Thread: how many layers of epoxy???

I'm not a great fan of epoxy coating because it's a rigid layer that can be cracked, allowing water in. It is tougher than paint but harder to repair if you get moisture in hence allowing rot. Paint also 'breathes' so scratches, etc aren't as much a problem as glass or epoxy.

The epoxy isn't going to add any strength, but will be a tougher surface than paint.

Personally, and this length boat is in the same category as what I play with, I'd buy a good, professional quality enamel and use its primer. Prime the timber well and a few good, top coats. The trouble with enamels is that while they dry in a couple of days, it takes a few months for them to achieve full hardness, so you'll find yourself touching up a fair bit in the early days, but they work well and are long lasting.

If you've got the money, one of the very thin, epoxy timber preservatives is the way to go. These ghastly creations are like water and soak into the top layer of plywood, this protecting it, but the fumes are horrendous so do it outside and with protection.

Normal epoxy (West, etc), just sits on the surface - try sanding it and seeing how quickly you get through it. You can thin it and it will soak in further, but if you thin it enough to soak in like a specialist preservative, the thinners will evaporate as it cures leaving worm holes in the epoxy - it's not water proof. Not a problem if you are putting another coat of unthinned epoxy on top.

If you do go the epoxy coating route, and many do for the added toughness, use a roller. Just a cheap, foam roller (the dense foam, not the squishy foam) - cheap because it's going to be a throw away job. Put a plastic bag over your roller tray so that clean up consists of just chucking the bag away. Roll on one coat. Next day, roll on another - if you do it the next day, the epoxy will still be green and you will get a chemical bond between the layers. Leave it longer and you'll have to sand the first layer to give a mechanical bond between the layers.

Once the second layer is on, sand it within a couple of days, while the epoxy is still green. You'll find it sands exceeding easily and you'll have to watch you don't go through it - you'll also have to wear a face mask as that epoxy dust is still curing and you don't want it doing that in your lungs. If you leave it a week before sanding, it'll be like rock, but still quite sandable.

Personally, I've found that epoxy coating a boat is expensive, time consuming and doesn't produce a result I find satisfactory. A good enamel will be needed anyway, so let that do the work. Any surface, even a glass one, will get breached and once moisture gets under a layer, you're in trouble. Paint breathes and so the problem isn't as bad - it's also easier to fix. When stripping back my 12' yacht earlier this year (it's for SALE if anyone wants it), I pulled off the old fibreglass tape on the seams - under one piece of tape, I copped a very strong, musty smell as it came off. That tells me there was rot starting under that tape and no sign of damage to the tape.

BUT, others have different views so ...

Now, time for a gentle reprimand. The description '11ft boat' provides no gratuitious gratification. We want BOAT . Piccies. Piccies. Piccies.
Please
What is is?

Cheers
Richard

Sorry about the long post, but I have a different view and I'll put the reason behind each of Richard's quotes, note that both of us are "right" it's just that I think I am the most right!! :

Originally Posted by Daddles

I'm not a great fan of epoxy coating because it's a rigid layer that can be cracked, allowing water in.

I am a fan, it is not so rigid that normal panel flex will cause crack, and if the epoxy cracks, generally I reckon you will have lost the paint only finish long before!

It is tougher than paint but harder to repair if you get moisture in hence allowing rot. Paint also 'breathes' so scratches, etc aren't as much a problem as glass or epoxy.

You are only likely to get rot in areas which are constantly damp, or between mating surfaces. Repair on a "normal" scratch means sanding back, drying and dobbing on epoxy, the only tough bit is that it is one more step than just painting, but the process is the same. You would only be using glass in a structural situation, and paint can't overcome that.

The epoxy isn't going to add any strength, but will be a tougher surface than paint.

Wrong! The epoxy will add considerable stiffness to the ply, if you don't believe me, grab three bits of 4 or 6mm ply, leave one uncoated, coat one on one side with two coats of epoxy and one on both sides and compare the stiffness.

Personally, (snip)..., I'd buy a good, professional quality enamel and use its primer. ...(snip)... so you'll find yourself touching up a fair bit in the early days, but they work well and are long lasting.

If you've got the money, one of the very thin, epoxy timber preservatives is the way to go. (snip)...

Note all of Richard's advice re use of epoxy is sound and I won't repeat it, however to an extent the material depends on how you are going to use your boat. I would (and do) go the diluted route every time, with a purpose bought diluent, and use a second full strength coat (sometimes three) depending on where on the boat it is.

My skiff is 10 years old, and I am about to remove all the varnish and do it again (it's been carefully kept under cover when not used) and the hull is two-pack over epoxy and unmarked (almost!).

