Is leather stronger when laminated with an additional layer of leather?

[thekid77]

Hi friends, 

I was wondering......which is stronger-----a single ply of leather, or two layers of leather laminated together (assume that in either case they both add up to the same weight/thickness)...

Thank you in advance for sharing!!

[Chief31794]

Two layers is much stronger, and somewhat "stiffer".  The "strength" of the leather is in the grain and when you glue them, you have two grain sides resisting each other, they don't bend as well but they are much stronger.

Chief

[thekid77]

1 hour ago, Chief31794 said:

Two layers is much stronger, and somewhat "stiffer".  The "strength" of the leather is in the grain and when you glue them, you have two grain sides resisting each other, they don't bend as well but they are much stronger.

Chief

Thank you for sharing Chief, much appreciated

[thekid77]

12 hours ago, nstarleather said:

"Stronger" and longevity might be too different things, if they actually end up at the same thickness the strength would roughly the same.  With 2 layers you have to worry about that bond (glue) in the center breaking down over time, which would not happen with one thickness. Also if 2 layers are stitched, you add some strength but also the possibility of wear in the stitching.  The only really good reasons to double layer things is to add thickness which does obviously add strength, or if one of your materials is weaker or more stretchy, say lining a Chromexcel belt with something that doesn't stretch like Chromexcel does.  Or you can layer for the "look" of adding a lining, perhaps in a different color than the other side.

 

Thank you for sharing.....so, even if they wind up to be the same thickness,  according to what chief said (see above comment), they are "much stronger" because there are two grain sides resisting get each other....do you agree or disagree with the this?

 

Thank you 

[JLSleather]

Chief has a point, actually.  From a technical view, the grain layer is the strongest part of the leather, so 2 grain layers would be "stronger".  More important, two layers together "pulling against each other" is "stronger" much in the way a braided rope is stronger than a single fiber -- the fibers aren't actually "stronger" (the tensile strength of the fiber would be the same) but the ASSEMBLY is.

 

[thekid77]

39 minutes ago, nstarleather said:

 

I don't disagree but especially if you're talking about shaving off the suede side and adding another top grain to it, of course it's stronger.  I just think that in an actually scenario of using something you have some forces that will break that bond with time. If it's just glue and not stitched, then you can bet one layer is better, any day. 

I 

Thank you for the input.....another question if I may...

From ym experience, when properly "set", contact cement such as dapper weldwood from the red can is virtually indestructible....to get the leather to separate you'd have to destroy the article, whatever it may be, from my experience.......just my opinion, but I feel like dapp doesn't really need stitching to reinforce it....

Thoughts?

[Dwight]

Bluntly, nstarleather is wrong.  

Two pieces of leather bonded with Weldwood contact cement will not come apart and is seriously much stronger than any single layer of leather.

The other side of the single layer is that the flesh side will abrade and wear off much faster and easier than the hair side, . . . so bonding flesh to flesh, only leaves the strong side to weather whatever comes at it, . . . making the overall product a much better product.

I've been using Weldwood contact cement since the late 60's or early 70's and the only time I've ever seen two pieces come apart that were bonded with it is when one of the pieces gives away, . . . whether it is fibers of wood, leahther, formica, or whatever you use.

May God bless,

Dwight

[Big Sioux Saddlery]

There could be two correct answers to this question.  Both can be stronger than the other, depending on end use.  I'm going to refer to horse tack, because that's most of what I make.  For heavy, everyday use, I can guarantee that one, good heavy layer will normally outlast two layers sewn together to equal the same thickness.  I've seen it countless times, two light layers sewn together under heavy use will break down faster than one good heavy layer.  One reason is every stitch pokes a hole close to the edge of the leather, making it possible for dirt and moisture to work it's way into the interior fibers of the leather.  The leather will dry out faster, and it CAN delaminate.  Against the strength of a horse, a little old thread (no matter how heavy) isn't going to add much strength.  I'm sure someone is going to reply telling me I'm wrong, but after 25 years of repair work, that's what I've seen.  I have headstalls out there still in daily use after 25 years. They were made with a single heavy layer of russet Hermann Oak harness leather.  The buckles are darn near worn out, but the leather is still holding.  I do not believe that if I had made them doubled and stitched out of two lighter layers they would have lasted this long.  The first cracks usually to appear in a strap start at the holes.  Think about how many holes are in a strap that is sewn all the way around. That's a lot of holes!  That's why doubled and stitched stuff is generally for "goin' to town" and the single heavy layer stuff is the everyday working tack.  Somewhere in an old book about harness making, the author talked about how injurious a splitter is to leather.  I believe it was in the same book that it was claimed that removing a third of the thickness removes half of the strength of a strap. 

