Replies

1. 
   jigs_n_fixtures@icloud.com | Aug 04, 2008 07:08am | #1

   You have to be sure that it is really clay you are dealing with, and that there are no sulfates or sulfites in the soil. 

   The sulfates and sulfites are more soluble in water than the lime.  If you add lime to the soil, the soil will shed the sulfites and sulfates to dissolve the lime.  The resulting crystals that form are several time larger than the lime they replace, and will cause heaving. 

   True lime stabilization requires that the lime be mixed into the soil in sufficient quantity to bring the pH of the soil above 11.  Typically this requires large specialized equipment, that will be expensive to mobilize to your site, unless they happen to be in the vicinity doing work.  If you have a large area to do, it makes sense.  But not for a typical residential structure. 

   You will probably be better of over excavating the soils, and being sure they are well compacted at higher than "optimal" moisture.  Then construct a post tensioned slab on a good gravel foundation, with a vapor barrier between the gravel and the native soil. 

   The final step in making this work is a xeriscape landscaping to avoid moisture near the slab. 

   The only way to know for sure whether treating the soil with lime or Portland cement make sense is to hire a geotechnical engineer to do the testing, and see what will be required.  If you are working on a problem site, hiring a good geotechnical engineer with local knowledge will be money well spent.  They will be able to recommend the most cost effective, (and acceptable to the permitting agencies), solution. 

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   Edited 8/4/2008 12:12 am ET by Jigs-n-fixtures

   
   

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   Edited 8/4/2008 12:32 am ET by Jigs-n-fixtures

2. 
   Hiker | Aug 04, 2008 02:53pm | #2

   Most clay soil treatment utilizes quicklime-not hydrated lime.  Different beasts entirely.  A quick call to local agriculture agency will be helpful.

   Bruce