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Old 13-09-2015, 10:34   #16
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Re: Lightweight but strong backing material

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Cabin tops are usually curved. Ply bends. Thinning epoxy allows it to penetrate the wood. G10 is glass. If you want more glass why not lay up more glass.

Builder's all do things a little differently and either way would work well.
New portholes are not yet in our budget but we would like to move to bolt-through New Found Metal ports when we are able.

Also, I'm not sure what you call the sides of the coach roof but on our boat they are straight as you can expect an unfinished fiberglass layup to be. Previously, they just glued the ply to the fiberglass using maybe 5200 but it has since gotten wet and rotted. On top of that they put 1/4" thick teak.

So, I originally was thinking of using a foam but quickly realized that it was not strong enough to hold the screw of the existing ABI ports.

Then I was thinking G10 but big sheets of thick 1/4" G10 is really expensive and heavy. I had also thought about glass but I am worried about adding extra weight to the boat up high.

Now, I'm thinking the best route without investing in a new ports is simply replicate what the builder originally did (ply glued to the fiberglass then teak) and when we have the money, upgrade to new found metal.

THEN I say... WHY? If we are going to go through all the trouble of rebedding all the ports, do we just go ahead and move budget from some where else to new portlights. HOw do you balance what is important and what can wait? My screwed in ports are in fine shape and have kept the boat floating for 27 years... so why change?

BUT

It seems that on a boat - everything is important and everything is an equally important safety item. The ports are not just for show - they keep water out - so are definitely a safety item.
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Old 13-09-2015, 10:49   #17
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Re: Lightweight but strong backing material

You Are Here: Home » Projects » Techniques & Materials » Thinning WEST SYSTEM epoxy
Thinning WEST SYSTEM epoxy

