Slipcasting for tiles?

[moh]

Hi all,

I recently did couple of large trade shows and the overwhelming number of feedback received was about making my work into large tiles. 12", 18" squares.
My work includes no undercuts, but very fine inlays that need mishima-ed. 

I purchased a electric slab roller for the purpose but am getting feedback that it makes the particles align in weird ways and I haven't been able to get it completely flat (tried the drywall sandwiching, no overhandling)

With that said, I'm thinking to go the route of slipcasting to fill in the gap between where I'm now and where I will be when a RAM becomes financially viable. Any cons and pros about slipcasting tiles would be appreciated.

 

[hitchmss]

I have no experience with slip casting tiles, however I do with handmade, pressed tiles. After you roll out your slab in your slab roller, are you compressing the slab in numerous directions to remove the memory?

We used to roll our slabs so they would be about 1/4"-3/8" thicker than the tiles final pressed thickness; we'd then use a large drywall knife (12-14") and would compress the slab in numerous directions (left to right,  right to left, up and down, down and up) a couple of times, then the slab would get cut to the mold's size and would be pressed; after the tile was pressed, the excess was wired off, and the back of the tile was compressed with soft rib (L-R, R-L, U-D, D-U a couple more times).

Whenever the slab was moved (from roller to workstation, from work table top to mold cavity, from mold cavity to ware board, from ware board to drying rack) the slab was kept as flat as possible, and always transferred by a board, not by picking it up and carrying it by hands. The tiles were dried in a tented box (frame made from 2x4's, plastic all around, carts inside, numerous small fans, and dehumidifier), and they were placed on fluorescent light box diffusers (1/4" x 1/4" squares in a big grid), which were placed on the shelves of wire carts, which evened out the drying across the tile. The dehumidifier was set to run around 50-60% relative humidity (take out a lot of moisture in air, but also not dry the tiles in a day), and the small oscillating fans (table top or smaller size) placed in the corners (top & bottom) of the room moved the air in a consistent pattern, eliminating "dead zones".

Doing all of this produced wonderfully flat hand pressed tiles (done in arbor, and hydraulic presses, but no where the force of a 30 ton ram press). The tiles were fired on cordierite kiln shelves, which were about as flat as we could get them, but if we had advancers (about as perfectly flat as you'll ever get in kiln shelves) the tiles would have settled onto the shelf during firing, and been even flatter, if they had any warp at all.

While slip casting may eliminate a lot of the memory/warping issues you are having, it comes with its own set of issues/nuances, especially if you have little/no experience with it. I would suggest trying to make what you have work ( I know it can) since you already have it all there and going. If you have to retune your glazes because your slip body is a different color, or if you have to make new prototypes and molds because the slip shrinks more.....

[Mark C.]

This is an important point

( After you roll out your slab in your slab roller, are you compressing the slab in numerous directions to remove the memory?)

After that the sandwich with the sheetrock as you have done you can stack them up as well. Dry really slow.

The only other thing is some matt glazes can pull the tiles up when fired-is this an issue??

slip tiles in my experience are very weak.

[Min]

1 hour ago, moh said:

I purchased a electric slab roller for the purpose but am getting feedback that it makes the particles align in weird ways and I haven't been able to get it completely flat (tried the drywall sandwiching, no overhandling)

If you are using the same plastic clay you use for throwing this could be the problem. 

[moh]

Thanks everyone for the tips.

What I've been doing -- if the tiles were to be 0.42" (3/8" once fired), start at 1.25" and work my way down in quarter increments, turning 90 degrees to ultimately end up at the 3/8".
It's been hit and miss. Now that you mention the cordierite kiln shelves, I think it may be the issue with my kiln shelves. I'll start debugging there... Those advancers don't come cheap (!!)

Note about glazes - my tiles are not glazed. I just sand the hell out of each one (bought a sandblaster for the purpose). 

@hitchmss -- did you build your own press?

@min - I use grollegg porcelain, something that was recommended to me as a tile clay

 

[hitchmss]

31 minutes ago, moh said:

Those advancers don't come cheap

Nope, but if you make your living firing ceramics, its a no brainer IMO.

In regards to building your own press; a couple of the presses in the shop were commercially built arbor presses which had been outfitted with a made in house press bed (numerous plywood layers laminated together, with softer foam layers to prevent mold breaking), and one of the presses was a large hydraulic press which was made from I beams, and a car jack. If you have any metal fab/welding experience its quite easy to build. Welding the frame is a little faster/easier, but it also means when you move it, it has to go as one unit. So if you make a very big one, be prepared to lift; if it was a light small frame, I would build it with through bolt connections, this way it could be broken down for transport. If you buy your metal from a scrap yard, and not virgin stock, youd likely spend no more than $150 for all your components (steel, jack, springs, plywood, assort fasteners). If you have to pay someone to do the metal fab it will get substantially more expensive, especially if you go to a specialized metal shop, but hopefully you know someone who could do the work for a case of beer, a steak dinner, and a set of dishware, or do it yourself!

