The Re-core: process

[Figment]

The boat has been picked clean. All deck hardware (including the stem fitting), wood trim, odds, ends, portlights and deadlights are piled in a corner of the shed.
It's time to put blade to boat and get this party started.

In terms of access, does it make sense to finish the recore of the lower-coachroof area first, and then start on the foredeck and side decks?

Is there a rule of thumb for how far from the edges I should cut through the top skin?

I enthusiastically solicit any and all advice on the process.

[Tim]

It probably does make sense to start as "in and up" as you can--in other words, coachroof/cabin trunk first, and then the sidedecks. That way, you need not have to wait for materials to cure or some such before continuing. I'm sure this is exactly your thought process, so I would confirm those thoughts. Doing this would also give you an opportunity to overcome any learning curve in a more controlled space.

For cutting, you just need to allow adequate room at the edges to allow you to work easily and, of course, to allow room for tabbing. The tabbing doesn't need to be super-wide, so cutting 2" or so from the edges is sufficient. If you leave too wide a flange, it's tougher to remove (and then replace) the core from those areas.

The table on a typical circular saw is usually about 1-1/2" - 2" on the narrow side, and this happily corresponds with the appropriate width to leave behind, so you can just let the saw follow its own way along the toerail and cabin trunk. I found this to work very well, and left an adequate flange for reglassing. 2" is probably better than 1-1/2, at least on the inside (cabin trunk) edge of the sidedecks.

On the coachroof, I'd probably cut along the nonskid line or thereabouts, which is 2" or more from the edges.

[Figment]

Thanks, Tim.

My loose plan is to recore the lower coachroof and reinstall the top skin, and then do the same to the foredeck and side decks in a separate operation, and then go back and do all fairing as one big mutha effort.
I hope to get started this week.

[James384]

When I first recored Atom's deck I also reused the upper glass skin to save time and materials. Unfortunately I botched the job and ended up with the upper skin not adhering well, numerous lumps and voids and eventually cracking at the seems in places. I'm not saying this is inevitable when reusing the upper skin - in my case it was a combination of errors of poor materials and bad workmanship.

A few years later I recored using 4" square sections of urethane sheet set in a thickened vinylester resin. The core pieces were set down with a gap about the thickness of a penny between them to increse the strength of the bond and stop any future leaks from migrating under the skin. After some laborious blocksanding I laid several layers of glass over the top and discarded the old upper skin.

I'm curious how some of you have successfully reused the upper skin and if you have any tips on how to do this right the first time since I often have people ask me about this. What is the big benefit of reusing the skins particularly when it's so troublesome to get them set down level?

Also, in many countries, vinylester resin is commonly used on boat projects because it's less than half the cost of epoxy, wets out nicely and adheres well to old polyester. I wonder why it's not so popular in the states?

James
#384

[Tim]

Vinylester is an excellent resin for boatbuilding, with better properties than polyester. I wish more builders would use it, but since it's much more expensive than polyester (though less than epoxy), profit rules the day. Vinylester works just like polyester in that the amount of hardener can be modified to affect (i.e. speed up or slow down) cure time, unlike epoxies, which are highly sensitive to proper mix ratios. Vinylester's main advantage as a boatbuilding resin is that it resists the sort of hydraulic and/or osmotic action that can affect polyester boat (i.e. blisters, etc), and therefore is used by some high-end builders throughout the boats.

Vinylester is a type of modified polyester resin, and therefore lacks the pure adhesive qualities that make epoxy such a good choice for boat repairs. It is better than polyester in this regard, but still less good overall than epoxy. Since all repairs are by nature secondary bonds, the premium material choice is epoxy, which excels at bonding to just about anything. Other materials can be made to work, but may lack the longevity of the premium repair.

Reusing the skins during a recore is something that I think must be addressed on a case-by-case basis. In some cases, the skins are probably in such bad condition that reuse would be a waste of time. In other cases, however, the top skins may be generally sound, and using them can be effective. I think that there's probably a sort of mental block for some new DIYers about the perceived difficulty of laminating new material over their core repair. To the untrained eye, it seems like reusing the top skins is easier; fiberglass lamination tends to have a sort of mysterious aura about it, which is kind of silly because it's really very easy once one has tried it.

