glass or dynel over plywood decks - like tim's daysailer

[boatsnh]

Tim used 2 layers of fiberglass on the plywood decks he did on the daysailer project a while back - seems like a lot of glass & a lot of work to fair to a smooth finish. A bunch of the "wood boat" guys just use a single layer of Glass or Dynel/Xynole to waterproof plywood decks/cabin tops...

My old polyester/glass (from 1973) is shot, so I'm replacing it all this spring - oh joy - and thinking I'll use 8 oz glass & fill the weave or xynole/dynel and do the same. So.....The old deck was Polyester & 8/10 oz glass....probably did it's job for 30-35 years....Not too bad a run. I suspect Epoxy & anything in the 8 oz range will be here after I'm in the ground I'm not going to leave the "weave" showing, since I've had a "non-skid" type deck and like the look (Epifanes non skid deck paint) Anyone out there have any experience with this operation - covering plywood decks?? If I use heavy fabrics I can see Lots of epoxy vanishing. The cabin top is 80 sq feet and the decks are substantial (36 foot long) - oh, and the cockpit sole too - 9 x 3.....

I did some "test" panels a week ago on plywood - A. 4 oz Xynole B. 8 oz glass & B. some 5oz polyester cloth I had. The Xynole is tough stuff....beat on it and not much happens. The glass is smoother & easier to fill * not quite as tough with sharp objects (screwdrivers, hammer claws) - the polyester is smooth but more of a pain to wet out - so that's out. An interesting study.... I might try a "test panel" of the Xynole and 4oz glass cloth to act as a "scrim/finish" coat to soak up excess resin & provide a smooth surface - worth the 1/2 hour to see......

I'm sure there is some reasonable mix of performance and ease of application for this project - I suspect the glass added no strength at all to the decks & doghouse top - so I'm not looking for any real strength - just a tough waterproof covering.......... My sense is a finer weave will make finishing easier - and that's a good thing.

Comments??

[Hirilondë]

I think the primary reason Dynel (it is a trade name) is used is that it looks like canvas, not that is it a better material. A lot of Concordias have had this done. It is probably the least "offensive" modernization to a classic wooden boat in many traditionalists' eyes. Regardless of what you use I would not fair it smooth. Some texture adds significantly to the non-skid property.

[Zach]

I've done a few big decks, but haven't worked with Dynel. I understand that it fuzzes up a bit while grinding, but haven't ground on any that I know of.

A new trick from a build I've been watching: http://forum.woodenboat.com/showthread. ... n-Viet-Nam

The trick is to rout a rabbet or groove for the glass to overlap into the plywood rather than trying to butt the layers together. So long as the groove is a low spot, even after the glass is in place it is easy to come back and fill.

Two layers of 1708 is what I've done, but that boat has a 120lb anchor to drag around and is a favorite of seagulls to drop conks on its deck. One layer is 1708 plenty and one layer of 1208 would be fine too. I would test a ball peen hammer drop to see how well each of your samples holds up to keep from star cracking/crazing from a localized impact as that is what rots out plywood decked boats. Water gets in and next winter it freezes and starts to soften up the substrate and opens up the cracks wider. Glassed and resin coated plywood has one big downside, and that is water can get in through those cracks but can't leave from anywhere else. I've torn apart some serious delaminated wet spots that have no visible source other than a dry spot in the glass and a star shaped crack.

The carolina cold molded sport fishing boats have 1 layer of 1708 on deck that is butted edge to edge.

I haven't done much with 8 and 9 ounce biax, other than decorative curved work so I can't speak to its strength. I like thicker stuff as you don't have to be as gentle with handling as the lighter weight bi-ax is easy to stretch and then it won't lay flat no matter what you do. 1 layer of 1708 is a fat 1/16th and 2 layers is a real fat 1/8th thick... more after microballoons and putty.

You will end up using 1 ounce of resin per ounce of glass cloth, plus 2 ounces per square foot of plywood you are glassing. So if you have 10 pounds of cloth, it takes 10 pounds of resin. Which is a fancy way of saying all but the last 1/4 of a kit of 105-B 206-B. You are well and far ahead to try to find someone with wholesale access, roll of cloth or resin drum you can dip out of for a project of that size. The retail markup is absurd.

I've done the glassing a few different ways. One way was to lay full sheets of glass after popping a centerline, and running the centerline so the glass doesn't get puckered. Then lay out the glass and weight it down and trim the sides to fit with the seams running fore aft. This works well for boats that don't have much shape. Sometimes its worth the time to cut the 50 inch center strips to 3 feet, so that you can split one 50 inch run into two 25's scribed and cut to the toe rail or cover board and have two 1 foot pieces you can use for something else rather than a pie shaped piece 2 feet wide at one end that weighs ten pounds and is useless for anything else. You probably could lay out the whole boat on a floor and put together all the pieces if time is less important than minimizing cost, since you are doing all the surfaces.

