How to roll a large clay slab - 70 - 100 cm

[VladCruceanu]

For the moment I don’t have a slab roller and I need to roll 2 large clay slabs - 70 cm x 50 cm and 100 cm x 70 cm. 

My clay comes in 10 kg packages. 

Tried to roll a 70 cm x 50 cm clay slab from 10 kg and I had 2 issues:

1. Coudn’t did it evenly.

2. In the end I had a small area.

How would an experienced potter do it without a slab roller machine? Is it doable?

[Magnolia Mud Research]

I roll small pieces to the proper thickness, and then join them together using a beveled edge at the joins.   tedious and time consuming keeping the small slabs moist ( I keep them on sheets of art foam and just stack the foam sheets) and doing the dance of joining.   use a rolling pin (originally the rolling pin was a wine bottle wrapped with newsprint) and sticks for thickness control.  

LT

[moh]

I'd try this:

Roll out thick first with a rolling pin. It'll probably be uneven. 
Then Use dowels as leveling guides on both ends and use a very thick dowel (they have those 2" ones) as a rolling pin alternative.

I've used this method and works well for me personally

[neilestrick]

Will you be manipulating/bending the slabs into shape after rolling, or will they stay flat? If you need to manipulate them, I would roll them in one piece. Joints will not survive handling very well. If they will stay flat, then joining smaller slabs can work. Also, if they're staying flat, have you considered how you will load a slab that large into the kiln?

[VladCruceanu]

37 minutes ago, neilestrick said:

Will you be manipulating/bending the slabs into shape after rolling, or will they stay flat? If you need to manipulate them, I would roll them in one piece. Joints will not survive handling very well. If they will stay flat, then joining smaller slabs can work. Also, if they're staying flat, have you considered how you will load a slab that large into the kiln?

I want to build a large pot in 2 ways:

1. By joining large slabs. I cut the bottom and the walls from slabs and then I join the pieces.

2. Creating the bottom from a large slab and them using the coil method.

In both ways I need to roll large slabs and I cannot find the right way. 10 kg of clay are very hard to roll evenly and are not enough for a 100 cm x 70 cm slab. 

Joining 2 large slabs seems impossible. How would I move them, push together and join? 

Starting with 10 kg of clay and rolling evenly will stress the clay a lot and the rolling pin is very long to cover 70 cm and very hard to press. 

How are people building large or very large pots? All of them have slab rollers or how they are doing it?

[neilestrick]

Large pots would be easier to build with coils or slab strips.

[Sofusryge]

Fill a pvc tube with concrete and use it as a roller. It will be sturdy and heavy, and you can scale it to your needs.

I think the real challenge will be to combine the slabs to make the pot. Slabs tend to be harder to handle as they get bigger, so very large slabs = very hard to handle.

/Sofus

[VladCruceanu]

7 minutes ago, neilestrick said:

Large pots would be easier to build with coils or slab strips.

When using coils, the bottom is not supposed to be made from a slab? How can I make a 100 cm x 70 cm even bottom other than from a slab? 

What do you mean by slab strips?

3 minutes ago, Sofusryge said:

Fill a pvc tube with concrete and use it as a roller. It will be sturdy and heavy, and you can scale it to your needs.

I think the real challenge will be to combine the slabs to make the pot. Slabs tend to be harder to handle as they get bigger, so very large slabs = very hard to handle.

/Sofus

Great idea, thanks!

[Benzine]

For rolling out large slabs, you could join smaller ones, as mentioned @Magnolia Mud Research, or you can just find a cylinder long enough to act as your rolling pin (This is assuming you are also using slats to give you a consistent thickness).  Wooden dowels work well for this, as you can buy some that are long enough to create a slab to the size you mention.  We don't work anywhere near that size, in my classroom, but when students want to go wider, than normal rolling pin width for a slab, I just unscrew the head off of the studio broom, wrap it in paper towels so it doesn't stick to the clay, and use that.  It's not ideal, but it works in a pinch!

As @neilestrick noted, for large pots, coils or clay strips are ideal.  It might not be as quick as using one large slab (Which you'd have to support anyway), but coils allow more control in the change of the surface, as you are only building a bit at a time.

In regards to your question of "Does the bottom of a coil pot need to be a slab?"  The answer is no, but I would personally recommend it.  Coiling the bottom, instead of using a slab, tends to crack more, during the drying and firing.  I would attribute that to  the clay not being compressed enough, same as wheel thrown work, that develops a "S-crack".    With a slab base, the clay is compressed as it is made, so it's really a non-issue. 

[Callie Beller Diesel]

For those not doing the conversions, 100 cm= 1 m = not quite 40".  10 Kg= 22 lbs.  This is a job best done in parts.

Vlad, here is a video of an American potter who studied with some Korean potters who make onggi jars, or really large jars for fermenting a lot of traditional Korean foods. In this video, I think the pot he's building is only about 1/3 the size I think you are describing if you want a 1 m base, but I believe the technique will be similar. It also begins with him wedging with a large hammer.  You might also try googling "onggi pottery videos" and see what you come up with in your location. 

 

[VladCruceanu]

6 hours ago, Callie Beller Diesel said:

For those not doing the conversions, 100 cm= 1 m = not quite 40".  10 Kg= 22 lbs.  This is a job best done in parts.

Vlad, here is a video of an American potter who studied with some Korean potters who make onggi jars, or really large jars for fermenting a lot of traditional Korean foods. In this video, I think the pot he's building is only about 1/3 the size I think you are describing if you want a 1 m base, but I believe the technique will be similar. It also begins with him wedging with a large hammer.  You might also try googling "onggi pottery videos" and see what you come up with in your location. 

 

 I am looking to build rectangular pots, the wheel is not helping me. 

I will use coils to build it but I need the flat, even base. 

[Callie Beller Diesel]

Even so. The video shows a reasonable method on how to go about that. Just use their low-technology method to get slab pieces, and then trim to shape. The method is used for large pots and will at least in theory address the structural issues one might encounter with large pots. And he's not using a motorized potter's wheel: the turntable is a really large banding wheel that you can find plans for easily online. It looks like a big electrical spool.

[oldlady]

vlad, if you want to see how the man in the video attaches the coils, watch you tube.  look for Joyce Michaud and watch the video that is 12.21 long.  she shows exactly how to do it.

she also shows how to make a base, if you make a square instead of a circle and work the s corners as you go, you would be able to do what you like.  you will need to find a way to work, whether walking backwards around the pot as you work or supporting it on a giant turning base using ball bearings. 

follow the steps shown in the korean video to condition the clay so it is more pliable, that pounding makes it softer and easier to work.  love his use of cloth to work it on.

[JohnnyK]

As for support of your slabs as you try to assemble your rectangular pots, you might consider rolling them out on a piece of plywood (for each of them) that is the same size as each side in the width with braces (as shown at 70 cm) and the other 2 sides at 75+cm in width. Roll the clay out onto the boards and trim the clay with a bevel to the edge of the boards with the braces. Then on the wider boards, trim the clay to 70cm with a bevel. Then you would join the boards after scoring and slipping the beveled edges of the clay. you can then screw or clamp the boards together to form a box. Roll a bead and press into the inside corners of your clay box for reinforcement. You can do the same thing for the bottom of pot... All this is assuming that, using the previous suggestions, you can roll out the size slabs you want for the sides of your pot.

JohnnyK