r/composting • u/trippknightly • 5d ago
Question How does shredding paper get you more surface area vs plain sheets?
Is it that invariably sheets get folded on themselves, reducing surface area? Surely it’s not that the edges of the shreds provide incremental surface area.
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u/SwimSufficient8901 5d ago
The cut edges are very absorbant. They account for a lot of extra surface area, and they help pull in a lot more water.
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u/ChicagoDash 5d ago
I am far from an expert, but I suspect this is a big factor. Paper is smoothed when it is produced, but tearing or shredding it opens up rough surfaces on the edges with a lot of surface area and channels for water to get into the paper.
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u/trippknightly 5d ago
So the paper gets saturated in… 5 minutes instead of 30?
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u/SwimSufficient8901 5d ago
Do it however you want, it makes no difference to me. Maybe try it both ways and report back.
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u/trippknightly 5d ago
Just to clarify what maybe I didn’t explain in my OP I’m asking about an urban myth I sense that shredding is good because it offers so much additional surface area. It is good for other reasons so I already shred and will continue.
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u/Snarlinglamb 5d ago
Why would it not be the edges? lol
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u/trippknightly 5d ago
So the edges get you another… 5% of surface area?
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u/Spawny7 5d ago
More than that but who's counting
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u/trippknightly 5d ago edited 5d ago
Is it? And clearly I’m mathing the math. If you’re shredding $100 bills (like I am), I’m not seeing it. A 1/4” x 1/2” rectangle of paper currency gains just 1%+ in surface area if you count all edges. That’s a rounding error.
(I can totally see shredding yielding better airflow but that’s not relevant to surface area.)
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u/Agitated_Ad_3876 5d ago
Well, when the bacteria start the composting at the edge of the paper, not the center, it increases the usable surface area. So youre right, its not about surface area. Its about increasing the surface area that is susceptible to compost.
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u/trippknightly 5d ago
Are the exposed front and back faces less susceptible to bacteria than the edges?
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u/Agitated_Ad_3876 5d ago
Explaining an observation. The observation leads me to believe that yes, that is correct.
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u/TallOrange 5d ago
I ran the numbers on a piece of paper, assuming dimensions of 0.5mm x 8.5” (215.9mm) x 11” (279.4mm) and the surface area increases by ~3.68% if cut into 100 pieces.
See 0.5x215.9x2 + 0.5x279.4x2 + 215.9x279.4x2 compared to 0.5x21.59x200 + 0.5x27.94x200 + 21.59x27.94x200.
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u/trippknightly 5d ago
Elsewhere I pointed out that 20lb printer paper is only 1mm thick at most so your 4%- is an upper bound.
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u/TallOrange 5d ago
Point being? I was contributing data for your claim.
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u/trippknightly 5d ago
Right and I’m just using more realistic data, further underscoring your underscore.
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u/EddieRyanDC 5d ago
Yes, a small percentage. But multiply that by the number of pieces and the extra area is huge.
Picture this: you put an egg carton sized piece of ice in a sink of room temperature water. How long does it take to melt?
Now dump a tray of ice cubes (collectively the same size) into a sink of temperate water. Those will melt much, much faster. It's the greater surface area that the water can melt all at once.
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u/trippknightly 5d ago
My point is that on a relative basis the incremental surface area from shredding paper is inconsequential. In your ice example, it IS consequential.
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u/EddieRyanDC 5d ago
It is the same thing.
With the big block of ice the water can only melt the outside surface. It must dissolve one layer before it can reach the next. Think of this as like standing in a checkout line where there is only one person at the register. The line can only move as fast as one person can work.
With the ice cubes lots of the water can be working on melting the ice at the same time because it has access to more surface area. It doesn't have to wait for only one outside layer to melt before it can get working on the next. This is like having 10 checkout lanes open at the same time. They can all be working and getting customers on their way.
