I built a concrete countertop for a kitchen on a rental with my dad a few years ago. Quick rundown of that story and my takeaways.
- poured the concrete on site and finished in place
- used 1/2 backer board on top of cabinets for a base
- built edge and sink cutout with melamine board and caulk (what a PITA)
- used quikrete 5000 mix (has fiberglass support) and added a few shovels of cement (quikrete tends to run light on cement and too much aggregate)
- additional support with screws into the backer board and tie wire criss crossed
- mixed in a wheelbarrow with a liquid coloring agent (added to the water and mixed with that first)
- mixed on the dry side (too much water and you'll crack)
- poured in place (more like shoveled), vibrated with a putty knife with small hand sander on handle
- screed and finish with float
- every 30 minutes or so, re trowel with stainless steel blade
- repeat until glass smooth and starting to set.
Total build time for complete noobs - 12 hours, material cost approx $200
Pulled the forms off the next day, color was not even, and edges weren't smooth. Sprayed on coloring agent with water and wiped with microfiber (2-3 times) until color took evenly. Small batch of cement with color and used a putty knife to fill in edges. Let cure another day. Bought finish, applied sealant finish, then apply wax finish.
What I learned when I found the concrete supply house for the finishing agent:
- buy the premade edge forms!!!!
- build your own concrete mix, add fiberglass reinforcement separate (you can mess around and use fancy aggregate to get better colors, textures, etc)
- pour in place, use chicken wire as additional reinforcement (set wire on screws from backer board)
- purchase a "plasticizer" for part of the liquid. The concrete will cure faster and it does NOT shrink when it dries. This will make the continually troweling of the counters work a LOT faster
- mix coloring agent more completely (potentially rent a small mixer)
Go find a concrete supply house and ask a lot of questions. I learned more from them in 15 minutes than I did from hours of online research.