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Anke and I are building our next boat, and writing about it at ABargeInTheMaking.blogspot.com. Access to the net comes and goes, so I'll be writing in fits and spurts.

Please feel free to browse the archives, leave comments where you will and write, and I'll respond as I can.

Fair winds!

Dave and Anke
triloboats swirl gmail daughter com

Monday, January 11, 2016

Deck Sheathing: Alternatives to Fiberglass Fabric and Plastic Resins

DYNEL Acrylic Fabric
as sold by MAS Epoxies
(Only $8.50/54"yd at this writing!)

 

Rain on the flowers,
Rain on the trees,
Rain on the rooftops,
But not on me!
 -- Mother Goose


Deck Sheathing: Alternatives to Fiberglass Fabric and Plastic Resins

Plywood decks are strong and easy to build, but not naturally waterproof. Sealers, paint and/or saturating resins help, but are relatively fragile... wear and tear from traffic soon allows water to penetrate. Sheathing is an attractive option.

Sheathing is a layer of fabric which is saturated by - and provides a matrix for - a waterproof substance which, once cured, bonds this layer to plywood, forming a composite structure.

Nowadays, a matrix of fiberglass cloth set in epoxy or polyester resin is nearly universal. For many reasons, Anke and I prefer an alternative suite of materials and techniques, which we learned about back in the day. To my mind, they are much more amenable to amateur construction, and worth considering in many applications around a home-built or modified vessel.


Current Practice

GRP (Glass Reenforced Plastic aka fiberglass) is undeniably wonderful stuff. It can take on most any shape, and be layered up into a skin which is itself structurally adequate for hull construction. But for sheathing its strength is wasted.

Pros are that the matrix is reliably waterproof and generally long-lived. There is abundant information available for its application. These resins are very versatile, and may already be in service for other tasks around the boat, spreading the costs of special tools and accessories.

Cons...

Fiberglass isn't particularly nice to work with. It tends to fray messily, and when trimmed, it often produces needley, itchy li'l hairs. Both are made worse when smeared with uncured resin. No fabric likes to make a sharp turn, but glass fabric is particularly fussy. Grinding to smooth is toxic and itchy.

The relatively hard matrix can craze or shatter under impacts, leading to delamination and requiring a wider area repair. This is of particular concern for bottom sheathing where grounding the boat is desired. Even small rocks can compromise GRP sheathing, so substantial repairs can be a seasonal chore.

Worst, glass is inelastic and plastic resins little more so... plywood expands and contracts a bit with humidity and temperature, and glass doesn't like to move with it. The result is shear forces between wood and sheathing, increasing chances of delamination. White finishes help considerably to reduce thermal movement.

Note: In this regard epoxy, which has smaller molecules, is preferable to long-chain polyester resin, and its performance is generally considered to be acceptable. Good results have also been obtained with polyester resin with good attention to surface preparation, catalyst proportions and thermal sequence). In other words, the problem aren't insurmountable in either case.

Plastic resins are toxic, exothermic chemical admixtures (can spontaneously burst into flame) involving solvents; they do best in fairly well controlled building environments and impose strict working times; they're expensive and require special tools and heaps of disposable accessories.


Acrylic Fabric, an Alternative to Glass

Acrylic fabric – often referred to as DYNEL after a former, proprietary product of Dow Corporation – is an inexpensive, soft yarn synthetic (rot proof) which wets out well, conforms well, frays only moderately, and is both elastic and highly abrasion resistant. It is often used for drag strips to protect the keels of GRP kayaks from chafe.

Acrylic has been extensively used with epoxy resin to sheath high-end plywood hulls by Reuel Parker and others. It does not contribute significantly to total strength, but that is supplied by the wood it protects (note that dry wood is much stronger than wet).

Being elastic, it moves with plywood. Crazing or shattering, when it happens at all, is limited to a local area. Shear stresses are low, so local damage is much less likely to spread, making repairs a much smaller task.

Grinding acrylic doesn't throw a cloud of glass shards, but does tend to fuzz and pill. This can be shaved, however, and if necessary, a final topcoat of pucky may be applied after grinding.

