Hi, I am in the process of casting a concrete tabletop with visible stones/marble chippings 8-16, so that it gets a terrazzo look.
I am using Finja's expanding concrete but my question is whether I should mix the stone with the concrete in the mixer or if it's better to mix the concrete separately and then "sprinkle" in the stones during casting.
I'm thinking that with the first option there might be a risk that the stone ends up in the middle of the mold rather than at the bottom, but I don’t have much experience with this. I also saw something about micro-cracks with option 2.
Anyone with experience in terrazzo or casting who can help me with this?
Thanks in advance
//N
I am using Finja's expanding concrete but my question is whether I should mix the stone with the concrete in the mixer or if it's better to mix the concrete separately and then "sprinkle" in the stones during casting.
I'm thinking that with the first option there might be a risk that the stone ends up in the middle of the mold rather than at the bottom, but I don’t have much experience with this. I also saw something about micro-cracks with option 2.
Anyone with experience in terrazzo or casting who can help me with this?
Thanks in advance
//N
I tested when I was casting my own slab for the living room, it didn't result in what I expected after I sanded the test piece, so I skipped the white stones in the black slab.
You get a clearly better surface by casting against form plywood or melamine than having a finished surface facing upwards in the mold, so to avoid having to sand everything flat, I put the stones in the mixture. You can sort out some of the larger stones from the bag with a sieve so you don't alter the strength more than necessary.
I believe that sanding like terrazzo requires some kind of jig that holds a sander straight, like a planer for wood.
You get a clearly better surface by casting against form plywood or melamine than having a finished surface facing upwards in the mold, so to avoid having to sand everything flat, I put the stones in the mixture. You can sort out some of the larger stones from the bag with a sieve so you don't alter the strength more than necessary.
I believe that sanding like terrazzo requires some kind of jig that holds a sander straight, like a planer for wood.
Thanks for the reply, I've built a mold from form plywood, but then it should give the best result if the stones are sprinkled in the bottom of the mold and then hit the concrete over it?pjapen said:
Do you have any pictures of your previous castings?
I think you'll get the best results with a lot of work. There are pictures on the forum in some old thread about concrete benches. Unfortunately, I don't have pictures of the tests I did, it was around 2012. If you can't find the thread, I can send a PM with pictures.
Searched around, there are quite a few threads, but feel free to send a pm if you want.
What didn't go as planned with your test casting?
What didn't go as planned with your test casting?
found the forum thread with pictures.
https://www.byggahus.se/forum/threads/betong-foer-att-gjuta-baenkskiva.245749/#post-2111748
I tried a few variants with stone to be polished with or without black FeO2, as well as different amounts of iron oxide.
concluded that just Fe02 was best without colors on stones as it was very time-consuming to polish a surface on my test piece.
the test piece was 20x10 cm and 5 cm thick.
https://www.byggahus.se/forum/threads/betong-foer-att-gjuta-baenkskiva.245749/#post-2111748
I tried a few variants with stone to be polished with or without black FeO2, as well as different amounts of iron oxide.
concluded that just Fe02 was best without colors on stones as it was very time-consuming to polish a surface on my test piece.
the test piece was 20x10 cm and 5 cm thick.