Composite(?) slalom kayak repair questions

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nopeda
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Composite(?) slalom kayak repair questions

Post by nopeda » Wed Jun 06, 2018 9:34 pm

Hi,

I have an old slalom kayak, written on it is: Peak Concept Sandwich Technology Airex and a sticker on it says: World Cup Final Ocoee '93. So I'm guessing it's some sort of composite and at least 25 years old. I'm just using it paddling around on a flat lake but would like to be able to put it in some whitewater. Just paddling in the lake after about 30 minutes it has about 3/4 inch of water in it. I can't tell exactly which cracks are leaking and which are not, so am thinking about putting one sheet of fiberglass or maybe kevlar(?) on the bottom and then using West Systems 105 resin and 206 slow hardener. Is that as good as any way to solve the problem? I've never done it before but looking at some Youtube vids it doesn't seem too hard. If anyone can suggest any good tuturorials it would be much appreciated. The can says one part hardener to five parts resin. It weighs next to nothing and I don't want to change that, but the leaky business is a bit much. Should a 32 oz can of resin and 7 oz can of hardener be enough to do the job, or hopefully more than enough?

Thank you for any help learning about this!
David
GA, USA

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Re: Composite(?) slalom kayak repair questions

Post by Chris Bolton » Wed Jun 06, 2018 10:10 pm

The Airex Sandwich means it has a layer of foam between two skins of composite (probably kevlar). This is a method used for serious international events as it produces a very stiff and light boat, but with less resistance to impact, ie, it's built to be brilliant for that one event but may crack afterwards. When it does crack, water gets into the foam - I'm not sure how bad that is.

An extra sheet of glass or kevlar probably will not help. You need to find out where the leaks are seal them with epoxy resin. To find the cracks, lay the boat on dry ground and fill it with water, see where it comes out. Once you know, get it as dry as possible, keep it in a warm place to let the cracks dry out then run epoxy into them. Get the most fluid epoxy you can; it runs better when it's warm.

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Re: Composite(?) slalom kayak repair questions

Post by Lewperren » Thu Jun 07, 2018 8:08 am

I am no expert, but my mate is and I have watched him repair my slaloms. What Chris says sounds a good approach for a more permanent fix. A quick bodge job to make the boat water tightish can be achieved with super glue on the crack, allow to dry and cover by Duct/Gaffer tape. Every composite boat I have has ends up with duct tape on it, this could be because of my paddling and lack of DIY ability :-)

Safety note: if you do go for a 'proper' repair then make sure you get the right type of protective gloves, I believe some are porous to expoxy and get a mask. Expoxy is not nice stuff.

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Re: Composite(?) slalom kayak repair questions

Post by Jim » Thu Jun 07, 2018 9:51 pm

At that vintage the boat is likely to be pretty flimsy especially with apparent world cup provenance (the top paddlers would have had their boats as light as the rules allowed), even with the airex core.
I'm trying to remember what airex is, I think it is one of the fibreglass 'mats' with air bubbles that soak up resin, so not as thick or efficient as more modern core materials? Either way, if you have a core, it is possible that the leaks are from cracks that are in different positions on the inner and outer skins so filling it up to search may or may not work. It is worth doing though, the deck is usually built lighter than the hull, and you may well find the leaks are there and not the hull at all, or they may be along the seam, in which case re-seaming might be all you require.