Stirrup leathers on western saddles are a good example. It is common practice in production saddles to sew a one inch wide strip of leather down the center of the stirrup leather where the adjustment holes are located. Within 5 years or less, most of these are coming apart or have already broken.  Too light of a base stirrup leather is used, and then "reinforced" with this strip (usually a strip of latigo) and then when they separate from wear, which I guarantee is going to happen, neither layer is heavy enough for the intended purpose.  Certainly there are instances in other areas of leather working that this would not be the case however, and two layers would outlast one.  But it's not ALWAYS the case.

[JLSleather]

1 hour ago, Big Sioux Saddlery said:

every stitch pokes a hole close to the edge of the leather, making it possible for dirt and moisture to work it's way into the interior fibers of the leather

At last, someone who understands (and admits) the harm done by pokin' holes where they don't needa be nun   That second row o' stitchin' on that fancy go-ta-meetin' holster is basically a tear line.. like scoring concrete ..

1 hour ago, Big Sioux Saddlery said:

doubled and stitched stuff is generally for "goin' to town" and the single heavy layer stuff is the everyday working

Hey, I make quite a bit o'the 'shiny' stuff, but I'm in with ya on the put no holes where they don't needa be.

 

[Les No6]

Single strap is strongest the strength is in the coarse fibres as referenced in the Hasluck books, not the grain that’s just a brain fart or marketing BS as is over 90% of the internet including this website these days.

[thekid77]

9 hours ago, Les No6 said:

Single strap is strongest the strength is in the coarse fibres as referenced in the Hasluck books, not the grain that’s just a brain fart or marketing BS as is over 90% of the internet including this website these days.

Could you be more specific about your reference in the Hasluck book? I found the book but I don't see that info in there...

How about a page number?

Thanks

Edited December 21, 2016 by thekid77

[TinkerTailor]

10 hours ago, Les No6 said:

Single strap is strongest the strength is in the coarse fibres as referenced in the Hasluck books, not the grain that’s just a brain fart or marketing BS as is over 90% of the internet including this website these days.

This is also why the old books say a strap is best from unsplit leather, as mentioned above. These coarse fibres are also long, and intertwined, which is where the strength comes from. Same idea makes cotton fibers strong when woven into denim. Splitting cuts these fibers shorter. Shaving denim thinner and then doubling it up will not be anywhere near the strength of thicker denim.

 

[thekid77]

51 minutes ago, TinkerTailor said:

This is also why the old books say a strap is best from unsplit leather, as mentioned above. These coarse fibres are also long, and intertwined, which is where the strength comes from. Same idea makes cotton fibers strong when woven into denim. Splitting cuts these fibers shorter. Shaving denim thinner and then doubling it up will not be anywhere near the strength of thicker denim.

 

With all due respect, what "old books" are you referring to?

And where does it say this..not trying get to argue just trying to learn......lots of info out there, some bad and some good..

[TinkerTailor]

I have a library of hundreds of pdfs of old leatherworking and tanning textbooks. I have aquired these from many places on the net over the years, some i forgot where and many have disappeared behind paywalls and are not available to view without memberships. This information is in quite a few of them. You can find a few books on archive.org if you look around. I would post the pdfs here but they are all way too huge. Some are 100mb....

From "The manufacture of leather"  by Allen Rogers, PHD , printed in 1922: (sorry for the formatting)

4. Analysis of Skins. — At
first glance, the pelts of
various animals appear to have
little in common. On closer
examination, however, a very close similarity will be observed.
In structure, all animal skin is made up of several readily
defined layers. The skin is not merely a covering for the
animal, but also serves as a container for nerves and secretive
glands, and as a bed, or ground, for the hair, or fur. It is
made up of two principal layers : the epidermis, or cuticle, and
the corium, or tnie skin. These two layers are totally distinct
in structure, origin, and functions.
5. The epidermis is a thin covering of the true skin
and is entirely removed before the tanning operations begin.
In life, the upper, or external, part is being constantly worn
away, falling off in the form of dry scales. The interior part
of the epidermis is made up of numerous living nucleated
cells ; as the surface of this layer is reached, these cells
become flattened and finally dry up and form the exterior part
of the epidermis and ultimately drop off as dead
scales.
These cells, which renew the horny external tissue of the epi-
dermis, are in turn renewed by vessels situated in the corium,
or true skin. The epidermis does not combine with tannin
and is therefore removed, laying bare the true skin, which is
known to the tanner as the grain.

