Tips for Using Soft Slabs to Make Pottery

Ian Marsh’s dropped dish has taken the shape of the wooden frame. Dia: approx. 30 cm (11 3/4in.) square. Photos: Ian Marsh.

Ian Marsh’s dropped dish has taken the shape of the wooden frame. Dia: approx. 30 cm (11 3/4in.) square. Photos: Ian Marsh.

I have been so fired up about slab built pottery lately. In today’s post, we’ll concentrate on working with soft slabs in particular. If you’ve ever used soft slabs, you know that they are extra susceptible to finger marks, distortion and collapse. This posts contains tips to help avoid those problems and a project that takes advantage of soft slab malleability to make some really cool dishes. – Jennifer Poellot Harnetty, editor.


In From a Slab of Clay you’ll learn about what it takes to start out on a journey that’s sure to last a lifetime. From setting up a proper working space to selecting the right tools and equipment—including complete instructions for building your own slab roller—Daryl doesn’t miss any details for you to consider to assure your success.

Wooden frames of varying sizes make useful molds.

Tips for Working with Soft Slabs

When the slab is first prepared, it is generally best to resist picking it up by its edges, as at this stage it is prone to stretching and distortion. Even when laid down again, the slab has a tendency to remember this change of shape, and will try to recreate it during the drying cycle.

 

Ian Marsh constructs a dish by use of a wood frame. Soft slabs are overlapped.

When rolled out, the slab often sticks to the cloth or other surface, and may resist being picked up at all. The solution is to peel the cloth from the clay rather than try to pick the clay from the cloth. If you sandwich the clay and cloth between boards, and turn them over as one, the cloth can easily be removed from the clay without distortion of the slab. A paper sheet placed on the slab before it is turned over onto another board will assist drying and allow movement of the slab from one place to another. I use brown wrapping/parcel paper when available, as this resists tearing and comes off in one piece, even when wet.

It is best to make all the slabs for a piece at the same time so that they contain similar amounts of moisture throughout assembly. When you are in production mode, it is useful to be able to stack the slabs one on top of another until they are ready for use. Layers of paper will prevent them from sticking together.

Just one cautionary note: if left for an extended period of many days, newspaper will soften to the point of disintegration, go moldy, and need to be scraped off with a metal kidney. This is the last thing you need when you are finally trying to get going.

Slabs join securely and take on pleasing contours when dropped from waist height (note supporting board placed underneath first).

The Drop Technique

With simple slump or hump molds, bowls, dishes or shell-like shapes are possible. We get pleasure out of a simple drop technique. Place the soft slab over a wooden dish mold, similar to a picture frame. Place the frame and clay on a supporting board and drop it from waist height onto the floor. Its own weight and gravity will force the slab into the mold on impact (with a satisfying bang). This method allows very wet slabs to be instantly shaped into bowls or plates without the surface of the clay being touched or smudged. This is helpful when slip decoration has been applied.

To watch a video clip on slab building with soft slabs, check out this post!

 

**First published in September 2010
Comments
  • Forget the paper! I’ve been slab building on a production level for a couple of decades, and, after the slab roller, the indispensable tool in the studio is Tyvek (housewrap).

    You can buy it at Lowes/Home Depot, in 8 and 4 foot widths. Not exactly cheap, but it lasts for years.

    I use a Red Devil “Trim guard & wallpaper smoother” to remove the canvas texture, then put a piece of Tyvek on the slab, a piece of 1/4″ plywood on that, and flip the whole thing over. Peel the canvas off, squeegee, and you’re ready to go!

    For the techies, Tyvek is a breathable membrane that allows moisture to pass through, but not air infiltration, so your house stays warm and cozy- and your clay doesn’t dry out unevenly.

  • Thanks Ian never thought of dropping. Thanks for the tip Steve.