I'm struggling to describe a certain look that old boats can develop, new ones are very smooth and shiny, older ones can start to become almost furry as the gelcoat wears off (if it even had any, some light boats dont) If it is in the latter state I would actually disagree with Chris and sggest your first plan is not so bad after all, but with some modifications.
First you would need to sand the whole bottom (deck too if you suspect it is leaky), ideally you will take off any gelcoat and get back to the first resin/composite layer but that is a lot of work and it may be hard to identify, so getting an even mechanical key all over would be OK.
Next I would mix some 105/206 (5:1 as instructed) and add some colloidal silica to get a consistency like peanut butter. With a plastic scraper apply this over the hull and scrape it back off ensuring that it penetrates into any porous areas - you should only scrape it off the surface, not out of the pores. Mix small batches and work small areas at a time, but keep going all at once. This should seal the leaks, but will not be mechanically strong.
Next (immediately before the 105/206 cures) mix some 105/207 (be careful, this needs a 3:1 mix as I recall!), 207 is the special coating hardener and has UV inhibitors in it so you can use it as a final top surface, if you use 205 or 206 hardeners you should overcoat with something else to prevent UV degradation in future. With a foam roller (use the West ones) roll this resin all over the hull.
For a sheath I would probably go for a fine glass cloth, to keep the weight down and also to make it as smooth as possible - the heavier the cloth the larger the weave and the more texture you will end up with on the final surface. Probably no heavier than 165gsm, possibly as light as 50gsm (sorry not sure what these are oz) - you want to pre-cut this roughly to shape before starting with any resin. if you are going for a single piece, which is quite feasible, the rolls are usually over a metre wide, I would suggest rolling or loosely folding from the ends to the middle, noting where on the bottom you need to place the middle of the roll/bundle before unrolling it (I would probably use a marker pen and make some location marks - they will be visible through the cloth later though.
Once the hull has had resin rolled all over (just as wet as if you were painting a wall, no more) place the cloth and gradually unroll/unfold it smoothing it out with gloved hands as you go wiping any air bubbles away from the middle to the edges as you go. The cloth will turn transparent as the resin soaks into it which helps identify when it is wet or when there might be air under it. When you are happy, carefully roll more resin into the cloth from above until it is all completely transparent and there are no voids - if you roll too enthusiastically you might move the cloth, if so smooth it out by hand again. Have lots of disposable gloves handy and change them frequently. Finally trim the cloth with sharp (but sacrificial) scissors to fit it neatly along the seam line.

At this point you will just have to smooth the edges down and leave it to cure overnight and hope they stay down OK. For small repairs I apply peel ply over the top and then tape over the peel ply to hold the edges flat, but to peel ply the whole boat will be expensive, and will leave you with the texture of the peel ply after you peel it off, which should be more pronounced than the glass I suggest - I flow coat (either with coating epoxy or polyester gel/resin mix) to smooth off small repairs after peel plying, but it adds an extra steps and extra weight - the flow coat invariably needs flatting off by wet sanding through the grades...

I have never sheathed the whole bottom of a boat like this (strip builders do it all the time) but have done many larger repairs in this way. My WWR K1 was in a terrible state when i got it, I sanded several layers of paint, resin and gelcoat off the bottom, did a bunch of small repairs and then refinished it by sealing with thickened epoxy and then overcoating with several coats of a different brand coating epoxy applied before the previous coat cured, and the results have been quite successful. I only did the bottom, which is now non porous, but the deck has a lot of porosity still. The finish isn't perfect but I was racing it last week (with a couple of new repairs to the stern from practise mistakes).
I also have a WWR C2 in my garage which needs extensive low cost repair to use for introducing kids on the flat, my idea for that is to sheath it roughly as described above, except I am planning to use a slightly heavier cloth, and will try to vacuum bag the repair (I've been wanting a vac bag setup for a while and this is the project that will give me an excuse to get one) so I don't need to trust to luck that the glass will stay down whilst the resin cures. It is not going to be all plain sailing, to get the vacuum to hold I am going to need to repair some of the bigger cracks first, and I will have to peel ply the whole lot to prevent the bag sticking which means I may need to flow coat it afterwards (but maybe not important for its intended use).

Assuming you are going to roll the resin thinly but without leaving the glass dry, you can expect to use about the same weight of resin as cloth for the main sheath, plus a bit more (maybe half as much, probbaly less) for the sealer - so if you work out the surface area and multiply by the cloth weight, and then by 2.5, you should be able to predict roughly how much weight you will add.

