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black_brook t1_jb3roe5 wrote

Reply to comment by Indemnity4 in Why does sand keep clay from shrinking as it dries? by UnderBridg

That doesn't really explain what was asked though. How does the grog or sand slow down shrinkage?

Also how does having the grog or sand allow some of the clay to melt to fill in the voids? Why wouldn't that happen also without the grog?

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WazWaz t1_jb3ykr9 wrote

For the obvious case, there is less material shrinking. If the mixture is 50% grog, then clay that otherwise shrank by 10% should at most shrink by 5% since the sand won't shrink at all.

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[deleted] t1_jb413sr wrote

[removed]

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black_brook t1_jb44w0j wrote

Also "grog particles don't shrink" does not explain anything because clay partials don't shrink either. They condense by sliding together like u/Indemnity4 explained. I assume the grog particles must block some of the clay particles from sliding together and affect shrinkage that way, but that is only an unexpert guess.

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jeffersonairmattress t1_jb5udhi wrote

They sort of obliquely refer to it, but omitted the attraction of clay to the surface of the grog/sand particles- the clay would rather stick to each particle than allow gravity or other force to separate them. this bond is “fluxed” by moisture while workable (a pug or other milling process acting just like a mason back-buttering stone/brick/tile) but once smeared all over each particle, the drying phase doesn’t weaken the bond and the particles of sand are each captured by clay, the clay wants to stick to itself and the sand so it cannot shrink- the loss of moisture instead creating tiny pores and a lattice of strong bonds like a huge brick cube. During firing, the clay is welded/“brazed” to each particle so you get enormous compressive strength.

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