Marine plywood vs luan plywood

[f leblanc]

At almost any local lumberyard you will find a plywood sold under the generic name "luan" for a stuningly moderate price (15.00$ canadian for a 1/4" sheet here in eastern Québec). It has only three ply, the outside faces being thin rotary cut philippine mahogany veneer glued on a thicker and lighter core, so its mechanical properties are at best mediocre. However one of its face is wihtout flaw, it is much lighter than a marine plywood of the same thickness and it will bend into fair curves. For building say, a hard chine kayak hull, I would suggest that such a plywood is perfectly appropriate if the hull is to be laminated with epoxy and fiberglass, that is most of the time. But I would like to be convinced otherwise.

[f leblanc]

At almost any local lumberyard you will find a plywood sold under the generic name "luan" for a stuningly moderate price (15.00$ canadian for a 1/4" sheet here in eastern Québec). It has only three ply, the outside faces being thin rotary cut philippine mahogany veneer glued on a thicker and lighter core, so its mechanical properties are at best mediocre. However one of its face is wihtout flaw, it is much lighter than a marine plywood of the same thickness and it will bend into fair curves. For building say, a hard chine kayak hull, I would suggest that such a plywood is perfectly appropriate if the hull is to be laminated with epoxy and fiberglass, that is most of the time. But I would like to be convinced otherwise.

[f leblanc]

At almost any local lumberyard you will find a plywood sold under the generic name "luan" for a stuningly moderate price (15.00$ canadian for a 1/4" sheet here in eastern Québec). It has only three ply, the outside faces being thin rotary cut philippine mahogany veneer glued on a thicker and lighter core, so its mechanical properties are at best mediocre. However one of its face is wihtout flaw, it is much lighter than a marine plywood of the same thickness and it will bend into fair curves. For building say, a hard chine kayak hull, I would suggest that such a plywood is perfectly appropriate if the hull is to be laminated with epoxy and fiberglass, that is most of the time. But I would like to be convinced otherwise.

[Junkman]

Luan is OK stuff.
I built a small punt with Luan sheets and used cut up Luan door casing for chines, gunn'ls and rubbing strakes.
%&#@*glass taped the seams only and coated all inside and out with WEST.
I think that was 6 years ago, still holding up well. In fact i'm about to do another one.
Are we Canadians cheap or just thrifty? -

[Junkman]

Luan is OK stuff.
I built a small punt with Luan sheets and used cut up Luan door casing for chines, gunn'ls and rubbing strakes.
%&#@*glass taped the seams only and coated all inside and out with WEST.
I think that was 6 years ago, still holding up well. In fact i'm about to do another one.
Are we Canadians cheap or just thrifty? -

[Junkman]

Luan is OK stuff.
I built a small punt with Luan sheets and used cut up Luan door casing for chines, gunn'ls and rubbing strakes.
%&#@*glass taped the seams only and coated all inside and out with WEST.
I think that was 6 years ago, still holding up well. In fact i'm about to do another one.
Are we Canadians cheap or just thrifty? -

[trull]

I built my kayak using luan, glassed both sides. It is very durable.

[trull]

I built my kayak using luan, glassed both sides. It is very durable.

[trull]

I built my kayak using luan, glassed both sides. It is very durable.

[David Tabor (sailordave)]

It's okay stuff, not very durable so just coat w/ epoxy or better yet glass/epoxy. The big difference is as you stated: 1/4" but only 3 ply. Good 6mm (1/4") stuff is 5 ply which is better at bending and not developing hard spots. But hey, if you don't have a complex hull shape or no tight bends. . . Good find!!!!

[David Tabor (sailordave)]

It's okay stuff, not very durable so just coat w/ epoxy or better yet glass/epoxy. The big difference is as you stated: 1/4" but only 3 ply. Good 6mm (1/4") stuff is 5 ply which is better at bending and not developing hard spots. But hey, if you don't have a complex hull shape or no tight bends. . . Good find!!!!

