All and took Fibra Glass to be his Queen, there lived a simple lagging compound named Arabol, and his true love, Dynel.

Wait. No. Is this any way to talk about boatbuilding??? Let me start again...

Arabol was once made by Borden, Incorporated, a dairy on steroids. Trademarked in 1905, it was a milk-based  product which was essentially waterproof Elmer's Glue (better known Borden product).

Arabol's main commercial use was as lagging compound.

I know... I had to ask, too. Lagging is the cloth once used to wrap hot water pipes for insulation and protection of those who might otherwise burn themselves. Lagging compound is a latexy substance used to saturate and waterproof lagging, making sort of a softly plasticized cast.

Someone along the way realized that this stuff could be used to sheath boats (generally, but not always above the waterline). BRILLIANT!!!

To apply, lay down fabric - anything from burlap to mosquito netting to fiberglass. Wet it down with water and slap on a first coat of compound. Once dry (which can go quickly on a warm dry day), add another full-strength layer. Repeat until the desired thickness is achieved. Topcoat with flat, latex primer/paint (one among many options).

The result was said to last 15 years or more.

Borden quit making Arabol by the time we built LUNA in 1997, so we tried Childers Chil-Seal (Marine variant CP-50A HV2) over fiberglass cloth. Nineteen rough-shod years later, it's still looking good.

These decks are a bit soft... one can dent it with a fingernail or pierce it with a dropped anchor, but tougher than most traditional canvas. But they're not easy to harm, and easily repaired if you do. Should you want to take up a section for any reason, they have relatively low peel resistance and come up easily with no grinding.

Further alternatives might be other lagging compounds or water-based, concrete sealer?

Recently, we're trying the same approach with TiteBond III, made by Franklin International. It's applied by the same procedure, but finishes to a much harder surface, almost indistinguishable from epoxy. Our new hull's decks are sheathed with it, and it has now survived a year of Southeast Alaskan weather with no sign of trouble.

As noted in the comments by astute readers, it may be that new TBIII won't readily bond to itself after full cure. For multi-layer applications, we've always done 'wet over green (not fully cured), and ditto for any topcoating of primer (though one topcoat test bonded well to fully cured TBIII). My intuition is that, roughed up, the bond should be reasonable to good, but that has yet to be seen.

Dynel is a trade name for woven acrylic fabric once made by Union Carbide. Jamestown Distributors still sells 5oz under that name, and my guess is most any woven, and possibly knit acrylic will do. Alan Jones reports good texture results from acrylic fleece, but that it drinks glue.

Acrylic is highly resistant to abrasion, and often laid over kayak keels to protect fiberglass/resin. It's cheaper, easier to handle and better conforming than glass fabric without those itchy shards. Grinding can 'pill' or 'fuzz' it, but that's easily shaven smooth with a sharp scraper.

So our state-of-the-art is Chil-Seal (proven) or TiteBond III (awaiting further results) with acrylic cloth.

Cheap, easy, pleasant, non(or ver lowly)-toxic, easily maintained...

...Just the thing for the quick and dirty among us!


More on water-based alternatives, here.

By the way...

We used Chil-Seal between LUNA's 2x2, red cedar, strip-planked deck planks, since it was on hand and extra. Turned out to be quite adhesive and filled the gaps easily between the un-bevelled edges as they followed a 6in crown. Undiluted, it was about like gap-filling toothpaste, as I recall. Dried to a sandable solid, like old chewing gum.

We didn't clean up right away with water, and regretted it later. I set up firm enough that we couldn't easily cut it. Burred it away with a Dremel tool along the underside grooves. The things we do for vanity!

I'm thinking Chil-Seal or equivalent would make a very friendly adhesive for general strip-plank construction. It's modest elastomericity would help prevent longitudinal edge failures sometimes seen with epoxy and other rigid glues.

