I originally posted this at the SuperGardeners Forum. I'm duplicating here for info from another post.

I was concerned that my numbers didn't match, because Tapla and others have reported up to 60% waste (fines) when sifting Turface and my numbers were not even close to that. I later found out why: I was sifting with Fiberglass insect screen, not aluminum. Fiberglass has rectangular mesh, 1/16 x 1/32 vs aluminum being 1/16 square. I was fortunate because I live in a hot arid climate and definitely need the slightly smaller particles. There is still no PWT in my containers even using the fiberglass and I use a smaller #10 grit size.

========================= Original Post ===================================

Here is some data I gathered last year when I did my initial product purchases and testing.

In case you don't want to read ahead, here are MY conclusions:

* Napa Floor Dry is the most cost effective solution and offered an even distribution of particle sizes from 1/8 to 1/16.

* Turface by far has the largest amount of waste compared to the other products.

* Turface has 3x as many smaller particles (1/16 to 3/32) than larger ones (1/8+).

Disclaimers: These numbers are largely influenced by my insect screen (fiberglass) and how I sift. If you sift longer, you'll remove more waste. The waste calculation by weight is based on stated weight, which I did not confirm prior to sifting. By volume also does not reflect settling. Also, the volume numbers are rough estimates and the cost figures are obviously local. Al/Tapla has also experienced varied Turface waste by bag batch.

I took these measurements to compare waste between 4 of the water retention products recommended. Waste calculations by volume will never resemble ones based on weight. Dust/fines are the heaviest part of the product where measurement by weight could be triple the volume. But I believe they are helpful when comparing against each other, which was my goal.
MEASUREMENTS OF WASTE BY WEIGHT

1/8+ 1/16- Usable Waste* Stated Est.

PRODUCT 3/32 Product Weight Waste

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Axis 10.75 10.50 21.25 3.75 25 15%

Playball 11.50 13.00 24.50 0.50 25 2%

Floor Dry 14.75 16.25 30.50 2.75 -- ~8% Turface 10.25 31.00 41.25 8.75 50 18%

Numbers are weight in US lbs.

* Calcuated based on stated weight of product.

All amounts were weighed and recorded. Afterward, they were re-weighed and recorded separately and then checked against the first recording for accuracy. Discrepancies were negligible.

I simultaneously double-sift, the top screen is a 1/8th hardware cloth, the bottom screen is fiberglass insect screen -- it appears 1/16th x 1/32th. What remains above 1/8th is the largest of the particles, what remains above the insect screen is the small to medium size. What falls through both is the waste/dust i.e. definitely smaller than 1/32 (which is the key size to avoid PWT). The calculations in the first table were performed by weight -- not volume. I used a typical home scale which obviously is not precise especially when measuring Even though I never measured by volume (wish I had), I did take basic measurements (filled up the same #5 containers and took pictures). After reviewing the photos, here are very rough estimates of usable volume after my sifting.
VERY ROUGH ESTIMATES OF WASTE BY VOLUME

1/8+ 1/16- Usable Stated Est.

PRODUCT 3/32 Product Vol Waste

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Axis 3.4 3.5 6.9 7.45 7.4%

Playball 3.8 3.6 7.4 7.45 0.7%

Floor Dry 5.9 5.9 11.8 12.00 1.7%

Turface 1.7 6.9 8.6 10.43 17.6%

Listed in US gallons

Glancing at MY cost and MY usable product for the above measurements, here is my basic cost per gallon.
PRODUCT Usable My Cost $/Usable G

==========================================================

Axis 6.9 $17* $2.46

Playball 7.4 $14* $1.89

Floor Dry 11.8 $13 $1.10

Turface 8.6 $12 $1.40

*Unsure if this price is inflated. Only asked & found this at one vendor whom I later found out was ripping me off on another product, charging $22 for a bag of Turface which was only $10.99 at a competitor one block away.

Hope it is useful to someone other than me.

-- Chris