One caveat... I've read that acrylic should not be used with polyester resin. Dunno why. Our samples showed no short term problems with polyester resin, catalysts or cured resin (that is, nothing melted). In the longer term, we used acrylic/polyester for our dory chine chafe strips... they held up as well as their glass epoxy predecessors despite much poorer application conditions.


Non-PlasticResin Pucky

For many years, DIY boat builders decked with various fabrics (even burlap!) set in asphalt tar, paint and (of particular interest) lagging compounds – various latex puckies used to saturate cloth wrapping for hot water pipes. The huge advantages are economy, ease of application and water clean-up. It is also very easy to repair.

One favored product was ARABOL (now unavailable), which was essentially waterproof Elmer's Glue (both made by Borden Corporation as lagging compound). We used this with glass fabric to sheath LUNA's decks, which were still looking good at the 18 year mark. We know of one lapstrake(!) hull which was fully(!!) albeit sloppily sheathed in ARABOL/burlap to give it an extra decade of live-aboard life.

Lagging compounds tend to finish rather soft... a thumbnail can leave a dent, and a floppy block can wear a hole. Chafe protection in choice spots and prompt repairs easily keep up. 

Overall adhesion, while sufficient, is rather low. This can be an advantage when replacing as the entire matrix, once started, can be peeled away with relative ease. This makes it a good underlayer for asphalt products without commiting the underlying wood.

In WAYWARD, Anke and I are experimentally decking with acrylic plus TiteBond III. It cures to a plastic, slightly elastic sheet which is harder than lagging compound and fairly similar to epoxy/polyester. It is cheap (in bulk), very low toxicity, needn't be mixed and wears a lot of hats.

This method passed our 7 month immersion tests in salt water. It adheres to our wood (radiata pine)'s full fiber strength, so is very strongly bonded.

At present, WAYWARD's sheathed and topcoated deck has been sitting out in winter rain/freeze/thaw cycles for four months, and reports are that it's "looking good".

In a sense, we were fixing what weren't broke; we were perfectly happy with the soft deck. But TBIII certainly wears more hats than lagging compound, so we decided to take the risk for science.

You're welcome!  8)


Application of Fabric plus Water-Based Pucky

Application consists of the following steps:

  1. Sweep and wet-tack for a dust-free deck
  2. Lay out fabric (may be overlapped, but abutting is sufficient and smoother)
  3. Wet out fabric (Yep. Water... drippy wet)
  4. Paint on pucky (may thin somewhat with water, if necessary for low-drag)
  5. Dry
  6. If not satisfied, repeat from 3 (a bit of weave left provides texture)
  7. Prime and top-coat

The first round of 1-4 is the primary adhesion step. As the water dries out of the weave, waterbourne pucky wicks (is drawn by capillary action) down into pores of the plywood substrate, creating a permeating bond interface. Subsequent layers build to coat and fill the weave.

On a warm, dry day, water evaporates quickly. If the fabric is drying ahead of you, consider keeping a water-brush on hand to refresh the wet. Without that water, wicking is reduced, and glue may not dilute and penetrate the fabric or wood surfaces for full adhesion.

At the end of the first pass, the fabric is only lightly bonded, however, and can be fairly easily torn away. It is reenforced by subsequent passes, however, and the result is firmly attached.

Consider whether to leave some weave for texture (thin matrix), or fill past the top of the weave for longevity (thick matrix). In the latter case, you might consider added texture in the topcoat.

My only semi-eddicated opinion is that green (not completely cured) layers bond better. Thus many layers can be applied in a single day. I especially like to prime over a green layer, in effect gluing the primer to the matrix. The whole seems to cure well over ensuing days (possibly even faster than the generally indicated 24 to 48 hours).


Topcoats

Most standard topcoats can be used, keeping in mind that the more elastic the matrix pucky used, the more elastic should be the topcoat.

Our preference is for flat latex housepaints (trim or porch enamels are most durable). If we leave the weave unfilled, this provides sufficient texture for good footing. If desired, SKID-NO-MORE adds ground rubber to a latex base.

