Water absorption by epoxy-coated plywood
Dave Carnell
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
not greatly affect the rate of water absorption.
KernHend
<snip>
>If you seal the edge grain of high-quality plywood with epoxy perhaps epoxy
coating the faces of that plywood will not greatly affect the rate of water
absorption.<
_____________________________
Help me out here, Dave. One reading of the above sentence implies that you did
not seal the end grain in you test. Am I missing something?
Kern
oink
says...
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.
Interesting, and it confirms my eperience that the wood is only there to hold
the gluelines apart, so the more gluelines (veneers) the better!
As well, I had an old boat which had been under worm attack, but they could get
no further than the first glueline. I ended up with a slimmer boat.
Dave Carnell
My samples were completely coated. My suggestion is that you may be able to get
most of the benefit of encapsulation by just sealing the edge grain of plywood and
relying on the moisture barrier properties of the glueliones of the plywood to slow
water absorption almost as much as encapsulation might.
Dave Carnell
Dave Kruger
> Interesting, and it confirms my eperience that the wood is only there to hold
> the gluelines apart, so the more gluelines (veneers) the better!
>
> As well, I had an old boat which had been under worm attack, but they could get
> no further than the first glueline. I ended up with a slimmer boat.
FWIW, if the plywood is held together with the usual resorcinol matrix, the
phenolic components in that glue line are most likely what the worms do not
like. It's worth noting that the bark of conifers is very rich in
phenolics, and that the bark is rejected by many worms in preference to the
underlying wood. Toredos and gooseneck barnacles go through bark, I
believe.
What variety of worm "slimmed" (not "slimed") your boat?
--
Dave Kruger
Astoria, OR
sea kayaker
chemist
KernHend
>My suggestion is that you may be able to get most of the benefit of
encapsulation by just sealing the edge grain of plywood and relying on the
moisture barrier properties of the glueliones of the plywood to slow water
absorption almost as much as encapsulation might.<
When the plywood starts to check and distort due to uneven water absorption,
what are your recommendations to the boatbuilder who follows the above
suggestion?
Kern
Paul VandenBosch
>When the plywood starts to check and distort due to uneven water absorption,
>what are your recommendations to the boatbuilder who follows the above
>suggestion?
>
>Kern
>
checking in plywood. The best way to stop checking is to sheath ply
with a layer of fiberglass cloth in epoxy.
Paul VandenBosch
The Guide to Sailing and Cruising Stories
http://cruisenews.net
Delete the anti-spam dodger to reply to admin at cruisenews.net
Oink
Dave Kruger wrote:
I'm not certain which brand of worm Dave.
Interestingly, when stripped, some sheets were what was called in the early 60's,
Phillipine Mahogany (probably now Luan?). They were wormed as far as the first glue
line. Other sheets were good old North American Douglas Fir, and these were all
untouched and as good as the day they were conceived. Do you have a theory about
this?
Dave Kruger
> > > As well, I had an old boat which had been under worm attack, but they could get
> > > no further than the first glueline. I ended up with a slimmer boat.
> > What variety of worm "slimmed" (not "slimed") your boat?
> > Dave Kruger
> I'm not certain which brand of worm Dave.
>
> Interestingly, when stripped, some sheets were what was called in the early 60's,
> Phillipine Mahogany (probably now Luan?). They were wormed as far as the first glue
> line. Other sheets were good old North American Douglas Fir, and these were all
> untouched and as good as the day they were conceived. Do you have a theory about
> this?
No, unless the doug fir was treated with something. I'd expect the
reverse, OTBE.
--
Dave Kruger
Astoria, OR
chemist
KernHend
>Epoxy encapsulation alone is not sufficient protection against
>checking in plywood. The best way to stop checking is to sheath ply
>with a layer of fiberglass cloth in epoxy.
________________________
This is exactly what we say in The Epoxy Book. The operative statement is
"fiberglass reinforced epoxy". Try that with ethylene glycol.
