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Dave Carnell
08-13-2000, 06:57 AM
My long time experiments on water absorption by epoxy-coated wood demonstrate that epoxy does not prevent water absorption, but just slows it.

An interesting observation is that epoxy-coated plywood absorbs water much less rapidly than epoxy-coated solid wood. Apparently, the glue lines of the plywood are better barriers than the epoxy. Plywood glues are heat-cured phenol-formaldehyde resins. The closest materials that will cure at room temperature are the resorcinol-formaldehyde glues. I-d like to experiment with them, but haven't used any since the Cascophen® I built pram dinghies with 40 years ago.

I would appreciate hearing from any of you what resorcinol-formaldehyde glue/resins are available, especially if you have had any experience with them.

Thanks.

Syd MacDonald
08-13-2000, 09:53 PM
Check out Aerodux 500 from CPindustries.
They advertize in Woodenboat. It's imported from the UK. It seems expensive at first glance but when you buy a gallon you get a gallon of resin and a gallon of hardener.

redjim777
08-14-2000, 10:07 AM
Aerodux 500 is a great glue but it's not made for encapsulating.

swingking
08-17-2000, 08:09 AM
test

swingking
08-17-2000, 08:22 AM
I work in a plywood like industry that uses
a lot of phenol-formaldehyde resins. Our
resin will get very hard at 80 - 90 degree
room temps but is slow to cure. I live in
the south and was thinking about plastic
tenting my boat to get high temps. I have
not checked about reduction in properties
at low cure temps, but would like to find
out. Thanks for your info, I was thinking
along the same lines.

johnh94927
10-07-2001, 11:36 PM
info at:
http://www.custompak.com/Adhesives/aerodux500a.htm

JimJ
10-08-2001, 02:19 AM
Dave

You may be able to obtain this Selleys product over there.

http://www.selleys.com/products/adhesives/p_resorcinol.htm

[This message has been edited by JimJ (edited 10-08-2001).]

Paul Brooks
10-08-2001, 04:23 AM
Hi Dave
You said:

"My long time experiments on water absorption by epoxy-coated wood demonstrate that epoxy does not prevent water absorption, but just slows it."

Would you be a bit more specific about this as my understanding is that epoxy is pretty good as a water resistant coating - particularly if it is backed up with paint.

Best regards
Paul

motoretro
10-09-2001, 01:09 AM
Japan Woodworker Co. carries a product by Systems 3 called Grizzly glue which they openly advertise as a replacement for Epoxy.
Have not tried it but it looks interesting. they also carry the Smith line of penitrating epoxies. Web site is:
http://www.japanwoodworker.com/
The glue is not on website although is in catalog which is free.

Ruaridh
10-09-2001, 02:33 AM
If you read the Gougeon Brothers book on epoxy / wood boat construction, they state throughout that epoxy doesn't totally stop wood from absorbing water, but they believe that it slows it to an acceptable level to allow the wood to remain stable.
It's interesting to read the sections on water content before one starts to apply epoxy, and also how specific they are about the amount of coatings, etc. that should be used for the epoxy to remain an effective moisture barrier.
I know this isn't exactly what you were asking, but thought you might be interested.
Ruaridh.

Dave Carnell
10-09-2001, 06:46 AM
What made that one resurface after all this time, I wonder. Anyway, here are my (and others) data on water absorption through epoxy:

The data below are mine accumulated
beginning in 1992 and continuing for almost 4 years. An interim report was published in
Boatbuilder magazine, May/June 1993, titled “Does Epoxy Keep Water out of Wood?”