Aluminumized trailer paint (ATCO SILVER SEAL is the best we've tried), applied with a short nap roller, provides great footing, and can be built up to an independently waterproof layer, especially along interior corners. It's messy, however, with lots of solvent... we've abandoned it for the most part.


Repairs

Puncture – Repair any wood damage. Patch with fabric, if necessary. Rebond as above. For small punctures, a shot of latex caulk or dribble of latex paint will do.

Abrasion – Patch, bond and topcoat. Consider a chafe patch or ropework, or eliminate the source.

Delamination – Slice the matrix to peel back. Inject latex caulk as deeply as possible. Work away from the slice to fill the blind pockets, then reverse and work toward the opening. Squeeze any excess out and smooth. Topcoat.

Repaint – We like to spot paint as the topcoat wears through to primer, and repaint fully when it gets widespread. On SLACKTIDE, that seems to be a full recoat every four or five years. We've never tried it, but I see no reason not to add pucky over paint if general re-thickening of the matrix seems advisable. In general, we try to avoid wearing down into the fabric itself... so far, no more than paint has seemed necessary.


* * * * *

Acrylic is great stuff, and useful in many places where glass fabric is structurally unnecessary. It happily works with epoxies, but also with much friendlier, water-based products.

Consider the application and what is demanded of it. Will a cheaper, easier, more benign suite of materials do the trick?

If so, why not?





A Note on Longevity

Rule of thumb on fishboats was that a lagging/burlap deck would last about 15 years. Synthetic fabrics were thought to last longer somewhat longer, perhaps to 20 years. Use and quality of application likely played a role.

Epoxy decks are generally considered to last 20 to 25 years, I've read.

The problem for comparison had been that most side-by-side data was generated by yachts vs non-epoxy workboats (which have only fairly recently 'gone over'). Even full-time cruisers don't give their decks the workouts that a fishboat takes. In addition, a mid-season epoxy repair is a non-starter for a working vessel. That being said, non-epoxy fishboat decks likely gets/got more new layers slathered on, here and there, than the yacht.

My guess is that they may be fairly comparable if traffic loads are taken into account?

17 comments:

  1. what about polyester/titebound III over rigid foam?

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  2. what about polyester/titebound III over rigid foam?

    ReplyDelete
    Replies
    1. Hi Everitt,

      My guess is that TBIII will work with any woven fabric.

      We've been using it and Gorilla Glue on foamboard, and both get a fair grip.

      They can be peeled off the smooth faces, once started, so maybe a light sanding of these to provide 'tooth' and increase surface area? Can probably skip this step (we do) where the edges are interior and/or protected.

      Consider that the bond is only as strong as the foam itself (which will usually tear away long before the bond gives).

      Dave Z

      PS. If you mean polyester RESIN and foamboard, test for sensitivity to acetone and MEK catalyst. Chances are the board will melt somewhat in contact with these.

      Delete
  3. Great post Dave...I'm tempted to try it with our boat but will likely stick with the Epoxy/Dynel treatment below the w/l. Everitt, I think that dynel (I think you meant) with Titebond III over foam would be a great idea! The Titebond will not attack the foam, and I know that it sticks really well.

    ReplyDelete
    Replies
    1. sandwich? dynel/foam/dnyel construction? would plywood bee needed at all?

      Delete
    2. Forgive me if I'm getting stupid..but I have a question.
      Suppose...the boat was assembled from rigid foam..the interior surfaces were laminated with dynel (nylon, polyester, burlap, whatever )...and TiteBound III

      Suppose the Exterior surfaces and high wear areas would be ferrocemented using basalt fiber ( fiber, grid, what ever, it comes in many configurations)...and cemented. Portland cement and sand...concrete..Make a thin shell cement structure with the foam as the mold..

      no ferro no rebar...basalt fiber only. It has interesting properties , such as having the same expansion coefficient as cement...and seems like it should work well for boat building...someone made a cement canoe with it.

      it that configuration completely off the wall?

      Delete
    3. Hi Everitt,

      You're beyond my experience, but sounds promising.