As already mentioned PPE is essential when working with epoxy, the hardeners particularly can cause contact dermatitis which can be nasty, I put barrier cream on first, then nitrile gloves, and for wet work thick rubber gloves on top of those, however for smoothing the cloth down (relatively dry work) I will take the heavy gloves off and just use the nitrile ones so I can feel what I am doing better. I wouldn't bother with a mask when working wet (it is a contact issue not inhaled as far as I know), but do put one on when mixing silica in to make sealer - that stuff is a really fine dust.

Good luck!

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Re: Composite(?) slalom kayak repair questions

Post by PlymouthDamo » Thu Jun 07, 2018 11:55 pm

Just to add to Jim's explanation on how to sheath an entire hull in glass: I wouldn't apply resin to the hull first. Sand the hull so it's smooth and dry, then lay the fine fibreglass cloth (often referred to as 'twill') over it, use a soft dry brush to shape it round the contours of the hull then pour a load of epoxy mix over it and drag it around using any straight-edged tool along the lines of a large plastic credit card. Once you've spread the epoxy around so that the twill is just wetted and has gone translucent, walk away. After it's dry to the touch, you can roller on 2 or 3 extra layers of epoxy to fill the weave pattern and then flatten it (e.g. using a random orbit sander), then varnish or gelcoat to get a shiny finish. Sounds scary, but it's actually an easy and satisfying job. (Doing it on the inside of the hull is a lot more awkward...) The main health risk in this is the sanding - dust from uncured epoxy is extremely bad for your lungs/skin so cover up and use a well-fitting dust mask.

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Re: Composite(?) slalom kayak repair questions

Post by nopeda » Fri Jun 08, 2018 1:07 am

Thank you folks for all your help! I did put water in it and found that the leaks are around the seat which makes sense since that's where the weight is. Also around that area the hull is pretty soft and you can feel it push in when you press on it. So at this point I'm thinking of doing a variation on the original idea after what people suggested and fill the leaking cracks as a first step, then go back later and put some fine weave fiberglass over the area of the hull in the middle of the boat hopefully making it stronger as well as more water tight. Maybe put some inside as well for added strength?

On a video a guy was talking about "release film" which was a type of plastic he put over the fiberglass to hold it in place so it would stay down while drying. The West Marine down the road has everything to do the job except that, and I'd like to get on with this instead of waiting a week or two to get some online. Will regular plastic wrap work for that, or do I need to put this off until an order of the correct stuff can be delivered?

Thanks again!!!
David

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Re: Composite(?) slalom kayak repair questions

Post by Chris Bolton » Fri Jun 08, 2018 8:31 am

The softness below the seat means that the Airex core has either debonded from the skins or broken up, so an extra layer in that area is a good idea. You may find that if you can get resin to penetrate the soft area it will stiffen up the damage. Jim says he disagrees with me, which is fine, listen to him as he was a professional laminator and I'm not. The 'release film' is, I think, the same as the 'peel ply' Jim mentions. The point about peel ply is that it's porous, so doesn't trap air, and it's also strong enough that you can rip it off. Ordinary cling film is likely to leave a lumpy finish and be hard to remove, so I would just do as Jim says and roll it flat. If it sticks up at the edges, sand it flat then apply a coat of resin to seal it. You can sandpaper glass cloth and get it smooth, but you can't sand kevlar cloth, it just goes fluffy, which is a good reason to use glass.

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Re: Composite(?) slalom kayak repair questions

Post by Jim » Fri Jun 08, 2018 8:09 pm

If the cracks are local to the seat I would seriously think about removing the seat, and just putting a largeish patch of something internally in way of the seat and not worry about the external job especially if it seems smooth. Under the seat I would be very tempted to use a carbon/kevlar mixed weave cloth to strengthen the area since it does tend to take more abuse than other areas - my river racer was originally built mostly from fibreglass but with carbon/kevlar under the seat and in the bow and stern because those are the 3 areas of those boats that tend to get damaged most.