Back around 1960 DuPont’s Plastics Dept. tried valiantly to make paper-reinforced
plastic pipe. Dry kraft paper is quite strong, but wet it is like a wet paper
bag. The research group I managed spent several million dollars trying to encapsulate kraft paper to make pipe that would retain its strength when buried and wet. We failed
completely.
Water penetrated every polymer we tried. This made me very skeptical of claims for
epoxy. The results of Forest Product Laboratory research going back to 1913
supported my conclusion that no resin would keep water out of wood, as does all of their
most recent research on excluding moisture from wood. None of their work is done on
immersed samples-only high humidity environments. They do not calculate water
absorption as weight %, but use a MEE unit that is the ratio of the amount of water
absorbed by a coated sample compared to an uncoated sample. For pine coated with
three coats of epoxy in their 1985 research paper FPL 462 they show an MEE of 70 ater 60
days at 90% RH. Put another way, the epoxy-coated sample had absorbed 30% as much
water as if it had had no coating; that is not keeping water out.

Though epoxy does not keep water out, it may prevent rot by excluding oxygen. I know
of no published data on oxygen permeability of epoxy resin. It is a difficult,
expensive test for which there has been no commercial justification. Epoxy must keep out rot spores also. Though it doesn’t keep out water epoxy resin for glue and laminating must be the invention of the century for wooden boatbuilding. My explanation for the reason epoxy coating stops blistering of FRP boats is that water absorbs through the epoxy
more slowly than it is carried away by passing through the polyester resin, so it does not build up and form blisters.

Water Absorption Through Epoxy

Here are Forest Product Laboratory data and my data on absorption of water through epoxy coatings on pine boards. My immersion data are the only ones I know of. Anyone having other data please add to the collection.

Data on epoxy-coated plywood will follow:


WATER ABSORPTION THROUGH EPOXY RESIN

Absorption of water through epoxy coatings on pine boards:

Forest Products Laboratory (Research Paper FPL 462)
Samples: ponderosa pine; 3” x 5” x 5/8”
Exposure: 90% R.H. at 80°F.
Epoxy coating: three coats for a total of 0.00874 gal./sq.ft.
(“Two-component sheathing epoxy (adhesive”))

Days exposed: 1
7 14 21 28 35 60
Water absorbed 2
5 9 12 16 19 30
(% of absorption by uncoated sample):

Carnell:
Samples: western pine; 3” x 10” x ¾”
Exposure: 100%R.H. at room temp. (50-90°F.)
Epoxy coating: three coats for a total of 0.01682 gal./sq.ft. (1.92
times FPL) (Dow 330 resin, System
Three No. 2 hardener)

Days exposed: 60 100 200 300 400 500
600 720
Water absorbed 1 2 4.6 7.2 9.8
12.6 15.7 18.2
(% of orig. wood wt.)
Samples removed to ambient conditions and allowed to dry:
Days dried: 20 40 80 120 160 200
240 280 320 360
Water content 12.3 9.2 5.8 4.5 3.7 3.0
2.6 2.2 0.4 0.9
(% of orig. wood wt.)

Samples: western pine; 3” x 10” x ¾”
Exposure: submerged in water at room temp. (50-90°F.)
Epoxy coating: three coats for a total of 0.0l682 gal./sq.ft. (1.92
times FPL) (Dow 330 resin, System Three
No. 2 hardener)

Days exposed: 60 100 200 300 400 500
600 720
Water absorbed 7.3 11.5 19.4 24.6 29.7 34.7
39.4 44.7
(% of orig. wood wt.)
Samples removed to ambient conditions and allowed to dry:
Days dried: 20 40 80 120 160 200
240 280 320 360
Water content 26.5 21.8 18.7 14.8 10.9 7.8
5.0 2.5 0.4 0.9
(% of orig. wood wt.)

Note: Thicker coatings of Carnell samples probably result from higher
viscosity of Dow 330 undiluted resin
compared to diluted resins used by most formulators.


Here are my data on water absorption by epoxy-coated plywood.
Epoxy-coated plywood absorbs much less water than epoxy-coated wood;
apparently the glue lines of the plywood are significant barriers
slowing water absorption.

Absorption of water through epoxy coatings on plywood:

Carnell:

Samples: ¼” lauan underlayment plywood (two thin face plies, one thick
core ply); 3” x 10” x 0.20”
Exposure: 100%R.H. at room temperature (50-90°F.)
Epoxy coating: three coats for a total of 0.01682 gal./sq.ft. (Dow 330
resin, System Three No. 2 Hardener).

