Unable to use epoxy

Hi everybody. I've reading the posts for almost two weeks and it seems like the best option for amateur boatbuilding is epoxy. However I have been unable to find it at my location (Ecuador). I've called to every marine distributor and even to the chemical companies with no positive answer. Also I am not sure if the "marine plywood" they sell is really marine grade and nobody here knows about biaxial fabric, only mat and woven. However I don't want to give up at my dream of building an small "stitch and glue" boat for fishing and have some fun outthere with my wife and family. The questions are:
- Is there any way for increasing the adherence to plywood for the polyester resins?
- Is polyester safe to use for stitch and glue boatbuilding.
- Can I replace biaxial tape and fabric with woven and mat.
I would import the resin and fabric for the project but our goverment is trying to "resist the economic crysis" increasing the taxes for the imported items to almost 50 percent (stupid thinking).
Any suggestion will be apreciated. Thank you.

 

Hi fjapa,

Let's start with the plywood. If you're not convinced it's marine grade, see if you can get an offcut or scrap of it- a six-inch square is plenty. Float it in a pot of water on your kitchen stove, set to a low boil, and keep the water topped up for a few hours. Take the plywood scrap out, let it dry, and repeat. If, after boiling and drying a couple of times, the glue lines are beginning to come apart, it's not waterproof and will disintegrate in marine use. Of course, this only tells you about the glue- as far as the wood is concerned, look for voids (there should be none, or only tiny ones, visible in the edges) and see if you can figure out what species it is. Often, a cheap "junk" species will be used in the core of a panel that appears, on the surface, to be made of good wood.

Now, the fabric. Biaxial is nice, and because the fibres are straight, is a little stiffer and a little stronger for a given weight. But for taped-seam plywood construction, I doubt there will be any noticeable difference if you switch to woven cloth and tape. Chop-strand mat is of little use in this kind of construction.

Now, the resin. And I know I'm going to take some flak for this. Having built a taped-seam plywood runabout using polyester (yes, it worked, and yes, it's still in perfect condition eight years later), I will always use epoxy from now on. Poly is a royal pain in the backside whenever wood is involved.

But if poly is all you have, it's better than having no boat at all. First order of business: An organic-vapour respirator, this stuff STINKS to high heaven. Next: A very accurate way of measuring the catalyst, and catalyst ratio correction tables for varying temperatures. (If the supplier doesn't have these, you may have to experiment for yourself.) Being out by 0.2 mL of catalyst on a cup of resin can make the difference between a perfect cure, a hot block of solid the shape of your mixing tub, and a week-old gooey mess. Add to that a good thermometer for your shop and a way of preventing it from getting too cold in there. You'll need an easy way of mixing the catalyst into the resin; if you do it by hand, you'll inevitably stop before it's mixed well enough. (A paint stirrer in the chuck of a cheap half-dead drill press works fine.)

Getting it to stick to the plywood is a bit tricky. The plywood must be clean- no oil, no paint, no sawdust. (Going over it with a shop-vac and stiff brush a few times should get most of the dust out.) You need to prime the plywood first- on my boat I used plain resin, but some folks thin it with acetone a bit. Once that starts to kick off, but before it cures, prime it again with resin. Let the second layer of resin kick off, but not cure, before you start laminating the fibreglass. The key to getting it to stick is that you need a continuous chemical bond between the first layer (that soaked into the ply) and the layer that the fibreglass actually sits in. This is not easy to do, and is very sensitive to timing. The plywood will tend to suck the resin out of the glass if you don't prime it thoroughly enough or put the glass on too early, but if you wait too long after priming, you're trying to glue to a cured, shiny surface. In either of these cases, you have to either peel it all off two days later, or let it peel off on its own after a year or two of use.

Then you'll need a good, waterproof paint system over this, because the polyester itself does not like long-term immersion all that much. (It's very slightly porous, just enough for water to slowly migrate in over time.)

So it can be done, but be prepared for a lot of frustration. Figure on an entire day, with no interruptions whatsoever, when you're trying to glass. And definitely, for sure, you really should do some test runs with small batches on scraps of plywood before you try the real boat. Scraping it off when it fails is not fun.

 

Quickie suggestion... Build the dingy before you build the boat...
Practice on the simpler stuff first...After you make a couple of pieces then you will know how to do rest. On epoxy try calling any Oil companies in your country they might be importers and resellers.

 

Thank you so much guys for your advice I know it's going to be a lot of work but I am sure it will be worth.
What do you think I should use for filling the gaps between the plywood panels, I mean is it possible to make putty with polyester and wood flour or there is another material that I can use.
I am planning to build a canoe with a cheap plywood first for testing the resin and the other components.
About the painting I haven't done any research yet but there is a reseller that have a white top coat (also poly based) so I am going to try it.
Marshmat you say that I can switch to woven mat and tape, but can you believe that nobody here uses woven tape either, so I am going to cut 6 inches pieces for the seams.
It's incredible.... isn't it?

 

I have a book which I bought before epoxy was in common use in boatbuilding that described the best techniques for building Stitch and glue small boats. "Dinghy Building" by Richard Creagh-Osborne

http://www.abebooks.com/servlet/Sea...eagh osborne&sts=t&tn=dinghy building&x=0&y=0

It does work but needs more attention than building with epoxy. If I were faced with your problem, I'd look seriously at building a plywood on wood frame boat rather than messing with an inferior material like polyester. As said, it will work and I have seen some nice examples as well as some disasters.

 

What type of boat are you looking to build? I have designs that use no epoxy and incorporate commonly available materials and parts.