BY Brian Knight Download PDF version of this article

A question frequently posed to our technical staff is "can I thin WEST SYSTEM epoxy so it will flow or penetrate better?" The answer to that question is "yes, but not without consequences." Many of the advantages of thinning epoxy are offset by disadvantages in other areas of epoxy performance.
Thinning epoxy means lowering its viscosity (Figure1). Low viscosity epoxy flows better, is easier to roll or brush, saturates fiberglass fabric quickly, and penetrates more deeply and more easily into porous surfaces like partially rotted wood. There are two methods of temporarily thinning epoxy. One is to heat the mixture and the other is to add solvent to the mix. The goal of both methods is to reduce the epoxy’s viscosity. This article explains what happens to WEST SYSTEM epoxy when it is thinned either by heating the components or adding solvent to the mixture.
Through knowledge gained from our comprehensive test programs and from 30 years of practical experience, we have learned that epoxy formulation is a balancing act. When one characteristic is altered—e.g. changing handling attributes by adding a volatile solvent—other characteristics like moisture resistance and strength are also changed. Our chemists formulate a well balanced, versatile epoxy that provides excellent structural strength and moisture resistance. If you elect to modify it, you become an epoxy formulator and need to understand the effects of your changes. Armed with the information in this article, you can decide if thinning epoxy is worth the tradeoff in performance.
Is thinning necessary?
There is a perception that epoxy needs to penetrate deeply into wood to be effective. Sometimes this is true, but most of the time it is not. Some common misconceptions are that deep penetration of epoxy 1) makes rotted wood as strong as new, 2) increases adhesion, and 3) makes wood more waterproof. The following is a brief discussion of these points.
1) Rotted wood impregnated with epoxy does not make the damaged wood as good as new. Deep penetration of epoxy into rotted wood will make the wood hard but it will not restore its original strength. This is not important if the rotted material is non-load bearing. A rotted door threshold does not need to be strong, just hard. However, when the wood fiber is damaged, wood loses its ability to carry loads and unless the fiber is replaced, it will not regain its full strength. A rotted deck beam or sailboat mast needs more than epoxy consolidation to return the wood to its original load carrying capacity.
2) Adhesion in all but the highest density wood is not enhanced by deep penetration of the glue into the wood. Research performed at the Forest Products Laboratory showed that adhesion to birch was increased slightly by using thinned epoxy. In lower density wood species like Sitka spruce or Douglas fir, the weak link is the cross grain strength of the wood. It does not matter if the epoxy penetrates 1/4" into the wood or 5/1000". The strength of the wood, the amount of surface area and the adhesive ability of the glue determine the strength of a glue joint. Most types of wood glue do not penetrate deeply, yet, if used properly, they can exceed the grain strength. Epoxy is no exception.
3) Water resistance of a piece of wood is not enhanced by deep penetration. Wrapping wood in plastic makes a pretty good waterproof seal without any penetration at all. Likewise, an epoxy coating on the surface is more water-resistant than a thinned epoxy coating that has penetrated deeply into the wood because, in most instances, the epoxy thinned with solvent is porous.
The USDA Forest Products Laboratory developed the Moisture Exclusion Effectiveness (MEE) test. It is a measure of how much moisture is absorbed by wood when it is continuously exposed to 100% humidity. Higher numbers mean the wood has absorbed more moisture while lower numbers indicate less moisture is absorbed. You can see that epoxy with solvent added is not nearly as moisture resistant as un-thinned epoxy (Figure 2). However, if you need an epoxy coated surface that is less of a vapor barrier, thinning WEST SYSTEM epoxy with solvent is a valid way to achieve this
Thinning epoxy with heat.
Heating the resin/hardener components and then mixing them together results in a thinned epoxy mixture that, when cured, retains all the characteristics of epoxy cured at room temperature. The viscosity of epoxy is very sensitive to changes in temperature, and warming the components (resin and hardener) and/or the substrate substantially lowers its viscosity (Figure 3).
With wood, the best method of thinning epoxy with heat is to warm the wood and have the resin and hardener at room temperature. Mix the components and apply the mixture to the warm wood surface. Remove the heat source just before the epoxy is applied. When the epoxy mixture comes in contact with the warm wood, it gets warm and its viscosity becomes lower. As the temperature of the wood falls, the thin epoxy is drawn in deeply before it begins to gel. By heating the substrate instead of the components, you get the best of both worlds—low viscosity epoxy on the work surface and longer working time in the mixing pot.
Potential Problems
Thinning epoxy with heat can create problems, however. Warm epoxy cures much more quickly than you may be accustomed to. Have things organized before you mix the resin and hardener and move quickly. Use one of the slower hardeners—206, 207, or 209—to increase the working time.
How warm is warm? You should be able to comfortably touch the substrate or the component containers when they are appropriately warmed—about 115°F maximum. Excessive heat will cause the epoxy to harden too fast, especially in thick applications. Very rapid cure will overheat the epoxy. If smoke rises from the curing epoxy, it is likely the epoxy is damaged and should be replaced.
Thinning epoxy with solvent
Adding solvent is a quick, simple method of thinning epoxy, but unlike using heat to thin it, the strength and moisture resistance of the cured epoxy are drastically affected. Below are some of the effects adding solvent has on WEST SYSTEM epoxy. While there are a large number of chemicals available to thin epoxy, we selected acetone, lacquer thinner and denatured alcohol for this discussion because they are commonly available and do a good job of reducing viscosity. Additionally, these solvents evaporate quickly and are less likely to be trapped in the cured epoxy—an important characteristic. For a variety of reasons, fast evaporating lacquer thinner appears to be more appropriate for thinning purposes than acetone or alcohol.
  • Adding a small amount of one of these solvents has a significant effect on the viscosity of the epoxy. For example, adding 5% lacquer thinner makes about a 60% reduction in viscosity (Figure 4).

  • Adding 5% lacquer thinner to epoxy reduces the epoxy’s compressive strength by 35%—a big hit in the mechanical properties of WEST SYSTEM epoxy (Figure 5). The addition of more than 5% solvent results in an excessively flexible cured material. Thinning epoxy with solvent causes enough loss of strength that we (and most other reputable epoxy formulators) cannot recommend using it as a structural adhesive.
  • Adding a volatile solvent extends the pot life and cure time of epoxy and jeopardizes the reliability and predictability of cure. Additionally, with slow rate of cure, it takes longer before work can be sanded.
  • Adding volatile solvent may cause shrinkage of the cured epoxy. Applying thinned epoxy in large, confined areas (like consolidating a large pocket of rotted wood) is likely to trap some of the solvent. In thick applications, the epoxy cures very quickly and not all of the solvent has time to evaporate before the epoxy hardens. Over time, the solvent works its way out and as this happens, the cured epoxy shrinks and in many instances cracks. Shrinkage also causes print through. You may have a surface sanded smooth only to have the resin shrink. This shrinkage often reveals the texture of the substrate. Shrinkage can continue to be a problem until all the trapped solvent works its way out of the cured epoxy.
  • Adding solvents, especially acetone, alters the color of the cured epoxy. While the effects are not immediate, adding acetone to epoxy causes the color to change from slightly amber to very dark amber.
  • Adding solvent results in a temporary reduction in viscosity. Volatile solvents evaporate quickly as they are agitated during brushing or rolling, causing the viscosity to continually change as time passes.
  • Adding solvent to epoxy may damage the substrate. Many materials (Styrofoam™ for example) are not attacked by epoxy but may be attacked by the solvent used to thin the epoxy. Be certain to test the substrate with the solvent before using it to thin the epoxy.
  • Adding volatile solvent to WEST SYSTEM epoxy has some adverse health and safety effects. WEST SYSTEM epoxy components are nonflammable but the chance of fire or explosion goes up in proportion to the amount of solvent you add. Also, the vapors of many volatile solvents are hazardous to your health and proper ventilation is mandatory to prevent inhaling harmful quantities of them.
  • Adding volatile solvent to epoxy which is then applied as a coating may cause problems with various regulatory agencies. If your business is inspected for air quality, adding volatile solvents to WEST SYSTEM epoxy may make your business non-compliant.
  • Adding solvent to epoxy to enhance fiberglass wet-out will result in more "drain out" of the resin on a vertical surface. The fabric will wet-out quickly but it may become resin starved when too much epoxy runs out of the fabric.
Does thinning epoxy make sense? In some situations, thinning is appropriate. In others, it is not. We feel that in most circumstances using heat to thin epoxy is preferred to using solvents. As long as the epoxy does not overheat during cure, the full physical characteristics of the cured epoxy remain. Adding solvent is a quick, simple method of thinning epoxy, but the strength and moisture resistance of the cured epoxy are significantly reduced.
We will continue to research this subject and publish our findings in Epoxyworks.
Epoxyworks 14 / Fall 1999
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Old 13-09-2015, 10:56   #18
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Re: Lightweight but strong backing material