Days exposed: 60 100 200 300 400 500 600
720
Water absorbed 1.8 2.7 4.5 5.8 6.9
7.8 8.4 9.0
(% of orig. plywood weight)
Samples removed to ambient conditions and allowed to dry:
Days dried: 20 40 80 120 160 200
240 280 320 360
Water content
(% of orig. plywood wt.) 7.8 7.3 6.5 5.8 5.2
4.7 4.2 3.8 3.5 3.0

Samples: ¼” lauan underlayment plywood (two thin face plies; one thick
core ply); 3” x 10” x 0.20”
Exposure: Immersed in water at room temperature (50-90°F.)
Epoxy coating: three coats for a total of 0.01682 gal./sq.ft. (Dow 330
resin, System Three No. 2 hardener).

Days exposed: 60 100 200 300 400 500
600 720
Water absorbed 2.3 3.5 6.2 8.2 9.7
10.9 11.9 12.5
(% of orig. plywood wt.)
Samples removed to ambient conditions and allowed to dry:
Days dried: 20 40 80 120 160 200
240 280 320 360
Water content 11.3 10.3 8.7 7.5 6.5 5.7
5.0 4.4 3.9 3.5
(% of orig. plywood wt.)

Samples: ¼”fir plywood (three equal thickness plies); 3” x 10” x 0.25”

Exposure: 100%R.H. at room temperature (50-90°F.)
Epoxy coating: three coats for a total of 0.01682 gal./sq.ft. (Dow 330
resin, System Three No. 2 hardener).

Days exposed: 60 100 200 300 440
Water absorbed 4.5 6.5 10.3 12.7 14.5
(% of orig. plywood wt.)
Samples removed to ambient conditionsand allowed to dry:
Days dried: 20 40 80 120 160 200
240 280 320 360
Water Content 10.4 7.8 5.8 5.4 4.7 4.0
3.6 3.2 2.7 2.0
(% of orig. plywood wt.)

Samples: ¼” fir plywood (three equal tickness plies); 3” x 10” x 0.25”

Exposure: Immersed in water at room temperature (50-90°F.)
Epoxy coating: three coats for a total of 0.01682 gal./sq.ft. (Dow 330
resin, System Three No. 2 hardener).
Days exposed: 60 100 200 300 440
Water absorbed 5.8 8.3 12.7 15.8 17.6
(% of orig. plywood wt.)
Samples removed to ambient conditions and allowed to dry:
Days dried: 20 40 80 120 160 200
240 280 320 360
Water Content 15.0 12.5 8.2 6.9 6.2 5.5
5.0 4.4 3.8 3.5
(% of orig. plywood wt.)

Interpretation:

Please do not conclude that epoxy-encapsulated underlayment lauan is a
practical boatbuilding material.
My explanation of the fact that the epoxy-coated fir plywood absorbed
more water than the epoxy-coated lauan
plywood is that the glue lines of both plywoods are significant moisture
barriers. Therefore, once the water
penetrated the epoxy coating of the fir plywood there was only a barrier
to water absorption of one-third of the
plywood; two thirds was exposed to the water coming through the epoxy.
In the case of the lauan plywood, when the
water came through the epoxy there were still the glueline barriers to
at least 80% of the plywood-the thick core ply.
If you seal the edge grain of high-quality plywood with epoxy perhaps
epoxy coating the faces of that plywood will help reduce
the rate of water absorption.

Paint, except for epoxy and polyurethane, is of no value in preventing water absorption.

Thaddeus J. Van Gilder
10-09-2001, 06:47 AM
Great!!!!!!!!!
I am not the only one who has read the epoxy fine print!!!!!!!!

Paul Brooks
10-09-2001, 08:45 AM
I've only just seen that this thread is a year old. Still, thanks for that data - very interesting. I'd always assumed epoxy to be pretty inpenetrable.

