Plastic Limit Test Procedure | Lab Result | Graph | ASTM Standard D 4318

Sponsored Links :

Plastic Limit test procedure should be done well to get the good result. In this article we are trying to provide you complete information about Plastic Limit Test Procedure. We have arranged the information in this post to make you understand it easily. We hope that you can understand it well. Please check the information below.

Plastic Limit Test

plastic limit test procedure

Importance of Plastic Limit

Plastic limit definition is the percentage moisture content at which a soil changes with decreasing wetness from the plastic to the semi- solid consistency or with increasing wetness from the semi-solid to the plastic consistency.  Plastic limit is the lower limit of the plastic state. A small increase in moisture above the plastic limit destroys cohesion of the soil. so that is the importance of plastic limit test. Plastic Limit test is defined by ASTM standard test method D 431.

Plastic Limit apparatus

Plastic limit apparatus are:

  • Plastic limit plate, 300×300 mm
  • Stainless steel rod 3 mm dia.
  • Mixing dish 120 mm dia.
  • Flexible spatula
  • Moisture content tin dia. 75 x 30 mm (Q.ty 6)

plastic limit apparatus

Plastic Limit Test Procedure

Here is plastic limit test procedure. The plastic limit (PL) is determined by rolling out a thread of the fine portion of a soil on a flat, non-porous surface. The procedure is defined in ASTM Standard D 4318. If the soil is at a moisture content where its behavior is plastic, this thread will retain its shape down to a very narrow diameter. The sample can then be remoulded and the test repeated. As the moisture content falls due to evaporation, the thread will begin to break apart at larger diameters. The plastic limit is defined as the moisture content where the thread breaks apart at a diameter of 3.2 mm (about 1/8 inch). A soil is considered non-plastic if a thread cannot be rolled out down to 3.2 mm at any moisture possible.

For more detail about Plastic Limit Test, you can check this following youtube video:

Plastic limit test lab report

Plastic limit test lab report should be put in the following datasheet:

Sl. No.

Observations and Calculations

Determination No.






Moisture content container number





Mass of empty container ()

Sponsored Links :





Mass of container + wet soil ()





Mass of container + dry soil ()






Mass of water =





Mass of dry  soil =





Water content = w = [(5) / (6)] x 100




Plastic Limit Graph

The result of this plastic limit should presented as plastic limit graph in relationship with liquid limit. Below is an example of plastic limit graph as a result

plastic limit graph

So that is all about Plastic Limit Test Procedure. We think that it is good information about Plastic Limit Test Procedure. We hope that this information is useful for you. Please share if you think that this information can be useful for others. If you need more article related to Plastic Limit Test Procedure you can simply subscribe this blog. Thanks for visiting and have a nice browsing. source:

Leave a Reply