Pounding Vs. Rolling Slabs

[Biglou13]

bob my big tile is still drying  big for me 11 x 15 x 1/2 so nothing conclusive yet,     bob how did you transfer said tiles from roller to drying surface?   also i think some error may have entered at tile on clay wafer.   as stated above the silica or other high refractory between shelf and tile acts more like ball bearings as clay shrinks in firing.   if you re make     can you pound some.... finish on roller,    then   just roller some and see what the difference is, then fire some on silca or other high refractory, some one clay wafers,       

 

were clay wafers bisque fired also

 

until your post i was assuming it was the drying process that is major determining factor in warping. 

[Bob Coyle]

I looked up several sites on the internet that talked about forming tiles.

 

One of the things they said was that lifting a tile off the bat that you roll it on can cause warping. So I rolled the tiles on a board then cut them then inverted the board onto the drywall and just let it flop off.

 

I then stacked the tiles and drywall sandwich so it was about five high and put a pound weight on top.

 

I let these dry for about three weeks ( in Santa Fe the humidity is about 15% if that)

 

I removed the tiles and placed each of them them on five per-fired clay disks about 3/4†wide and 3/16†thick. I fired them at the normal cone 5-6 firing I usually do.

They came out warped. Some worse than others. Didn't seem to have anything to do with kiln placement.

 

Maybe I need a much slower firing? I think I did everything else right

[Biglou13]

pictures of warped tiles?

[oldlady]

there is a brand new segment of video of someone making tiles.  it is out today at the cad site.  i want to flip the clay he is working on and trim it better but that is why there are so many different ways of working.  check it out.

 

i put a post between bob coyle and big lou but it is not there.  did i miss that da&*_)^&   POST button again???

 

the question is are you putting these nicely flattened tiles on top of the disks as though they are feet at the corners?  i can see sagging like something in a hammock if that is the case.  lay the tiles flat or on a bed of sand or grog so they can slide around as they shrink.

[Bob Coyle]

The tiles are supported with five buttons. four on the edges and one in the center.

 

Do you have a link address to the new video?

[LovesPurple]

I have done hundreds of tiles, big and small, and have had very little warpage.  I bisque fire them standing up in tile racks.  I glaze fire them with one small stilt under them, or stacked horizontally in tile racks.  Maybe it is your clay. 

[perkolator]

For me it depends on how big of a slab I'm making and the intended purpose - but my opinions are slightly skewed since we usually do large-scale sculpture in our studio.  If it's just a slab of clay that is going to be added to something else or further manipulated (like made into a large hand-built cylinder) then I will just make by hand (pound and throw/stretch) or put it in a slab roller for speed because it doesn't really matter a whole lot.  I find that slab-rolled slabs tend to warp if not flipped over, or depending on how they were picked up, also depends on thickness.   You'd be amazed at how much warping you can achieve on a a 3/8" thick slab made on a roller without being flipped over when being made. very seldom do I use a slab roller for a slab smaller than 18"x18" - it's easier and faster to make smaller than this by hand.

 

If it's a structural slab that needs to stay flat, or a large slab (large slab for me is 24"x36" - same size as my large ware boards, and maybe 1-2" thick) then I will usually pound it by hand and sometimes roll it flat on the slab roller after I've done most of the work by hand to get rid of high-spots, but not always.  Usually for the largest slabs I will throw clay directly onto the plywood board in baseball-sized chunks, making sure they overlap.  Then I'll pound the hell out of it to even out the surface, sometimes walking on it barefooted or pounding with a 2x4.  To get an even surface, I'll first rake my fingernails across it in opposing directions, then a stiff rib tool in the same manner - usually works quite well as long as you go diagonal opposing directions.  I ALWAYS make sure to flip the slab over and compress from the other side - to flip a large slab, sandwich it with two boards, grab it tight and flip quickly (or with help).  If it's a large, thick slab that needs to stay flat, I will usually wrap the edges with plastic or even make a "frame" to build the slab in so the sides dry slower (since more surface are for air to wick away from corners = more prone to cracking on the sides), and the edges can get compressed using the frame as well.

 

I usually once-fire a lot of sculpture, so when firing large slabs like this I like to prop them up on a fields of 1" balls of kiln putty/wadding (equal parts silica, kaolin, grog) so that they stay flat and are evenly supported.  I suppose a bed of grog/sand would work but that'd only work on the base-level of a kiln stack for me unless it's all bisk.  sometimes we'll fire a large slab like this on edge, leaning against the bricks supporting the stack, only really warp if the slab was poorly constructed IMO.

 

I will definitely have to start experimenting with "dropping" a slab after it's made to reorient the particulates, to see if it makes any difference.  I recently learned about this and have never tried it before.  sounds like it makes some sense.

[Bob Coyle]

I have done hundreds of tiles, big and small, and have had very little warpage.  I bisque fire them standing up in tile racks.  I glaze fire them with one small stilt under them, or stacked horizontally in tile racks.  Maybe it is your clay. 

Could be. I'm using MR-5 which is the same clay I use for throwing.

[Biglou13]

how does grog/ grit  (wedged into factory clays) factor into the warpage equation?  and does grit size have affect?