Q&A for How to Finish Concrete

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  • Question
    Can I use a skill saw with a diamond blade to cut the concrete?
    Community Answer
    You can use a concrete blade for your skill saw. They're much cheaper than diamond blades.
  • Question
    Are sprinkling and plastic critical to curing a concrete slab?
    Community Answer
    Sprinkling or plastic are two ways of keeping the concrete from drying out too fast. If it dries out too soon, curing stops before it becomes strong enough to resist cracking. Keep it moist for a week or longer if you can. If not, at least a few days.
  • Question
    What is the time element between stage 2 and 3 of the finishing process?
    Community Answer
    This is weather-dependent and also variable depending on the MPA of the mix, but in the vicinity of 30 minutes to 2-3 hours.
  • Question
    I poured a slab in my daughter's coplin, but it's rocky, pitted, and rough. How do I make it smooth?
    Community Answer
    Use a concrete sander then a concrete surfacer to fill voids in concrete.
  • Question
    How soon can the form be removed?
    Community Answer
    It depends on the drying conditions, such as concrete strength, weather, pad moisture level, etc. Typically, common type forms can be removed within 24 hours to 48 hours.
  • Question
    Can I continue to cast a week later?
    Community Answer
    If you continue a slab a week later, you will create a cold joint, and you must use something to fasten the two slabs together, like re-bar. You can cut 12" re-bars and embed them (3-4") into your old pad in the center (height) and 2' apart. Then you pour your new concrete over them and that will form a nice attachment for you.
  • Question
    How do I screed a 20' wide pad?
    Community Answer
    A few methods can be used for a basic screed job using a 2x4. One method is to place steel rebar pins in as height guides down the center every 10'. You then pour a strip of concrete through the center and screed it out 1' wide. After that, start at the edge again and pour the 10' wide section using the freshly poured center strip as one of your guides. (Be careful using the freshly poured strip so as not to sink into it and end up with bumpy concrete).
  • Question
    How do I slow down the curing rate of concrete?
    Community Answer
    If you mean the initial set (you want to make it workable for longer), add a retarder into the mix. This can be bought online.
  • Question
    What is the curing time for concrete?
    Community Answer
    It gains most of its strength in about 7 days, and will be fully cured in about a month.
  • Question
    Do I use any metal reinforcement when finishing concrete?
    Community Answer
    It's not necessary for sidewalks, but I would. I'd always use it for a driveways or patios. You can also substitute a fiber blend, or even use both.
  • Question
    How do I remove tar from concrete?
    Community Answer
    Use a solvent after the concrete has cured. Don't try to burn it off, the uneven heat will damage the concrete.
  • Question
    Are concrete repairs to columns done immediately after removal of formwork or after curing?
    Community Answer
    It depends on the purpose of the columns. Concrete doesn't reach full rated strength until it has wet cured for 28 days. If you don't need full strength you can stop the cure by letting it dry and utilize it sooner.
  • Question
    How would I do a sugar water finish?
    Community Answer
    You would mix three pounds of sugar with three gallons of water. Mix well and apply with a sprayer.
  • Question
    I got rectangle knee board shadows starting to show in my driveway about two months after the pour. What can be done?
    Community Answer
    You could take a concrete sanding block and sand in the direction of the broom finish. Go lightly until the squares start to show less.
  • Question
    What concrete do I use for a polished concrete floor? Do I need expansion joints?
    Community Answer
    It's not the type of concrete you use, but the process you go through. If you've never finished concrete before, it's best to get someone to show you the steps.
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