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I'd like some tips on estimating clay needed for large slabs.  I'm aware that experience will help doing a ballpark estimate, or maybe even better.  My slab roller is 30", so that's the max in one dimension.  Some of my forms so far require a 30 x 30 slab,   My current method is to keep making slabs until I get one right, then mark on the form what it requires.  I'm hand rolling to get the first dimension, then using the slab roller to get the final size and set the final thickness.  The slab roller definitely doesn't like a large piece of clay more than 1 1/2" thick rolled to final thickness, usually somewhere around 1/4"

I'm guessing the max size I can get the Bailey roller to is about 30x40 or so.  Not very easy to make a second pass on a slab when dealing with something this size, 

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When I roll a slab this size on my Bailey  the first slab through is much thicker,  it is easier to handle but it is still heavy.   My final thickness is a half inch,  I don't like working  with thinner clay when hand building,    A practice roll will tell you how much you will need.   I am guessing around a half of bag.  Denice

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Just an idea but if you know the size of the finished slab (roughly) and you know the size of a bag of clay you could do the math and go by the volume of slab and clay bag. Laguna box of clay is 12X12X6 so one bag is approx 12X6X6 which has a volume of 430 cubic inches. Your 30X30X0.25" slab has a volume of 225 cubic inches. Since the bags of clay aren't quite as big as the box and to make the math easier I'm rounding the bag of clay down to 400 cubic inches.  225/400 rounds down to 9/16th of a bag of clay, or just over 1/2 a bag. 

 

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I found the fastest way to get to dimensions is by cutting rough 6x6in slabs off the block with slats at thickness. Cut em on a heavy bevel for at least a half inch join area, then overlap as many as you need to make your dimension. 

I hand seal the joins first, usually wet enough to not need water, it also remains thicker so compression back to size helps that seal.

Haven't had any problems. I don't mind the slight texture change near the joins. It'll probably look nicer ran thru the roller!

Sorce

Edited by Sorcery
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I cut my pugs down the length of them so they are already angled and you can do that with 1/3 or 1/2 or 2/3 depending on whats needed. My 30 inch baily with the long rolloff table can  doa slab 5 feet long if needed. I make it all in one pass. The Bailey is  an 30 inch electric  model and does whatever I dial up in one pass. Most slabs are 1/4 some 3/8 no thick stuff usually.

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On 12/28/2020 at 1:29 PM, Min said:

Just an idea but if you know the size of the finished slab (roughly) and you know the size of a bag of clay you could do the math and go by the volume of slab and clay bag. Laguna box of clay is 12X12X6 so one bag is approx 12X6X6 which has a volume of 430 cubic inches. Your 30X30X0.25" slab has a volume of 225 cubic inches. Since the bags of clay aren't quite as big as the box and to make the math easier I'm rounding the bag of clay down to 400 cubic inches.  225/400 rounds down to 9/16th of a bag of clay, or just over 1/2 a bag. 

 

I think this is the right approach.  I don't know where the math failure is here, but half a bag of clay will not give you a 30x30x 1/4" slab,  just from experience  estimate.  I don't know why Min's calculation is off.  The pug is a little smaller than  12x6x6 to actually measure it,   Not by that much (half). The rough calculation of 432 cubic inches by 25 pounds is  0.05 lbs per cubic inch. 

I rolled out a 1/4" slab and cut it to 12"x 12" and it weighed 4 lbs almost exactly.  That comes out to 0.11 lbs per cubic inch.  This seems to work for my calculation and gives me a better way to estimate what I need. 

30x30x .25= 225 x .11= 24.75  A whole bag.

 

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