Potters plaster reclaim boards

[Gonepotty]

Can these be reused continuously  or will they eventually stop absorbing the water from reclaim ? I have a few which I have made and wonder what do I do with these when they no longer fit for purpose? Also wondering if they should be thicker or thinner? Mine are currently 5cm deep and wonder if this is why they take sooo long to dry out I between reclaim batches.

Thanks:)

[Hulk]

My reclaim slabs are ~2" thick, about same as yours.

It does take several days for them to dry out! I load them up with as much reclaim as I can heap on top without it oozing over the edges.
I've found it helps to prop up the slabs so air can circulate underneath, for the plaster will absorb water up to the point where they are saturated, then they can take more as moisture evaporates off the exposed edges and underneath. The reclaim dries quickly at first, then slower as the plaster becomes saturated. If I had extra plaster slabs, I'd rotate the reclaim to dry slabs!

My slabs have been in service for over four years now, seems they work just as well as when new.
They're much lighter once fully dried out - they don't feel as cool when fully dry, and there's the mineral fuzz - efflorescence.
Eventually, the plaster may get crumbly and it will be time to make new ones? That's what I've read here somewhere...

[Callie Beller Diesel]

If you’re finding your plaster slabs are saturated and you’re in a humid area (England, ahem), put your slabs next to your kiln when it fires to take advantage of the heat. 

[Gonepotty]

Thanks both:) Seems like I am on the right track . Thanks for the excellent tips! 

[Jeff Longtin]

Interesting fact: once a plaster form has thoroughly dried, after the initial pouring, re wetting it, and allowing it to dry a second time, will completely open the pores contained within. This is probably inconvenient, regarding a wedging table surface, but it would enable you to take the utmost advantage of the plasters aborbing capabilities.

The degree to which the plaster slab no longer can absorb water is dependent upon the clay you use. If your clay contains soluble salts, sodium silicate or barium carbonate, for instance, it may slow down with age, but most likely your clay doesn't so you can expect many years of use.  

As for drying a plaster form: heat is good but air movement is better. Too much heat, above 120 for instance, can start the breakdown process, too much air movement, has no bad impact at all. Put a fan on your plaster slabs and they should dry much sooner than simply letting the still air dry them. 

[Pyewackette]

I use 1/2" hardiebacker board for reclaim.  So far I use the same board for wedging and reclaim because its the only one I have.  I was intending to build a worktable to go with my new kiln but that all blew up last summer when it turned out we were going to be moving again.  *sigh*  The kiln now resides at a local pottery studio.  It was apparently too late for me to cancel the order.

Anyway.  I intended to try a double layer of the hardiebacker but since I didn't build the studio I didn't build the work table, but the single layer laid on my tile floor seems to work just fine for the little bit of reclaim I've been doing lately.  You can tip the board up on its side and it dries out super duper fast.  Unless you let it freeze/thaw repeatedly when wet it should last forever.  Can't say if doubling the thickness would have made any real difference.

NOT DUROCK.  Hardiebacker board.  I use it for ware boards too.

[Gonepotty]

8 hours ago, Jeff Longtin said:

Interesting fact: once a plaster form has thoroughly dried, after the initial pouring, re wetting it, and allowing it to dry a second time, will completely open the pores contained within. This is probably inconvenient, regarding a wedging table surface, but it would enable you to take the utmost advantage of the plasters aborbing capabilities.

The degree to which the plaster slab no longer can absorb water is dependent upon the clay you use. If your clay contains soluble salts, sodium silicate or barium carbonate, for instance, it may slow down with age, but most likely your clay doesn't so you can expect many years of use.  

As for drying a plaster form: heat is good but air movement is better. Too much heat, above 120 for instance, can start the breakdown process, too much air movement, has no bad impact at all. Put a fan on your plaster slabs and they should dry much sooner than simply letting the still air dry them. 

Brilliant:) thanks so much! 

[Gonepotty]

1 hour ago, Pyewackette said:

I use 1/2" hardiebacker board for reclaim.  So far I use the same board for wedging and reclaim because its the only one I have.  I was intending to build a worktable to go with my new kiln but that all blew up last summer when it turned out we were going to be moving again.  *sigh*  The kiln now resides at a local pottery studio.  It was apparently too late for me to cancel the order.

Anyway.  I intended to try a double layer of the hardiebacker but since I didn't build the studio I didn't build the work table, but the single layer laid on my tile floor seems to work just fine for the little bit of reclaim I've been doing lately.  You can tip the board up on its side and it dries out super duper fast.  Unless you let it freeze/thaw repeatedly when wet it should last forever.  Can't say if doubling the thickness would have made any real difference.

NOT DUROCK.  Hardiebacker board.  I use it for ware boards too.

Thanks:) never cake across these boards before...Will have a look! 

[High Bridge Pottery]

11 hours ago, Jeff Longtin said:

If your clay contains soluble salts, sodium silicate or barium carbonate, for instance, it may slow down with age, but most likely your clay doesn't so you can expect many years of use.  

Will soaking the plaster in water reverse the effects of sodium silicate or once it is in the mold it is there for good and you are better off making a new one?

[Pyewackette]

@Gonepotty - You can get it at any big box store:

Home Depot HardieBacker 1/4" = 1/4" for real

Home Depot HardieBacker 1/2" = 0.42"

You score and snap it with this tool unless you are crazy like me, have a big drill, and use the hardiebacker all the time, then you use THESE shears which you run off your big powerful drill that you already have.  The version with its own motor is over $200.

I've been using 1/2" for everything because that's what I have but I'll be switching to 1/4" for everything but the worktable-wedging table and/or reclaim.  I don't have a ware board longer than 2' because I simply can't carry a ware board longer than that full of ware.  Not sure I SHOULD be carrying one that long, time will tell.  And I'll use it for my shelf liner.  1/4" is plenty for that.

This stuff never warps, I've never seen it mold, it dries fast, it helps what's on it dry properly.  I have lots of individual piece sized "ware boards" and if I want something to dry slower, I just dip the Hardiebacker in a bucket of water, put a piece of newspaper on it, and set the piece on that and cover it.  It provides moisture at an even pace while its wrapped - not too fast, not too slow.  Adjust for local humidity by how you wrap your piece.  I've used it in humid NC and here in dry Tejas.  Love the stuff.  

Especially for a worktop.  NO CANVAS!  If I have some sloppy stuff I want to work up I can slam it onto the hardiebacker and the slop doesn't get all stuck onto the canvas. The hardiebacker will pull excess moisture out and I can work it up lickety-split.  If the board is a little dry a quick spritz with a spray bottle will give me a good worksurface.  Its just way more flexible than canvas or plaster, and longer lived.

Edited February 15, 2023 by Pyewackette

[Jeff Longtin]

6 hours ago, High Bridge Pottery said:

Will soaking the plaster in water reverse the effects of sodium silicate or once it is in the mold it is there for good and you are better off making a new one?

I'm not a chemist but it seems the salts move through the mold and accumulate on the surface. Washing the plaster might help but sanding the surface, and actually removing the salty buildup, would be more beneficial. (People who slip cast a lot have told me this.)

Drywall sanding screen is a wonderful way to take plaster down easily and quickly. (Though it is kind of messy.)

[Pyewackette]

25 minutes ago, Jeff Longtin said:

Drywall sanding screen is a wonderful way to take plaster down easily and quickly. (Though it is kind of messy.)

Wear a good mask just as you would for mixing glaze.  Or at least should LOL!