Plywood Deck Core Work

[Ujin]

Hi all, I have a 1976 Aries 32 and am working on the deck. There are soft spots only aft of where the cockpit begins. However much of the rest of the deck was covered in fiberglass with west system 105 epoxy by the pv. All that glass peeled up leaving bare wood!

My questions: replace whole deck? Or feather and fill the rough patches as seen in the first photo, and replace the 6 soft spots then reglass the whole deck - this is the method I was going to do.

But I have no idea why the previous glass peeled up. What would cause that? The original glass seems well secured but there are a few places where it too was easy to peel off the wood.

I don't want to lay glass down and have it come off like that. Any one seen that before?

The second pic is how the glass just peeled up and the white in the bottom corner is the original.

Let me know if I can provide any further info or pics.

[mbowser]

What kind of plywood is it? I know plywood is used quite a bit as a core material, but it isn't the best choice, and depending on what type was used it could be a pretty poor choice.

[Ujin]

Thank you for the reply. I don't know what kind of ply it is. Whatever was available in 1976 in Taiwan I suppose. However, reviewing the condition of the other areas I think it is prudent to replace the entire deck especially to maintain the integrity of the framing under the deck. It is a ply deck on a fiberglass hull. The deck sits on the framework and is exposed underneath- so not really a core. I will replace it with a doule layer of 1/4 inch marine ply with glass over. I've read I don't need marine ply but think it's the best bet for all the work and time going into this project.

I guess a new deck once nearly every 40 years is okay.

[Cheechako]

It may be peeling up due to moisture in the wood when it was covered. Or the wood may not have been saturated with a coat of resin prior to glassing. Hard to say for sure. If the wood is still good then get the boat covered well, take the old glass off and let it dry out thoroughly prior to reglassing. A coat of resin on the wood is mandatory for boding. Be sure to use the right kind of resin on the wood and all but the last layer also... the type that doesn't have a wax blush when it hardens.

[Ujin]

Cheechako, I believe you're right in that there was moisture in or on the wood. Some sections that peeled off show wood that looks darker and a bit like it may have mold spots on it compared to clean dry wood. Thank you.

[Zach]

Take some more pictures... If you can get a shot of the whole deck that would be ideal.

Does the deck have a fiberglass skin under it, where the plywood core was laid up in a mold? If the boat has a wood framed deck with plywood skin then the fix is a bit different.

To my eye it looks like you've got a layer of polyester over the deck, the grey fiberglass, and a layer of epoxy over the top... the yellow.

The epoxy turns yellow after 2 years or so in the sun, and has zero strength and is almost like chalk.

Polyester over wet wood doesn't adhere.

It looks like you've got two layers of 10 ounce finish cloth, ideally when you go back use a layer or two of 17 ounce biax so you have enough meat over the wood that if someone drops an anchor or hammer, it doesn't star crack and let water back in to rot it back out.

You can do two layers of 10 ounce finish cloth successfully over wood, but it takes perfect maintenance and a fresh paint job every year or so. The multi-hull guys have this down to an art form, but give it two or three years without fixing dents and dings and you are right back to square one.

If the deck was laid up in a mold I'd strongly consider using divinycell foam or corecell foam and use polyester to do the work. It'll cost about the same as marine plywood and epoxy, but you'll have a lighter and longer lasting repair that goes a lot faster.

Zach

[Zach]

Re-read your message, went to edit my post and I'd written longer than 30 minutes..

Here is what I would do:

To my eye it looks like you've got a layer of polyester over the deck, the grey fiberglass, and a layer of epoxy over the top... the yellow.

The epoxy turns yellow after 2 years or so in the sun, and has zero strength and is almost like chalk.

Polyester over wet wood doesn't adhere.

It looks like you've got two layers of 10 ounce finish cloth, ideally when you go back use a layer or two of 17 ounce biax so you have enough meat over the wood that if someone drops an anchor or hammer, it doesn't star crack and let water back in to rot it back out.

Is the existing deck two layers of 1/4?

1/4 is actually fairly tough to get a good lamination over framing, as you can't put but some much weight on it before it deforms... and you can't really screw laminate it either unless you run a bunch of strips on the underside. You'll use about 1/2 gallon of epoxy per 4x8 sheet to laminate it, on the dry side. If you mix it to thick, you'll get pockets where the epoxy didn't move out from between the layers. If you mix it to thin, you'll get dry spots. Dry spots are bad as two 1/4 inch pieces of plywood held apart by air sound like a drum skin when you rub your fingernails across them. About the only way to repair that is with a grinder and take off the top skin.