[David Tabor (sailordave)]

It's okay stuff, not very durable so just coat w/ epoxy or better yet glass/epoxy. The big difference is as you stated: 1/4" but only 3 ply. Good 6mm (1/4") stuff is 5 ply which is better at bending and not developing hard spots. But hey, if you don't have a complex hull shape or no tight bends. . . Good find!!!!

[Dave Hadfield]

I also built an 8ft punt out of the stuff. Since it is encapsulated in epoxy (and the bottom has glass as well), it worked fine, though there has been slight discolouration under the coating. Three seasons of hard use.

I would use it for a throw-away boat only, one you'll build very simply and cover with epoxy and paint. If you're going to go to the trouble of varnish, the labour intensifies, and you might as well make it of better material.

The light weight of Lauan is very nice though.

[Dave Hadfield]

I also built an 8ft punt out of the stuff. Since it is encapsulated in epoxy (and the bottom has glass as well), it worked fine, though there has been slight discolouration under the coating. Three seasons of hard use.

I would use it for a throw-away boat only, one you'll build very simply and cover with epoxy and paint. If you're going to go to the trouble of varnish, the labour intensifies, and you might as well make it of better material.

The light weight of Lauan is very nice though.

[Dave Hadfield]

I also built an 8ft punt out of the stuff. Since it is encapsulated in epoxy (and the bottom has glass as well), it worked fine, though there has been slight discolouration under the coating. Three seasons of hard use.

I would use it for a throw-away boat only, one you'll build very simply and cover with epoxy and paint. If you're going to go to the trouble of varnish, the labour intensifies, and you might as well make it of better material.

The light weight of Lauan is very nice though.

[paladin]

I have made this statement elsewhere in this forum...Philippine Mahogany is not a true mahogany but a tropical cedar. It will discolor in sunlight, it will generally turn urine yellow when exposed. If you want to finish it bright it must be stained, although the stain is not permanent....epoxy coat and paint. It takes paint well.

[paladin]

I have made this statement elsewhere in this forum...Philippine Mahogany is not a true mahogany but a tropical cedar. It will discolor in sunlight, it will generally turn urine yellow when exposed. If you want to finish it bright it must be stained, although the stain is not permanent....epoxy coat and paint. It takes paint well.

[paladin]

I have made this statement elsewhere in this forum...Philippine Mahogany is not a true mahogany but a tropical cedar. It will discolor in sunlight, it will generally turn urine yellow when exposed. If you want to finish it bright it must be stained, although the stain is not permanent....epoxy coat and paint. It takes paint well.

[landlocked sailor]

Luan is HIGHLY variable. I bought some for patterns last fall and it was fabulous; totally clear and smooth both sides with thick outer plys. No voids that I found. I did not subject it to the dishwasher test because I doubt I'll find as nice again soon. Rick

[landlocked sailor]

Luan is HIGHLY variable. I bought some for patterns last fall and it was fabulous; totally clear and smooth both sides with thick outer plys. No voids that I found. I did not subject it to the dishwasher test because I doubt I'll find as nice again soon. Rick

[landlocked sailor]

Luan is HIGHLY variable. I bought some for patterns last fall and it was fabulous; totally clear and smooth both sides with thick outer plys. No voids that I found. I did not subject it to the dishwasher test because I doubt I'll find as nice again soon. Rick

[Bayboat]

Years ago a group of us built a dozen El Toro dinghies for frostbiting. I had specified Bruynzeel 1/4" plywood but the group opted for lauan--Philippine-faced softwood. The fleet began to fall apart from delimination in about the fifth year. However, that was before epoxy coating came along. Lauan is nice and light, so the additional weight of epoxy or even epoxy-fibreglas (oops, sorry: f$#&*@!s) might not make a small dinghy overweight.
What does anyone think of using lauan for glued plywood lapstrake construction of, say, a fifteen foot Whitehall type? What thickness? I wouldn't use cloth, but how about coating with epoxy before hanging the plank? My present thinking is to use the best plywood available, in view of the time and cost to build such a boat, but I'm open to suggestion.