6. The corium, or true skin, is the skin with which the
tanning agents combine to form leather. There is an inter-
mediate albuminous layer between the corium and the epidermis.
Both layers are composed of interlaced bundles of fiber running
across and above one another and parallel to the surface of
the skin. These fibers are surrounded by fluid matter, which
serves to keep the skin in a moist and pliable condition. On
removal of this fluid the fibers alone remain, and if dried by
a gentle heat they assume a horny appearance and become in
substance about one-third of the raw hide.
The corium determines the quality of the leather that can be
made from a hide. Its thickness, flexibility, and strength are
reproduced in the leather. Between the fibers of the corium
is an albuminous substance called coriin: in a dry state this
holds and connects the fibers.
The connective tissue of the corium gives form to the skin,
the intercellular substance, coriin, lying between the fibers.
When boiled with water, these connective tissue fibers form
glue, losing their organized structure, and making a homo-
geneous jelly.
7. The intercellular substance is probably a decomposition
product of the connective tissue. This coriin is soluble in
lime water and other alkaline solutions ; frequent treatment of
the skin with these reagents withdraws fresh quantities of
soluble matter with every treatment. This fact should be
noted in connection with the liming of skins to remove the hair.
Dilute inorganic acids swell the connective tissue. The
swelling of the skin by acids is made use of to facilitate tanning
;
it not only makes the skin more sensitive for the reception
of the tanning material, but also effects the disintegration of
the fiber bundles into individual fibers, thereby increasing the
surface.
8. The under skin is made up of loose connective tissue,
embedded in which are the sweat and fat glands, the blood
vessels, and muscular fiber. Fig. 1 shows an enlarged micro-
scopic transverse section of the skin in which the Malpighian
net, or lower layer of the epidermis, is shown at d ; the corium,
 

Edited December 21, 2016 by TinkerTailor

[TinkerTailor]

7 hours ago, thekid77 said:

Could you be more specific about your reference in the Hasluck book? I found the book but I don't see that info in there...

How about a page number?

Thanks

I could not find it in the Hasluck leatherwork book, but i did see referenced to his harness making book, which i have not seen. I did find this on page 30 of THE HARNESS-MAKERS ILLUSTRATED MANUAL., W.N.Fitzgerald, 1875:

 

So well is this understood by leading harness-
manufacturers who make up full lines, that they
never cut a harness from a single side, but select
the leather carefully and use a specific grade or
weight for each particular strap; while the leading custom manufacturers purchase or cut only
backs of the best quality. The great majority,
however, buy their leather in small quantities, and
by so doing commit the error of not procuring
a proper assortment.As a rule, they select the
weight best adapted to the greater portion of
their work, and when lighter stock is needed they
resort to the splitting-machine, entailing on them-
selves extra labor, and wasting no inconsiderable
amount of leather, besides materially weakening
the straps thus manipulated, as the portion of the
flesh side which is removed is the strongest part
of the stock.

[MADMAX22]

I tried for a little while to search for any test results for leather but didnt find any actual results information. Saw some pretty cool pictures of the old break test machines, alot of test requirements for leather and textiles in general but that was about it. 

Only results I actual found were rub wear test for motorcycle racing suits of various materials, apparently the racing grade leather outfits were the highest rated with exception of some thick Kevlar compound woven material, and that was a specific one other Kevlar compounds didnt fair half as well.  

