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In remodeling, I come across a lot of situations where I’m hired to fix, replace, or repair small amounts of concrete, particularly flatwork (a step here, replace one section of a sidewalk, etc.). Nothing more than 1/2 a dozen bags of some premix. Most of this work is in the summer, where typically I’ll mix and pour, screed it off, float for a couple minutes until it’s smooth and water stands A LITTLE, then I do any tooling after it’s setup and the water’s gone. Now that it’s getting colder, though, I just had a job where after screeding, the water came to the surface almost instantly. I couldn’t get it very smooth, and just a little floating basically ruined it; three days later, it’s completely spalled. I’m going to make it right and redo it gratis, but my question is kind of simple; should I float after screeding, or wait to set up and then float just before tooling and being done? Thanks.
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Jason,
most of the pre-mixed that people use in repairs is not mixed properly and too much water is added to give it premature flow.
Are you using a small electric/gas mixer or are you doing it by hand?
Only a minimal amount of water should come to the top during and after screed.
Be a little more patient with your trowelling and make sure that it has started to set up before you work it too much.
Gabe
*Gabe. Thanks a lot. You were correct. As sooon as I saw the word "paitence", I knew exactly what you were talking about. I know now that really my problem is that I don't let it set up enough at first, and I float too much (just got to get that ONE more little mark out...). Anyhow, I appreciate your time.
*Try adding some cement to that premix. It will make it stronger and more workable. That stuff is probably 3-sack mix, if that. I would add about 5 lb of portland for every 80lb sack of redimix. This is approximately equal to 2 additional sacks per yard, I think (2 sacks cement= 180 lbs, 40 or so - 80lb sacks of redimix per yard, 180/40=about 5). This would bring it up to maybe a 5-sack mix. Much stronger and much more workable. The purpose of floating is to bring the "cream" up to the surface and level out any high or low spots left from screeding, not to get any marks out. The cream is basically cement paste. With the small amount of cement in the redimix, there is almost no cream to be had, just water. Adding some cement will help. Float it once, right after screeding. Like Gabe said, have patience, dont overfloat or you will have to wait forever to have it set up enough to finish. I just placed a slab for my house. We poured out at about noon or 1. Floated it all right then and had a barbeque for the crew (volunteers). It was in the mid 40s. I couldn't make the final run with the power trowel until about 7:30 pm, using the headlights of the truck. Good luck!Sami
*Jason ,I agree with Sami.....adding portland cement will definitely aid the whole process . Working with my father as a mason's helper and eventually finishing all the flatwork he contracted , i garnished some good pointers . Never try to finish concrete when it's wet...it will only result in a very soft finish . The harder it is when troweled the harder the finish and more durable (provided it is not so hard that you "burn" it by trying to trowel)As far as floating is concerned i always use a magnesium float to bring up the "fat" and smooth out marks of edgers ,screeds, or bull floats .It leaves a pourous surface while the concrete is setting up and allows it to breathe where a smooth finish with a finishing trowel tends to seal in the water somewhat.Troweling with a mag float repeatedly will not hinder the set but it will bring all the fat up ,make a flatter job and a better finish .
*Thanks again everyone.
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In remodeling, I come across a lot of situations where I'm hired to fix, replace, or repair small amounts of concrete, particularly flatwork (a step here, replace one section of a sidewalk, etc.). Nothing more than 1/2 a dozen bags of some premix. Most of this work is in the summer, where typically I'll mix and pour, screed it off, float for a couple minutes until it's smooth and water stands A LITTLE, then I do any tooling after it's setup and the water's gone. Now that it's getting colder, though, I just had a job where after screeding, the water came to the surface almost instantly. I couldn't get it very smooth, and just a little floating basically ruined it; three days later, it's completely spalled. I'm going to make it right and redo it gratis, but my question is kind of simple; should I float after screeding, or wait to set up and then float just before tooling and being done? Thanks.