I like brown butcher paper to make templates for oddball shapes, If you can dart the paper to fit you can for sure get the glass to conform. If you wet out the glass and take your gloved hand and wiggle it side to side the weave will loosen and stretch out to conform into odd shapes if you are a few inches away from the edge. (Say 5 or 6 inches max before the weave is to tight for this trick to work very well...)

If you have toe rails, you can turn the side pieces 90 degrees, breaking the glass every 4 feet so that the weave is more plyable to make the bend up and around. The glass doesn't conform very well to radius corners with the seams going inline to the corner, much easier to work with if the stitching runs into the toe rail or edge.

Pay attention to how you kill out the glass, and your corner fillets. The fillet on a west systems mixing stick is all you need to get the glass to conform to inside corners, I don't pull my fillets until right before the glass is wet so the air roller defines a fillet that is the same shape the whole length. It also saves a sanding cycle on the fillet its self.

You can come back and pull a straight smooth fillet on top once both surfaces are flat and straight with fairing compound and be miles ahead. Glass does add strength, but its a plywood deck not a plywood bulkhead an 1 1/2 radius fillet is a nice painted fillet when you are done... and a nice fillet for a bulkhead tabbing... but not at all appropriate for what is under the glass sheathing your deck.

Your cabin sides and deck should intersect at a sharp flat and straight line before you glass... A fillet hides sins, but a wavy fillet doesn't look very nice, and thats what a lumpy joint does. I digress. If you pull your finished fillet to shape now, you'll spend hours and days sanding and fixing nicks, and the deck won't fair to the corners since you are sanding into a high spot... that is the fillet.

It is worth your while to grind into the inside side corners of your cabin, and recess a 2 inch wide strip (4 inch wide glass) into the deck and cabin so you can glass in a tab before you glass the sides of the hull and deck, otherwise you will have either a butted seam that is begging for a water leak, or a big mounded bulge where the glass is two layers thick in an overlap that is a pain to fair out smooth. (put it on the deck if you overlap... past the non-skid line!) This is the spot that will rot out you boat. If she works, and the glass pops a seam under the paint all the water running off the cabin has to run down this crack it will find its way in. If you grind through the glass, and grind through the fillet or the fillet has an air pocket that connects to wood... water will get in, and you will one day get rot.

If you glass that inside corner and smooth everything out, and then put your sheathing glass on top of it, it is double thick and you can do what you need to with the top layer to get it fair without compromising the water barrier, or strength of the corner.

The same thing applies for outside corners, as you can toughen them up substantially by relieving the top face, and adding another layer of glass that is doing the work of holding the joint together and solid... while the sheathing doubles it up and the actual edge of the round is twice as tough as the flat panels for when your anchor swings in and hits it. If you are glassing an outside rounded corner, on a rounded or bowed front make sure the glass extends down past the corner onto the other face 4,5,6 or 8 inches, while it is still green come back and cut a straight line to it with a razor blade and peel off the scrap glass... then butt up another piece to it and keep on going. It also helps to mix up a bit of cabosil and butter the edge of the corner to keep the glass stuck down. I mix a little batch and smear it on with a gloved hand. The tighter the radius the more help it provides. Glass is flat, and some boat parts are like trying to wrap a piece of paper around a basketball. Doing it all at one time, can be done with darts and lots of sanding later but with a little thinking you don't have to do any of that for all but the most complex shapes.

Outside corners... Sand both flat faces super flat. Destroy a round over router bit, and run it along after your first layer of glass but before the second. It might seem like a weird thing to do, but you can apply fairing putty and get the corner straighter before you add your next layer of glass to save some headaches of sanding. (Sanding an outside corner is an x shape motion from one face to the other diagonally with a long board and 80 grit sandpaper... filling lows as you go.) Also your low spots show, but the other thing that matters is that a template of the corner profile reads the same along the length. If the two faces are puckered, pulled, or not square straight, you can't use a long board as it will tell you to do strange things to the corner that add filler where it isn't needed. Then it is a hand block, a soft hand pad or hand sanding till things look right. Look at the batten, and your template before you pick up the sanding block to know what you are in for... otherwise you'll sand, fair, sand and fair... and still be scratching your head. This fits the category of things learned the hard way. Get it right before you glass it, sometimes its not worth the effort to try and fix in paint a carpentry problem and it will save you time and money in materials to cut out the troubled spot and re-do it from scratch.

I've also done bows with full width sheets running side to side, and cutting one piece in half to stagger the joints. Wetting out and laying the first 2 foot bottom layer, then the next bottom layer... Then laying a full width top layer on top of the 2 footer... laying the next bottom layer... the next top layer and so on until the end or work space is gone. This doesn't have as much waste when cutting as the bevel of one side is pretty close to the bevel of the next run, if you turn the cloth around 180 so the waste side of the cut for the port side turns into the starboard cut of the next run.

I microballoon as I go to fill the weave and avoid having to water wash, grind off the top of the weave, and fair. Instead its just water wash and fair. I use air rollers and paint rollers on a 4 foot extension pole for big jobs to hit dry spots that you can't quite get to. A 4 inch air roller is nice, as 4 feet away you don't get much pressure on the glass with a 6 inch.

