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  • From: Clansgian AT wmconnect.com
  • To: homestead AT lists.ibiblio.org
  • Subject: Re: [Homestead] Stone Walls
  • Date: Fri, 6 Jun 2008 12:04:20 EDT



> >Of course if you overdo it and make it too thin it
> will not be strong enough, but if you put the least
> amount of water possible it won't fill the voids.
> This application would not require the strength of
> something like a loading dock

THe old saw that drier is stronger and wetter is weaker is over simplistic.
Too dry is far weaker than too wet because the unoxidized dust does not get
distributed around the aggregate well enough.

Mortar or condrete that is rather wet will be weaker initially, but a
mysterious thing about concrete is that it becomes stronger with time.
Initially the
CaO (and other similar molecules) combine with water to make Ca(HO)2. As the
water is driven off and replaced by carbon dioxide CaC03 is formed. The
exact amount of water means that the exchange of H2O for CO2 is quicker and
the
concrete sets harder quicker.

What gives concrete its strength, however, is that the calcium atoms will
randomly begin to share bonds. This continues for hundreds of years so the
properly made concrete or mortar continues to harden for years.

Adding extra lime (CaO) to the portland is done to make the mix easier to
work and stick to the work surfaces. It weakens the concrete. The amount of
lime that is in concrete is the right amount already. If you don't need
rock
hard mortar joints, then adding lime to 'fluff' up the mixture does not harm.

The foundation of my house is made of laid stone. A sort of permanent slip
form of 4" block was laid straight for the inside wall, stones laid 12" thick
outside that. The space in between the stones and block was poured full of
concrete, and as has been suggested here, it was mixed thin so that it would
fill
the form completely.

Understanding what hardens concrete in the long run, I used limestone sand
rather than silica sand. THe paces where this mix filled between stones, I'm
not saying you can't break it, but you' better bring a lunch and plan on
staying
all day.

A mason was visiting when I was doing the masonry of the house. Along the
concrete footing were bits of conventional mortar I had used building some
inconsequential parts of walls and bits of the above described mix. He
picked up
one of the mason's hammers and was idly chipping up the bits of mortar while
were talking until he came to none of the bits made of limestone sand. He
hit
it and the hammer jarred in his hand, the bit or mortar didn't move. He hit
it
harder and then harder. A tiny bit chipped off but the rest stayed firmly
fixed. "Damn, " he says, "What the hell is that stuff??"

Just look beyong the dry-good, wet-bad saw to how concrete works. </HTML>




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