If the finished deck needs to be half inch, Use 1/2 inch plywood.

Doing a bit of scarfing work... or even doubling blocks between the framing will make your life much easier and it will cost a lot less, as it won't take nearly as much epoxy.

Lay some battens across the frames once they are exposed, and glue 1/8th inch marine plywood shims to any low frames, rather than pulling a pucker into the new deck you can fair the framework in once. Screw a 2x6 to the underside of the deck down the centerline and put a stiff leg under the front of the cabin coach roof. She will sag, without her deck.

The biggest time saver, is to dry fit the plywood and use the same screw holes to set it back in place... That way you can go inside with a pencil and mark them. A needle nose vice grip with a 3 inch stub of pencil works well for corners you can't quite reach. pre-paint the underside of the deck after marking for the framing... I like to use epoxy paint, and leave the wood exposed. Resin coating is grand, but not only is it an extra step... its a mechanical bond rather than a chemical.

When you go to laminate on the plywood, tape along the paint lines leaving only the sanded plywood left to be glued. Tape up the sides of the frames... Then when you butter up the frames and set the plywood down into place, and screw it down, go under and wipe off the excess, then pull the tape lines 10-15 minutes later. When the epoxy kicks, pull a finger fillet of your favorite paintable caulk.

No sanding overhead, no painting overhead.

After the deck is laminated in place...

Route the seams down an 1/8th of an inch on the top surface of the deck at each butt joint, if you use butts. If you scarf it, grab a long board and long board sand the top of each scarf until they lay down flat. Then lay a piece of tabbing across it. Do the same at the sides of the house, if they are still in good shape. Tab the deck in to the house, then lay the fiberglass up into the fillet but no further. It makes for a lot cleaner job, and a lot less sanding if you make the tab a low spot that can be covered with putty instead of re-fairing the cabin sides. Same goes for the hull to deck joint. Wrap it with tabbing, and don't try to do it with one piece of glass from the cabin sides to the topsides. You can do all the glass work in one day, or all at the same time... Just don't punish yourself if you can avoid it. Grin.

If you have to stop for the day, put peel ply on the last piece of cloth that will accept the next layer tomorrow. As a general rule, I prefer using finish cloth to peel ply... but I do use it to save having to amine wash, right beside raw plywood. Water and plywood that is to be glassed the same day don't mix very well. You can use denatured alcohol for the wash down instead of water.

I use a west systems black stir stick for glassing corner fillets. They are big enough to let the cloth lay in smooth. Cabosil works well, with a touch of chopped glass fiber. I pull these fillets wet, where right before the fiberglass goes on, the fillet is pulled and cleaned up. Work the air roller in to the fillet and any get no bumps.

Use tropical hardener and do it in the shade. It makes for a lot less waste, as everything is less likely to kick off on you. Don't over work the cloth, once it lays down true move on to the next piece. biax will unravel at the edges if you work it to hard. This is a good thing to remember, a gloved hand and a quick rub will unlay the fibers enough to work a wrinkle out.

17 ounce biax without a mat backer is a little tougher to work with but takes a lot less resin to wet out, saving a bit of money and weight. Wet the plywood with unthickened resin, until it will absorb no more. Normally takes 2 ounces per square foot, though sometimes the grain is a bit more open and it wants more.

If you have the deck fair before the plywood goes down, and the seams already taped and ground smooth, the fairing work after fiberglassing should go very quickly. I normally lay a layer of 10 ounce finish cloth over the wide open spaces and a 4-6 inch wide piece of finish cloth over the tabbing, and use a 6 inch air roller to work things smooth and fill the weave of the biax.

I want to see the weave of the biax after air rolling, which is a good indication that the layup isn't overly wet. Wet layups, the fiberglass will actually float on top of the resin and make high spots. Wet it until it goes clear. I use a 9 inch paint roller, in a white plastic roller tray. 3/8ths or 1/2 inch nap works well... You waste a little resin wetting out all that nap, but its what i use.

Once you are satisfied that you don't have any dry spots, and aren't to wet... (Lift up any excess with a plastic squeegee, and spread it around) let your work begin to gel.

Now roll on a layer of epoxy, and lay some 10 ounce finish cloth into it. I roll the layer of resin first, in the event any localized spots have gotten extra sticky, and to fill the weave of the biax so air doesn't bubble through the finish cloth. Air roll the resin through the finish cloth and work any excess over to the dry spots.

Finish cloth is the cheapest fairing material there is...

Once it starts to gel, roll a layer of neat epoxy over the top, and squeegee it out so you can't see the weave of the cloth.

