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[Cob] Marlin's rubble trenchPeter Ellis dukegavin at hotmail.com
Tue Nov 1 14:15:38 PST 2005
It seems to me that the material in that trench isn't chosen just for its loadbearing character - in fact, might even not be primarily for loadbearing qualities. I would expect that if it's not going to be a monolithic waterproof block (say poured concrete with a waterproofing coating) that it is very important for water to flow through it readily. No matter how well the material can withstand compression, water freezing and thawing within it *will* break it down. I would go along with Marlin on this one. Peter >From: Marlin Nissen <marlin_nissen at yahoo.com> >To: Mary Lou McFarland <louiethefifth at hotmail.com>, Coblist at deatech.com >Subject: Re: [Cob] Marlin's rubble trench >Date: Tue, 1 Nov 2005 08:21:38 -0800 (PST) > >We used 'river stone' or washed stone - 1 , 1 1/2 >inches usually...it's actually from glacial drop >around here. > >I have read (and it made sense based upon experience) >that crushed limestone (finds etc.) packs down and >actually becomes a type of lime/mud. If you drive on >country roads (and I know you do, you're probably >happy that it's not just dirt roads where you live!) >you see the limestone and fines break down into finer >and finer particles on the gravel roads. > >I assume underground that small limestone particles >pack down into this same fine mud. While that may be >'weight bearing' for awhile it also concentrates >water, possibly heaves and can become a mud flow >instead of foundation. Eventually, even if it's >decades, a foundation of crushed limestone/fines seems >like it would become indistinguishable from the mud >around the foundation. That's what road base becomes >as it breaks down if you dig into it with backhoe. >I've seen the underlayers of a gravel road and it >didn't look like a good foundation to me. Potholes, >ripples, trenches, heave cracks ..... > >UNcrushable glacial washed stones will never (in our >short lifetimes or human span) breakdown, drains water >around them very well and supports and distributes >weight very well. We even put landscape fabric around >the sides of the trench to try to keep all >organic/compactible matter out of the rubble trench >itself. On a house I'd try bentonite or another >barrier as a skirt going out from the foundation to >make it dry and better insulated as well. > >BTW, a sandy/fines subfloor seems very different as >it's not expposed to outside water (different drainage >and temp shifts) so it's main function is to allow >floor blocks to be layed or a thin layer of cob on top >of it. When it's exposed to mud it becomes ONE with >the mud. Sand still seems better then limestone as it >too doesn't really ever breakdown and is excellent of >nestling something into it like concrete or >flagstones. > >Marlin > >--- Mary Lou McFarland <louiethefifth at hotmail.com> >wrote: > > > Marlin you mentioned in your post that you like the > > washed gravel over the > > crushed limestone. Just wondering why you had that > > preference. Hadn't > > thought about it before but had assumed that I would > > use the crushed stuff > > because of it's greater stability when taking on > > weight or impact like > > floor or arena base or shoulders on secondary > > highways. For clarification, > > when you say crushed limestone, I am assuming that > > you mean what we call > > base gravel around here and it has all the fines in > > it and that is what > > gives it it's strength. Also wondered what size you > > usually go with. > > > > > > > > _______________________________________________ > > Coblist mailing list > > Coblist at deatech.com > > http://www.deatech.com/mailman/listinfo/coblist > > > > > >__________________________________ >Yahoo! FareChase: Search multiple travel sites in one click. >http://farechase.yahoo.com > >_______________________________________________ >Coblist mailing list >Coblist at deatech.com >http://www.deatech.com/mailman/listinfo/coblist
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