[Bayboat]

Years ago a group of us built a dozen El Toro dinghies for frostbiting. I had specified Bruynzeel 1/4" plywood but the group opted for lauan--Philippine-faced softwood. The fleet began to fall apart from delimination in about the fifth year. However, that was before epoxy coating came along. Lauan is nice and light, so the additional weight of epoxy or even epoxy-fibreglas (oops, sorry: f$#&*@!s) might not make a small dinghy overweight.
What does anyone think of using lauan for glued plywood lapstrake construction of, say, a fifteen foot Whitehall type? What thickness? I wouldn't use cloth, but how about coating with epoxy before hanging the plank? My present thinking is to use the best plywood available, in view of the time and cost to build such a boat, but I'm open to suggestion.

[Bayboat]

Years ago a group of us built a dozen El Toro dinghies for frostbiting. I had specified Bruynzeel 1/4" plywood but the group opted for lauan--Philippine-faced softwood. The fleet began to fall apart from delimination in about the fifth year. However, that was before epoxy coating came along. Lauan is nice and light, so the additional weight of epoxy or even epoxy-fibreglas (oops, sorry: f$#&*@!s) might not make a small dinghy overweight.
What does anyone think of using lauan for glued plywood lapstrake construction of, say, a fifteen foot Whitehall type? What thickness? I wouldn't use cloth, but how about coating with epoxy before hanging the plank? My present thinking is to use the best plywood available, in view of the time and cost to build such a boat, but I'm open to suggestion.

[Don Maurer]

BayBoat,

I am about 6 months into building a 13' 6" glued lapstrake boat. I work on it about 10 to 15 hours a week and just finished the planking. Considering my investment in time, I wouldn't want to use luan. I did use what the local home center called 1/4" luan (some of the poorest quality plywood you would ever hope to run across)for the strake patterns and it seemed to take the bending and twisting OK.

[Don Maurer]

BayBoat,

I am about 6 months into building a 13' 6" glued lapstrake boat. I work on it about 10 to 15 hours a week and just finished the planking. Considering my investment in time, I wouldn't want to use luan. I did use what the local home center called 1/4" luan (some of the poorest quality plywood you would ever hope to run across)for the strake patterns and it seemed to take the bending and twisting OK.

[Don Maurer]

BayBoat,

I am about 6 months into building a 13' 6" glued lapstrake boat. I work on it about 10 to 15 hours a week and just finished the planking. Considering my investment in time, I wouldn't want to use luan. I did use what the local home center called 1/4" luan (some of the poorest quality plywood you would ever hope to run across)for the strake patterns and it seemed to take the bending and twisting OK.

[Mark Van]

I used 1/4" Luan for the interior paneling on my 39 foot houseboat, it has a nice smooth surface for painting, unlike Fir. None of the Luan was used for critical structural stuff, though. The stuff I got had a thick inner core, and very thin outer cores. It was sold as "underlayment".

[Mark Van]

I used 1/4" Luan for the interior paneling on my 39 foot houseboat, it has a nice smooth surface for painting, unlike Fir. None of the Luan was used for critical structural stuff, though. The stuff I got had a thick inner core, and very thin outer cores. It was sold as "underlayment".

[Mark Van]

I used 1/4" Luan for the interior paneling on my 39 foot houseboat, it has a nice smooth surface for painting, unlike Fir. None of the Luan was used for critical structural stuff, though. The stuff I got had a thick inner core, and very thin outer cores. It was sold as "underlayment".

[Ron Williamson]

Anyone who wants to build a boat out of 1/4" luaun underlay should look at the delaminating disappointment in my yard.
On the other hand, the kayak that I built from 1/8" and skinned with 4oz. glass,is still going strong.
Have fun
R

[Ron Williamson]

Anyone who wants to build a boat out of 1/4" luaun underlay should look at the delaminating disappointment in my yard.
On the other hand, the kayak that I built from 1/8" and skinned with 4oz. glass,is still going strong.
Have fun
R

[Ron Williamson]

Anyone who wants to build a boat out of 1/4" luaun underlay should look at the delaminating disappointment in my yard.
On the other hand, the kayak that I built from 1/8" and skinned with 4oz. glass,is still going strong.
Have fun
R

[NormMessinger]

Not all luan is created equal....

