EPOXY and POLYURETHANE, random jottings

[mike160304]

In various threads on various Forums, I have written comments on these materials and I thought it might be useful to some people if I put some of them together. Epoxy can be mischievous, and either you are in control, or the Epoxy is in control.

I mix Epoxy by weight, not by volume. I have no measuring jugs or pumps. My epoxy resins and hardeners go into the older-fashioned ketchup or brown sauce squeezy bottles with flip lids and very small holes in the top.

I have 2 tiny cheap modern electronic taring scales, a 50g and a 500g (also a 3000g cheap kitchen scale and a 16 kg luggage scale with remote display, but I use these more for weighing boat components). I don't waste much epoxy, for small jobs I can make mixes as small as 1g, quickly and accurately. For small mixes I use cut-off alu beer cans for mixing in, they help to dissipate the heat of the epoxy, if needed, even floating the can on cold water, if necessary, or on warm water if it needs warming up (or I use a hair dryer). For larger mixes I use baked-bean tins, etc. I discard all cans after use, I never clean them out.

My resin systems (MAS) are 2:1 ratio systems by volume. Having tare-weighed the resin batch I multiply that x 0.45 to get the hardener weight and then add that.

I love this weighing system, I am in control and there is no mess. I would never, ever, ever, go back to mixing epoxy by volume.

If you mix too much epoxy, one trick with epoxies in general is to put the mixed epoxy into the fridge or freezer to delay its setting. After hours or days, it can be fetched out, warmed up and used.

I use MAS Retail epoxies and, more recently, MAS Trade Epoxy A (aka Blue Dolphin) with fast and slow hardeners. These are cheaper, I have to buy more, but they store for ever if stored above 10-15 degrees C. (All epoxies can "crystallize" if stored too cold, this is usually reversible with heat and stirring, but is a nuisance.)

Caution - I am using the thin version of the Trade Epoxy A system and it is a relatively slow setting system, even with the so-called Fast hardener. I have not tried the thick version. For small fast gluing jobs I still use MAS Flag thick resin and its Fast hardener.

With any epoxy, I often use 2 hardeners in one mix, e.g. 70% Slow, 30% Fast hardener, or whatever, to get the setting speed I want. With tare-weighing it is easy to do this for each individual mix.

In the Epoxy A system, the Resin and Fast hardener are clear-looking. The Standard, or as I call it, the Slow hardener, is brown. So the exact shade of yellow or brown depends on the mix.

For coating, comparing Epoxy with varnish: There is "varnish" as in 1950s-like oil-based varnish and there is "varnish" as in modern 2-part polyurethane varnish, the former being warm-yellow-to-brown, the latter being almost colourless. I never got hooked on the latter, in aesthetic terms, so the exact colour of the epoxy when used as a coating is not too important to me.

What is important to me is that all the MAS hardeners are non-blushing when used in sensible dry-ish/warmish working conditions, and that as a coating, the MAS system is said to last for years with no varnish or paint on top whatsoever. Peter Johnson at MAS UK has a mast that has been 100% outside for 6 years and it is fine. As my boats probably spend under 1% of their lives outside,  I don't feel the need to overcoat MAS epoxy, unless I want to, and I often just use 3 coats of it, but preferably 4.

Incidentally the hardeners sold with the Trade version are compatible with the hardeners sold with the Retail version.

I avoid "sheathing", I am sure it is lovely but I am usually trying to make things lighter, not heavier. I am a lunatic fringer and I tend to think of a boat as a nicely shaped block of air, trimmed with a minimum of lightweight Okoume plywood, preferably 3-ply as 5-ply is heavier. But that's just me, you may be more sensible.

Other than Epoxy, for joints/laminations with no end grain and no gap I often use Everbuild Lumberjack Polyurethane glue which comes cheap from the Builders' Merchants in a handy 750ml squeezy bottle. I use both the 5-minute version and the 30-minute version. I can unclamp the 5-minute version after 30 minutes, to be on the safe side, and it has full strength in one hour. For appropriate joints, it is better than epoxy, e.g. I use it for bare unprotected woodwork outside in the yard or wherever, where epoxy would crack up in the first wet-and-frost unless well protected with paint or whatever. But if there are gaps, forget polyurethane, the expanded foam has no strength, whereas epoxy, filled, is a structural filler.

Regards,
Mike

[mike160304]

One "weight" area that intrigues me is whether or not to protect the keel runner and bilge runners with steel or brass strip.

Many SFD builders leave these wooden strips bare, treat them as sacrificial wear parts and "re-shoe" them as required.

But in 2012 I briefly owned an old, much too heavy, cheap GRP 8' dinghy, and added a 25 x 3 mm flat mild steel strip to the keel (not worrying about the rust finish that it acquired). As far as I recall, the strip and screws weighed under 3 lb. The iron-on-shingle sound was very satisfying and reminded me of a dimly remembered Norse or Anglo-Saxon text about iron-shod prows on shingle and the ensuing mayhem. Maybe it was about the Lindisfarne raid in 793 AD in which Vikings and, reluctantly, monks participated.