I guess I just have to hope that the rate of absorption of the outside of the hull under water is matched by the rate of evaporation on the inside.
Best regards Paul

Bruce Hooke
10-09-2001, 10:45 AM
Thank you doing this research and posting the results. I think it is worth noting that your tests show that epoxy IS effective at greatly reducing the amount of water absorbed, which is the only claim I have seen made by reputable sources. Once you factor in the counter-effects of having the inside of the boat exposed to air, it seems likely that epoxy would keep the wood below the moisture level at which most rots flourish, which is ultimately the main goal.

johnh94927
10-09-2001, 10:54 AM
>>> "What made that one resurface after all this time, I wonder. Anyway, here are my (and others) data on water absorption through epoxy: " <<<
Searched under username=Carnell. %\

Dave Carnell
10-10-2001, 06:48 AM
Some of my data and all FPL data are on high humidity exposure, but most of my data are on submerged samples-liquid water. It goes through faster.

thechemist
10-10-2001, 12:42 PM
The bottom line of all such experimental configurations is that they are worthless if they cannot be applied to the real world.

In a boat, there is an inside surface and an outside surface.

Outside, there is liquid water.

Inside there is an epoxy coating, RELATIVELY impermeable to water molecule diffusion.

Inside of that there is wood, much more permeable to water molecule diffusion than the external epoxy, or WHATEVER moisture-diffusion-barrier.

Inside of that, there may be paint or other stuff, but it should be MUCH MORE PERMEABLE than the outer epoxy coating.


Inside of all that is the air inside the boat hull, and we assume it is moving sufficiently to carry away whatever water molecules diffuse through all the other stuff AT A FASTER RATE THAN THEY COME IN THROUGH THE OUTER BARRIER.

Under those conditions, the humidity of the wood will move to near-equilibrium with the water-vapor concentration in the air inside the boat hull.

That is the right way to use an epoxy coating in or about a wooden boat.

Now, let's do it wrong.


Put antifouling paint on the outside, and a relatively thin coating of it.

Inside of that is all the wood, and inside of THAT is an excellent coating of epoxy, quite thick, mineral-filled, great resistance to moisture-diffusion. Inside of that is the moving air inside the bilge.


What happens here, and I think you can see it, is that the humidity of the wood tends to an equilibrium with the humidity of liquid water. The net result is that all the below-the-waterline wood will be completely waterlogged.

If you can understand the above two examples, then I think you can see that the resulting humidity of the wood, and its tendancy to rot, depends on what sort of balance you have between the rate at which water can get into the wood, and the rate at which water can get out of the wood.

The only condition that leads to a dry wood hull is where the outer barrier is much more effective than anything else inboard of that. Any middly-diddly ratio leads to an indeterminate, usually excessive, level of moisture in the wood.

It follows from the foregoing that "encapsulating" wood by coating both inner and outer surfaces with a comparable level of epoxy will lead to some significant [excessive] level of humidity in the wood, and that opens the door to rot.

It has nothing to do with epoxy, as such. Claiming epoxy is bad because it can be misused is a false argument. Any barrier-coating on the outside would be equally effective in destroying or preserving the boat. It all depends on how that barrier-coating is used.



[This message has been edited by thechemist (edited 10-10-2001).]

Earl Hall
10-24-2001, 10:17 PM
to thechemist or Dave C:
I was planning on painting the inner surfaces of a plywood Hartley Trailer sailer 16 dinghy that will be dry sailed with epoxy paint. The outer surface is coated with epoxy and fibreglass plus enamel. Would you expect moisture in plywood problems when the boat is only in the water for hours or perhaps a day at a time? Is the difference between a solid epoxy coating plus paint on the outside to the single layer of epoxy paint on the inside sufficient on the plywood (3 ply)which also has internal layers of waterproof glue? The majority of the time it would be tarped and sitting outside on a trailer in the Pacific Northwest area. Earl

[This message has been edited by Earl Hall (edited 10-25-2001).]