We all know that, right?

--Norm

[NormMessinger]

Not all luan is created equal....

We all know that, right?

--Norm

[NormMessinger]

Not all luan is created equal....

We all know that, right?

--Norm

[Bruce Taylor]

The following turned up on rec.boatbuilding recently under the subject heading "Luaun underlay hull one year later -- no problems".

I especially enjoyed the bits where he had to shave his hairy boat.


"Condition after one season of lauan underlay 11.5 ft skiff.

Bevelled chine construction with zinc plated screws and plastic
resin (urea formaledyde) glue. Plywood edges sealed with glue.
Exterior painted with 2 coats acrylic latex house paint. Interior
one coat linseed oil. Bottom stiffened and protected by 2 red
cedar 1x1.5 skids.

Boat used one season (20 or more times, longest time in water 24
hrs), stored in unheated garage between uses and over winter.

Condition of boat examined during spring maintenance at start of
second season.

exterior: there is no peeling or lifted paint. most of the wear was on the
skids and along the chine. there was a foot long scrape on the bottom
where the hull rode up on a rock or old bridge pile (both happened). there
is a split in the surface ply parallel to the scrape, probably because the
thin plywood buckled. there are hairline cracks in the edge at the chine,
in the surface ply at the chine and along the seams at the butt blocks,
probably due to water getting into the plywood at these points. (a reason,
perhaps, to seal chines and butts with resin soaked fibreglass cloth
during construction which was not done on this boat.) maintenance
consisted of sanding any worn or cracked surface areas. gouges and dings
were then sealed by brushing in acrylic medium (a flexible water resistant
glue) except along the edges where tougher epxoy glue was spread with a
toothpick. only a couple teaspoons of each glue was needed. these
materials were used because they were at hand. polyester resin could have
been substituted. the worked spots where painted with white acrylic primer
(a pint found by chance at the building materials recyle centre),
carefully working the paint into any cracks and pinholes. the whole
exterior was given a thin colour coat with the same paint as the first
year.

interior: during the boating season the boat was left out overnight in the
rain. in the morning there was 4" of water in it. when the water was
poured out the inside of the hull had little spikes of wood standing up
from the surface as if the boat were trying to grow hair. they were sanded
off. during spring maintenance a hand was run along the interior of the
hull and bits of "hair" could be felt. they were sanded off. I have no
idea what that hair is. before putting the boat away for winter the inside
had been scrubbed. in spring another brushing worked more sand and dirt
out of the wood grain. the wood itself was in fine condition. after two
coats of thinned linseed oil were brushed on it was good as new. six of
the screw heads showed surface rust. on two it did not extend down the
shaft and they were reinserted. on the other four, all attaching the cedar
skids (cedar does soak up water if it can), the shafts had rust. the screw
holes were filled with linseed oil and after drying new screws were
inserted.

a word about spring working temperature: spring maintenance was done
before the outdoor temperature was warm enough to apply linseed oil or to
cure the epoxy glue. two techniques were used to heat the hull. one was to
wait for the sun to warm the black asphalt driveway and place the boat on
the diveway in the sun. another was to portage the boat to the back of the
house out of the wind and set it up in the sun.

--
------------------------------------------------------------------------------
National Capital FreeNet www.ncf.ca Ottawa's free community network
website: www.ncf.ca/~ag384
------------------------------------------------------------------------------"



[This message has been edited by Bruce Taylor (edited 04-29-2001).]

[Bruce Taylor]

The following turned up on rec.boatbuilding recently under the subject heading "Luaun underlay hull one year later -- no problems".

I especially enjoyed the bits where he had to shave his hairy boat.