Once you get into trying to finish a laminating job in one go there are various 'consumable' layers you can choose from.
- Peel ply (I think PE or PP) is a fine woven cloth that won't bond to epoxy, but eoxy can soak up through it. It has 2 uses, firstly for separating items you don;t want to leave permanently stuck to the job (in vac bagging there will often be a layer of breather cloth which is like a fleece that you don't want to leave stuck to the final moulding), and secondly because the resin soaks through, the waxy amine layer ends up above the peel ply, thus when the laminate is cured and you rip off the peel ply, you also take the waxy top surface away leaving a lightly textured surface which you can bond to right away without any sanding.
- Release film comes in perforated and non perforated forms, its use is basically the same as the first use for peel ply (for example to stop breather and vac bag sticking to the moulding), but the epoxy won't soak through (it will come up through the holes in perforated type) so when you peel it off the surface should be smooth, with the waxy amine layer. For doing repairs in a single operation a lot of people use release film or cling film (seran wrap), or any plastic film they can find, and tape that over the patch to hold the edges down as it cures with the idea being that when they peel it off the repair will be smooth and shiny. Sometimes it is, most people end up with wrinkles and ripples as Chris says.
- Other layers are only useful in vac bagging and infusion.

PlymouthDamo has touched on something about cloth types which is relevant if you do go for the external sheathing.
Woven roving is a simple 1 over 1 under weave, it gives a regular chequerboard pattern, but it has no 'stretch', to go around smaller radius curves you will need to cut darts out like in dressmaking.
Twill cloth is typically 2 over 2 under in a herringbone pattern and can be draped around curves, it doesn't actually stretch but it can be pulled more in one direction than the other due to the weave, this would be the better choice for sheathing, and the lighter weights of cloth tend to be twill anyway.
For small patches either can be used.
Release film will not drape around compound curves, plastic wrap will but will be difficult to smooth over such a big area.

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Re: Composite(?) slalom kayak repair questions

Post by nopeda » Sat Jun 09, 2018 1:51 am

How would you remove the seat? Would you put it back in again later with fiberglass and resin? I never would have thought of that, but at this point now it seems like it would make sense.

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Re: Composite(?) slalom kayak repair questions

Post by Chris Bolton » Sat Jun 09, 2018 9:16 am

To remove the seat, I would cut through the sides, near but not at the top. To replace it, I'd make backing pads of glass & resin, resin coated plywood or high density polyethylene, and bolt them across the back of the cut using countersunk bolts. I wouldn't try to laminate glass and resin across the join - it's possible, but tricky on the back face and has to be a good job on the front face to avoid making the seat uncomfortable - and bolts mean it's easy to remove if you have to do any more repairs.

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Re: Composite(?) slalom kayak repair questions

Post by nopeda » Sun Jun 10, 2018 5:40 am

Tonight I filled in the worst of the cracks and had enough of the mix left over to do some of the lesser ones also. It's the first time I've used enough resin to be able to apply it with a brush like painting, and so far it feels good. In the past I've just spot patched with epoxy from little syringe type tubes and used a stick or something...this is a whole new thing :-) So would it be an okay approach tomorrow night to "paint" the entire hull with resin to double up on tonight's crack filling and also reinforce the rest of it, then the next night do the fiber cloth under the seat on the outside of the hull, then maybe later go back and do it inside under the seat? And if so, does it need to be sanded and roughed up after every layer of new resin is put on? I'm using the slow 206 hardener. Does that mean it needs more days for drying between additional layers? Or maybe it's better (or doesn't matter) for it not to be entirely hard before the next application?

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Re: Composite(?) slalom kayak repair questions

Post by Chris Bolton » Sun Jun 10, 2018 9:08 am

As Jim mentions above, epoxy forms a layer of amine on the surface as it cures, and this has to be removed before the next coat, or it won't bond. You can certainly overcoat immediately it's set, but whether the window between setting and the curing process forming the amine is 2 hours or 2 days I don't know. The slow hardener may make a difference, as will the temperature. Jim will know.