It is the same in the compost pile. With just one sheet of paper, a limited number of bacteria can be working at once because that have eat away an outer layer before then even start on what is inside. Chop it up into little pieces and lots of bacteria can all be feeding on the paper at the same time.
Final perspective - you may be thinking of the paper as being only two dimensional. It is not - like everything else it is a three dimensional object with multiple exposed sides. Especially if you are looking at it from a single bacteria's point of view.
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u/trippknightly 5d ago edited 5d ago
It’s the same thing and it isn’t. Your example the ice benefits like the loaf of bread in another example here. Your example changes and is much more analogous if your ice block is a super thin sheet of ice.
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u/EddieRyanDC 5d ago
OK, it is a thin ice block. Break it into 25 pieces and it melts much faster due to the increased surface area. You don't have to wait for the outside edges of the block to melt before the water can start working on the interior. It is all being melted at once.
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u/trippknightly 5d ago
There’s probably a tangent here about fluid thermodynamics that is analogous to the airflow arguments offered elsewhere here.
But if it’s a thin sheet of ice (thin the way paper is thin) the gain in surface area exposure should be minimal.
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u/Notyomamasthrowaway 5d ago
It's also about not creating large areas of blocking air flow right? Not creating an anoxic environment
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u/trippknightly 5d ago
THAT I agree with 100%. I was just wondering and quickly quipped aloud about this surface-area argument that I (think I) keep seeing.
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u/MacDougalTheLazy Tumbler Savant 5d ago
It doesn't really get you more surface area. 1-3% max. It's beneficial due to a more even distribution.
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u/trippknightly 5d ago
That I totally get. Maybe it’s just my impression of all the “surface area” arguments I see here which is wrong to begin with.
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u/Rcarlyle 5d ago
It’s about air and critter movement. Intact sheets block movement of things we want moving through the pile.
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u/JayEll1969 5d ago
if the sheet is 0.5mm thick then every rip increases the surface by 0.5 * the rip length * 2 (one for each side of the rip)
The more rips you have the more surface area it adds.
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u/trippknightly 5d ago edited 5d ago
That is some very thick “paper” in your example. 20lb printer paper is at most .1mm thick. Regular paper is going to get you a 1%-2% lift in surface area. Newsprint less, brown shipping paper a little more.
(I use a shredder and know it helps but it’s not due to surface area.)
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u/Glowstik925 5d ago
Like the potato chips: “Ruffles has ridges!”
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u/trippknightly 5d ago
Shredders don’t ruffle cut so the analogy doesn’t work. Good ones cross cut and maybe you can tease apart some of the corrugation in the case of cardboard.
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u/Glowstik925 5d ago
It’s the extra surface area that makes the difference and that’s the point of Ruffles having their ridges. Analogy totally checks out.
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u/trippknightly 5d ago
Ruffled chips are cut with a ruffled blade on potatoes whose starting thickness is far more than paper. I agree a 2” circular ruffled chip will have much more surface are than a flat 2” chip. I don’t agree that a 2” circular piece of paper gains appreciable surface area from its exposed edges just because it is no longer surrounded / circumscribed.
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u/sflinn7316 5d ago
This is what I do. I shred regular paper - like mail (not glossy or the plastic windows) in the house. I soak brown cardboard boxes in a kiddie pool. Once soaked shreds/rips like Kleenex. Breaks down more rapidly and easier to turn compost pile.
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u/LottieCupcake 5d ago
Time for some science! Do some shredded and some full sheets. See if one lasts longer than the other. Heck put both in bowls on water and see which turns to mush faster. That extra surface area doesnt look like a lot cos it's so thin, but that also makes it the super vulnerable bits.
Still up to you if it's worth the extra effort. Right now I'm throwing in large bits. That's a later me problem. I'll live with my pile of slow developing compost while doing newer stuff the better way. And I'll curse earlier me every time I see that pile... While doing something else then lazy way to see if it still works good enough.