Sounds like a few of you reviewed the data posted above!!!

I can tell you what I have found. By addng a smidge of Xylol to low Viscosity epoxy and coating dry Meranti with very thin rolled coat with short nap stiff rollers the epoxy goes deep. Let it dry for a couple days. Then recoat with regular epoxy and what you get is a great strong deep coating.

That article is from 99.

How do I know this. I tested it over and over and over again.

But yes it is safer to just "follow the rules."

Sorry for ruffling feathers.

So in short DO NOT THIN EPOXY Ever.
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Old 13-09-2015, 11:40   #19
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Re: Lightweight but strong backing material


Thinning epoxy means lowering its viscosity (Figure1).

Sorry for the hijacking. Refer to graph above.

Note by extrapolation after careful review of above graph. Cheap and dirty is one coat penetrating epoxy (xylol thinned Low Viscosity epoxy) followed by one regular coat will get you into really low moisture absorption quickly, easily and CHEAPLY.

My former post of 15% was missing a decimal 1.5% Xylol.

Also please note you need to let the thinned epoxy dry for a LONG TIME. The longer the better. Many of the failures of the coating are because subsequent regular coats are applied too early. Note above graph stipulates good results with 2 coats of penetrating followed by regular with long dry times. I have found this unnecessary. One coat of penetrating followed by one coat regular will do the trick especially for the inside. The ply will be glued with epoxy thickened so the waterside would get 2 coats regular in essence.
Have a great day.
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Old 13-09-2015, 11:43   #20
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Re: Lightweight but strong backing material

Never...thin...epoxy.

Use marine plywood to replace the rotted core.
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Old 13-09-2015, 12:24   #21
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Re: Lightweight but strong backing material

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Never...thin...epoxy.

Use marine plywood to replace the rotted core.
It's not a core I am replacing, just backing paneling between the fiberglass and the teak - something to mount the interior decorative teak on. So, I think exterior grade plywood with "epoxy waterproofing" is good enough.

I would not use plywood as a core anyhow.
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Old 13-09-2015, 12:51   #22
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Re: Lightweight but strong backing material

It is, in fact, a core...the inner substrate between a single f'glass skin and your hull ceiling material, teak veneer(?). One of the reasons marine grade is required is that you are relying on this thin core for sealing and to hold screws, which cannot hold well in voids, which are located throughout the cheap plywood you would so love to use. Additionally, you are mistaken that this cheap plywood is just as good because it also uses exterior glue. You must understand that the quality of the veneers is far lower in the cheap ply, beyond the void issue. And some of the veneers are not even well bonded, in places.

Don't be foolish in trying to save pennies while risking dollars. You're not talking about that much material.
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Old 13-09-2015, 12:59   #23
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Re: Lightweight but strong backing material

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Don't be foolish in trying to save pennies while risking dollars. You're not talking about that much material.
True.

Its not veener... its 100% real teak 1/4" thick.
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Old 13-09-2015, 13:50   #24
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Re: Lightweight but strong backing material

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Never...thin...epoxy.

Use marine plywood to replace the rotted core.
FYI I'm laughing just laughing.....

You could just buy epoxy from the manufacturer that they already thinned for you.

The difference between marine ply and the other stuff. Glue. wood quality, voids, type of wood, etc.