"Condition after one season of lauan underlay 11.5 ft skiff.

Bevelled chine construction with zinc plated screws and plastic
resin (urea formaledyde) glue. Plywood edges sealed with glue.
Exterior painted with 2 coats acrylic latex house paint. Interior
one coat linseed oil. Bottom stiffened and protected by 2 red
cedar 1x1.5 skids.

Boat used one season (20 or more times, longest time in water 24
hrs), stored in unheated garage between uses and over winter.

Condition of boat examined during spring maintenance at start of
second season.

exterior: there is no peeling or lifted paint. most of the wear was on the
skids and along the chine. there was a foot long scrape on the bottom
where the hull rode up on a rock or old bridge pile (both happened). there
is a split in the surface ply parallel to the scrape, probably because the
thin plywood buckled. there are hairline cracks in the edge at the chine,
in the surface ply at the chine and along the seams at the butt blocks,
probably due to water getting into the plywood at these points. (a reason,
perhaps, to seal chines and butts with resin soaked fibreglass cloth
during construction which was not done on this boat.) maintenance
consisted of sanding any worn or cracked surface areas. gouges and dings
were then sealed by brushing in acrylic medium (a flexible water resistant
glue) except along the edges where tougher epxoy glue was spread with a
toothpick. only a couple teaspoons of each glue was needed. these
materials were used because they were at hand. polyester resin could have
been substituted. the worked spots where painted with white acrylic primer
(a pint found by chance at the building materials recyle centre),
carefully working the paint into any cracks and pinholes. the whole
exterior was given a thin colour coat with the same paint as the first
year.

interior: during the boating season the boat was left out overnight in the
rain. in the morning there was 4" of water in it. when the water was
poured out the inside of the hull had little spikes of wood standing up
from the surface as if the boat were trying to grow hair. they were sanded
off. during spring maintenance a hand was run along the interior of the
hull and bits of "hair" could be felt. they were sanded off. I have no
idea what that hair is. before putting the boat away for winter the inside
had been scrubbed. in spring another brushing worked more sand and dirt
out of the wood grain. the wood itself was in fine condition. after two
coats of thinned linseed oil were brushed on it was good as new. six of
the screw heads showed surface rust. on two it did not extend down the
shaft and they were reinserted. on the other four, all attaching the cedar
skids (cedar does soak up water if it can), the shafts had rust. the screw
holes were filled with linseed oil and after drying new screws were
inserted.

a word about spring working temperature: spring maintenance was done
before the outdoor temperature was warm enough to apply linseed oil or to
cure the epoxy glue. two techniques were used to heat the hull. one was to
wait for the sun to warm the black asphalt driveway and place the boat on
the diveway in the sun. another was to portage the boat to the back of the
house out of the wind and set it up in the sun.

--
------------------------------------------------------------------------------
National Capital FreeNet www.ncf.ca Ottawa's free community network
website: www.ncf.ca/~ag384
------------------------------------------------------------------------------"



[This message has been edited by Bruce Taylor (edited 04-29-2001).]

[Bruce Taylor]

The following turned up on rec.boatbuilding recently under the subject heading "Luaun underlay hull one year later -- no problems".

I especially enjoyed the bits where he had to shave his hairy boat.


"Condition after one season of lauan underlay 11.5 ft skiff.

Bevelled chine construction with zinc plated screws and plastic
resin (urea formaledyde) glue. Plywood edges sealed with glue.
Exterior painted with 2 coats acrylic latex house paint. Interior
one coat linseed oil. Bottom stiffened and protected by 2 red
cedar 1x1.5 skids.

Boat used one season (20 or more times, longest time in water 24
hrs), stored in unheated garage between uses and over winter.