Kern
Dave Carnell
finish treatment.
Dave Carnell
karena...@erols.com
encapsulated wood? Does paint make the epoxy less water permeable?
Thanks,
Glen
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karena...@erols.com
actually absorbed much of the water as opposed to being a permeable barrier
that only allowed the water to passed through it but didn't absorbe any
itself?
karena...@erols.com
in limiting water absorbtion by encapsulated wood or are some significantly
more water permeable?
Habbi
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Dave Carnell
encapsulating the next boat.
Dave Carnell
karena...@erols.com wrote:
> What can be done to reduce the amount of absorbtion of moisture by
> encapsulated wood? Does paint make the epoxy less water permeable?
Dave Carnell
to be going into the wood and the plywood. Epoxy pucks boiled for four hours
pick up almost no water and there is some similar data in various epoxy product
literature from Shell, Dow, etc. The water is passing through the epoxy.
Dave Carnell
karena...@erols.com wrote:
> Dave, when you did your test were you able to determine if the epoxy itself
> actually absorbed much of the water as opposed to being a permeable barrier
> that only allowed the water to passed through it but didn't absorbe any
> itself?
>
karena...@erols.com
tap water all pass through equally well?
KernHend
>Does it make any difference what kind of water? Do fresh, salt and
>clorinated tap water all pass through equally well?
_______________
Assuming, of course, that Dave's data is correct and applies to all boats in
all situations. This would make Gougeon Brothers, System Three and other epoxy
suppliers along with tens of thousands of boatbuilders wrong for these past
twenty-five years. But, hey, David slew Goliath once before.
W. Kern Hendricks
System Three Resins, Inc.
P.O. Box 70436
Seattle, WA 98107
Technical Support: 206/782-7976
Orders Only: 800/333-5514
e-mail: sup...@systemthree.com
website: http://www.systemthree.com
karena...@erols.com
> Assuming, of course, that Dave's data is correct and applies to all boats in
> all situations.
Kern, can you cast any light on this issue. Dave seems to have done a
reasonable test. But, it doesn't seem to square with a lot of experience to
the contrary. For one thing, I thought that some kind of epoxy paint is what
is used to keep polyester resin boats from absorbing water and blistering.
I've talked to several long term epoxy builder/repairers and they haven't
seen epoxy blister from water absorbtion. Nor have they seen well built
encapsulated boats with damage due to epoxy failing to keep the wood dry. Nor
have they seen swelling that would be breaking glue joints, etc. One guy
said he has drilled holes while installing equipment in many encapsulated
hulls that stay in the water without finding soggy wood. Could it be that
hulls are normally sheathed with cloth and Dave's samples weren't? Could
cloth explain the difference?
Dave, the amount of moisture you measured....was it enough to swell the wood.
Also, I think you said that the highest percentage was 12.5%. How wet is
that? Would that be wet enough to swell lumber? If I touched a piece of bare
(without epoxy) wood that was that wet, would it feel wet.
George Roberts
Epoxies containing non-reactive thinners will be more porous.
karena...@erols.com wrote:
>
> Are all major brand epoxies created nearly equal in regard to being effective
> in limiting water absorbtion by encapsulated wood or are some significantly
> more water permeable?
>
> Thanks,
> Glen
>
Leo Voorneveld -Netherlands
wood.
>Also, I think you said that the highest percentage was 12.5%. How wet is
>that? Would that be wet enough to swell lumber? If I touched a piece of
bare
>(without epoxy) wood that was that wet, would it feel wet.
I do not know of the woodsample as no moisture in it, but he calculated a
12,5 weight difference.
Normal wood used in boatbuilding has a moisture content of 12 percent.
Still we talk then of dry wood.Wood with more moisture is (here) called
green wood.
If wood was totally dry it would be less strong, remind you our body is
made of water.
I am not a rot doctor and do not know at which moisture level fungi needs
to start eating.