Same with everything else you get what you pay for (mostly)



NEVER THIN EPOXY
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Old 13-09-2015, 19:08   #25
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Re: Lightweight but strong backing material

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Then I was thinking G10 but big sheets of thick 1/4" G10 is really expensive and heavy. I had also thought about glass but I am worried about adding extra weight to the boat up high.
If you don't want to pay the price for G10, that's one thing.

But worrying about the extra weight is a bit silly on "Boat: Cabo Rico 38" - your boat will never ever notice the couple extra lbs.

G10 will bond perfectly, hold threads (machine screws) perfectly, and never ever rot or swell.
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Old 13-09-2015, 19:44   #26
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Re: Lightweight but strong backing material

That article from West pretty much disproves your point Lojanica. Yes you can thin epoxy but it changes the characteristics and there is no need to do that.
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Old 13-09-2015, 21:08   #27
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Re: Lightweight but strong backing material

G10 is challenging stuff to work. Tough on cutting tools. You'll go crazy trying to cut and sand it to fit.

Realize that there are a lot of different marine plywoods. Okume is very light and absorbs epoxy (or any sealer) really well.

Sapele marine ply (Mahogany) is denser but very rot resistant.

http://www.boulterplywood.com/MarinePlywood_4.htm

Or since you have small areas, use solid hardwood. It's much more rot resistant than ply. Mahogany, white oak, or fir would all be good. Lay the boards in with epoxy in the gaps between boards.

The simplest rot control is paint. Or get a penetrating stain/sealer. If you must go the epoxy route, pick one that is designed for the purpose. CPES is a great product on wood.

CPES™-Wood based epoxy products to repair and resist wood rot.
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Old 13-09-2015, 22:05   #28
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Re: Lightweight but strong backing material

I agree that the marine plywood is being used as a core material between the teak inner layer and the outer fiberglass. Plywood vastly increases the stiffness (but not necessarily the strength) of the structure compared to an equivalent weight of fiberglass. It is also used to improve shear strength.

Marine plywood is not the same thing as exterior plywood. The glue, wood and lack of voids are key differences.

The following article discusses the OP's question in detail, but relates to transoms.

Fiberglassic Guide to: Transoms, Floors, and Stringers - fiberglassics.com
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Old 13-09-2015, 22:10   #29
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Re: Lightweight but strong backing material

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Originally Posted by CarlF View Post
G10 is challenging stuff to work. Tough on cutting tools. You'll go crazy trying to cut and sand it to fit.

Realize that there are a lot of different marine plywoods. Okume is very light and absorbs epoxy (or any sealer) really well.

Sapele marine ply (Mahogany) is denser but very rot resistant.

http://www.boulterplywood.com/MarinePlywood_4.htm

Or since you have small areas, use solid hardwood. It's much more rot resistant than ply. Mahogany, white oak, or fir would all be good. Lay the boards in with epoxy in the gaps between boards.

The simplest rot control is paint. Or get a penetrating stain/sealer. If you must go the epoxy route, pick one that is designed for the purpose. CPES is a great product on wood.

CPES™-Wood based epoxy products to repair and resist wood rot.
The statement that solid wood is more rot resistant than marine plywood appears to be incorrect: from the above article...

Solid Wood Cores
It didn't take long for boat builders to realize this was the worst possible core material. In fact, I find it shocking that it wasn't automatically dismissed by every boat builder on earth from day one. Solid wood is great for building wooden boats. Solid wood as a core material in a fiberglass construction is a disaster waiting to happen.
The only reason it's included in this list of possible core materials is to explain why it shouldn't be on this list.
Solid wood expands and contracts at a much greater rate than fiberglass. Solid wood has very low shear strength. Solid wood is more rot-prone than any other material. Solid wood had very low compressive strength. Solid wood is not a suitable core material under any circumstances!
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Old 13-09-2015, 22:18   #30
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Re: Lightweight but strong backing material

While it seems logical to try to remove organic material from a laminate, it would be safest to rebuild the coach roof at least as strong as the original designer intended. There are few options to replace the organics in this situation, honeycomb material used by some builders is one. For horizontal decks it is possible to remove the outer skin, laminate additional fiberglass to both the inner and outer skins then pour thickened epoxy into the remaining void- not practical for the side wall of a coachroof. If a rogue wave strikes the coach roof or there is a rollover, the stiffness and shear strength of the material supporting the portlights to keep them from losing their seal could become very important, or at least contribute to an early seal leak from routine flexing of the hull.

Another interesting point is that water intrusion to the core can spread great distances, especially if grooves were cut into marine plywood to help "bend" it, for example in the roof of the coachroof which is typically crowned slightly.
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