Reusing the skins may seem easier, but there are plenty of potential pitfalls along the way. Chief among them is the problem with misalignment and unevenness of the skins during reinstallation. This seems to be a common problem, and its potential is something anyone should be aware of before beginning. I'm not sure why it seems to be a big problem in some cases and not in others; I had no problems with level or alignment when reusing my own top skins, other than the inevitable areas of minor and insignificant differences in height that were easy to fair out. But I've watched another recore job where the skins were so far off as to stand their entire thickness proud of the surrounding areas. In these cases, I think it's likely that too much of the original skin material gets removed during the sanding and fairing process, which would lead to increased flexing and, ultimately, failure of the bonding.

I think a better overall repair can be made with new material, but I think effective and long-lasting repairs can also be made by reusing the skins, if they're in good enough shape. Lots of weight (or, in the ultimate, a vacuum bag) is required to ensure a good bond between the core and the skins, and the seams need to be reinforced with glass. The success of the repair--any repair--is to ensure this good bond between the materials.

If I were faced with a full recore again, I'd certainly look long and hard at the two options. I would lean towards using new material for the top skins, but wouldn't discount reuse of the old skins out of hand. Reuse does require care to ensure good bonding, as does new material.

[Rachel]

I've thought a bit about this topic, since I'm Triton shopping and there seems to be a lot of wet deck core out there...

The only re-coring I've done was to my first boat, a Montgomery 17, on which I did most of the foredeck, the side decks under the jib tracks, and part of the cockpit sole. In that case, I worked from below because the deck was in very good condition and there was no liner in the cabin. Not sure I'd want to do that again - it was definitely "anti-gravity" :-)

I'd like to know what, exactly, folks use when they put a whole new top skin on? How many layers of cloth and what type? Do you lay it up all at once or in sections or layers? Do you still leave a "tab" of old decking at the side by the toerail for joining the two?

Thanks --- Rachel

[grampianman]

I'm a good ways through the re-core of my thirty year old Grampian 23 and went the route of reusing the old top skin. I did this because:
a) I'm a rank novice when it comes to using 'petrified snot',
b) I thought it would be better to have as much of the stock non-skid pattern when I was finished,
c) I'm easily intimidated
and
d) I am cheap and didn't want to spend the money on extra layers of glass material.
There are probably other reasons, but I can't think of them right now. Did I mention I can be easily intimidated?

The curve of the foredeck was a bit of a problem, but drywall screws put paid to that. The curvature was such my proposed solution of gallon jugs of water kept sliding all over the place; my panic then sent me for the cordless drill and the screws. (I took the screws out after.)

On the side decks, I cut the top skin into smaller pieces and shaved the plywood underneath to make sure it would be a good fit. I did find the top skin had some pretty big variations in thickness, but by planing the plywood or chiseling in some places produced a level fit. Once the epoxy mixture went on, lots of water filled gallon jugs placed closely together kept the layers together. No great curvature on the side decks.

I then trowelled on the thickened (ketchup consistency) epoxy with a notched trowel and pushed the top skin down onto the epoxy mixture. I suppose time will tell, but I have done some jumping around on the foredeck and cannot detect any flexing my (ample) girth would have produced otherwise.

I plan to continue cutting and reusing the top skin when I go to the cabintop. If you can put up with the adverts, my humble pages can be found at grampian23 dot tripod dot com. I don't have much text, but do have a few photos.

Cheers,
Ian

[Figment]

Well, I (predictably) for got to bring the digicam in with me today, so I have no pics to share. However, the sky is overcast today, so the shed/greenhouse is bitterly cold, and the phone isn't ringing, so I may as well take a few moments to hack out some thoughts on the progress thus far.