Condition of boat examined during spring maintenance at start of
second season.

exterior: there is no peeling or lifted paint. most of the wear was on the
skids and along the chine. there was a foot long scrape on the bottom
where the hull rode up on a rock or old bridge pile (both happened). there
is a split in the surface ply parallel to the scrape, probably because the
thin plywood buckled. there are hairline cracks in the edge at the chine,
in the surface ply at the chine and along the seams at the butt blocks,
probably due to water getting into the plywood at these points. (a reason,
perhaps, to seal chines and butts with resin soaked fibreglass cloth
during construction which was not done on this boat.) maintenance
consisted of sanding any worn or cracked surface areas. gouges and dings
were then sealed by brushing in acrylic medium (a flexible water resistant
glue) except along the edges where tougher epxoy glue was spread with a
toothpick. only a couple teaspoons of each glue was needed. these
materials were used because they were at hand. polyester resin could have
been substituted. the worked spots where painted with white acrylic primer
(a pint found by chance at the building materials recyle centre),
carefully working the paint into any cracks and pinholes. the whole
exterior was given a thin colour coat with the same paint as the first
year.

interior: during the boating season the boat was left out overnight in the
rain. in the morning there was 4" of water in it. when the water was
poured out the inside of the hull had little spikes of wood standing up
from the surface as if the boat were trying to grow hair. they were sanded
off. during spring maintenance a hand was run along the interior of the
hull and bits of "hair" could be felt. they were sanded off. I have no
idea what that hair is. before putting the boat away for winter the inside
had been scrubbed. in spring another brushing worked more sand and dirt
out of the wood grain. the wood itself was in fine condition. after two
coats of thinned linseed oil were brushed on it was good as new. six of
the screw heads showed surface rust. on two it did not extend down the
shaft and they were reinserted. on the other four, all attaching the cedar
skids (cedar does soak up water if it can), the shafts had rust. the screw
holes were filled with linseed oil and after drying new screws were
inserted.

a word about spring working temperature: spring maintenance was done
before the outdoor temperature was warm enough to apply linseed oil or to
cure the epoxy glue. two techniques were used to heat the hull. one was to
wait for the sun to warm the black asphalt driveway and place the boat on
the diveway in the sun. another was to portage the boat to the back of the
house out of the wind and set it up in the sun.

--
------------------------------------------------------------------------------
National Capital FreeNet www.ncf.ca Ottawa's free community network
website: www.ncf.ca/~ag384
------------------------------------------------------------------------------"



[This message has been edited by Bruce Taylor (edited 04-29-2001).]

[PugetSound]

Hold on a second! First of all, the description of the Luan given by Fleblanc indicates that it is INTERIOR plywood and not at all suitable for building boats. Keep in mind that Luan is just a wood -not a fabrication process.

Marine plywood differs from exterior grade plywood in that the marine plywood is guaranteed not to have any interior voids nor is it permitted to have any voids which are filled with glue. Exterior grade ply can have interior voids filled with glue (no tensile or bending strength) while interior ply can have unfilled voids. Also, marine grade has layers that are more uniform in thickness so that the outer layers are more than just decoration.
What you are describing sounds like a good deal -if you're panelling your den. For building a boat? No thanks. For the effort I'm putting into building the boat, it would be false economy to buy the cheap stuff. For a kayak, you won't be buying more than mabey 4 sheets anyway so buy the good stuff. For something larger, like a dory, exterior grade might sufice (perform a boiling test first).
Note: I have some 6 mm (1/4 inch) Luan marine grade that has 5 layers of ply. Compare this with one thick inner layer and two rather anemic/thin outer layers. I bought these sheets (4'x8') at Edensaw for $35/sheet.

[This message has been edited by PugetSound (edited 04-30-2001).]

[PugetSound]

Hold on a second! First of all, the description of the Luan given by Fleblanc indicates that it is INTERIOR plywood and not at all suitable for building boats. Keep in mind that Luan is just a wood -not a fabrication process.