      I see no off-hand objection to foam molds for ferro-cement, so long as they can stand up to the pressures involved. I've seen concrete spilled on foam, and it adhered as well as anything.

      The fabric should be glass or equivalent, and thicker if you want a structural girder to result. Other fabrics okay if just creating a cleaning surface, though it may be puncture prone.

      Hard to say with the glue, but TBIII might work in lieu of epoxy/polyester resins.

      Small scale testing, tested to destruction is informative and fun! Try to stress the test structure as it would take it in the real world (i.e., compression, tension, sheer, torque and peel forces as applicable). Lot's of creative ways to test.

      Dave Z

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    4. Hi Again,

      Above you asked:\

      Sandwich? dynel/foam/dnyel construction? would plywood be needed at all?

      Dynel doesn't have a lot of structural strength compared to glass fabric (this is mostly in tension... acrylic will pull apart or tear much sooner), so glass would be preferred.

      MAYBE in a very small, lightly strssed hull (like a paddling kayack), but I'd be sure my lifejacket was buckled up!

      Dave Z

      Delete
  4. Never knew what the deck covering was made of in the 5 years we had Luna. In that time any problems were solved with aluminum paint and sometimes a bit of clear caulk. Thanks for experimenting with TB3. Yet another great cost saver.

    ReplyDelete
    Replies
    1. Hi Bob,

      That was a non-Arabol lagging compound, whose name I've forgotten. Was white and creamy (Arabol was very like Elmer's, and translucent).

      Funny LUNA story... we strip-planked her deck from 2x2s, finished flush above and a pretty, seamed look below. But we had more lagging compound that we needed, so thought, "Why not try between strips?"

      Worked great, but left snot-noses dripped slightly down like mini-stalagtites. But soft... no problem... we'll get to them later.

      Well, later they hardened to stubborn, rubbery consistency. Chisels shot through and into the wood, marring the interior surface.

      A cold, winter month went into Dremel tooling them smooth, sanding and filling, all overhead in sitting headroom!

      Nowadays, immediate wipe-down is the rule!

      Dave Z

      Delete
  5. Hi Dave,

    Way to stick your neck out for science!

    Agree ... great article on subject matter I've been wondering about. Some questions please, basic as they may be:

    1. Pucky? From context, I think I can deduce you mean TBIII, but I'd like your definition. Where I come from, "pucky" is what the gentler grandmothers say instead of "bullshit".

    2. What is the purpose of using acrylic fabric (or any fabric) on the deck vs. using the TBIII alone? Seems the fabric doesn't provide structural strength, and the TBIII has to protect the fabric, vs. the fabric protecting anything.

    3. Regarding application:

    a. When applying over green (or still tacky) previous layers, how long do you wait? Looking for the Goldilocks spot.

    b. After the first layer, do you wet the surface again before applying subsequent layers?

    c. You mentioned the possibility of adding texture to the topcoat. I've heard of clean, dry beach sand being used. Any reason to avoid that?

    4. When you used Atco Silver Seal, didn't it cause you to have to put sunblock under your chin due to reflection?

    Yoda

    ReplyDelete
    Replies
    1. Hi Yoda,

      Okay, here goes...

      1. Pucky? From context, I think I can deduce you mean TBIII, but I'd like your definition. Where I come from, "pucky" is what the gentler grandmothers say instead of "bullshit".

      >>> Pucky, glop, schmooey... all general terms for glues, beddings, and coatings that are generally (but not always) thickish and smeared or spread.

      Not sure how far these terms travel, so test the local waters! Don't want to start a boatyard brawl. 8)

      2. What is the purpose of using acrylic fabric (or any fabric) on the deck vs. using the TBIII alone? Seems the fabric doesn't provide structural strength, and the TBIII has to protect the fabric, vs. the fabric protecting anything.

      >>> Glues and resins aren't always that abrasion resistant on their own, and often weak in lateral tension (can pull apart across their thin dimension, resulting in cracks an crazings).

      A weave provides much stronger resistance in lateral tension, and reenforces the film against direct abrasion. Dynel, with it's own high abrasion resistance seems especially good at this.

      You'll see a similar effect in asphalt tar roof patch directions, which call for embedding fabric tape when spanning gaps.

