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Best way to smooth sand and cement repair

Discussion in 'Building' started by AP77, 21 May 2019.

  1. AP77

    AP77

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    I have been reading lots of posts bout smoothing concrete and render.

    I need to repair a manhole cover and am using a pre mixed sand and cement. I really want to make the finish on the cement as smooth as possible as it will be in a very visible position.

    Please may I have some advice on the best way to get this smooth finish. Iam thinking that I will trowel the cement to get it as smooth as possible first but then am unsure of next steps:

    1) Should I then leave the cement (not rapid setting) for say 30 mins before troweling smooth?
    2) Or maybe I should use a sponge after 30 mins?
    3) Is it a good idea to damp the cement again at this point to help get smooth?
    4) Any other tips, please?

    Many thanks.
     
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  3. 23vc

    23vc

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    Forget the sponge
     
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  4. KenGMac

    KenGMac

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    AP77, good evening.

    A lot will depend on the actual mix used, also the volume of water incorporated in the mix.

    What can work well is if you gently "pat" the top surface of the cement just after pouring, this will bring to the surface of the pour a cement slurry that is itself easier to smooth of and will not [hopefully] have any aggregate actually on or immediately below the top surface of the pour

    Allow the cement to just start to go "of" [become firm] then gently smooth with a trowel sprinkle water if needed, do not flood the area. I am not a fan of Sponging

    Ken
     
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  5. 23vc

    23vc

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    We’re talking mortar, not concrete, right?
    I’d say trowel it with a pointing trowel when it’s not too wet so you can apply some pressure and get a nice hard, trowelled surface. It’s gotta be firm for that to work.
    Do a practice run somewhere out of sight if you’re not sure how to approach it?
     
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  6. AP77

    AP77

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    Thanks KenGMac and 23vc, much appreciate your advice.

    Yes, I am using mortar. A bucket of sand and cement mix from wickes which you just add water to.

    When I have done a similar job before, I used a trowel to get the mortar around the manhole cover and managed to get it fairly smooth. But just trying to get the best possible smooth finish I can now, so this time I will do as suggested and sprinkle with water after it has started to go off.....would this be after approx 30-60 mins do you think (depending on how wet the mix is I guess)?
     
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  8. cdbe

    cdbe

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    A nice soft brush, in the direction water will run off, a few hours after you've done it, gives a nice finish.
     
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  9. KenGMac

    KenGMac

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    Do not "flood" your mix with water, it will weaken the cements ability to gain strength and it will take longer to get to a state where you can begin the finishing process.

    Ken
     
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  10. AP77

    AP77

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    Thank you for all the tips.

    I think I will apply the mortar round the manhole, smooth as best I can, leave for about one hour, then smooth the mortar with a trowel dipping it in a bucket of water every few stokes to help get the mortar really smooth.

    Practice makes perfect!
     
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  11. ^woody^

    ^woody^

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    The best thing to do is not mix it wet in the first place. It needs to be semi dry, so that when you trowel it and press on, you get a slight sheen from the water coming to the surface, not a puddle. What this does (the pressing) is bring the water and cement to the surface which in turn hardens the surface, seals the pores and gives it its weathering face to last for years to come. No brushing, but firm passes with the trowel or float. This is the same concept for an cement based product, screeds, wall pointing, flaunching anything. And refrain from brushing afterwards as this will then roughen the surface and remove the weathering face.

    Just remember to brush any debris away and dampen the base first. Cover it if its sunny whilst it sets and a day or so afterwards.
     
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