I've also found there's a period when the resin has set, but sanding it is difficult because it's too soft and clogs the sandpaper, so overcoating before the amine forms is best.

There's a trap I've fallen into. You say painting on the resin feels good - and I agree - but it's easy to get carried away with that and paint a big area, which looks great until it flakes off. If you mean to coat the surface, it's essential to sandpaper it thoroughly first (and protect yourself from the dust). If my intention is to fill cracks, I don't sand the surface first, and the excess around the cracks falls off when I use the boat.

Do take protecting yourself from epoxy seriously. A friend of mine spent a while repairing race boats and became so sensitized to it that he couldn't even sit an boat made with epoxy without coming out in a rash.

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Re: Composite(?) slalom kayak repair questions

Post by Jim » Sun Jun 10, 2018 11:23 pm

I haven't seen any data for an overcoating window for 206, it will probably be a few hours at most so if it has been left overnight I think you will need to sand.
Temperature affects cure (not quantity of hardener) so if it is soft but no longer liquid, move the boat somewhere warmer to finish the cure, I have screws in the beams in my lounge for hanging boats to cure...

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Re: Composite(?) slalom kayak repair questions

Post by nopeda » Mon Jun 11, 2018 6:02 am

Sanded and then painted the entire bottom of the hull tonight, doubling up on the cracks covered last night. Also with what was left over added more to soft areas. Used a filter mask during the sanding. Thank you guys so much for the help! Now I'm wondering what exactly does the fiber do? Does it somehow add strength itself? Or is its value in holding a lot of resin, like an amount that would be equivalent to many layers of just adding coat after coat after coat...of resin having to sand again and again after each coat?

Thanks again to you nice people for helping me learn about this basic stuff !!!

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Re: Composite(?) slalom kayak repair questions

Post by Chris Bolton » Mon Jun 11, 2018 9:02 am

The fibre is the main strength - when making a boat, the idea is to use only enough resin to hold the fibres, and a vacuum bag might be used to squash out excess resin. When anything bends, the outside of the curve is stretched and the inside is compressed. The fibre carries the tension on the outside. The resin holds the fibres together and keeps them aligned, and transfers the forces into the fibre. It also keeps the water out of both the boat and the fibres.

Where cracks have occurred, the fibres may have broken, or they may have become debonded from the resin. In a boat with a foam core, the core holds the two structural layers apart, like the flanges on steel girder, so that the whole is stiffer; when it cracks, the two skins can get closer together, which makes it easier for the laminate to bend, and the shear strength of the core is lost (like you can flex a stack of paper, but if you hold the sheets together you can't). Your repair is glueing the fibres back together, filling gaps that allow compression, repairing the core and re-waterproofing. The resin won't have penetrated everywhere, and the broken fibres only have a short length of resin bonding each one, so it won't be as robust as the original, but it will be good for your purposes. More resin makes it heavier, but you're not trying to win an International race.

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Re: Composite(?) slalom kayak repair questions

Post by Jim » Mon Jun 11, 2018 12:27 pm

Resin + fibres = stronger than either resin or fibres.
The resin is actually the weakest component by most measures, but without it the fibres are just cloth... kind of like adding rebar to concrete.