Regards Leo Voorneveld
Mark Anderson
> Assuming, of course, that Dave's data is correct and applies to all boats
> in all situations. This would make Gougeon Brothers, System Three and
> other epoxy suppliers along with tens of thousands of boatbuilders wrong
> for these past twenty-five years.
Dave's samples were totally immersed 100% of the time weren't
they? Perhaps having one side exposed to the air, as is the usual boat
case except for the keel, allows enough transmission and release of
vapor for the wood to remain dry in actual boat use.
Plus, a starting moisture of 12%, and then an additional 12%
after absorbtion is still a long way from saturated. It's probably
below fungal rot moisture also.
Kern,
What do you think of the combination of Dow resin with System
Three hardener? I don't know why Dave did this, but would this
significantly affect results?
--
Mark Anderson, DBA Riparia, www.teleport.com/~andermar/
"The trouble with good ideas,
is that they soon degenerate into a lot of hard work." Anon.
Mark Anderson
> Oink wrote: > Other sheets were good old North American Douglas Fir, and
> these were all > untouched and as good as the day they were conceived. Do
> you have a theory about > this?
>
> No, unless the doug fir was treated with something. I'd expect the
> reverse, OTBE.
My old homebuilt Duet had fir plywood bottom, "mahoghany" ply topsides,
deck and cabin. ALL problems after 30 yrs. were in the mahoghany
(probably lauan) plywood. None of the fir plywood deteriorated. The
entire hull was treated with Cuprinol when it was built in 1960.
My 1960 Thompson runabout has a lapstrake fir ply hull and Honduras
mahoghany shear plank and deck. During it's recent restoration I had to
replace all the mahoghany plywood. None of the fir plywood deteriorated
except a few inches of some upper planks near the transom. The fir was
originally varnished on the interior, (probably never again), and
painted exterior. The deck was varnished on top and left bare
underneath.
Both boats spent virtually their entire use life in fresh water.
Dr...@rotdoctor.com
<Regards Leo Voorneveld>
From about 15% to 30%, more or less, and assuming the right temperature and
oxygen availability.
The Rot Doctor
http://www.rotdoctor.com
E-mail: dr...@rotdoctor.com
Phone: 206 783 0307
Fax: 206 783
Don Rumrill
was
torn in half and smashed flat from an inside out tree wrap. In the process, I had
to replace the gunwales, orignally aluminum, which I did by laminating up 1/4"
strips
of spruce (ripped a 20' 2X10). I rebuilt it using 6 oz glass and the Sys3 epoxy, I
also
used the epoxy to seal the new gunwales. The canoe sits outside or on my truck, or
preferably in the water all the time. After 6 years I have some rot in the
gunwales,
but only in the spots where I was careless and did not completely cover the wood.
I do keep a cover on it that keeps out the UV but not water. BTW, with my wife
and daughter paddling, this boat has taken a 2nd in the state points championship
and trophied in a number of races. This boat is at least 30yrs old, Gene Jensen
did
a heck of a design job here.
Don
KernHend wrote:
snip>
KernHend
>Dave's samples were totally immersed 100% of the time weren't
>they?
____________
Who knows? When I asked him to publish his methodology he stated that it would
be too long for this N.G.
>What do you think of the combination of Dow resin with System
>Three hardener? I don't know why Dave did this, but would this
>significantly affect results?
____________________
Probably would not make much difference in the results. But again, who knows
what the methodology was.
Kern
Dave Carnell
included how moisture content was determined, how the samples were treated to known
contents of water and antifreeze, how the joints were made and cured, and how the
strength tests were made.
Dave Carnell
karena...@erols.com
test results on April Fools Day. I wonder if that is only coincidental?
Glen
KernHend
>I published the whole methodology in my most recent post on the subject.
>This included how moisture content was determined, how the samples were
>treated to known contents of water and antifreeze, how the joints were made
>and cured, and how the strength tests were made.
__________________________________________
Perhaps I missed it. Please e-mail me a copy at the address below.
Kern