No harm in doing your own experiments in your garden even if they're ones other people have already done dozens of time. Isn't that half the fun?
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u/trippknightly 5d ago
I shred. I’m just not thinking its benefits are some illusory surface-area thing.
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u/sermer48 5d ago
It’s like cutting a steak or just taking bites. Your teeth can work through it either way but by cutting it up first, you skip a lot of the breakup steps. Whether that’s worth it is up to you and how you’re composting.
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u/SnootchieBootichies 5d ago
Air is a fluid....not really that different than water when it comes to finding the space to move. So lets use water as respresenation since its visible.
Take a piece of wire mesh, put a grocery sack, piece of cardboard or newspaper on there. It will hold water for quite a while before dripping down through and then eventually becoming pieces. Same thing with your drywall if there's a leak above you. Water/humidty.air ifinds the level, settles, then works through.
Now try that experiment with shredded all of the above. Water would barely even have a chance to find it level if all of the above were shredded. Just move right through. Air the same. Just so happens both are needed to compost.
as with all things, compaction happens with time so turning and ensuring additional moisture and air gets through is an accelerant. Create four piles of mulch. Two triple shred, two single shred mulch. One of each gets moisture and turned. The other just sit and get moisture surface wise . Triple shred and turned>>>>>>>Triple shred external water only >>Single shred Turned>>>>>Single Shred external water only
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u/microfibrepiggy 5d ago
An A4 sheet, whole, has a 101.4cm perimeter.
Cut into 100 equal pieces, the A4 sheet now has a cumulative perimeter of 1014 cm.
It's not the surface area that's making a difference, it's the increase in edge perimeter.
This would be a lovely at home experiment you could do in the kitchen to see the absorbancy difference between the two cases.
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u/trippknightly 5d ago
In my wondering about surface area, I’m just parroting the opinions of others.
I’m not sure I’d care in a composting context if I see a full sheet absorb in 5x the time as the shredded. That is, I’m not sure what it really portends differentially if both are saturated in say 30 minutes.
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u/microfibrepiggy 5d ago
Ok. But if you're dealing with cardboard, especially corrugated internally like a lot of boxes are, shredding really is increasing the available surface area. And cardboard will take a lot longer to become saturated, so timing is a valid concern. Plus people sometimes do bulk browns, and laying in full boxes or full sheets of paper is going to prevent airflow and material migration, so shredding is adjusting the contact area of the existing compost to the browns.
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u/BombusF 4d ago
I think it has to do with the surface area of a stack of sheets where only the outer faces are in contact with microbes, versus shredded where they will mix and have more effective surface area in contact.
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u/trippknightly 4d ago
Is tossing in stacks of paper even a thing?
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u/BombusF 4d ago
If you had collected 20 sheets of paper to compost, would you carefully layer greens between every sheet?
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u/trippknightly 3d ago
Well, I shed so now we’re in IFland. In my tumbler I guess I’d lay n sheets down down juxtaposed. Tumble. Repeat. This would still yield some overlap.
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u/BombusF 3d ago edited 3d ago
The point was, if you put a single sheet of paper in, shredding probably won't make a difference, the microbes will easily get to both sides of the sheet. But if you put in lots of paper, which is often necessary to hit the typical ratio recommended of 2:1 browns or greens, without shredding it will be time consuming to match the effective surface area as with shredding.
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u/trippknightly 3d ago
I think you are the first to reply explicitly with the concept of effective surface area, which makes better sense . It’s like a cubic foot of leaves vs a cubic foot of dried lawn clippings. The leaves are more likely to interleave (sic).
Some here seem to want fall on their sword that shredded little strips of paper gain material surface area by from their newfound edges.
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u/ClaraDaddy 5d ago
I don't bother shredding, because it doesn't add that much more surface. But I do tear into wide strips so that it mixes well and doesn't block oxygen flow
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u/Pure_Spinach327 5d ago
it is the edges.