Carbon fibres are the stiffest - so a carbon fibre component will flex less than one the same thickness/weight made from other composites
Kevlar (Aramid) fibres are strongest in tension - a kevlar component will flex more than carbon, but is less likely to break and when it does the fibres often don't break only the resin
Diolen fibres are similar to kevlar but cheaper and not quite as strong
Glass fibres are the weakest (there are different grades, structural S glass is stronger than electrical E glass) but cheapest (E glass is cheapest and widely used as a result), stiffer than kevlar but nowhere near as strong, and available in a lot more fabric weights.
There are other fibres which are sometimes used in other sectors, such as innegra and aluminium, but these haven't really foun their way into boat building yet.
It is not uncommon to combine several types of reinforcement in one laminate, for example I built racing dinghies for a while which were primarily glass fibre, but with strips of carbon to stiffen certain areas where the rigging was attached. Often a kevlar or carbon boat will use one heavy layer of the exotic cloth, but the weave would leave a texture through the gelcoat, so a finer glass fibre cloth will be put down first to prevent that. In canoes and kayaks an interwoven carbon/kevlar cloth is quite common - there are alternate strands of carbon and kevlar, thus getting stiffness from the carbon and strength from the kevlar, it can also be done by using alternate layers of each cloth, but because there is always a risk of shear between layers, it is preferred to use as few layers as possible, and the interwoven cloth allows for that, even though it may be used with a glass layer to prevent texturing, and may be incorporated into a foam sandwich where a foam core is bonded to the outer layer and then another layer bonded inside of that. For foam sandwiches the interwoven cloth is ideal because you need 2-3 layers rather than 4-5 if you were to use entire layers of carbon and kevlar.
My river racer (which I stripped all the original gel coat off to do extensive repairs) was built from glass fibre with a strip of carbon all along the keel to stiffen the back ofthe boat, and areas of carbon/kevlar interweave at the bow, stern and under the seat whch are the 3 areas that take most impacts during racing. As part of the repairs I added some extra carbon strips in hoops around the most flexible parts of the hull to stiffen it up a little locally without adding the weight of a full layer of carbon.

I only paint resin on without re-inforcement when I want a smooth surface not for strength, and for that I either us a special coating resin with UV inhibitors, or I use a mixture of polyester gel coat and polyester resin as a flow coat. The polyester won't stick that well to the epoxy even after sanding but it is easier to put on a little thick (as a flow coat), can be adjusted to cure rapidly and can be wet sanded to get a really smooth finish - you can wet sand epoxy resin but it is harder to sand and because the coat will be thinner there is more risk of going right through to where you started...

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Re: Composite(?) slalom kayak repair questions

Post by nopeda » Tue Jun 12, 2018 4:44 am

Wow, you guys really know about this stuff! Thank you for such great explanations!! Last night I painted the entire hull and today it looked great imo, but because of what you people explained I sanded it with 80 grit sandpaper until it looked pretty much white to get the amine layer off. Then brushed the dust off and then cleaned it with alcohol. Tomorrow evening around 5:00 I hope to lay some cloth on it dry, then pour some resin on the cloth and use a stiff plastic card type object to squeegee it around like PlymouthDamo suggested though that is still scary to me since in a video the guy painted resin on the hull, then laid the cloth, then more resin on the cloth all done with a paint brush, so I don't understand the advantage to the laying it on dry type approach. Anyway, later around 8:00 I hope to put on another coat before the first one gets hard to fill in the weave and hopefully after it dries that should do it for the outside of the hull. Is that a correct interpretation? Also I'll be using 2 pieces of cloth and plan on overlapping the front piece over the back piece by about an inch. Would that be the way to do it?

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Re: Composite(?) slalom kayak repair questions

Post by Chris Bolton » Tue Jun 12, 2018 8:34 am

My approach is resin first, lay the cloth over it and draw the resin through. Cloth first, in my experience, has ended up with air underneath the cloth, as the resin makes it impermeable. I'm sure that depends on the closeness of the weave, and there will be materials which work well with PlymouthDamo's approach; getting the cloth to drape correctly will certainly be easier if it's dry. So if you're going cloth first, I would do a small trial with a bit of scrap and check that you won't get bubbles under it.

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Re: Composite(?) slalom kayak repair questions

Post by Jim » Tue Jun 12, 2018 11:15 pm

1" overlap is what we always used to use when building dinghies.
I'm also in the school of painting resin first and then laying cloth, PlymouthDamos method is probably fine with glassfibre because it wets out very easily, I wouldn't reccommend it if you ever end up working with carbon, or worse still kevlar because that stuff really doesn't wet out easily so you want to be trying to draw it into the back as well as rolling it into the outside simultaneously.

