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#1 gary_varner

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Posted 31 October 2011 - 02:05 PM

Hi all. 40 years ago I learned to throw and became fairly competent and then life intervened. This last year I had the strong desire to once again delve into pottery, took a few classes, bought a wheel, etc and am having a great time--except for tiles! I enjoy doing relief work with tiles but every time I join two slabs together, regardless of the size, as they dry they crack down the seam where they are joined. I score and slip but obviously I am doing something wrong. Can anyone give me a suggestion to get past this difficulty? Thanks so much!

Gary Varner

#2 Pres

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Posted 31 October 2011 - 04:42 PM

Hi all. 40 years ago I learned to throw and became fairly competent and then life intervened. This last year I had the strong desire to once again delve into pottery, took a few classes, bought a wheel, etc and am having a great time--except for tiles! I enjoy doing relief work with tiles but every time I join two slabs together, regardless of the size, as they dry they crack down the seam where they are joined. I score and slip but obviously I am doing something wrong. Can anyone give me a suggestion to get past this difficulty? Thanks so much!

Gary Varner


I would ask a few questions about your tiles. How large are you joining together? Are you allowing for invariable air pockets between the two pieces of clay? Do you use needle holes from the back of the slab up to allow air to escape? Are you doing anything to compress the slabs together, ie paddling, pressing, or re-rolling? What is your firing schedule? And finally. are you using slip or magic water to join the slabs together.

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#3 gary_varner

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Posted 31 October 2011 - 04:59 PM


Hi all. 40 years ago I learned to throw and became fairly competent and then life intervened. This last year I had the strong desire to once again delve into pottery, took a few classes, bought a wheel, etc and am having a great time--except for tiles! I enjoy doing relief work with tiles but every time I join two slabs together, regardless of the size, as they dry they crack down the seam where they are joined. I score and slip but obviously I am doing something wrong. Can anyone give me a suggestion to get past this difficulty? Thanks so much!

Gary Varner


I would ask a few questions about your tiles. How large are you joining together? Are you allowing for invariable air pockets between the two pieces of clay? Do you use needle holes from the back of the slab up to allow air to escape? Are you doing anything to compress the slabs together, ie paddling, pressing, or re-rolling? What is your firing schedule? And finally. are you using slip or magic water to join the slabs together.


The tiles are 10 x 5" with two 5x5 slabs joined or 10 x 10". They crack prior to firing--I never get that far with them! I always use a roller to compress and I have used both "magic water" and slip with the same results. Not sure if using needle holes will work as the cracking is always on the seam. Thanks for your post!

#4 lynny

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Posted 31 October 2011 - 05:43 PM

When I first read this I assumed you were joining 2 slabs on top of one another to carve relief through, but re-reading I think you are joining 2 slabs beside one another?
Difficult to describe your work in words.
But if that is the case (joining sides to sides) have you tried a 45o seam? ie cut the join seams at 45 degree rather than vertical.
This allows more surface area to be joined and it then is more stable.
Not sure if that helps, but I could not see any other reason for the seperation.
If you are joining one on top of the other I would definitely slow the drying time down by covering with plastic and slowly (over a week) open the bag up- this will reduce stress- particularly if one slab is thicker than the other
regards, Lyn

#5 gary_varner

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Posted 31 October 2011 - 05:50 PM

When I first read this I assumed you were joining 2 slabs on top of one another to carve relief through, but re-reading I think you are joining 2 slabs beside one another?
Difficult to describe your work in words.
But if that is the case (joining sides to sides) have you tried a 45o seam? ie cut the join seams at 45 degree rather than vertical.
This allows more surface area to be joined and it then is more stable.
Not sure if that helps, but I could not see any other reason for the seperation.
If you are joining one on top of the other I would definitely slow the drying time down by covering with plastic and slowly (over a week) open the bag up- this will reduce stress- particularly if one slab is thicker than the other
regards, Lyn



Sorry for my incomplete description--you are right. I am joining them side by side, not on top of the other. You suggestion sounds like a good one and I will try that! Thanks so much!

#6 TypicalGirl

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Posted 31 October 2011 - 08:43 PM

Hi Gary...
A couple of things I might suggest are #1, add a small coil of clay to the inside of the seam (see Keith Phillips doing so to the lif of his butter dish here:
http://ceramicartsda...-pottery-wheel/)

And perhaps really slow your drying time down.

Those things have helped me...
Cheers!

