Thread: Hello, new GIS build by Simon in ST Pete FL

MAS epoxy recommend thinning the first coat up to 10% with denatured alcohol for clear coating wood. According to them this promotes penetration of the first coat. They talk about this in part two of their video series on clear coating wood here: Epoxy - MAS Epoxies: Clear Coating Wood - Build & Repair Boats & Marine, Non-Skid Repair, Cars & Automotive, Woodworking, many other projects - Composites, Fiberglass Resins, Hardeners, Glues, AdhesivesI have used their technique in the past on teak and it is amazingly durable.

I suspect that all of this endless discussion about viscosity and penetration is somewhat irrelevant. Modern epoxy is so good that I would bet slathering any viscosity on a piece of wood is plenty waterproof as long as you get complete encapsulation.

I don't know of any testing done by MAS, nor how old this "advise" from them actually is, but testing across several sources has confirmed, that it's best not to dilute your epoxy. The reason is simple, penetration amount is irrelevant for water proofing and the peel strength of epoxy exceeds the fiber rip out strength of wooden substrates. A 10% solvent dilution will weaken the epoxy by about 30%, so subsequent coatings of epoxy, will be holding onto a 30% weaker epoxy.

There was a time when this type of recommendation was fairly common from some reformulaters, though it's interesting to note the industry leaders have never recommended it. This is no longer the case. I suspect MAS has yet to update it's user's guides and DVD's.

Yes thinning does weaken the epoxy. I guess then it boils down to is the 30% weaker epoxy still stronger than the wood i.e. do you still get wood tearout. If so, it should not affect joint strength, no? But then as PAR says if research has shown that penetration does not affect waterproofing, why bother with thinning.

Don't get me wrong I'm not obsessing about this in the least. I think the margin for error in these glue joints is huge due to the performance of the epoxy. But it is fun to discuss, cause I'm weird that way.

BTW I have done a lot of highly loaded epoxy to aircraft ply joints on very high performance model airplanes with joint loads far in excess of what our boats are subjected to (when is the last time your boat pulled 10+G ) Aircraft ply used in engine firewalls, for example, is much stronger than Okoume. From my experience a thick two part epoxy like 5-15 minute will sometimes fail by peeling away from the ply. A thinner epoxy like MAS will always tear out chunks of wood. This difference could have something to do with poorer adhesive properties of the fast setting epoxies but I wonder if part of the difference is not due to better penetration of the thinner stuff.

Howdy,

In the spirit of discussion - I am on the edge of what I know here and am suggesting some things for which I don't have a great deal of evidence.

Not sure an aircraft is under higher loads than a boat - both are designed for the joints to just not fail. So maybe there is a case to say the loads between components are pretty similar. Suspect that spar (the bit that takes the main load from the wings) loads for both are pretty similar because both break very occasionally and shortcuts in building (like scarfs shorter than spec) inevitably result in failure

I think there are two factors that make the comparison with 5 minute epoxies a weak example for suggesting thinning the first coat.

1/ The thickness of the mix. It seems to be a different mix altogether - whereas normal boatbuilding epoxy glues are two thinnish liquids with a powder additive the 5 minute seems to be two stiff liquids.

The regular epoxies never stop flowing as the thinnish liquids that they are. I don't see much of this behaviour in 5 minute epoxy - for example if you put it on a piece of absorbent kitchen paper you don't see the thinner liquids spread out in the kitchen paper quickly leaving the powder modifiers behind to some extent.

Or I am pretty sure this is true ... if someone has regular 'pox and some five minute they could mix up a little bit to see.

In other words the viscosity of the base liquids is not affected with regular boatbuilding epoxy even with the powder modifiers added.

2/ Regular boatbuilding epoxy mixes have lots of minutes to soak into the surface of the wood before they start curing and they stop flowing - maybe 15 minutes to an hour - as they will still wet a surface when they are starting to gel. They are unworkable in bulk in terms of brushing or rolling, but they can still wet a surface sufficiently to stick.

The 5 minute epoxies really do give the feeling that they cure so fast that the combo of fast curing and viscosity that they sit on top of the surface. They never get down into the ends of the wood cells to increase the surface area they bond to.

This "getting down into wood cells" does not need to be spectacularly deep to work, but the 5 minute products just don't get the chance much at all. They feel very different when you have to peel them off the surface as Simon points out.