Marine plywood differs from exterior grade plywood in that the marine plywood is guaranteed not to have any interior voids nor is it permitted to have any voids which are filled with glue. Exterior grade ply can have interior voids filled with glue (no tensile or bending strength) while interior ply can have unfilled voids. Also, marine grade has layers that are more uniform in thickness so that the outer layers are more than just decoration.
What you are describing sounds like a good deal -if you're panelling your den. For building a boat? No thanks. For the effort I'm putting into building the boat, it would be false economy to buy the cheap stuff. For a kayak, you won't be buying more than mabey 4 sheets anyway so buy the good stuff. For something larger, like a dory, exterior grade might sufice (perform a boiling test first).
Note: I have some 6 mm (1/4 inch) Luan marine grade that has 5 layers of ply. Compare this with one thick inner layer and two rather anemic/thin outer layers. I bought these sheets (4'x8') at Edensaw for $35/sheet.

[This message has been edited by PugetSound (edited 04-30-2001).]

[PugetSound]

Hold on a second! First of all, the description of the Luan given by Fleblanc indicates that it is INTERIOR plywood and not at all suitable for building boats. Keep in mind that Luan is just a wood -not a fabrication process.

Marine plywood differs from exterior grade plywood in that the marine plywood is guaranteed not to have any interior voids nor is it permitted to have any voids which are filled with glue. Exterior grade ply can have interior voids filled with glue (no tensile or bending strength) while interior ply can have unfilled voids. Also, marine grade has layers that are more uniform in thickness so that the outer layers are more than just decoration.
What you are describing sounds like a good deal -if you're panelling your den. For building a boat? No thanks. For the effort I'm putting into building the boat, it would be false economy to buy the cheap stuff. For a kayak, you won't be buying more than mabey 4 sheets anyway so buy the good stuff. For something larger, like a dory, exterior grade might sufice (perform a boiling test first).
Note: I have some 6 mm (1/4 inch) Luan marine grade that has 5 layers of ply. Compare this with one thick inner layer and two rather anemic/thin outer layers. I bought these sheets (4'x8') at Edensaw for $35/sheet.

[This message has been edited by PugetSound (edited 04-30-2001).]

[f leblanc]

The luan plywood that is the object of this discussion is indeed a poor material that will not tolerate exposure to water. But remember that a lot of strip built small crafts have their strips glued with white glue, a bond that is certainly not water resistant. The structural integrity of the core, in a fiberglass sandwich construction, is of little relevance. A piece of luan plywood fiberglassed on both sides will likely have a higher stiffness/weight ratio than a piece of okoume plywood fiberglassed similarly.
A legitimate objection would be that if the epoxy coating is breached, the boat will fall apart faster. It is not a good idea to paddle around in a boat that has its epoxy coating broken anyway. The bruised fiber of the fiberglass will quickly draw moisture in, something that should be avoided, marine plywood or not.

[f leblanc]

The luan plywood that is the object of this discussion is indeed a poor material that will not tolerate exposure to water. But remember that a lot of strip built small crafts have their strips glued with white glue, a bond that is certainly not water resistant. The structural integrity of the core, in a fiberglass sandwich construction, is of little relevance. A piece of luan plywood fiberglassed on both sides will likely have a higher stiffness/weight ratio than a piece of okoume plywood fiberglassed similarly.
A legitimate objection would be that if the epoxy coating is breached, the boat will fall apart faster. It is not a good idea to paddle around in a boat that has its epoxy coating broken anyway. The bruised fiber of the fiberglass will quickly draw moisture in, something that should be avoided, marine plywood or not.

[f leblanc]

The luan plywood that is the object of this discussion is indeed a poor material that will not tolerate exposure to water. But remember that a lot of strip built small crafts have their strips glued with white glue, a bond that is certainly not water resistant. The structural integrity of the core, in a fiberglass sandwich construction, is of little relevance. A piece of luan plywood fiberglassed on both sides will likely have a higher stiffness/weight ratio than a piece of okoume plywood fiberglassed similarly.
A legitimate objection would be that if the epoxy coating is breached, the boat will fall apart faster. It is not a good idea to paddle around in a boat that has its epoxy coating broken anyway. The bruised fiber of the fiberglass will quickly draw moisture in, something that should be avoided, marine plywood or not.