My old canoe on the other hand was house paint over epoxy. It didn't stick very well but the epoxy never wore through on beaching. My next canoe will probably be waterbased poly over epoxy.

I think if you add up the total cost of the boat, the additional life the epoxy will give you is a tiny percentage of the cost (and extra $30 or so?) and well worth it.

Personally, I've found that epoxy coating a boat is expensive, time consuming and doesn't produce a result I find satisfactory. A good enamel will be needed anyway, so let that do the work. Any surface, even a glass one, will get breached and once moisture gets under a layer, you're in trouble. Paint breathes and so the problem isn't as bad - it's also easier to fix. When stripping back my 12' yacht earlier this year (it's for SALE if anyone wants it), I pulled off the old fibreglass tape on the seams - under one piece of tape, I copped a very strong, musty smell as it came off. That tells me there was rot starting under that tape and no sign of damage to the tape.

This is where I seriously disagree. Moisture will only travel under an epoxy layer through the substrate itself, not between the substrate and the finish, so it is relatively easy to find and fix.

You should be looking for those sorts of scratches anyway, and fixing when they occur, NOT relying on paint or epoxy to keep you out of trouble.

The removal of fibreglass tape was almost certainly a boat built with polyester resin. Most stitch and tape boats were until relatively recently. Polyester does not have anything like the same properties as epoxy and many people are confusing failure of Poly with epoxy.

Typically one can simply lift off failed glue joints, and often they have cracked and allowed water under giving the symptoms that Richard has described. THIS IS NOT AN EPOXY FAILURE!

Dunno if I've been helpful or not, but that's my somewhat contrary view:

In summary, if you are going to use the boat often, or keep it for a long time: go two coats of epoxy, one of the diluted with the recommended product.

Cheers.

P (who hates epoxy, but uses it while wearing one of every known saftey thingo!)

Before we confuse the new bloke too much, we should point out that this argument is one of those perennials and there is no 'right' answer and in many cases, possibly depends on use.

You are going to have a safe and servicable boat whichever route you take.

One thing to consider, says he as he looks at the Mouseboat he's building that now has gunwales, top decks and awaits only a seat and skeg, is the amount of timber that's been covered with epoxy through the stitch and poo ... err, glue process - IF that's been the method of construction you've used.

By the time you prime the surface for the tapes, glue the tapes on, have over runs (coz I'm a messy builder) and generally dabbed at areas spreading the drippage instead of wiping it up, you often find that much of your boat has been epoxy coated by default. That's certainly been the case with my 8' Mouseboat, but I'm also using 100mm wide tape (it was cheap in the hardware ... and I won't be repeating THAT experiment). As a result, epoxy coating the rest of the boat would be tempting if I were doing a 'good' job. Sadly, Toad is a budget special and so I won't be.

On the other hand, my Yellowtail is lapstrake and will be done 'properly'. Once it's cleaned up, there will be little epoxy on the surface of the timber. She'll get the timber preservative and enamel treatment.

Interestingly, Iain Oughtred is firmly against epoxy coating his boats, even against things like the timber preservatives. His designs are all glued plywood lapstrake, a method that is more modern (in that it was developed later) than stich and glue, so it's not because he's an old traditionalist. The proponents of epoxy coating tend to be stich and glue specialists and working with wider, flatter areas of ply. Perhaps there's something in there. Perhaps there isn't.

The thing to remember la Huerta, is that this is one area where there aren't any rights or wrongs, so don't stress on it - if in doubt, follow the designer's instructions slavishly. It does make an interesting discussion for a sunday arvo while the epoxy sets, even if Midge is wrong

Cheers
Richard

Originally Posted by Daddles

By the time you prime the surface for the tapes, glue the tapes on, have over runs (coz I'm a messy builder) and generally dabbed at areas spreading the drippage instead of wiping it up, you often find that much of your boat has been epoxy coated by default.

My sentiments too.. so it's not much to do the rest!

How do you seal the watertight compartments Richard? Just curious?

Cheers,

P

The two Mouseboats have had their floatation chambers sealed with epoxy. The first because I was new to boat building and wanted to seal everything with poxy. The current one was done with 100mm wide tape (an experiment with cheap tape from a hardware store that I won't be repeating) and the chambers are only small so by the the time I'd done it all, it was easier to seal with poxy than mess about with paint. I use inspection ports on all sealed chambers and release them when the boat isn't in the water.

