Patching A Concrete Fountain

[Beardy]

Yes a blade should do it for you,it is a bit of an open question as blade qualities vary but you should be fine with that

[petec]

Well I thought I should report that I did something to solve this problem in case someone else has a similar problem.
Please forgive me for not using the metric system. All the material is sized in inches. I'll switch to metric at the end.

So, I was wandering through my local building supply store and spotted a sheet of pressure treated exterior plywood. It was 24" by 48" by 3/4" ("= inches) and cost $14 (less then a case of beer......Fosters???). The bowl I am repairing is about 26" in diameter and has a "bulge" out the back side.

I cut the plywood in half making two 24"x24" sheets and glued them together with construction adhesive. Then I cut the shape with a saber saw, including the bulge by placing it on the diagonal.
Then I glued the concrete pieces together and to the sheets using:
https://retail.usa.sika.com/en/produ...ction-adhesive
I considered epoxy but thought this would allow a little flex and it was about 1/3 the cost of epoxy.
I then bound the concrete parts together with:
https://www.lowes.com/pd/SmartStraps...e-Down/3740799
After a few days I considered it done and painted the edges with gray oil based paint and put it in place outside on the base.
Final size in "real dimensions", 61 cm diameter with 10 cm "bulge'. About 3.8 cm thick.

Things I could have done better.
The part I made is too large. I didn't consider that the edge of the bowl tapers toward the bottom so it is barely as large as the part. So it is very visible. i wanted it to be set back from the edge.
I wanted to sand the rim and round the edge under but I couldn't. The table I set it on to do the work started to give me concern that it would hold up. All the parts together must weigh 150 kg and I was afraid the side pressure of the sander might be the straw that breaks the camel's back.

So, it could have been better but now it is time to crack open that Foster's . ;-)

Thanks everyone for all the great ideas and guidance.