Not an expert here but I think all cement products are extremely basic before they are activated and set, it’s part of the reaction that makes it harden. I can’t imagine it would remain that caustic once it has set and the reaction stops.
Making Slabs With New Materials
- Thread starter Hartinez
- Start date
Well, looks like I was off. Did a little Google research and found that many concrete products do retain high ph for some time. Some processes that occur with time can lower the ph. This is pretty interesting though since concrete pots are not uncommon and I have yet to hear that they kill trees. 
Some more info;
www.floorexpert.com
Some more info;
Concrete pH – Floor Expert
www.floorexpert.com
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WNC Bonsai
Masterpiece
Well, looks like I was off. Did a little Google research and found that many concrete products do retain high ph for some time. Some processes that occur with time can lower the ph. This is pretty interesting though since concrete pots are not uncommon and I have yet to hear that they kill trees.
Some more info;
Concrete pH – Floor Expert
I have seen websites on concrete slabs where they always leave them out in the weather for a year to lower the pH. This is also commonly done when making a concrete pond. I wonder whether spraying the slabs with vinegar or some other acid will speed the process?
Wulfskaar
Omono
I just read on yashu's link that you shouldn't do that because it may cause buildup of salts on the surface.
WNC Bonsai
Masterpiece
Interesting since various pond sources recommend either filling the pond and draining until the pH is acceptable of treating with vinegar. Where is @Leo in N E Illinois when you need him?Well, looks like I was off. Did a little Google research and found that many concrete products do retain high ph for some time. Some processes that occur with time can lower the ph. This is pretty interesting though since concrete pots are not uncommon and I have yet to hear that they kill trees.
Some more info;
Concrete pH – Floor Expert
Gabler
Masterpiece
The chemical reaction in the cement continues over time, gradually making the concrete harder. I would worry that an acid bath would stop the hardening of the cement and weaken the concrete.
Hartinez
Masterpiece
Ive got these all soaking in water now in fact, plus I had been spraying them down as constantly as possible over the winter. I will also be curious to see how trees respond to the conditions. But ultimately, I'm not worried and excited for the maiden voyage on all of these slabs!
radhatter
Sapling
Any chance you’re able to test water that’s been standing in the pot for a while?
Hartinez
Masterpiece
A level I did not take it. I’d be shocked if these slabs/pots poisoned the tree in any way. And if they are clearly detrimental, I’ll take em out.
Hartinez
Masterpiece
Repots so far. A few more I haven’t snapped photos of as well.
radhatter
Sapling
Well done, these look so good!
littletreefarmer
Yamadori
What have your results been on size/weight ratio? I've been building slabs in the background with a different product for about 2 years now. Would be very curious on how the weight compares. Weight and longevity seem to be the greatest limiting factors.
Also, as others have said, very good looking work!
Also, as others have said, very good looking work!
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WNC Bonsai
Masterpiece
I’m convinced, heading to Ace Hardware tomorrow to get a bag and a case of WD-40!
Hartinez
Masterpiece
incredibly light for the size of each piece. I haven’t weighed them, but I’d say the weight is almost 1/3-1/2 lighter than what concrete would be.
Hartinez
Masterpiece
I really liked the expanding foam as a form. Allowed me to create a mold rather quickly with less mess. And laying a think piece of plastic over the foam kept the form in good shape for multiple uses. And don’t be afraid to do multiple layers/coats of the material to get the desired texture or finish. May seem a bit brittle the first couple days, but After a full week it is incredibly hard.
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