Cathi
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http://www.CNewlin.com

#7 gary_varner

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Posted 31 October 2011 - 10:00 PM

Hi Gary...
A couple of things I might suggest are #1, add a small coil of clay to the inside of the seam (see Keith Phillips doing so to the lif of his butter dish here:
http://ceramicartsda...-pottery-wheel/)

And perhaps really slow your drying time down.

Those things have helped me...
Cheers!

Cathi



Thanks Cathi--sounds like an excellent idea! Some things seem so simple but I sure didn't think of them! I'll give it a try tomorrow. Thanks again!!

Gary

#8 SShirley

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Posted 01 November 2011 - 11:29 AM

I saw a video online very recently (within the last two months I think) of a guy making slabs and joining them at the corner. I have searched for the video but can't find it. I thought it was on CAD, or you-tube, but can't find it anywhere. He was making a vessel of some kind, not a tile, but perhaps the technique could be adapted. Anyway, to avoid cracking, he slipped and scored as usual, joined the pieces and then stood it up and made deep cuts through the joined edges (perpendicular to the clay) with a knife lots of times, all the way up and down the length of the corner. It was real messy until he smoothed it afterward with a rib. He said it was to avoid cracking. Apparently cutting drawing the knife through the two pieces of clay had the effect of melding them together deep inside the joint. I had never seen anybody do it that way, and plan to try it.

It is similar to the "sewing" technique used by Stephani Stephenson in this video: http://ceramicartsda...tural-projects/


What is the reason for joining slabs side by side to make a bigger tile? I assume there is some reason you don't just do a big slab to start with. Just curious.

Sylvia

#9 Benhim

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Posted 02 November 2011 - 05:55 AM

I'd have to agree with Lynny about the 45 degree seams. I'd also agree with the compression, it's imperative that the seams are compressed. I use a soft rubber rib to compress exterior or flat seams, and a rubber wipe out tool for inside seams.

I'd also like to ask why you're joining 5" in slabs instead of making 10" slabs from the start?

I'd have to ask how you're making your slabs, is this a rolling pin kind of deal or are you pounding them out with a tile press, slab roller, wheel thrown slabs, hand slapped out slabs, mallet pounded slabs?

So aside from your joining/cracking issue I'd probably investigate a different way of making larger slabs. As far as drying goes, if it's a single slab you can make pieces stay flat by laying them out on a clean dry piece of dry wall with the exposed gypsum edges taped off, and then cover with another piece of drywall. The pressure will keep them flat, and the drywall will evenly pull moisture out of the pieces.

BenCo Ceramics


#10 lakesidepottery

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Posted 06 November 2011 - 09:35 AM

Hi Gary,

See some tips for preventing cracking in the links below. Good luck and let us know how it worked out.

Clay Drying and Firing Process

What is Magic Water, Magic Mud / Paper Clay and Recipe / Instructions

For several other tutorials and videos, vist our tips page at:

http://lakesidepotte...Pages/Tips.html


Patty and Morty
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543 Newfield Avenue
Stamford, CT 06905
203-323-2222
www.lakesidepottery.com

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#11 gary_varner

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Posted 10 November 2011 - 01:29 PM

Hi Gary,

See some tips for preventing cracking in the links below. Good luck and let us know how it worked out.

Clay Drying and Firing Process

What is Magic Water, Magic Mud / Paper Clay and Recipe / Instructions

For several other tutorials and videos, vist our tips page at:

http://lakesidepotte...Pages/Tips.html


Patty and Morty


Thanks all. The 45 degree cut seems like a good fix--at least so far. I don't have a slab roller so have to cut my slabs and then try to join them to make a larger piece. When I did that in the past to make a 12" x 12" slab they invaribly cracked down the middle after a few days drying. I made another larger slab over the weekend using the bias cut at the joint and so far no cracks!

Gary

#12 Ben

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Posted 11 November 2011 - 11:09 AM

I think you need to avoid the joint alltogether.
Here's how I do it.

I slam wedge a block of clay a little larger than my final dimensions say 12"x12"x twice the desired thickness.
Make sure the bottom of the block is completely pressed against your work surface with no wrinkles or voids.
I have pairs of sticks that I lay down one on either side of the slab then use a wire to cut the excess thickness away.
If you have a hard time keeping the wire tight you can make a frame like a large cheese cutter frame or adapt a bow saw frame.
I use multi strand stainless steel fishing cable. So strong and so thin.
Next trim the outer edges to their final dimensions.

The slam wedging eliminates spiraling and homogenizes the clay and allows working a large enough piece to eliminate the need to join pieces.
Of course, you do need quite a substantial table to work on or you will break it quickly.

Ben




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