Using Wood Glue To Paper 1/16" Basswood - With A Strength Test

[lakeroadster]

I've papered fins before using white glue. This time I used 1/16" basswood, papered on both sides, and used Gorilla Wood glue instead of white glue.

Gorilla glue tends to be much stiffer when dry, compared to white glue. That's been my experience anyway.​

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I used some smooth boards to clamp the wet papered fins.​

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After the glue had 26 hours to cure I pulled the papered basswood pieces from the clamping fixture. They were still damp and not much stiffer than the raw basswood was so the pieces were placed on the drying rack, with some weight placed on them to keep the pieces flat.

I flipped the pieces every couple of hours... and they seemed to stiffen up nicely as they dried.

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Here's some data:

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I did a strength test on the wood glue papered fins. It feels so strong I just had to know how much stronger.

I tested the bending strength, in the weak axis, bending it along the wood grain.​

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The raw 1/16" basswood piece failed with 851 grams (1.8 lbs) of weight. The basswood snapped into (2) pieces.​

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The papered 1/16" basswood failed with 6,988 grams (15.4 lbs) of weight. The basswood snapped, the top paper ripped across, the bottom paper was still intact.​

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So that's about an 8:1 increase in bending strength. Pretty amazing, right?​

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[StreuB1]

These are called skin-core-skin composites and yes, its amazing when you apply a skin that has extremely high tensile strength relative to its mass.

Try using slow CA next time.

If you want to make them REALLY strong, use 0.002" polyester (PET / Mylar) film instead of paper. You likely will not break them.

 

[lakeroadster]

These are called skin-core-skin composites and yes, its amazing when you apply a skin that has extremely high tensile strength relative to its mass.

Try using slow CA next time.

If you want to make them REALLY strong, use 0.002" polyester (PET / Mylar) film instead of paper. You likely will not break them.

@Daddyisabar mentioned that previously in another thread. Wouldn't soaking these porous materials (wood and paper) with CA make the assembly more brittle than the wood glue version?

During the test I was impressed at the flexibility of the "skin-core-skin" sandwich under load. Seems like if it was more brittle it would fail with less of a load.

 

[bjphoenix]

I'm surprised that the glue was still wet for that long. I paper my balsa fins with yellow wood glue and after about 8 hours they are completely dry. I have a couple of flat wood scraps that I use, and I tape a piece of kitchen wax paper to the inside surface of each piece of wood to the fins won't stick to the wood.

 

[lakeroadster]

I'm surprised that the glue was still wet for that long. I paper my balsa fins with yellow wood glue and after about 8 hours they are completely dry. I have a couple of flat wood scraps that I use, and I tape a piece of kitchen wax paper to the inside surface of each piece of wood to the fins won't stick to the wood.

Sounds like basically the same set-up.

• Where are you located? Curious what the relative humidity is there.
• Also, are using basswood or balsa?
• What type / thickness of paper are you using?

Thanks.

 

[Kelly]

I'm surprised that the glue was still wet for that long. I paper my balsa fins with yellow wood glue and after about 8 hours they are completely dry. I have a couple of flat wood scraps that I use, and I tape a piece of kitchen wax paper to the inside surface of each piece of wood to the fins won't stick to the wood.

Yellow/White glue cures by evaporating water. Although, even if you encase it in wax paper, a lot of the water can leave the glue just by moving into the wood, so the glue can still cure.
Polyurethane (Gorilla) glue cures by absorbing and chemically reacting with water. If you cover it with wax paper, it's hard for atmospheric water to get in. Oftentimes I will aid the curing of Gorilla glue by painting one of the surfaces with water, and the other with glue, before assembling. Then you've got a nearby source of moisture for the cure.

 

[Kelly]

@Daddyisabar Seems like if it was more brittle it would fail with less of a load.

Brittleness and strength are actually two, largely unrelated, properties. "Brittleness" is a measure of how much something deforms under load in the process of breaking. "Strength" is a measure of how much force it actually takes to break it. (For example, glass can be extremely strong - that's why we strengthen things with fiberglass - but it is almost always very brittle).
What you're measuring in your tests is the strength, and that's mostly what we care about. I don't know if saturating wood/paper with CA makes them more brittle, but I doubt that it does anything to weaken them. So, no, I don't think that using CA will give you worse results. As has been noted, the strength comes from having a relatively strong material as the 'skin', as the skin is where most of the bending stress is concentrated.

I love seeing tests like this, with real data. I just finished papering the fins on a Der Big Red Max model (really didn't have high hopes for the survivability of the 3-piece glued-up fins). I knew it would help, but 8X strength? Wow!

 

[neil_w]

Polyurethane (Gorilla) glue cures by absorbing and chemically reacting with water. If you cover it with wax paper, it's hard for atmospheric water to get in. Oftentimes I will aid the curing of Gorilla glue by painting one of the surfaces with water, and the other with glue, before assembling. Then you've got a nearby source of moisture for the cure.

All true, but not relevant here, as it was Gorilla Wood Glue that was used. It’s a PVA glue.

 

[Kelly]

It’s a PVA glue.

Ah, good catch. I've always used their PU glue for wood, so I missed that "wood glue" is what they call their PVA.

 

[Jeff Lassahn]

The success of the Gorilla marketing machine has made my life really difficult. It used to be when someone says Gorilla Glue that meant a specific chemistry, now you have to ask: do you mean Gorilla brand CA or Gorilla brand Polyurethane Gorilla brand RTV or ...

 

[Blast it Tom!]