I don't think the CPES or penetrol products are harmful for boatbuilding and can help consolidate parts that are just on the edge of softening up. There are other products that can be added to epoxy to thin it that don't evaporate and cause the porosity that CPES products are prone to.

The other thing about CPES type epoxies is that there is zero realistic research. The only thing they seem keen on demonstrating are tests to show the mix, or at least some of the thinner component with a tiny amount of epoxy does get in deeper (the thicker components will be left behind by the thinner ones as in chromatography) but nothing at all about strengths, waterproofness, adhesion of following coats etc etc etc.

But the reputable boatbuilding epoxy companies usually have some degree of firm data - if not as an individual product ...at least as a class.

Here is some data from WEST. Note that the comparison is with FOUR coats of penetrating epoxy which is way more than most will bother with.



Again the CPES products dont' hurt, but I don't think they are worth spending money on in almost all situations.

Best wishes
Michael

Originally Posted by SimonLew

MAS epoxy recommend thinning the first coat up to 10% with denatured alcohol for clear coating wood. According to them this promotes penetration of the first coat. They talk about this in part two of their video series on clear coating wood here: Epoxy - MAS Epoxies: Clear Coating Wood - Build & Repair Boats & Marine, Non-Skid Repair, Cars & Automotive, Woodworking, many other projects - Composites, Fiberglass Resins, Hardeners, Glues, AdhesivesI have used their technique in the past on teak and it is amazingly durable.

Howdy

The thing I don't find tenable about MAS's position is that they will recommend not to thin the epoxy if using it as a glue between components. I think they will forcefully say it is a stupid idea.

So that leaves them in a strange position to say it is necessary when coating timber.

It's just weird and anti intellectual! (of MAS)

This is not a criticism of the MAS products - they are very well regarded. Bote Cote in OZ talks similarly about their TPRDA product which thins without evaporating later. In their book they say it should be added routinely for coating - but not for glassing or gluing because it will weaken the bond.

Other manufacturers don't suggest thinning and they work fine with Teak too. Or can work fine if care is taken - oily teak can be difficult to glue.

However, one new development is that WEST (might be others too) have developed more flexible epoxy systems specifically for gluing things that were hard to glue before.

Like many plastics, hard to glue timbers etc. They don't work by soaking in more, but by being more flexible - I would guess the mechanism is that they reduce the stress concentration across the join or at the glue/surface interface but might be wrong.

Best wishes
Michael

A lot of good info, thanks for the enlightenment Mik. I think you are dead on right about the 5 minute type of epoxies.

As to loads in models. I'm going to take this a bit off topic but some of you fellow tinkerers might find it interesting. And we are still talking about wood and epoxy structures. I agree that in many, maybe most cases the loads on airplanes are not that different as each wooden structure has to operate within the wood's stress limits. The difference is that you can't overbuild a high performance airplane and expect it to remain high performance so generally everything is running with pretty low factors of safety. I have folded wings on high G pull ups because of over stressing the spar. Those kinds of overload conditions don't generally happen in non experimental pleasure boats. Where airplane glue joints are especially highly stressed (I think) is in the firewall to fuselage joint. The basic structure looks very similar to the GIS transom attachment but the material (aircraft ply and sometimes carbon) can withstand much higher loads than Okoume and Cedar. So the glue joint is holding together stronger bits which allows the entire structure to operate at higher stress levels. There is also the vibration and G forces from a (usually) single cylinder engine.

We also tend to crash model planes regularly which gives ample opportunity to inspect failure modes

Just in case any are curious what kind of model I'm talking about they are about 6 foot wing span weighing 8-10lbs or so. My favorite has a 1.2 cubic inch supercharged four stroke engine spinning a 17 inch prop at about 9500rpm. This produces about 15lbs of static thrust which allows ridiculous aerobatics and unlimited vertical performance. This video shows what it's all about. I have the same plane but the video is not of my plane nor am I the pilot. [ame="http://www.youtube.com/watch?v=vtGI9NyIkUc"]YouTube- Broadcast Yourself.[/ame]

I do agree and I have learned more from aero modellers than I can say!

However ... how many Gs is this mast pulling?

[ame="http://youtube.com/watch?v=5PVkPHGE2c8"]YouTube- Broadcast Yourself.[/ame]

Actually you are spot on ... the difference is that the masts on our first PDRacers were too flexible for good sail shape. Once they were made stiff enough ... then they are strong enough too.