[TonyRV2]

I came upon an old reference online that was written in the 1880's that involved the use of leather belts being used to drive pulleys.  The article talked about both the tensile strength (stretching forces) and compression forces working on a belt as it drove a pulley system.  The compression forces, the article claimed are negligible and do not harm the leather.  These forces existed on the inside of the belt as the belt turned directly against the pulley.  As the belt travels in between the pulleys it undergoes tensile forces, and this is where the article place most of the emphasis.  The author referred to a test in which the leather was split and then subjected to testing.  The grain side ripped at a force of 468lbs while the flesh side was able to reach around 770lbs.  So it would seem when it comes to tensile strength at least, that the flesh is much stronger than the grain.  I found it noteworthy that the grain side should always be against the pulley since it provided a much better frictional contact against the pulley surface, significantly better than most other materials.  I wonder if this is where the misconception that the grain is stronger than the flesh got started?  

[TinkerTailor]

40 minutes ago, TonyRV2 said:

I came upon an old reference online that was written in the 1880's that involved the use of leather belts being used to drive pulleys.  The article talked about both the tensile strength (stretching forces) and compression forces working on a belt as it drove a pulley system.  The compression forces, the article claimed are negligible and do not harm the leather.  These forces existed on the inside of the belt as the belt turned directly against the pulley.  As the belt travels in between the pulleys it undergoes tensile forces, and this is where the article place most of the emphasis.  The author referred to a test in which the leather was split and then subjected to testing.  The grain side ripped at a force of 468lbs while the flesh side was able to reach around 770lbs.  So it would seem when it comes to tensile strength at least, that the flesh is much stronger than the grain.  I found it noteworthy that the grain side should always be against the pulley since it provided a much better frictional contact against the pulley surface, significantly better than most other materials.  I wonder if this is where the misconception that the grain is stronger than the flesh got started?  

Do you have a link for that reference? i would like to add it to my library./

I looked ain a bunch of books for the section i remembered reading on drive belting, but I could not find it. I have read that they shaved/sanded/buffed the grain off when they layered skived hides to make thicker heavy duty drive belting. They would arrange  them like a deck of spread out playing cards, with the hides half overlapped to get more thickness. The glue joint was not as strong grain to flesh as it was flesh to flesh, hence the removal of the grain.

Also, as to the original question, Leather belting was never stitched only glued. The sections of belt were joined with stitching or clips, but the pieces are way longer than a hide is. The individual hides were glued together. I am sure if glue worked good enough here, it will hold up the that dirty hairy gun on yer belt

I also have a few scientific journals that talk about leather tensile strength from the early 1900s but they are way too dry to read right now......

[JLSleather]

59 minutes ago, TonyRV2 said:

The compression forces, the article claimed are negligible and do not harm the leather.  These forces existed on the inside of the belt as the belt turned directly against the pulley.  

Your conclusion seems backwards.  The compression forces are "negligible" damage to the grain (pulley) side due to the flesh side's lack of resistance to stretch.  In short, the outside stretches more, so there is less compression of the inner radius fibers.  Or, to say the same thing another way, the grain side is less prone to stretch (increasing the compression if you put it on the outside).

We've all known about this for a good while.  Making a belt?  Then most know that you need to moisten the grain of the leather to make the bend.  BUT, the sueded side is bent all the time with no apparent damage -- apparent the key word here.

Basically, the test you quote confirms that the grain layer is "stronger" (less likely to separate willingly).

[TinkerTailor]

3 minutes ago, JLSleather said:

Your conclusion seems backwards.  The compression forces are "negligible" damage to the grain (pulley) side due to the flesh side's lack of resistance to stretch.  In short, the outside stretches more, so there is less compression of the inner radius fibers.  Or, to say the same thing another way, the grain side is less prone to stretch (increasing the compression if you put it on the outside).

We've all known about this for a good while.  Making a belt?  Then most know that you need to moisten the grain of the leather to make the bend.  BUT, the sueded side is bent all the time with no apparent damage -- apparent the key word here.

Basically, the test you quote confirms that the grain layer is "stronger" (less likely to separate willingly).

I think it was more in reference to the forces/damage flexing the belt  when going around the pulley being negligable compared to the forces lengthwise on the belt causing it to stretch. The grain has some effect on the belts longevity going around a pulley, and resisting bending damage, due to it holding the fibers tight while bending. The grain has much less effect on tensile strength because the flesh is the stronger part in this aspect as well it constitutes a greater portion of the thickness of the hide. I would imagine the treatments applied to the belting during tanning and manufacture have a much bigger influence on the ability of the belt to resist stretch and bending damage than the existence of grain.

