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Concrete for making concrete molds concrete cement I am trying to make some concrete items such as trays, vases, bowls etc. Can anyone please advise on recipes/ratios for this? I would like to make these in white, black and grey and want a smooth finish (lump free and non gritty) I cant get quikcrete in the uk. Thanks,

James

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    Welcome to Arts & Crafts. I started to try to answer this and realized that the question is really broader than it looks; too broad to do it justice within the intended scope of an answer. From your description, "concrete" is probably the wrong material (it contains gravel and coarse sand, which wouldn't be suitable for your projects). There are cement-based materials for fine castings. But there are also many other considerations for producing a smooth casting, and different requirements for a small solid tabletop item, a tray, (cont'd) – fixer1234 Aug 17 '20 at 3:45
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    anything that might hold food, items with detail or structure on more than one face, etc. There are pre-mixed materials you can use (sold for casting countertops or artwork), which will vary in availability. There are also recipes online, but some of the ingredients may take some hunting or preparation. You would want to invest in some PPE, because some of the ingredients are harmful to breathe or get on your skin. It would be worth doing some online research to get a basic education in the considerations that go into the item design, (cont'd) – fixer1234 Aug 17 '20 at 3:46
  • mold-making, material selection, casting procedures, curing, etc., for items of different shapes/sizes and requirements. Then maybe pick a specific project and ask a question focused on that. – fixer1234 Aug 17 '20 at 3:46
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Don't use quick-crete mix your own, for one thing you don't want gravel in detailed or smooth are casting, just sand, the finer the better. I have had a lot of success using a mix of sand and marble dust but I was casting giant pacific clam shell replicas so I wanted that very white sparkly surface.

Getting it really smooth requires a sealant, concrete by itself will not be perfectly smooth just because of the sand. Using a vibrating table will help a lot with getting a smooth void free surface.

I use a pool lining mix ratio since it is a gravel free minimum void mix, something between 1:2 or 1:3(portland cement:sand) but a little experimentation is best. The water ratio is more important, you want as little water as possible, 1:3 or less, but it is effected by climate so again experimentation is best. the DIY stack has help for counter-top cement which is pretty much what you want. https://diy.stackexchange.com/questions/90389/whats-the-best-ratio-for-sand-only-concrete

I have heard good things about plasticizers but have not used them myself.

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