I cut the topskin away from the upper-middle (whatever. you know where I mean) deck, raked out the wet and rotten balsa areas, laid new end-grain balsa core, and then spent a couple of weeks waiting on weather windows to lay a new solid pad of biax and resin under the mast step a few layers at a time. At present, this area is aaaaaalmost up to thickness.
I may reinstall the topskin at this area this afternoon if the heater catches up to the cold. (S3 publishes that their fast hardener cures at 35 degrees, so I don't mess around when it's under 40)

I've cut the topskin away from the remaining cored deck areas. Three big pieces: two side deck pieces, and then the whole foredeck as one monster piece. My thinking is that doing it in big pieces reduces the number of seams to grind, tape, and fair, but if somone wants to convince me that less cumbersome sheets will make for less labor, I'm all ears.

Both side decks are completely saturated and rotten. The port side deck had a repair (by previous owner of unknown vintage) that took several hours to grind, chisel, and curse away. It was an odd mixture of resin-starved layers of cloth, pockets of unthickened pink resin, veins of butter colored and buttery-soft compound, and pockets of unthickened green resin.
If ever I had a kernel of a thought in my head that unthickened resin was an effective filler, this exercise killed it. This stuff was as brittle as rock candy.
Anyway, I'm re-performing this repair with thickened resin and a hunk of biax tape before proceeding with the core installation.

The foredeck has about 6 s.f. of dry core. the perimeter is wet and rotten, forward of the cleat is wet and/or rotten, and the "spine" of plywood down the middle is wet and rotten.
Though these two remaining areas (just forward of where the house lands into the deck on either side of the spine) are dry, I'm leaning toward removing and recoring anyway. Even though they were dry, they didn't put up much of a fight when it came time to peel the topskin away.

I really want to get rolling with the raking/scraping away of the old core and the installation of the new, but I think I need to take some time to build some A-frames for staging first. Playing spider-man's version of "Twister" as I move around the boat (left hand, hatch frame. right foot, toerail. left foot, shed stringer....) is getting old fast.

[Tim]

Three big pieces: two side deck pieces, and then the whole foredeck as one monster piece. My thinking is that doing it in big pieces reduces the number of seams to grind, tape, and fair...

Those sections sound reasonable, though I recommend you have some help when the time comes to reinstall the topskins; that large a piece can be unweildy, and possibly challenging to get gooped and restuck by yourself. If you can do it with these large pieces, you're correct that it will save work later on. I did the sidedeck in two pieces, which was manageable by myself.

...but I think I need to take some time to build some A-frames for staging first. Playing spider-man's version of "Twister" as I move around the boat (left hand, hatch frame. right foot, toerail. left foot, shed stringer....) is getting old fast.

It is always worth the effort and time required to build staging. Always.

[grampianman]

Scaffolding is an excellent investment in time when working on re-coring the deck. I did this for my boat and it worked really well when I was hefting some of the more unweildy pieces of plywood or deck layer. Now that I am up working on the cabin top, I don't have the luxury of a scaffold, and my knees have borne the brunt of punishment as I stretch over the cabin either scraping, dry fitting, or epoxying the pieces in place. I found the scaffold on the sides of the boat allowed me to work at an efficient height, thus reducing a lot of aches and pains. I'll also add that with scaffolding, it's easier to work by myself.
The main thing I've noticed about the re-use of the top layer of fibreglass is how dry/brittle it is. As I peeled it off the core, I could hear the gel cracking. I plan to repaint the whole boat, so I think the brittleness will not be a problem, but if this were an offshore boat, as I write this note now I might approach the re-core/re-deck differently (read - new top layer).

Cheers,
Ian

[Figment]

OK. Pics to go with the narration.


Starboard side deck with the skin off, but the core untouched. If the saturated moisture wasn't frozen, I could've removed the core with my bare fingers. Three minutes with a 5-in-1 tool cleaned this area completely. Total moisture saturation and delamination.


Port side deck with skin off and rotten core removed. Under Jeff's arm is the area of previous owners' repair mentioned in the post above. Today I laid a piece of heavy biax to re-establish the fractured underskin.