LUNA's deck before sheathing


  1. I did experiment with the fleece but will not be using it on Autarkia. In my experiment I reduced Titebond 3 by half with water and saturated the cloth before simply laying it on the plywood. It did stick quite well but because the fleece had a natural tendency to 'puff up' it looked like it need many more coats of Titebond afterward, which I did not do with the experiment. My best result for the deck, which I will use on Autarkia is 2 layers of 10 o.z fiberglass. Here's how I put it down in my experiment: First layer went down dry, and then wet with water using a paint brush. Then blot with a towel. Apply the Titebond heavily and allow to dry but not fully cure. Apply the second layer with the same method. My test sample proved to be very tough, and it was impossible to peel anything away. For my house sides and roof though, I'm looking for some acrylic cloth from the local fabric stores around here - something fairly lightweight with an open weave to facilitate the glue application.

    1. Hi Alan,

      Thanks for the clarification!

      I'd guess that it would work, but I sure wouldn't want to take a tumble anywhere the nap stood up... it would be like cat's teeth!

      I'm interested that you blotted the wetted surface. We never felt the need, and in fact had to re-wet ahead of ourselves if it was drying too quickly.

      We heard that the theory behind that first wet-out is to wick the compound deep into the wood pores for best adhesion. Not sure it helped, but certainly didn't hurt.

      Another place we used acrylic (tape)/TBIII was over butt seams, both inboard and out. Z


  2. As an aside, Titebond is SO much more pleasant to work with than epoxy or polyester. I think it is a wonder product.

    1. Hear, Hear!

      And ditto for all the water-based alternatives to the various puckies and schmooies we inflict on ourselves, our pockets and our boats!

      As time goes on, the performance gap, if any, is shrinking fast!

      Dave Z

  3. Posted on behalf of JOHN:

    Hello Dave,
    I've heard that uncured TiteBond III adheres poorly to cured TiteBond III. If true, this would suggest it's a poor choice for glue/fabric laminations. Do you have any experience with TB III glued to itself?


    1. Hi John,

      This may be true, though so far I've not seen any hint of problems. Where we've spilled liquid TBII droplets on to cured surfaces (not even dusted or worked in), we have to pop it off with a knife once set up.

      I'd be real hesitant to try it on a structural join upon which I depended. But for sealing and (with some more testing) sheathing, I'd be comfortable.

      It hasn't seemed necessary, but if in doubt I'd consider roughing it up with sandpaper before applying, to give it 'tooth'.

      Another approach might be to use a heat-gun to soften the cured layer, slightly. This might work in conjunction with water or steam. Haven't tried it, though, and this feels like a last resort.

      So, while adhesion may be less than optimal in this case, it still seems pretty high. Certainly as much or more than paint.

      Dave Z

    2. When I did my test with the two layers of 10 oz fiberglass cloth and Titebond 3, the first layer was completely cured (over two weeks old) before I applied the second layer as an afterthought. It bonded very well and I could not peel it off at all. So I'm pretty sure that for laminating cloth anyway, gluing over cured Titebond is not a problem. I had read the same argument in the forums by the way 'Titebond 3 will not bond to its cured self'. That is why I made that test with the second layer. It is quite well bonded. For insurance though, when I do Autarkia's decks, I will do the second layer as soon as the first is dry enough to walk on in socks.

    3. I heard that you don't even need to overlap the seams between single fabric strakes... just lay them reasonably close. This worked well on SLACKTIDE (7 years, now, and no probs).

      Given that, you might consider going with a single layer of fabric? You won't gain any structural advantage, so it might add weight, cost and effort with little return.

      Of course, one can never stay too dry. 8)

      Dave Z

    4. Well, I going to use the two layers of 10oz fiberglass on the decks because of wear resistance. And because I have enough and can't see using it anywhere else. Overkill perhaps but then I'm not a 'proper boating footwear mandatory' kind of guy... :-)

  4. Dave, did you strip plank your deck? Looks like it in the picture at the top of the post....

    1. Hi Alan,

      Yes, on LUNA. Worked out well, but we decided it was a) more labor intensive, and b) those super nice 2x2s have gotten expensive.

      On SLACKTIDE and WAYWARD, we went ply/foam/ply. ST is sheathed in epoxy/fiberglass, and WW in TBIII/acrylic.