 

I am planning to build a 15 feet boat that can handle a small outboard (25 HP) and have a capacity for 4 people, with a moderated V hull and strong enough for semiprotected waters. It has to be light with a maximum weight of about 250 pounds.

 

Fjapa: en Ecuador jamas hallaras uno de esos materiales. Tendrias que importar todo y a alto precio. Ya en Mexico justo en frente de los USA, esta carisimo y casi imposible de conseguir esos materiales, un barco en madera epoxy resulta 1.85 veces mas caro que en los USA...

The polyester/ common fiber works (badly) on very small boats like prams. Do not last. Totally out of question on a sea going boat.

What do you plan to build? Que barco quieres hacer?

 

In this case, a 15 feet ouboard boat, go to polyester with a "decoration" in wood (seats etc...).
It's possible to make a polyester boat without mold, just with a table for making the panels.

 

Had no problem with polyester ...15 % acetone on the wood bits ...run your taped joint and pull tight longitudinally some cling film over it on the convex ones to hold the glass in place tight over the edge .....avoids that bulge it often wants to take on sharp corners ,,,use 500g matt ...saves time and layers ..Mix paint with the poly ..does not seem to matter what ...to colour it and away you go

 

Gracias Ilan por la información... (thank you Ilan for the info)...
pistnbroke: What do you mean with 15 % acetone? I have to put acetone on the wood before the poly or I have to mix it with the resin. Also I don't know what is a cling film. Is it a polyester veil (a very thin poly fabric)?
PAR: Do you have a design like the boat I want to build?

 

Sometimes poly does not stick well to some ply...do a test ..to make it stick real well mix 10-15% acetone with the poly resin and put that on as a first coat....it soaks in and then the second coat sticks real well ..takes much longer to go off ..
when you use matt around sharp corners it tends to bulge up so if you can hold it down with cling film ...the clear plastic stuff the ladies use in the kitchen to wrap things ..you will hold it in place and get a nice smooth finish ..pull it off afterwards ...for long runs on chines its fabulus

 

De nada...you're wellcome.

I have doubts about the quality of the plywood found in your country. Generally south american plywoods are just good for furniture. So I wouldn't go to any plywood boat.
My own experience makes me very critical of systems using wood, plywood and polyester resin. Polyester resin does not glue on plywood whatever the surface preparation, probably because of the wood's phenols:
- Vosschemie system: utilisation of a polyurethane monocomponent varnish as interface. Best duration between 3 and 10 years. Tried in the French Navy a costly failure.
- Preparation of the wood with styrene and cobalt naphtenate, plus a saturation coat of diluted resin with styrene and heavily accelerated-catalysed.
Duration between a few months to 10 years. Used in several navies. Total failure.
- Diluting polyester resin with acetone affects greatly the quality of the resin as the acetone stays trapped in the resin. Never do that. The lone good solvent for polyester resin is styrene.

Myself, I've rebuilt a 36 feet Cigarette hull last year... We have ended with a bare flimsy hull after stripping out all the plywood/fiber/polyester parts which were from totally rotten to totally delaminated...this combination looks good at the beginning but it is ill fated and won't last. I think Par himself will confirm that.

The method called in France Placo Plastic permits to make in polyester a boat previously designed for plywood. Easy to finish as the panels are made on a flat mold (a table of the length and width of the largest developed panel) with a good face with gelcoat. The construction is very close to a plywood boat.

A last word: do not hope to make a 4 persons (=600 pounds of load) 15 feet 25HP boat for semi open sea for just 250 pounds... at this weight is just for a very calm lake or using very expensive materials.
It's not a problem as small boats need some inertia, it's better to make it reasonably strong and safe. At this size it's easy to make it unsinkable.

 

You can make polyester and wood work, but generally you end up with such a laminate over the wood, that it becomes a redundant element or mold, rather then a structural segment.

Examples of this can be seen on most production boats of the 70's and 80's. The tabbing of structural wooden elements is usually substantial enough for the loads imposed, but then the stringer or whatever, received a light coat of resin and some mat slapped down to complete the seal. The result permitted moisture ingress from above where insufficient laminate was applied, gravity took it to the lower portions of the tabbed in piece, where the heavier laminate trapped it against the wood. The wood dies, the tabbing remains strong, but now has no core, nor "bridging" across the top of the two tabbed flanges on the hull shell. Had the tabbing laminate schedule been carried over the wooden element, it's likely the piece would have faired much better, but this requires more material and labor.

In short, I don't recommend polyester. By the time you incorporate enough to get the job done, you're heavy and the additional material costs, now rival using a better resin system.

Fjapa, I do have 15' V bottom fishing boat designs, but your weight requirement seems light. If the 250 pounds you mention is just the bare hull, then drop me an email and I can show you some plans that are suitable. If the 250 pound requirement is a full up 15' boat (engine, fuel in the tank, etc.) then I'd be hard pressed to offer a design that will work for you. Contact me by email (click on my mane) if interested.

 

Hi guys. I have good news. I've found a crafts reseller which sells epoxy resin. The bad news are that it's like 18 dollars each 8 oz. (288 USD per gal.) really expensive for me. The questions now are:
- This resin is not marine, do you think it's going to work for stitch and glue boatbuilding?
- It is too expensive so I dont know if it's possible using polyester resin over epoxy. What I mean is can I use the expensive epoxy for the seams and cover the hull and the entire boat with poly and fiberglass?
- Is the woven roving strong enough for laminating the seams instead biaxial tape?
I've heard that if you use epoxy, it's possible to build a boat even with regular plywood, so I am not worried about wood . Also you are right about the weight, it doesn't matter anymore because I prefer having a safe and strong boat.
I really appeciate all your replies. Thanks so much.