This is not something that happens quite the same with aircraft as providing there is not control robbing distortion you don't mind things bending quite a bit when pulling 10Gs

I happened across Pierre(?) Closterman's writing about flying spitfires and typhoons in WW2 and talking about watching the paint peel off and pop rivets shoot out of the wing when doing high G turns and pull outs close to the ground.

This can happen to masts too ... or at least ones that are fabricated - but usually the sail shape is so bad by that point that there need to be big changes.

MIK

I'd say you pulled just enough Gs to break it

The more I think about it your approach to minimizing weight and excess structure is identical to airplane design. And small boats have the luxury of testing a design at the very limit of structural strength without endangering the life of the test pilot. One of the reasons I like messing with model planes. You can really push the envelope with manageable risk.

OK, so we have established that in both cases the nuts in control are capable of subjecting the structure to enough abuse to break it and that all this is possible due to the wonders of modern epoxy, be it thick or thin but not too thin or too thick

I did not pick up on MAS contradicting themselves, interesting. I am going to risk all for the team by conducting a long term experiment. The front halves of the hull sides are already coated with the first coat thinned as MAS recommend. I won't thin the epoxy for the aft halves and we will see which end of the boat falls off first.

Forgot to add. If you are interested in aviation history and have not read it, a very good read is Chuck Yeager's autobiography titled [ame="http://www.amazon.com/Yeager-Autobiography-Chuck/dp/0553256742/ref=sr_1_1?ie=UTF8&s=books&qid=1264718828&sr=8-1-catcorr"]Yeager[/ame]. I'm in awe of what he and the men around him accomplished and the attitude they had towards what they did. They defined living life to the limit.

Originally Posted by Boatmik

I do agree and I have learned more from aero modellers than I can say!

However ... how many Gs is this mast pulling?

MIK

Actually, I'm surprised that you 2 scientists think that G-"forces" were at at work at all, which of course they are not!

However, I can't get enough of that shot of Mick taking a dumping

We definitely are taking poetic license with the G force term but Mik did feel a G or two falling in the drink.

I you really want or think you need deep (relatively deep anyway) penetration you might consider Robb White's technique. He hated working with epoxy so he would build an entire boat--strip planked--with industrial crazy glue drops here and there to hold the strips in position. When the hull was fully assembled he would crank up the heat in the shop--120-130F, just as hot as he could stand. Once the shop and hull had time to warm up he mixed a batch of epoxy, turned off the heat and tuned on the A/C. He would then slather everything with resin which, due to the warm but cooling wood, would be sucked into not only the pores but into the joints.

According to this article Gudgeon Bros. tested a laminated stem White had fabricated with this method. They sliced into it to see what kind of joints it had and reported the very fine epoxy glue lines ran through and through.

RudderPosts: Robb White Article

I wondered about how temperature changes affect penetration. Our temperature has been swinging from about 50F in the morning to 70-75F at mid day. I've stopped applying epoxy during a rising temperature because of the bubbles. If I also get a bit more penetration that's a nice benefit.

Howdy,

Penetration Schmenetration.

It doesn't matter unless it is a product that tends to sit on the surface to some extent.

He would then slather everything with resin which, due to the warm but cooling wood, would be sucked into not only the pores but into the joints.

Evidence please? And then Evidence that this "soaking in" positively affects the result. There are a number of people who use the same method without heating.

A properly formulated boatbuilding epoxy used within the framework of the manufacturer's requirements will work.

I could say ... I can glue at 80C and it also is effective.

So what does it prove to show it works just as well at higher temperatures.

Because he heats it and it works doesn't prove anything other than it will work at a higher temp. But I think you would need to do some serious testing to find differences.

My often used example of how things get more complicated over time is relevant here.

In the 70s they built kayaks out of 4mm ply with glass tape joins
in the 90s it became more common to glass the whole outside - 4oz
in the 2000s some designers started specifying glass on the insides too.
The 18ft jarcat cabin cat uses 4mm ply and 2oz glass on the outside only.

There is no evidence that the simple ply and glass tape boats were not adequate for most uses, but more complication is added on the assumption that it is somehow "better".

Some of the pro builders I know do keep the epoxy at thermostatically set temps ... maybe 95F (if I remember correctly)