      Dave Z

    2. I just smacked myself since you are not here to do it. If I had read your post more attentively you would not have had to answer that redundant question. Sheesh... I hate getting old :-)

    3. Good ole Dave ... back from the dead! ;-)

      "I hate getting old": Me too. I'm now starting to do dumb stuff that always made me mad when lesser beings did them! ;-)

      Joining this topic late. Not sure if I'm playing the role of "emperor has no clothes" or "questioner has no clue". In any case, despite all of the reading I've done on this topic, and questions asked and answered, I have somehow failed to grasp (or forgotten) the most basic fact about it:


      As far as I can tell, in nearly all cases (except maybe Al's e-glass), there is no structural advantage. And, epoxy or paint would adhere to the wood just fine without any fabric at all.

      So, I've read lots of fabric this and glue that, and the fate of the free world hanging on seams or overlaps, but why in the heck go through the trouble and expense of sheathing decks and superstructure with any fabric at all? Why is that substantially (justifiably) better than just using straight epoxy and paint? Or just paint?

      Please use small words in your reply ;-)

    4. In my case where I'm using fir plywood, it must be covered with cloth when exposed to the elements. A coating alone (epoxy, paint, glue, etc)won't keep it from checking. That's where the top layer of veneer splits and curls up. It usually happens after a few years of exposure. The advantages of fir - mainly strength - outweigh this one disadvantage. Other plywoods won't check and they will do well with just paint. But you have to stay on top of damage, bashes, punctures, etc. So a layer of cloth is beneficial in this case as well, because it creates a tougher surface.

    5. Why Fabric:

      Fabric is 'the carpet that ties the room together'. It reenforces and cross-links the binding compound, virtually eliminating splits in the film (as from the checking Alan mentions). It also provides an abrasion resistant matrix which protects compounds from direct abrasion and dings, as from foot traffic.

      Our practice has been to sheath decks, cabintops and seams, but not anything else. We do ding it and the radiata pine ply checks as well (most AC types do), but without (apparently) any worse than seasonal wear and tear. Wood can take some exposure in stride, or at least with acceptably low consequences, I believe.

      It's a tough call. I think that full sheathing is likely preferable, but likely doesn't pay for itself in time/cost/energy. That's for each builder to weigh.

      In THE NEW COLD-MOLDED BOATUILDING, Reuel Parker lays out a strong case for full, epoxy encapsulation, and such eminences as James Wharram agree, especially when using less than top-notch materials.

      It may well be that whether one lives aboard (can deal with small issues as they arise) or not (issues wait for seasonal remediation) may tip the scales.

      Good luck on seas of ambivalence! 8)

      Dave Z

      P.S. Many recent sheathing systems such as Tufflex and Syntex are elastomeric and supposedly do not require fabric. That is, they stretch by a percentage amount of elongation, and claim to 'move with the underlying wood. As usual with higher tech, they're expensive, toxic, finnicky and harder to repair.

      Lots of fisherfolk have used them, and some are happy with then. But many are not. And I see lots of hairline cracks that are not supposed to happen, even on new decks.

      Our first boat came with this type of sheathing, about 2 years old, but had already failed in several spots.

      Almost any system, including tar roofing, calls for fabric tape to span any considerable break or seam.

    6. matrix
      elastomeric (for Christ's sake!)

      What part of "small words" did you not understand, huh?????


      Actually, I dodged all of those mines successfully. Ironically, it was a small word that got me -- film.

      As in "Rocky Horror Picture Show"?

    7. "Supercalifragilisticexpialidocious!

      Or you could say it backwards, Dociousaliexpaisticfragicalirupes, but that would be going a bit too far, don't you think?"

      There... see what comes of a classical education?

      But I digress. 8)

      FILM as in a film (thin layer) of paint or plastic. Often you'll find its thickness specified in MILS, or thousandths of an inch.

      Basically, it's fabric-less pucky spread thin and dried solid.

      Dave Z

      Oh. I just received this note from Dr. Scott:


      That 'movie' was a PICTURE SHOW, harkening back to when the celluloid FILM used to generate one hadn't yet become the generic term associated with its end product. Yet another vulgar case of confusing the message with the medium.


      Dr. Scott

      (Great Scott!)

  5. Thanks all around. My "why" question has been well answered and in a most delightful way.


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