On straight runs you can either pre-wet the glass and put it on a pvc pipe and unroll it in place... or lay it down dry, fold it just past half way and wet the deck and the back of the glass... Fold it back and wet the top of the wet glass and fold the dry on top... wet the deck and wet the back side, lay it back down and keep on moving.

I think it is easier to sand and fair out the horizontal seams than the ones that run with the boat if the deck is cambered since you can long board fore and aft across a curve easier than you can a groove along the length. Long boarding a deck is a pain in the lower back. Surprisingly it is easier to work from a little stool 6 or 8 inches tall, than it is to kneel or crawl around. More leverage, and easier on the back...

I would suggest that you long board and fair the deck while it is in plywood, and take out all the screws if you laminated it down around a high spot. Check to see if things change after you back out the screws, because that means the deck isn't glued to the beams... and that you have to leave it higher than true so when you screw it back down its right. (If the deck isn't glued to the beams, remember to put the screws back in, and counter sunk and putty over them.) Run a power plane through the high spot and make them flat or at least low. You'll want to take light cuts from two or three different directions to keep the compound curved cambered deck true without putting in a flat spot. Study the spots with a batten and straight edge... but your eye guides you more than anything.

If you don't fair the deck non-skid gets stained where the lows that aren't quite bad enough to puddle are. You can also fair the plywood to some extent before you glass it, if the lows aren't much more than 3/16th. Cabosil/406 or 407. Doing it before you glass gives you a chance at fairing without hitting glass... which sands much harder than fairing compound. Anytime you hit the substrate while fairing or priming, just adds another cycle to it. Try to do everything in your power to get the project as straight as possible before starting.

I use west systems plastic spreaders (Tried every other cheap brand in the world... they are the best) and stainless steel sheet rock taping knives to spread filler.

Since you are somehow removing the old glass... I'd recommend Norton Blue Mag in 36 grit on an 8 inch pad sander... or renting a sand blaster for a day (cheapest day ever... no matter what it costs.) An 8 inch grinder with 36 grit is faster than a pad sander... but you'll have more detail work in the back end fixing the low spots and moons. You'll end up with low spots that either get ground in, or blasted in. Fill these before you glass. I would try not to resin coat the whole world prior to your glass job as I don't like amine blush and try not to work to hard of having to water wash and sand the whole deck... again.

The plywood will take a lot of resin to wet out. Really mop on the resin. Its about 2 ounces per square foot of plywood to get it wet, otherwise your glass will go dry in spots where the grain pulls more or less resin. Don't use resin that is kicking for this, or you'll end up with a high spot where the resin won't roll out from under the glass. Don't use resin that is kicking to microballoon either, as it won't lay out flat. I use straight microballoons no cabosil, and make it pretty stiff because as it heats up it gets runny. If it is warm or direct sun I use tropical hardener for the microballoons as it takes some time to mix.

West systems is compatible backwards and upside down, so long as each part is mixed with its own ratio in separate buckets. So you can do your fillet work with 105/205 your glass work with105/206 and then microballoon on top with 105/209 while everything is still green to no ill effect. I spread the microballoons thinly, so you can still almost see the weave through them. No sense making a mess to grind off later.

Cheers if you made it this far... grin.

Good luck,

Zach

[Zach]

Posted twice... somedays i think I shouldn't be allowed near a computer.

[boatsnh]

Zach,

A whole lotta food for thought....Thanks!
I've picked up a bunch of MAS epoxy - I've used it in the past with good results. I appreciate your resin/sq footage and usage numbers - The bottom line is that there is a lot of epoxy going on the deck. Thanks for the "schooner site". Kind of a far east "Maggie B"

I've got the whole cabin roof down to bare wood & have patched (3 layers of 1/4 inch ply) any weird/rotted sections by routing out the rot in "lifts" with 3" or so overlap per layer. Will work well & is almost done.

Most of the existing glass "peeled" off in sections (lucky me!) *& then I went to town with 36 grit on my 6in Festol Rotax grinder....Might not be the fastest method , but I can contain the demolition & I hate glass dust everywhere.... Learned to hate glass dust working in a local boatyard in the 1970's after school.....

3 years ago I rebuilt the 3 cabin sides that had rotted where every screw on the eyebrow entered the cabin side - water followed the screws in . Fixed/filled & glassed with 8 oz cloth & MAS - Installed 8 new Bronze (Spartan) Ports to replace the old junk aluminum ones that fell apart on removal. I Filled the bow port in with a deadman & faired/painted- I got a deal on 8 Ports & did not see the need for a 9th in The bow. Everything was painted with 2 part urethane (HMG Acrythane) rolled/tipped. Looks nice & I'm happy with how it all turned out. No Eyebrow mouldings on the re-build. I'll probably use the same coatings again, although I'm thinking I might take a look at System 3 water base urethane - from what I read it seems to dry as a "eggshell" finish - perfect for decks. A little more looking in order.....

I've got one more sample to "beat on". Xynole & 6 oz glass. I'll check out your "star" fracture test after everything has dried/cured for a couple weeks.

Thanks for the "tips"
Mike