[JLSleather]

Well, yah--- that's what I said.  The speed and circumference of the pulley is the same at all times, so the "tension" on the belt is constant (after start-up).  In teh "straightaway" ... there is tension, and in the bends, there is both tension and compression.  And regardless of the direction (grain in or grain out) of the leather, the bend radius -- the part actually doing the "curve", is not the middle of the leather.

BUT, the "tension" on teh belt is constant -- not increasing. Once it reaches full speed, the tension is not increased.  Still, the belt will fail over time, even though the tension is not increased.

But the question -- to get back to the original -- was concerning leather of the SAME thickness, either 1 layer or 2 adding up to the same thickness. Personally, I think :

1.)  Big Souix makes a great point above about putting holes in leather (or anything really).

2.)  This entire thing will go the way of that thing about Photoshop "brushes" for stamping tools.. lots of words, no action.

 

[TonyRV2]

Thats exaclty it TT.  The tensile forces are much, much greater on the belt in a pulley system.  The only reason the grain side is put toward the pulley is not because of strength, but because of the higher density of the cell structure (that which makes the grain side flat). The flatness of the grain side which is what gives it better properties to engage the pulley.  Frictional forces are much higher with grain to pulley rather than flesh to pulley, so there is less slippage.  Also, when the grain is toward the outside it tends to crack.  This is also something that tends to be better with the grain facing the pulley....what compression forces there are tend to keep the grain more compact.

I'll see if I can find that link again and post it.

[TonyRV2]

53 minutes ago, TinkerTailor said:

Do you have a link for that reference? i would like to add it to my library./

I looked ain a bunch of books for the section i remembered reading on drive belting, but I could not find it. I have read that they shaved/sanded/buffed the grain off when they layered skived hides to make thicker heavy duty drive belting. They would arrange  them like a deck of spread out playing cards, with the hides half overlapped to get more thickness. The glue joint was not as strong grain to flesh as it was flesh to flesh, hence the removal of the grain.

Also, as to the original question, Leather belting was never stitched only glued. The sections of belt were joined with stitching or clips, but the pieces are way longer than a hide is. The individual hides were glued together. I am sure if glue worked good enough here, it will hold up the that dirty hairy gun on yer belt

I also have a few scientific journals that talk about leather tensile strength from the early 1900s but they are way too dry to read right now......

Here's the link to the google book.  The explanation basically starts on page 182, section 26.
 

https://books.google.com/books?id=QV8IAAAAQAAJ&pg=PA183&lpg=PA183&dq=which+is+a+stronger+material+the+grain+side+or+the+flesh+side+of+leather?&source=bl&ots=H_oOqbEpfM&sig=oOIV8XoJqE_IGMlnreVk_-wOKlI&hl=en&sa=X&ved=0ahUKEwiYjffGlYjRAhUpqlQKHR91BdUQ6AEIRzAI#v=onepage&q=which is a stronger material the grain side or the flesh side of leather%3F&f=false

[thekid77]

When I originally posted this question, I should have been more specific...the context of the question are two plies stronger than one (assuming same thickness), was in reference to reinforcing the buckle ends on a leather belt.....my apologies for lack of clarity....the topic has gone six ways from Sunday....

Thank you everyone for your input and for sharing your experience....personally, I feel that two layers laminated together are stronger than one.....not saying this is the truth, but I'm relating it to comparison the strength of single plies of wood vs wood laminates...i don't see why the same theory would not be true for leather

[RockyAussie]

4 hours ago, thekid77 said:

When I originally posted this question, I should have been more specific...the context of the question are two plies stronger than one (assuming same thickness), was in reference to reinforcing the buckle ends on a leather belt.....my apologies for lack of clarity....the topic has gone six ways from Sunday....

Thank you everyone for your input and for sharing your experience....personally, I feel that two layers laminated together are stronger than one.....not saying this is the truth, but I'm relating it to comparison the strength of single plies of wood vs wood laminates...i don't see why the same theory would not be true for leather

If 2 top grains are used the answer is defiantly yes and I would guess by about 50% or more. The type of glue used if any would also add a further factor. If used against where the bar of the buckle comes in contact I would use the top grain to make contact. Making sure the stretch in the hide is cut in the correct way, will have a large bearing on the durability as well.