      3. Regarding application:

      a. When applying over green (or still tacky) previous layers, how long do you wait? Looking for the Goldilocks spot.

      >>> I don't have an educated opinion on this. Too soon and it redissolves with the new water content from the next coat. Too late and ???. Probably nothing too bad... it seems to adhere just fine.

      So I personally go for when it looks and feels dry, but is not fully cured (period specified in instructions). On a hot day, this can be as quick as cycling from one end of the deck to the other. If it looks like its softening with the new coat, I'd wait a bit.

      You can put your hand flat on it and, if it's still evaporating moisture, it feels relatively cool. This gives some feedback on where it is in its cure state.

      All in all, it's seemed very forgiving. We've never had a problem, whether erring this way or that.

      b. After the first layer, do you wet the surface again before applying subsequent layers?

      >>> No, only that first one. After that, the only water added is to the pucky... just enough to keep the brush from dragging.

      These are build-up coats from which the water is going to evaporate, anyway. The first water/pucky layer fills the threads and pores, so I doubt there'd be much if any wicking action after that.

      c. You mentioned the possibility of adding texture to the topcoat. I've heard of clean, dry beach sand being used. Any reason to avoid that?

      >>> Some don't like it as it's hard on sanders and other tools. Ground walnut shells are a traditional alternative. I kinda like ground rubber (which can be DIYed with an old tire and an angle grinder), if anything.

      One interesting method was to spread Epsom salts on the last topcoat, forming a micro-jagged surface. The salts wash away at the first rain.

      Not sure if that works with latex, but I seem to recall, yes.

      4. When you used Atco Silver Seal, didn't it cause you to have to put sunblock under your chin due to reflection?

      >>> That's what the beard's for! 8)D

      Seriously, we only used it on our mid-deck, so didn't spend much time there. The water's already quite the solar oven. Some sort of block recommended.

      Hope that helps!

      Dave

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  6. "Not sure how far these terms travel, so test the local waters! Don't want to start a boatyard brawl. 8)"

    Yeah, a few of your favorites probably fit in that category. When I read one of the common ones -- "spendy" -- I thought it was a Dave-ism. Then I decided to look it up and discovered that it is actually a regionally accepted term from the Pacific Northwest found in the dictionary. Who knew?!? I definitely would have lost the Scrabble challenge on that one ;-)

    Thanks for the great answers.

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    Replies
    1. Hi Yoda,

      On the flip side, it would never have occurred to me that 'spendy' isn't standard Murrican!

      Having been myself for so many years, I admit it's getting hard to tell which are Dave-isms and which from my native tongue.

      Worse, my addiction to spoonerisms can trip me up. Doesn't help my reputation as a fart smeller. 8)

      Dave Z

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  7. Hi Dave!
    I'm a little late to this post, but I'm looking to redo the deck of our pontoon. At first we considered fiberglassing the entire thing (8x20 ft) but that takes a lot of time, is very tempermental and can be quite expensive. Basically we want to make the plywood deck waterproof, then we will be covering it with carpet so footing won't be a factor in what we use to do it. I think maybe the acrylic fabric would be best per the post but wanted to get you opinion on it first. This is our first boat so we are kind of clueless!

    ReplyDelete
    Replies
    1. Hi, um... shall I call you Witness? 8)

      We're sure liking the acrylic, though Ive been getting reports that lots of synthetic fabrics do fine.

      TiteBond III is looking good, now for its second winter. Primed and painted with flat latex, footing has been good and is holding up well (will get a second coat this coming spring after 2 winters on 1st coat). Carpet might not be necessary... it's certainly harder to clean!

      All in all, synthetic (non-glass) fabric and TBIII (harder) or lagging compound (softer) have all proven easier and cheaper than glass/resin, and are looking good for longevity.

      Hope that helps!

      Dave Z

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    2. BTW, 8x20ft happens to be the size of our mid-deck. It only took a couple hours for the fabric and first glue, then a little more than a half hour for each subsequent coat of glue or primer/paint(I think we only went two coats of glue, but maybe three). -- DZ

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