For metal keel runner/ chine runner protection on a small light dinghy, I think I would use flat A2 stainless steel strip, ca 20 x 3 mm, same width as the wooden runner itself, from a stainless steel stockholder. Chandlery prices for such things tend to be a bit inflated, in my limited experience.

On the other hand, the bare sacrificial runner is more weight-effective. Errrrrm . . .

Mike

[Paul H (admin)]

Mike,

Have you found any suppliers of stainless steel strip? Also do you plan to drill the steel ?(difficult)

Al will probably chime in with his flattened copper pipe solution!  

Paul

Sent from Samsung Mobile

[momist]

Mike,

 If you are looking for lightweight wood for your keel/bilge runners, I can vouch for Keruing, if you can find it.  It doesn't feel hard in the hand, but it wears remarkably well.  Mine are now thirty years old and barely worn at all.  It is used for truck beds more than anything else, and is very lightweight.  From offcuts of mine, I made a wooden Chinese style broadsword for my wife to practice her Tai Chi with, and everyone is amazed at how light it is!

Ian

[mike160304]

Hi Paul,
I have found A2 stainless steel strip on the Net by googling for it, and some other suppliers on Ebay, and I have also found a small "personal" stockholder with no minimum order requirement in Worcester:
G W Metals & Tools
Unit O & Q
Newtown Road Trading Est
Newtown Rd
Worcester WR5 1HA
Tel [phone]

Bending before drilling is essential, and drilling is a tough proposition, and I dislike all forms of violence . . .

I am increasingly attracted to the "bare sacrificial wood" school of thought for the keel/chine runners, preferably laminated with no through-screws, so that there is no water path into the structure. I would probably use Type 53 staples just while the glue sets. As wear progresses, planing this down and gluing on a new strip is not very difficult.


Incidentally, the other stainless steel item I really like is A2 stainless steel tube 6/4 mm (OD 6 mm, ID 4 mm). I found this in any length on Ebay. So far I have used it for rudder hangings on a sailing coracle and for the shaft of a home-made pulley/block using a standard 6 mm bore nylon sheave. Lovely stuff.


Mike

[mike160304]

Thanks Ian, I did make a note of your "Keruing" comment when you mentioned it before. The lightness + durability combination is very attractive.
Regards,
Mike

[inwe]

Keruing is a bit like elm, lives to be kept wet. Beware of the splinters, they can be long and do a good job of penetration. The last time I bought some , for a grave cross, I got it from Fitchett and Woolacott, Lenton Lane , Nottingham. That was some years ago mind.
As regards stainless, it really ought to be A4 which is the old 316. I did buy some mid last year but cannot remember for the life of me where from. I can't find the receipt either. I did my running strips from marine grade aly.

Richard

[alopenboat]

On 3 Jan 2015 at 2:04, Paul (admin) [via UK HBBR Forum] wrote:

>
> Al will probably chime in with his flattened copper pipe solution!  
>

I was considering it, it's versatile stuff, but I don't need to now.

On the other hand, when I built my 8ft tender for my motor boat I
used plastic curtain track. Cheap, light and low friction on
concrete. Lasts well too.

--
Sail when you can, row when you must, motor
when you have to be at work in the morning.

Alastair Law
Yeovil, England.
<http://www.little.jim.freeuk.com>

[mike160304]

Thanks Alastair, great idea, how did you fix the curtain track to the keel runner?

Regards,
Mike

[mike160304]

Thanks John, Keruing sounds good, but if it's expensive or hard to find I'll use whatever, maybe Pine or Douglas Fir - for my few hours sailing per year, almost anything will see me out . . .

All the stainless on my boats is A2, for the same reason, plus the fact that they are even more rarely in sea water.

Mike

[mike160304]

Does water go through Epoxy???? On another Forum I am told:

"Epoxy by itself can adsorb moisture. You need to add in a barrier coat like West system 422 additive to totally eliminate moisture intrusion."

Until now I have worked under the delusion that 4 good coats of a good Epoxy like MAS Blue Dolphin will prevent water from going into my wood, provided that I soak lots of it into end-grains first.
 
Is this a "buy more expensive extras" thing that WEST promotes?

Regards,
Mike

[Paul H (admin)]

mike160304 wrote

Does water go through Epoxy???? 

Mike,

I did some research a while ago and found: Epoxy in permanent contact with water will very slowly absorb water, this can take several weeks and scientists proved this by seeing an increase in weight of a block of epoxy. But if you take it out of water it slowly dries out and loses that water as the weeks go by.

The key point is permanent contact with water. Boats used at the weekend naturally dry out during the week, also taking a moored boat out during the winter allows the epoxy to dry slowly.

As for special hardeners...if anybody remembers A-level chemistry, the presence of a hydroxyl group in the polymer encourage water absorption. So a different hardener may help, but taking the boat out of the water is the dominant factor.