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Re: Composite(?) slalom kayak repair questions

Post by Chris Bolton » Wed Jun 13, 2018 8:48 am

Overlap when you're laying up a new boat in a mould is different to overlap when sheathing. In the mould it forms a thickening on the inside, but you'll get a bump on the outside. You're aiming to stiffen and waterproof it, not add to primary strength, so I'd be happy to butt the pieces closely together and maybe mush the fibres across the join when they're wet. However, don't do that if the join is in the part of the boat where you'll be sitting - between the back of the seat and the footbrace - because you'll be creating a weaker line across the boat, and in the unlikely event you get it wrapped on a rock or across a gap it will fold at the weak point and trap you. Just behind the seat is fine.

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Re: Composite(?) slalom kayak repair questions

Post by nopeda » Wed Jun 13, 2018 9:05 pm

I took the wet it first approach and that worked very well. First time I've tried it and think it turned out pretty good. Left it alone for 4 hours before doing the second coat, which was an hour longer than intended. It felt pretty dry in the majority of areas but was a very little bit tacky in a few and since it was the slow drying hardener I took a chance and did the second coat. I believe it took, but don't know how to tell. If not, might it peel off in sections or what would it do? While applying the second coat it sort of felt like it sank in...sort of like the first coat became softened when it got wet from the second coat. Is that possible?

Another big question for me: When doing the first coat with the fabric the resin started getting warmer and warmer. It never did that with any of the other times I used it. The mix was the same but that particular time I stirred it a lot more than any other times. Could that be part of it? It also set up a lot quicker and that was the only time the resin got gummy before I got the job done. All the other times I had plenty of time. During that on I had to throw about a third of it away, with much profanity, and mix another batch. That one went fine and so did the second coat four hours later. Can anyone tell me what might have made such a big difference?

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Re: Composite(?) slalom kayak repair questions

Post by nopeda » Wed Jun 13, 2018 9:14 pm

Chris Bolton wrote:
Wed Jun 13, 2018 8:48 am
if the join is in the part of the boat where you'll be sitting - between the back of the seat and the footbrace - because you'll be creating a weaker line across the boat, and in the unlikely event you get it wrapped on a rock or across a gap it will fold at the weak point and trap you.
What a scary thought that is! I've never thought about that before but I guess it has happened and drowned people. I saw a canoe wrapped around a rock once but the hull was folded not the deck. What you mentioned is the stuff of nightmares. I've had a lot of dreams where I was trapped under water and couldn't get to the surface in time. The really bad part is that when I couldn't hold my breath any more I started breathing and survived. That could make for a big mistake if I'm ever actually in the situation and give in to taking a breath of water when if I instead hang in there a few more seconds might make it back to air again.

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Re: Composite(?) slalom kayak repair questions

Post by nopeda » Wed Jun 13, 2018 9:17 pm

Jim wrote:
Tue Jun 12, 2018 11:15 pm
I'm also in the school of painting resin first and then laying cloth, PlymouthDamos method is probably fine with glassfibre because it wets out very easily, I wouldn't reccommend it if you ever end up working with carbon, or worse still kevlar because that stuff really doesn't wet out easily so you want to be trying to draw it into the back as well as rolling it into the outside simultaneously.
That's the first way I learned anything about it from a video where the guy is doing it that way here:


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Re: Composite(?) slalom kayak repair questions

Post by Chris Bolton » Wed Jun 13, 2018 9:53 pm

Resin produces heat as it sets. As soon as it starts to heat up, the heat makes it set faster, which produces more heat.., etc. The main reason it gets too hot is if the heat doesn't escape fast enough, ie, a bigger batch heats up more. The shape of the container also makes a big difference, use a wide shallow tub - the worst shape is theoretically a sphere, but a cylindrical container full up to it's diameter is almost as bad. The second thing to do is to get the resin out of the tub as soon as you can - spread in a thin layer on the boat, it can't overheat.