Foredeck with skin and rotten core removed. The balsa that remains in the photo is still fairly well adhered to the underskin, despite being a bit on the wet side. Again, it's remarkable that the moisture entered at bow pulpit bolt holes and wicked aaaaall the way back to the cabin house.
All balsa and the plywood spine have been chiseled away since this photo was taken.
My thought is to replace the plywood spine with a solid glass layup. I know this is overkill, but I don't see the harm, and I don't have any suitable marine ply scraps on hand.


Mast step area with part of the topskin reinstalled. I include this pic primarily because it's a fun "exploded view" type image of the resulting composite nature of the assembly, showing the remaining plank-balsa, the new end-grain balsa, and the solid glass mast step layup all under the original skin.

[bcooke]

Looks like fun :-)

Just curious, what is the temperature inside your structure these days?

-Britton

[Figment]

well, as of this morning, I need to rebuild said structure. (see post in "Boat Shop and Facilities)

BUT..... The greenhouse effect on a non-cloudy day is good for 15 degrees above outside temp by 10:00 am. The oil-filled-electric radiator in the cabin of the boat warms the interior of the boat to 70 or so. Between these two, the thermometer I keep on deck near the day's work generally hovers around 50 degrees. On cloudy days I employ the help of a kerosene heater as well.

[Figment]

New core is in, topskins are on. It's a blast to be able to walk around on deck again.

Tomorrow I'll grind hollows at the seams, lay some tape, and then spend a few weeks fairing things out.

[s/v Faith]

I was very thankful to purchase 'Faith' with the balsa in her foredeck already replaced by the prior owner. (the Ariel is cored like East Coast Tritons).

He had used a foam honeycomb core (dynacore?) and had re-used the top skins.

Two years after the purchase, I was up on the bow raising the anchor. I thought I felt the deck deflect slightly under my heel.

I tried to ignore it, but it simply would not go away...... I did the old 'acoustic coin tap test' from aviation. Sadly the taps along the edge of the repair were not the satisfying tap, but the dull thud of doom.... I could not figure out how the water got in there. The deck fittings seemed well bedded, and the soft spots were not near them anyway???

I got my answer shortly after, I was up on the foredeck in the rain, and decided to step around and see if there were any more spots I could feel.

I noticed bubbles come up from a small crack in the paint when I stepped near it!

It seems that when the prior owner had repaired the deck, he found, and left the balsa core near the center of the foredeck.

He replaced the old skin panels and faired them in with thickened epoxy. The seams had been a natural stress point in the deck, and had given way over time... allowing water to seep in slowly and wet the remaining balsa that had not been replaced.

While the deck was still very solid, I could not stand the idea that there was cottage cheese lingering in there. I set the old circular saw to a 1/4" and started ripping things apart.

I found an area about 9" and a 15" strip in the starboard side, and a 12" strip on the port side.....

I removed all the balsa, and pulled back the skins that surrounded them.

Building and fairing the deck where they had been was not too tough. I then found the remaining 'seams' across the foredeck. I ground them out, and filled the low areas with 1" fiberglass tape.

I then faired them in, and overlaid the entire foredeck with 2 layers of just 6oz cloth. I just finished applying the second layer of cloth yesterday, the goal of this was to try to eliminate any stress points.

I doubt there was really any need to overcoat the entire deck, but I would encourage anyone who is considering re-use of old deck skins to look carefully at how they plan to re-join the seams where they come together..... or you might be doing some more work on it in the future.

(also, anyone who has re-used skins might want to check carefully to make sure that the seams have not started to crack.)

Sorry for the long post, I hope this is helpful for someone.

[Zach]

Question...

Could one use the inner skin of the deck to build up enough thickness to make a solid deck out of one that used to be cored?

Probably impracticle to the extreme, but it seems like doing that would alleviate all sorts of core related problems... (and probably introduce some new ones!)

Thanks!

Zach

[Jason K]

Core construction is not a bad thing and balsa is not a bad choice for core material.