@Min has it right in regards to the plasticity of your clay; the more plastic a clay, the more shrinkage which also relates to movement in your tile. I also agree with using a more fine grained particle for your clay body; it will press finer details, but I wouldnt choose a clay body that is devoid of some mixtures of particle sizes...just avoid anything below 60 mesh sand or grog. Depending on your tile design (go from high relief to low relief?) a more fine grained clay body may not handle the thermal shock in your firings as well either. I know at the shop where I worked we had some tiles that went from 2" thick, to 1" in a relatively short distance; drying and firing those tiles were more problematic and wanted to crack at those points. At this shop we used Bmix 5 with sand which worked well for most details; it had its own set of issues, but was the best choice at the time. A number of the designs had very fine (1/64-1/128") details in fur, hairs, feathers, grasses, all of which pressed just fine even though the body had a decent amount of sand in it. Being a throwing clay body it was quite plastic, but it worked fine for our purposes; the choice of locally stocked/supplied clay bodies at the time was limited, otherwise we would have chosen a more dedicated hand building/tile clay body.

[Mark C.]

Places like harbor frieght sell cheap presses as well.

Advancers ot new cordierites are a must for flat stiff.

Since your cross rolling -thats about as good as it gets. I think Mins suggestion on the body is a good solid one-it has to be the right clay body to stay flat.

When I made tile I used a fine grained stoneware . that stayed flay but the simi matt like to pull it up.

since you are not glazed a dense low shrickage clay would work well.

[neilestrick]

You can hand press tiles by pounding clay into the molds with a wide board, and cutting any excess off with a wire. I know several tile makers who do that and it works well. It eliminates the directional forces of a slab roller. I think the shelves are less of an issue, unless they are quite obviously warped. Corelite shelves are very flat, and don't cost any more than standard cordierite shelves. They are thick, however, so you lose a little kiln space. It's a fair tradeoff in my opinion. If the tile warp is worse than any warp of the shelf, then it's a clay issue. Tiles should be fired up slower, and cooled slower so that they go through the process evenly. A little silica sand on the shelf will also help, as it allows the tile to move during the firing.

[glazenerd]

Moh

look for a porcelain with a shrink rate in the 10.5 to 12 range. High plasticity in porcelain = higher memory.

unglazed once fire: try this stacking arrangement. Less drag, more pieces per square foot. I rarely loss a piece to inversion using this firing  stacking method.

i make this piece both ways: slab rolling then adding the raised deco. I have also slip cast this as well.

this piece starts as a 14 x 16, and ends up 12 x 14

[moh]

@hitchmss - If you press your tiles, why does it even need to be compressed in numerous directions before the pressing? I'd assume when the clay is out of the bag you can just wire it and press?

Thanks again everyone for the tips. Can't tell ya how it's good to hear there're solutions to the issues I've been having.

[hitchmss]

@moh The clay was initially ran through a pug mill, with an extrusion nozzle on the end of it; It would produce a 2" x (something like) 8-10" slab, and a full hopper on the VPM-80 produced about a 3' long extrusion. The extrusion was then run through a slab roller with the 3' end going through first (to make a long, wide slab). The slab roller would reduce the extrusion to about 1" thick (about half its original). Even though the slab roller was a bailey, and the action of the dual rollers helped eliminate any uneven stresses, we found that using a drywall knife to compress the slab in numerous directions helped with the warping. It also had the added benefit of removing the canvas texture. This "compressed" side was laid into the mold (lack of canvas texture produced cleaner pressings) and the tile was pressed. While a very powerful press (like a 30 ton RAM) would likely compress the clay so much, that any memory would be erased, because these were smaller presses, and the molds were made from #2 plaster (not nearly strong enough to handle the force from a 30 ton press), the pressing didnt likely remove the stress from the "uncompressed" side of the slab. As well, any excess clay from the pressing was wired off, which left a rough surface; so for compressions sake, and to clean up the back of the tile, the pressings all got burnished/compressed with a soft rib after pressing/wiring. As well, because the tiles could vary in thickness from one area of the tile to another, those different thicknesses were compressed at different rates. The ribbing helped even this compression out. While it is another step in the process, the ribbing of the back of the tiles took maybe 1 minute, and the benefits were worth it.

If I were pressing in a very powerful hydraulic press, with nice strong air release molds, and the mold surfaces were nice and perfectly clean/flat/smooth, I would just press the heck out of them, clean up my squeeze out, and call it good. Its amazing how much water is removed from the clay during a pressing like this, and how strong those pressings are because of the great amounts of compression.