# Any soil or clay experts **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [November 22, 2014, 9:17pm UTC](https://boards.straightdope.com/t/any-soil-or-clay-experts/705363 "2014-11-22T21:17:22Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [November 22, 2014, 9:17pm UTC](https://boards.straightdope.com/t/any-soil-or-clay-experts/705363/1 "2014-11-22T21:17:22Z")
I am working on something with a clay and sand base that I need to have a little bit of control over how hard it is when it dries. I have played around with sand and clay proportions, sand, clay and gypsum. And sand, clay. gypsum and sawdust. None of the above seem to be working. I have a feeling some kind of organic fiber might do the trick but I just can’t think of what form might be available, it needs to be fine and non toxic. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [November 23, 2014, 2:16am UTC](https://boards.straightdope.com/t/any-soil-or-clay-experts/705363/2 "2014-11-23T02:16:22Z")
Straw is used to strengthen earthen structures, adobe is an example of that. I don’t know that it will harden the material though. Usually earthen material has to be baked to harden, it can be baked with fiber in it, but that’s for large thinks like bricks and ovens. What are you making? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 23, 2014, 8:43am UTC](https://boards.straightdope.com/t/any-soil-or-clay-experts/705363/3 "2014-11-23T08:43:19Z")
> [@HoneyBadgerDC](#): > > I am working on something with a clay and sand base that I need to have a little bit of control over how hard it is when it dries. This might sound like a dumb question, but what is the opposite of ‘hard’ in this context - do you mean that you want it to be flexible-not-hard, or do you mean you want it to be crumbly-not-hard? If the former, you maybe need to add something like a resin (PVA glue or one of the waterproof variants thereof maybe). If the latter… dunno… ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [November 23, 2014, 10:58am UTC](https://boards.straightdope.com/t/any-soil-or-clay-experts/705363/4 "2014-11-23T10:58:51Z")
Regular adobe clay and sand mix dry just a little bit too hard. I need soemthing that will make it a tad softer as in more scratchable. But not destroy the structure and make it crumbly. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 23, 2014, 6:55pm UTC](https://boards.straightdope.com/t/any-soil-or-clay-experts/705363/5 "2014-11-23T18:55:10Z")
Maybe powdered chalk or slaked lime. I think you’re going to need something like a pug mill to blend it thoroughly. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [November 23, 2014, 8:54pm UTC](https://boards.straightdope.com/t/any-soil-or-clay-experts/705363/6 "2014-11-23T20:54:03Z")
> [@Mangetout](#): > > Maybe powdered chalk or slaked lime. I think you’re going to need something like a pug mill to blend it thoroughly. I will give that lime a try. When I blend it I use a paint mixer on my drill and have a wet mud similar to cement. ---
**Author:** ![butler1850](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@butler1850](https://boards.straightdope.com/u/butler1850)\ **Post date:** [November 26, 2014, 7:28pm UTC](https://boards.straightdope.com/t/any-soil-or-clay-experts/705363/7 "2014-11-26T19:28:37Z")
Slaked lime will dry hard hard hard. It turns back into limestone as it absorbs CO2. It’s often used as a waterproof coating (vapor can penetrate) on cob/clay ovens. I can tell you that of the two cob ovens I’ve built, mine is hard as a rock, and used good marine clay. The 2nd one I built used a very silty clay, and is soft to the touch and crumbly… it’ll be rebuilt next fall with better clay. Add some very fine silty clay/sand/mud and it’ll soften the mix right up.