In addition to being lighter, a cored structure is also more rigid.

The issues that arise from cores are often due to poor construction techniques or failure to maintain or properly install hardware. If it's kept dry, it will last for a very long time. Keeping it dry just takes some vigilance and care.

Inner skins are usually very thin. The only practical use for it would be to reuse it as a bottom skin, if it is salvageable. If you do intend to lay up solid glass, then it would be easier to just use new laminate.

[Tim]

Question...

Could one use the inner skin of the deck to build up enough thickness to make a solid deck out of one that used to be cored?

Probably impracticle to the extreme, but it seems like doing that would alleviate all sorts of core related problems... (and probably introduce some new ones!)

Thanks!

Zach

Something like that would be brutally heavy, expensive and time-consuming, and overly flexible when complete; even 1/2" of solid glass, on a wide-enough span, would feel soft underfoot.

The key to preventing recurring core problems is to install it right, and to isolate the core from known penetrations, like hardware locations; sometimes, in these areas one can use solid glass, eliminating the core in that particular area.

Boatbuilding is always a learning experience, and there have been plenty of lessons learned over the years regarding core; most builders have learned how to do things better now, and we little DIYers have learned from osmosis, logic, and others' experiences. But cored construction is still an outstanding method that is difficult to beat for all its positive points. Balsa wood remains an outstanding core material as well, as it is light and stiff.

[vindo40]

I am in the recore proces right now and after I remove all the damage core I noticed that the inner skin is really weak.... should I put layers of cloth to renforce or with the new core would be enough?
Also, I like the idea of playwood for replace the old core (like Tim did in his Glissando) should I have to treat the playwood with epoxy before install it?
Pictures will be soon.....

Thanks

[Jason K]

Inner skins are typically considerably thinner than outer skins. However, if it is very weak, go ahead and reinforce it with a couple layers of glass.

As to the plywood - it is a viable core material, but I think you'll be happier with balsa. The balsa is very workable, considerably lighter, and more rot resistant. Balsa's poor reputation among some is due more to misperceptions springing from poor building practices than from any real deficiences with the material. It has always been an very prevalent core material.

I believe Tim said that he went with plywood as Glissando had already been partially recored with ply and that, were he to do it over, he would go with balsa. If you do elect to use plywood, then choose a high-quality marine grade product and coat it with epoxy.

[Figment]

Unless those inner skins are fractured or too flimsy to survive the process of bedding new core, I wouldn't bother reinforcing. Save your energy for the fairing.

[Tim]

Note also that depending on your particular boat and the situation at hand, you may have to support the inner skin from inside the boat so that you can apply the pressure (however you go about it) for installing the core properly without distorting the skin and therefore the shape of the deck.

Reinforcement of the inner skin is unnecessary in most cases, unless it's badly damaged or somehow unsuitable. They always flex and tend to be lightweight laminates--perfectly normal.

Plywood's OK, but as I've disclaimed about 100 times, I'd not choose it as core material in most circumstances. You're better off going a different route, whether balsa, extruded plastic honeycomb (i.e. Nida-Core), or one of a variety of foams.

[vindo40]

I used Nida Core once and had very good results. Actually, it's a few miles east of where I live in Port St. Lucy. A friend of mine works there and I'm sure I can get a good deal on the pieces for the deck.

Thanks Tim!!!

[vindo40]

[vindo40]

[img][img]http://img2.freeimagehosting.net/upload ... b1906e.jpg[/img][/img]

[vindo40]

[img]url=http://www.freeimagehosting.net/][img]http://img2.freeimagehosting.net/uploads/45efb1906e.jpg[/img][/url][/img]

[Triton 185]

Does anyone know what the cost comparison is between re-using the old skins or tossing them and laying down new laminates?

[bcooke]

If cost is a factor then you need to reconsider your plans to attempt the project... ;-)

Really though, we are not talking big numbers here. The big cost in recoring is going to be the epoxy. Glass is relatively cheap.