These are called skin-core-skin composites and yes, its amazing when you apply a skin that has extremely high tensile strength relative to its mass.

Try using slow CA next time.

If you want to make them REALLY strong, use 0.002" polyester (PET / Mylar) film instead of paper. You likely will not break them.

So do you use the Mylar with slow CA? Does it stay shiny? That could help with tracking if it reflects the sunlight on a clear day...

Thanks to @lakeroadster for a good test and data. Love it!

 

[StreuB1]

So do you use the Mylar with slow CA? Does it stay shiny? That could help with tracking if it reflects the sunlight on a clear day...

Thanks to @lakeroadster for a good test and data. Love it!

Mylar is clear, aluminized mylar is shiny. I was referring to using clear PET film, not aluminized. So, its not really "shiny."

 

[Blast it Tom!]

Mylar is clear, aluminized mylar is shiny. I was referring to using clear PET film, not aluminized. So, its not really "shiny."

Any reason why it couldn't be? I'm thinking of cutting up one of those helium ballons you see in the stores and using that.

 

[bjphoenix]

@Daddyisabar mentioned that previously in another thread. Wouldn't soaking these porous materials (wood and paper) with CA make the assembly more brittle than the wood glue version?

During the test I was impressed at the flexibility of the "skin-core-skin" sandwich under load. Seems like if it was more brittle it would fail with less of a load.

Balsa wood bent the wrong direction is pretty soft, add CA and it becomes stiffer, but the CA is carrying the tension from bending and it will fracture at some point which makes the combination seem brittle. Overlay it with something that has additional tensile capacity such as paper or carbon fiber and even if the underlying materials crack, the tension stress due to bending is carried by the fibers in the outer layer.

 

[lakeroadster]

Balsa wood bent the wrong direction is pretty soft, add CA and it becomes stiffer, but the CA is carrying the tension from bending and it will fracture at some point which makes the combination seem brittle. Overlay it with something that has additional tensile capacity such as paper or carbon fiber and even if the underlying materials crack, the tension stress due to bending is carried by the fibers in the outer layer.

But.... the CA also soaks into the paper.. and makes it dramatically more brittle. I guess I'll glue up a test piece and try it.

Also note... the above test used basswood.

 

[StreuB1]

Slow CA has higher surface tension which prevents the normal capillary action that draws thin CA deep into the pores of the substrate(s) in question.

This essentially just bonds the skin material to the surface pores of the core material.

 

[neil_w]

By the way, exactly what kind of paper was used here? I've always been a bit curious about the difference in strength between copy paper and 65 lb cardstock. I assume the cardstock would be stronger but not sure by how much (it's certainly heavier).

 

[lakeroadster]

By the way, exactly what kind of paper was used here? I've always been a bit curious about the difference in strength between copy paper and 65 lb cardstock. I assume the cardstock would be stronger but not sure by how much (it's certainly heavier).

61 lb Staples Photo Supreme Double Sided Matte Paper, it's defined in the Excel screen shot in Post #1

 

[neil_w]

I missed the 61 lb note. Not sure about the general properties of a photo-intended paper, I guess it's reasonable to assume it would be similar to 65 lb cardstock, although I don't know if the photo-ready surface would affect strength of glue bond. Based on your results, probably not much.

 

[lakeroadster]

I missed the 61 lb note. Not sure about the general properties of a photo-intended paper, I guess it's reasonable to assume it would be similar to 65 lb cardstock, although I don't know if the photo-ready surface would affect strength of glue bond. Based on your results, probably not much.

The adhesion of the paper to the wood to me is the big issue. I peeled the paper off the fin in the area where it attaches to the TIE Fighter fuselage. Basically cutting through the paper and forming a rectangle (see photo's below). I could take the x-acto knife, lift the edge of the rectangle and pull the paper off. The paper delaminates from itself very easily. The adhesion of the paper to the wood is excellent. I had to scrape the remnants of it off the basswood with the x-acto knife blade, like using a paint scraper to remove paint from a wood surface.

So there's no way I would feel comfortable gluing anything to the paper, of the papered fin, as member @4regt4 is discussing on is TTW papered fin thread. With enough structural loading at the glue joint, the glue will simply rip some of the paper off the fin and the joint will fail.

That's where perhaps CA would work better, in it's ability to soak all the way through the paper? But, then you have to weigh in the brittle nature of CA soaked wood.

 

[neil_w]

Would be curious if plain old card stock behaves differently.

 

[mjennings]

Strength properties of composite laminates are a mixture of the resin (epoxy, wood glue, CA, thermoplastic, etc) and fiber (paper, fiberglass, carbon, kevlar, t-shirt etc). The amount of resin ie proper wetting, (to little, to much, just right) will change the strength, as will the fiber orientation and stacking sequence. Papers do have a grain, why they rip cleaner one way than the other.

 

[lakeroadster]

Would be curious if plain old card stock behaves differently.

So many variations of materials and processes...

It kind of comes down to everybody's personal "Manufacturing Methods". We've got a bunch of the printer paper that we bought on sale about 5 years ago.... and I dislike CA due to its "gotta be super careful if you're using it inside the home" related issues. So, wood glue and printer paper end up being my preferred combo.

 

[StreuB1]

One point about card stock. Card stock is generally either coated or polished, both can affect their ability to absorb a fluid like glue.

Photo paper now is also a coated product and the surface chemistry, texture, or both, are aligned with the type of ink and printer chemistry so that it adheres either by chemical or mechanical tooth.

Just something to be mindful of.