Monday, April 13, 2015

Testing Your Mix - What Do the Results Mean? - SILT AND CLAY

This is the third of 4 posts explaining in detail what each part of an infield mix test result includes and what does it mean to your infield.

Today we discuss silt and clay.  I prefer to explain these two materials together as they need to act in unison at the correct rates/ratios to allow for a properly performing infield at all levels of play.   Overall silt/clay content is any material in the .05 mm to below .002 mm range.  Let’s look at three aspects of silt/clay as all silt/clay is not created equal.

1.  Overall Silt/Clay Percentages - Recreational and high school play the acceptable range of overall silt/clay content is 25-30%.  Collegiate level of play the acceptable range of overall silt/clay content is 31-35%.  Professional level of play the acceptable range of overall silt/clay content is 38-42%.

2.  Silt Content Breakdown-When testing infield mixes, I prefer to spend the extra $15 and have the material tested via Hydrometer.  This type of testing provides a breakdown of the silt into a course and fine range.  Silt that falls into a more course range will act more like a fine sand.  Silt in the fine range will act more like a clay.  Typically the more course the silt the less stability under wet conditions.  

3.  Clay Content - Not all clay is created equal.  Clay is the mineral that provides the infield mix its color.  Do you manage a “red clay” material?  If so it is red due to iron oxide in the mineral.  Do you manage a “brown infield”?  It is due to the clay mineral being brown in color.  Clays expand and contract during wet and dry cycles.  The expansion and contraction cycle can “make or break” an infield mix.  That is why you can read different test results of mixes that contain similar clay percentages, but they perform differently during both wet and dry periods.  Its all about the mineral.

Below is a photo of an infield mix with elevated fine and very fine sand along with a large amount of course silt.  As you can see, this material has little to no structural stability.

In closing a little “eye test” of high silt infield mixes is that often a high silt infield mix will be light brown in color.  Almost khaki in color.  Also, high silt infield mixes will have a dust layer on the surface and be firm underneath.  Below is what can be present on high silt infield surfaces.  Note the wind erosion into the grass edges.

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Play on!

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