The research below showed a 2% gain of water at 95C which took 80 hours, then a 2% drop when dry at 95C and the noted that the diffusion (loss of water) is around 5 times faster than absorption. 95C is extremely high and most likely speeds up the absorption greatly and is probably only relevant for industrial applications of epoxy.

http://www.diva-portal.org/smash/get/diva2:348643/FULLTEXT01.pdf  (see pages 20-22)

Building MilliBee I gave her a heavy glass fibre coat with nearly 5 litres of epoxy to fill the weave. That gives a thicker coat of epoxy, which gives better protection in case I left her on mooring for a while.

Bottom line: if the boat is only in the water at the weekends there is nothing to worry about.

-Paul

PS: I get far, far more problems with rain, frost, condensation and sun with her covered by a tarp parked on the drive!

[mike160304]

Thanks Paul, that is a very detailed explanation.

As I am not into blocks of epoxy, nor into sheathing, my only interest is in whether water will go through 4 coats of good Epoxy and into the wood, whence it might have difficulty in drying out again.

Water soaking into the epoxy itself (and only up to 5% adsorption) is no problem, and at that rate, if it went through to the wood, the wood already has ca 12% water in it already, so the effect would be debatable.

My best course of action, as I go along making Epoxy mixes for my current build, is to repeat my previous tests, where I painted a wood sample with 4 coats and immersed it in cold water up to 14 days, surface-drying it and weighing it daily. As far as I recall, there was practically no weight increase. Or, of course, I could forget about the whole thing and stop worrying so much . . . .  

Certainly, buying a WEST system can be avoided.

Re "PS: I get far, far more problems with rain, frost, condensation and sun with her covered by a tarp parked on the drive!" . . . Yes, referring to glues not coatings, wet+frost is where Polyurethane glue and Resorcinol glue like Aerodux 500 are superior to Epoxy, in my experience. I would use either to glue bare untreated wood outside, but never Epoxy. And wet+frost seems to be able to get under an Epoxy coating too.

Regards,
Mike

[mike160304]

The Epoxy and Polyurethane debate is ranging far and wide on the Duckworks Forum:

https://groups.yahoo.com/neo/groups/dwforum/conversations/messages

Regards,
Mike

[Paul H (admin)]

mike160304 wrote

The Epoxy and Polyurethane debate is ranging far and wide on the Duckworks Forum:

That's good, because we don't want it here!

[Randonneur]

On Wed, Jan 14, 2015 at 11:08 AM, Paul (admin) [via UK HBBR Forum] <[hidden email]> wrote:

mike160304 wrote

The Epoxy and Polyurethane debate is ranging far and wide on the Duckworks Forum:

That's good, because we don't want it here!

Not to mention Openboat and SFD builders!

Just as well you haven't found microcruising, smallsailboats,smallboats, pico cruising, wooden boat forum, boat design forum etc. 

Oh b******s now look what I've done!

Luckily all of these have mostly the same members.

I wouldn't want ot have to create too many autodelete rules....

PP

 

[mike160304]

Why?

Mike

[mike160304]

Re "Luckily all of these have mostly the same members."

Sweeping statement - do you believe that?

My impression is that there is hardly anyone on SFD, and that the cliques on Openboat, DW and HBBR are completely different.

Do you dislike this topic?

Regards,
Mike

[Port-Na-Storm]

Now Guys.
Play nice, at least the subject is related to boat building.
 

[Port-Na-Storm]

Paul of course was expressing his own opinion and not necessarily that of others on this site. And I do believe his tongue was firmly in his cheek at the time.
The home boat-building community is small and those of us interested in the subject will probably gravitate towards those sites which interest us.
My perception, and these by necessity are broad brush strokes, is that forums like Selway Fisher tend to attract first time builders looking for help and advice from those who have gone that way before. They are of course restricted to Paul Fisher's designs and tend not to deviate far from the well beaten track.

The Iain Oughtred Forum, influenced by Iain's beautiful designs which tend to stick to conventional glued clinker, maybe show a higher level of finish and craftsmanship, but again don't deviate from normal practice and the excellent advice Iain gives in his book.

Openboat are much more about the sailing, getting out there and doing it, quite often pushing the limits of small boat sailing.

Duckworks on the other hand seems to attract the more cavalier approach to design and build. Designs are chosen and created based on pure practicality with a little less consideration given to aesthetics. Definitely function before form. They tend to be more open to using materials found in DIY barns than Yotty Chandleries. Some of their exploits are admirable e.g. PDA racers doing the Texas 200. I wish we had waters like those.

The HBBR folks are an eclectic bunch of souls who encompass all of the above, and some, manage to fit into all of the above at the same time. The original idea was to have a way of organising rallies where like minded builders could meet, a bit like the American messabouts. Turns out we aren't like minded at all, which makes it even more interesting.

I find some of the discussion on DW facinating, especially as they have now wandered into territory of using PVA glues and Drywall tape. I'd rather they did the research than have to do it myself, but its got me wondering if PVA of the type used to seal plasterboard would be a cheap alternative for sealing plywood on a quick and dirty build. I think I might have some lurking in the garage..............

If there is a discussion on another forum which might interest folks here then its good to point them towards it, but its probably not necessary to repeat, and re-post the content.  

Mike, keep us up to speed on your build, with photos please,  I will be very interested to see how it turns out. Good Luck.
Graham.