  • Forget the canvas. Forfet the Tyvek. For past ten years I’ve been rolling slabs by sandwiching between two pieces of cheap smooth floor linoleum, with the PAPER SIDE NEXT TO THE CLAY and the slick lineolem next to the rollers.

    Paperside doesn’t stick to the clay and lineolum doesn’t stick to slab rollers. Extra bonus it’s sturdy enough to support large slabs when moving them withoutwarping and it lasts a long time.

  • Steve, I misinterpreted your comment. My comment simply is a way to roll without marks and not use canvas that stretches and have a substrata to support slabs when moving from roller to workspace. But like your technique to have Tyvek end up on the underside. I assume you are able to leave it in place on the underside as it dries?

  • Great idea! Can’t wait to throw some down. Where do you get the wooden forms?

  • I find that butter muslin is best for rolling out slabs on as it gives to let the clay stretch. Linda

  • Yes, Barbara, the clay stays on the Tyvek until it is ready to put on a hump mold. Large (15″-20″) pieces stay on the Tyvek, which is lifted by the edges, draped on a hump mold, then peeled off, so the clay is never touched, never distorted. Warping is very, very rare.

    A tip: Keep you eye out for construction sites. A lovely handmade bowl can often be traded for a few feet of Tyvek cut from a hundred foot roll. . .

  • as far as making wood frames i like using styrofoam . I used some styrofaom forms at Appalachian Craft Center and I made my favorite soft slab piece, It was a while ago. I just finally got some sheets of styroform and will make a bunch of forms. Now I need a hot knife to cut the foam board.

  • When I take my clay off the slab roller I lay it on a piece of plaster board, roll 1 more time with a rolling pin, check for air bubbles, and wash surface with damp spunge flip it over wash other side. I the take dry cleaner bag between clay and whatever form I use.

  • For those of us who only need a small amount of Tyvek, you can buy it by the foot (it’s 9′ wide) on ebay.

  • Mark you can get a hot knife for foam from Harbor Freight.

  • I dedicate myself to making plaques with Faith messages. I only use the canvas over and under the clay, roll it and use a soft moist sponge to clear away the canvas marks. Sometimes, I also place the clay between a sheet of newspaper and roll it between the two canvas pieces.

  • I like the heavy duty interfacing found at fabric stores for rolling slabs,it also makes a great working surface.

  • great ideas all! home depot/lowes also sell heavy weight brown construction paper (don’t know name) in 3 ft rolls in paint “drop cloth” dept. heavy enuff and good for patterns too.
    mark—fab your own styro-cutter—-nichrome(sp?) wire stretched across u-shaped pvc handle(like huge cheese cutter) / electric wire / battery charger.

  • If you connect to a fan dimmer or a Variac (variable transformer), you can run a Nichrome wire foam-cutter from stepped-down house current. Make sure it’s all grounded, and that you never touch the wire while it’s running. A Variac is safer, because it actually lowers the voltage instead of “chopping” the power’s waveform.

    Depending on the gauge of the wire, either of these circuits will allow you to set exactly the amount of heat needed to cut smoothly, without flames or wire failure. Remember that the heavier the wire, the more current you’ll need. I like 20 or 22 Ga.

    There are 2 kinds of foam for this process: polystyrene foam, and Styrofoam. Both have different cell structure; the latter is made of foam beads rammed together, the former is crisp, with larger visible cells. Both make stinky smoke when cut. NEVER try this with polyurethane foams…you’ll be making cyanide gas!

  • The post office did have free mailing envelopes made out of Tyvec if you just need a small piece to try out. It isn’t written on them though. You can tell the difference from regular paper and cardboard because it doesn’t tear easily. Fran

  • The floppy FedEx and UPS envelopes also are Tyvek the others are cardboard. You can cafefully expand the envelopes and come up with a pretty good sized piece.

  • Your are all such smart, beautiful, talented and helpful people. I don’t think I’ve ever seen a list of postings with so many helpful hints and ideas. Cheers, CAD people, and thanks!