The next day, wipe down for amine blush, and sand it out until the shine is gone with a DA sander. 40 grit is fine... Don't sand through the finish cloth unless its just a bump the size of a quarter. Lay the same battens down on deck you faired the frames with.

I normally use an aluminum yard stick laid flat on deck. Mark out any air gaps, which are low spots... fill them with a 12 inch sheet rock knife. Finger sand any small low spot the size of a quarter, and circle them with a pencil.

Start in the corner of the cabin house and pull toward the toe rail. If you did your job fairing the first time, it'll take a quart of putty to fill the whole deck. Don't blob it on... 1/8th inch thick at the most. If you laid your fiberglass butting between layers instead of overlapping there shouldn't be any high spots to make a low spot that will accept any more than that.

Once the deck and cabin corner are straight, flat, fair and true, pull a decorative fillet around them with putty. I normally use a 1 1/2 pvc pipe. A sharp corner looks good on older boats... but you have to have a fillet of some degree to keep the paint stuck in the corners. 1 1/2 is the smallest that is easy to sand. Don't sand the fillet any more than it takes to take the shine off with your finger tips, if there are any sharp points sand them off.

Some folks float the whole deck in putty, then sand it back out the next day. If the work is fair, and the sander doesn't jump all over the place I prefer to resin coat, and in the polyester world... gelcoat... as it lays out an even coat, and builds the whole surface out. On flat stuff like decks, it is just so easy to pull a high spot in and not sand it all the way out... then spend the next few days filling around it until you've puttied the whole deck, I don't really see the need. Fill the low spots, once everything is level resin coat it to bury the sanding scratches.

I like to resin coat everything 3 or 4 times, on the last day after I'm pleased everything is flat. Treat the resin coating as a high build primer that fills 40 grit sanding scratches. Sand out with 80 grit.


Zach

[Ujin]

Zach, the deck is not cored, as I found out. It is a ply deck on a framework. Traditional wood deck on fiberglass hull, if you will. The ply is exposed underneath. Yes, I do believe the original glass was polyester. Thank you for the suggestion for the weight of glass. I was wondering what would be sufficient. I am not concerned with weight as she is a cruiser and around 16,000lbs now. I uploaded some more shots of the deck.

[Ujin]

Zach, thanks for the additional info. My concern with using 1/2 inch ply is the ability to bend the ply to the frames to get the rocker and to get the convex shape across the bow. The current ply is held with SS ring nails.

[sneuman]

I've done a complete deck re-core. The best material is balsa core. It's lightweight, strong, easy to use and someone resistant to water penetration:

Marine Balsa Wood: Pro Balsa Plus

[Ujin]

Sneuman, could I do a 1/4 ply over the framework then 3/8 balsa bonded to the ply then glass over the balsa. What do you think?

[sneuman]

Originally Posted by Ujin

Sneuman, could I do a 1/4 ply over the framework then 3/8 balsa bonded to the ply then glass over the balsa. What do you think?

Yes, I think you could. You could use epoxy or fiberglass resin to stick the balsa and ply together. The balsa is very light weight and because it's segmented (over a mesh mat), it's easy to cut and articulate.

[Zach]

You can do it, though you'll want to vacuum bag the balsa core into place, as 1/4 doesn't have enough support not to push low spots into the deck if you try to weight down the balsa with the gravity clamp. Grin... Paint cans, bricks, all sitting on polyetheylene painters plastic.

1/4 ply + 3/8 balsa is thicker than 1/2 inch, so more than likely you'll end up having to re-work your cabin corners if you take it all the way in.

I don't see why 1/2 marine grade occume wouldn't take the curve for you, fir is a bit tougher to bend, and meranti is in the middle.

I use 1 5/8ths stainless square drive screws with 1/4 inch stainless fender washers to laminate the plywood into place rather than ring nails. It works a treat.

You can either remove the screws and fill the holes with epoxy, so there are no screws to hit later on down the line... or remove the screws, set the fender washers to the side and drizzle a little epoxy in the holes and sink them home.

I use a piece of stainless welding rod with a finger loop on the end for epoxy drizzling duty. It is about equally messy as dunking the screws in epoxy, but keeps your drill and pail of screws a little cleaner.

Zach

[sneuman]

Having removed loads of soggy, delaminated Philippine mahogany from the old core, I'd be very reluctant to use plywood as a core material. Just my $0.02.

[Ujin]

Zach, I did realize the difference in height. However, it was a thought. If 1/2 should take the bend then that would be the most efficient route. That's definitely good to know about 1/2 inch.