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My wedging table has many small dots and now it turns black. I clean it with brush and water. Now letting it dry. Do You guy think I can repatch them with new plastic after it is completely dry? I'm trying to smooth out the surface.

 

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Since there are no cracks in the plaster, spray it down with some bleach which should wipe out the mold. wait a couple of minutes to see what happens to the mold. Wipe the plaster with some clean water to remove some of the residue. If the mold persists, spray with bleach again. Wear rubber gloves and some old clothes for this process so you don't ruin good clothes if you happen to get bleach on them. Wipe with a damp cloth and let the plaster dry. If you want a smooth surface, sand it wearing a mask. The surface has to be dry otherwise the plaster will clog your sandpaper more than it normally would. You might take a heat gun or a fan to the plaster to assure its dryness.

JK

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Bleach works as mentioned above but often not as well on porous surfaces. Here is a suggested hydrogen peroxide method:

Mold Removal with Hydrogen Peroxide

Hydrogen peroxide kills mold as it is anti-fungal as well as anti-viral and anti-bacterial. Hydrogen peroxide is a good alternative to chlorine bleach because it is safe to use and doesn't damage the environment, nor does it leave behind toxic residue or produce toxic fumes like chlorine bleach does. You can buy hydrogen peroxide from drug stores for around one dollar for a bottle of 3% concentration.

Hydrogen peroxide kills mold effectively on many materials such as clothes, floors, bathroom fixtures, walls and items such as kitchen appliances. Since hydrogen peroxide is a bleaching agent it may also help fade the stain mold leaves behind. Spot test hydrogen peroxide on the material you're going to be cleaning to make sure it won't fade the material's colors.
 

How to Kill Mold with Hydrogen Peroxide

  1. To kill mold pour 3% concentration hydrogen peroxide into a spray bottle.
     
  2. Spray the moldy surface completely so that the moldy areas are saturated with hydrogen peroxide.
     
  3. Leave the surface to sit for 10 minutes while the hydrogen peroxide kills the mold.
     
  4. Then scrub the area to make sure to remove all the mold and mold stains.
     
  5. Finally wipe the surface down to remove residual mold and spores.


You can also use vinegar with hydrogen peroxide during the cleaning to more effectively remove the mold. Afterwards store the spray bottle in a dark place since light diminishes hydrogen peroxide's effectiveness.

 

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Thanks above replies, instead of sanding can I just pour plaster to seal them, sanding seem to take a lot of work and its going to make a mess. So I Just make sure the surface is  dry before pouring new layer of plaster?

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allenc-

Your idea of pouring a new layer contains a flaw in the process. There will no mechanical or chemical bond between the new layer and the dry layer. This will result in chipping or flaking of the new layer which will inevitably get into your clay, causing more issues beyond those you have now.

Regards,

Fred

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I think that is what they are saying. Having never tried this  I have never been able to get cured materials to bond well even with a bonding agent and even then not so good, however plaster patching is a real thing so maybe.  If you are willing to mix and repair, why not just pour a new slab, clean this one of mold and save it for a backup or now you have a separate porcelain and red wedging area.

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15 hours ago, allenc27 said:

So it is impossible to patch these holes with a new layer of plaster?

Very probably impossible, yes.  There will be someone on this planet who will say it works, but if you do any mould-making, you will know that you have to pour a piece in one go or it won't take properly.  There are situations where you can add more, but you have to make a good and substantial "key" between the old and new - usually deep grooves on the old, before pouring the new.

My plaster drying/wedging slabs all look like yours.  I just ignore the black holes, leave them in the sunshine to dry out, they work fine.

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Plaster won't bond to plaster.  Sanding it down is a lot less of a pain in the butt than trying to mix and pour pottery plaster/hydrocal.

You may be able to rent an orbital or belt sander from the hardware store for cheap if you don't think you can sand out the marks by hand.  Alternatively you can break out the plaster that's in there and pour all new slabs.

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@allenc27, I think you're making work for yourself. The black dots won't hurt the clay, if they bother you just clean the surface, pour on some  hydrogen peroxide, let it sit for 10 minutes or so and then wipe it down and leave it to dry.  It's a wedging table, it's okay to look like it does.

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hmmm good solid base, would work to hold a thin layer of something like cement board, smooth surface. I have a concrete wedging table, 3" thick. It has a canvas cover, as it is a little uneven. I also have a plywood 1/2 surface that I cover the table with to wedge the white clay that I use. I can wedge fine on either surface. To me what you have is a good weighty base, cover it for a solid non wobbly surface for wedging.

 

best,

Pres 

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On 8/30/2019 at 6:10 PM, allenc27 said:

So it is impossible to patch these holes with a new layer of plaster?

yes that is what will happen-the two layers will never bond. Either sand it off or scrap it off (better than sanding) or forget it and use it and it will wear down oveer time-whats the issue with black spots????>

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Your slab looks good to me allenc - and so clean!

I wedge on a piece of cement board (tile backer board) which is easily moved off my (limited) counter space, can be taken outside to hose off and dry - works great for me. My plaster slabs for drying reclaimed clay have some spots, which lead to an ah-ha moment - the slabs work better when air can circulate on all sides, hence, I prop them up off the counter/shelf when they are in use or drying after being used. A block of plaster encased on all sides excepting the top will retain moisture and mold out, yuck.

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