  • I do a lot of work with soft slabs. Thanks for sharing your techniques. A question for Charles about the envelopes….the usps has floppy envelopes for priority mail….those envelopes are tyvek? They are ‘still’ free at the post office. I also use pantyhose as a release for some forms.

  • I bought the hot knife yesterday at Harbor Freight for $20 ,cant wait to try it. It will have to wait a few days because im firing my wood kiln this weekend
    Thanks again Shawn

  • “Tyvek” house wrap is not known in my country, and i hardly get deliveries from UPS… but i inherited old very fine (almost silk) white cotton bed sheets. i tore one of them to various sizes, and i use it to roll the clay on, the fabric leaves hardly any marks, and absorbs the moist while rolling. any mark left , wrinkle like, can be easily removed with semi wet sponge. this bed sheet can be washed — if used for colored clay.

  • Thanks for all of your comments! I feel like I’m in a class when I sit down with my coffee for Ceramics Arts Daily! I’m hoping to purchase a slab roller this winter. What are your recommendations for width and brand?

  • The wood execution is good, but this looks like a 5 year old put it together.

  • Kathleen, there’s some good info right on this site!

    I’ve been using a Bailey Dual Roller Drive, 30″ wide, for more than ten years, running about a ton a month thru it. Before the dual drive unit i had a single drive, and tiles warped. That can be overcome by flipping the canvas/board and running it thru again, but what a pain! The dual rollers squeeze the clay top and bottom (no drive board) so the clay doesn’t get unevenly stressed. I can make 18″ square tiles less than a quarter inch thick, and they don’t warp. Magic!

  • Oil up a dish easy or if doing a long tube shape use a plumbers pipe and cut a gap in it for drying out ..then slide off

  • I’m new to using clay for pottery and to slab work and I must say that this is a most valuable site. Thank you everyone for your extraordinary “hand on” tips and expertise.

    I am wondering whether I can use green soap as a release agent for using harder slabs on ceramic platters or stainless steel bowls used as slump molds. I can’t find any information on what to use to release the clay. I have been using saran wrap or thin plastic, but that leaves wrinkles in the clay. I want to keep the clay in the mold while I build up a bas relief image and when it gets leather hard, the wrinkles seem hard to eliminate on the back side of the platter or bowl. Any hints would be appreciated.

  • Ruth…I use Pam spray as a release agent, works great. If you have wrinkles from using plastic wrap, you can gently sand them out using a green scrubby, the kind you buy in the grocery store for dishes. Just sand gently and marks magically disappear. I also have used landscaping fabric to roll slabs. It is slightly absorbent and leaves a smoother texture than canvas. I leave the slabs on it when moving them, sandwich style, flip to finish smoothing. Never have to pick the slab up that way and it does cut down on warping. Good luck!

  • Thanks Jacki, I’ll try the Pam and the scrubby.

  • Wonderful idea, also for an upright pot, throwing the slab onto the pot also create wonderful happenings.

  • I’m so thankful I’ve found this place:)…thanks for all the tips, heading to the slab roller now to try these ideas out.

  • WOW…this is the most posting I have seen on any artical. Thank you for th great post and the wonderful ideas. As a student, and my main project this semester is tiles, this has been a very good artical to read, and the commits are great. thank you all for posting and helping the rest of us out.

  • Great site – just joined and love this! Thank you all!

  • Kathleen, Steve’s comments posted Sept 4th are right on

    Bailey 30″ slab roller is the way to go – once set up in your space you can really get rolling…….

  • You can also use a band saw to cut styrofoam for your forms…I use canvas stretchers for a form as they come in 1″ increments.

  • I use the foam sheet sold at wallmart…they come in all sizes and colours… no marks at all…

  • Okay, so really dumb question. What would you build the frame in the upper left corner of that picture with? Just a miter saw and rip down a board? Or is there an easier item that can just be cut to length – like a type of molding or frame stock or something?

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