Youtube has saved me more time and money over the years! I have repaired a clothes dryer that began to emit the smell of burning rubber, opened a stuck glove box on an expensive car, waterproofed a basement floor, taught myself to repair fibreglass and solved too many other problems to mention here. Youtube is awesome when you need to learn and are willing to dig around a bit and make sure the person in the video knows what they are up to. I have to say that I have not had any bad experiences with this resource, other than the time wasted in the rabbit hole I end up in once and a while....
In the over decade long experience of creating countertops and tables from concrete I have had at least two calls/emails per year that I can recall from someone and it usually goes like this:-
"I watched a Youtube video of some guy that built a cement (it's concrete)
(insert countertop/table/bbq surround) and it looked pretty easy.
(Insert Over the winter, last week, when my kid sat on it) it (insert cracked, broke into pieces)
or (insert its so rough we can't write on it, can't clean it)."
At this point I am asked either...
Can you fix it?
No. Even if we knew exactly what was used and how it was made, trying to repair concrete by others is almost impossible. We measure ingredients sometimes to a tenth of a gram and use specialty chemicals that make our concrete ultra dense and ultra hard. The equipment we use to polish our concrete would grind into conventional concrete like it was softwood.
How much to replace it?
Our concrete is made in a studio fitted with the raw materials, tools and machines to make a high end product. We have everything on hand to make just about any shape, texture or colour. We attend classes and peer groups to keep up with this evolving craft. Which is all to say - it isn't inexpensive, and sounds like you have already paid for raw materials to make a mold and the concrete that broke.
In this case I notice that several of the youtube videos where a table or countertop is made end with the maker saying something like "If I had it to do again - I wouldn't". Fine concrete is hard to make - even when you know what you are doing. If you want to attempt a DIY concrete project - call us, we will gladly sign you up for our next training class.