Redback was sealed with poxy from the first plank down. When I started her, I thought you coated everything so I did. But by the time I got to the second plank, I'd given up so half of her is coated and half isn't. The outside of the hull is all enamel. There are hardwoord rubbing strips along the bottom and another runs the full length of the hull along the centreline (and hence along the bottom of the skeg). Interestingly, the paint that's needed touching up has been on the sides where I dug it against things like trailers ... and there is a suspicious red stripe from the first day Dean had Scrat on the water with me (Scrat is red, Redback a sand colour).

I'm still not sure how I feel about Redback. All that work, all that money, for a boat that was hard to build ... but taught me a lot about lateral thinking, using four different methods for four apparently identical tasks, lousy plans, dodgy designs and getting the use right first. I'd be more forgiving if it did the job ... but even that's compromised (and not just by size). Grrrr. I'm grumping again aren't I.

Can't wait to start me new row boat (no excited smilie so I've got to use three green ones)

Cheers
Richard

i seemed to have opened up pandoras box on this subject...ok need to straighten some things out...first , it is similar to stitch and glue, the question is , instead of using fibreglass and chopstrand mat on the outside , it is recomended to use epoxy and mat as it is stronger and binds to the ply creating a solid unit , ok , so how many layers should be built up , if it was just fibre glass 3-4 layers would be pretty strong, should the same amount of layer be used with the epoxy...and yes i will take some pics ...

Not really a pandora's box!

Don't use chopped strand mat, it doesn't do anything structurally in this sort of structure.

How thick is the plywood?
What did the designer recommend?

You shouldn't need more than one layer of woven glass in anycase, but the weight will depend on the structural requirements.

Cheers,

P

ok lets start at the begining the ply is 6mm and is just used to get the shape of the boat and then to fibreglass around the whole boat(ply)y inside and out , fibreglassing as normal with chopstrand mat , this should make a very strong boat (a 9.9 outboard will be used ) perhaps about 3-4 layers each side (remember the ply is just for getting the shape, nothing else)...but would epoxy be a better choice than traditional fibreglass or is 3-4 layers of fibreglass strong enough, will the fibreglass bind to the ply ok to form a solid mass...

I understand what you are saying, but fear it won't necessarily make a very strong boat at all sadly. It will still need frames and strengthening ribs, and the inner and the outer skins will contribute very little to the structure.

My guess is that it will make a very heavy boat for less strength than a properly designed and constructed ply one, or a more orthadox glass moulded one.

Epoxy would be wasted on such a construction in my view, you may as well use polyester resin and save some bucks. From memory, the binders used in Chopped Strand Mat are designed to dissolve in polyester, and may not do so in epoxy?

Why have you decided on that method of construction?

Not only will it be structurally inefficient, and difficult to build, in order to get a fair (smooth) finish you will have an incredible amount of work as well!

I don't want to sound like a smarty, but I think you would save a lot of money buying a decent set of plans from a recognised designer, and you will have a safe and good looking boat to boot!


Cheers,

P

ok yes there will be ribs , thats all worked out, and infact i am actually helping a very good mate to do this boat , he has done a lot of fibreglassing in the past ...the funny thing about this project, is it used to be a 8ft tender and it was cut in half and a 3ft section fibreglassed in and 8 in added to the height, it has just kind of evolved on it's own , yes if i was building a boat from scratch i would do it propely, but the show must go on and this boat has got this far and it is almost ready to fibreglass , if infact fibreglass would be fine and strong enough to bind everything together ...

It's getting more interesting by the post!

No doubt the strongest solution would be to use woven mat, and epoxy, stay away from choppies.

I don't know anyone in Sydney who can give you advice, suggest you go to FGI, or the WEST System agents and get some recommendations. They are used to these sorts of projects and won't give you advice which will get you into trouble. (Like I might )

Take some dimensions and details of the frames with you.

I'm really keen to see some photos!

cheers,

P

ok yes there will be ribs , thats all worked out, and infact i am actually helping a very good mate to do this boat , he has done a lot of fibreglassing in the past ...the funny thing about this project, is it used to be a 8ft tender and it was cut in half and a 3ft section fibreglassed in and 8 in added to the height, it has just kind of evolved on it's own , yes if i was building a boat from scratch i would do it propely, but the show must go on and this boat has got this far and it is almost ready to fibreglass , if infact fibreglass would be fine and strong enough to bind everything together ...

that's odd when i refreshed my browser i sent the post again...sorry

i will give these companies a ring this week , i think the woven mat and epoxy is the way to go for this rig...i won't keep everyone in suspence to long , i'll get some pics of the project so far, it's really cool, kind of a short stocky deep barra boat...but i can't take credit i'm just helping my mate...