All resins are exothermic - polyester sets faster and gives off more heat if you put more catalyst in, but epoxy has to be in the correct ratio (and usually fails to set at all if you get that wrong) so the rate of heat production depends only which hardener you use, plus the ambient temperature.

So the batch that caused the trouble may have been a bit bigger, a different container or a warmer ambient that just tipped it into the runaway cycle.

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Re: Composite(?) slalom kayak repair questions

Post by Jim » Thu Jun 14, 2018 11:16 am

The main reason that batch got hot was because you were working more slowly using it with the cloth (and partly because you mixed it for longer). Once the resin is spread thinly the heat escapes fine, painting resin is quick so you spread it out quickly, stippling it into cloth takes a lot longer so it lingers in the pot as large volume with a small surface area allwoing the heat to build up. Also you probably had the pot in your hand so transferred extra body heat into it that way (I always try to grip near the top away from the resin).

The best ways to avoid this are to mix in a small pot and then tip out into something with a larger surface area, like a paint roller tray - if you roll rather than brushing this happens by default :), and to mix smaller batches so you can use all the resin before it starts to heat up. In your case you would probably have been better off mixing half the quantity for the cloth that you used for painting (use twice as many batches), but this is something you will only find by trial and error, because different people will work at different speeds and in different ambient conditions.

Working in a boat builders I have seen roller trays of epoxy rushed out the door smoking on hot days when the laminator encountered some problem and didn't use it as quickly as normal (problem like gloves splitting and needing to be changed, or the pre-cut roll of glass being out of order or missing or something) - so it can happen to the pros too! Never actually seen one with flames coming off, but we used to get them out in the yard where there was nothing else to catch on fire if they did!

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Re: Composite(?) slalom kayak repair questions

Post by nopeda » Fri Jun 15, 2018 4:07 am

Thank you guys for more great explanations! I'm going to try to do the roof on my houseboat now that I've had some pretty fair success with the kayak. It seems to have turned out well. Another question: running my fingers over the surface which is very smooth, it felt like it had a bit of an oily substance on it. Then rubbing my fingers together it felt like there was a thin bit of oil on them. Does this process produce something like a very thin film of oil after it cures?

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Re: Composite(?) slalom kayak repair questions

Post by Chris Bolton » Fri Jun 15, 2018 8:04 am

That's the amine, as above. Google 'amine blush'. I learned something there, it doesn't always happen to the same degree.

I would consider polyester resin for a houseboat roof, it doesn't take the stress a kayak does and that amount of epoxy would be expensive.

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Re: Composite(?) slalom kayak repair questions

Post by nopeda » Sat Jun 16, 2018 1:44 am

Chris Bolton wrote:
Fri Jun 15, 2018 8:04 am
That's the amine, as above. Google 'amine blush'. I learned something there, it doesn't always happen to the same degree.

I would consider polyester resin for a houseboat roof, it doesn't take the stress a kayak does and that amount of epoxy would be expensive.
What I found consistently said wash amine blush away with water (sometimes soapy water but they didn't all suggest soap) and an abrasive scrub pad, then dry with towels. Don't sand until after doing that, which I did after the first coat. Next time I won't :-) Don't try to get rid of it with acetone, which I was going to ask you guys about. Now I guess I won't :-) Here:

http://forum.woodenboat.com/showthread. ... sh-removal

some of the guys suggested toluene but if water works that sounds best to me. Thanks for the suggestion to Google it !!!

I might try the polyester resin on the houseboat roof but this stuff has been working so great it might be worth the extra expense. Also the roof of a houseboat is often walked on and sometimes by several people at the same time, plus things are stored up there. Some people put hot tubs up there, and a lot of people have bars and of course bar stools up there, so it might be best to stick with the West System stuff. Or have I missed something else that should be taken into consideration?

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