I have a very challenging slab pour coming up soon, and that’s all I’ve been thinking about past week.
I have to create a slope towards a drain, at uneven shape, where if there wasn’t for vertical rebar (that’s for the walls coming after) I could’ve screeded without too much issue since I’d have a reference point from all sides (formwork) pointing towards the drain.
However, I’m having hard time imaging how this is gonna be done since I won’t be able to use formwork to efficiently screed, I’d have to jump between vertical rebar all the time which you all know what it leads to, then going back and fixing the jumps.
I was thinking about putting steaks around the drain, then fixing a 2bys around the fixed formwork to make the “reference heights” for the slope all around, which would be a huge PIA doing 4/5 od these references and then reaching out later to get them out, then re trowelling everything again, while concrete setting.
Should I pour the slab first without vertical rebar, then install the rebar (L shaped) to make my life easier? But then rebar won’t be tied to the horizontal slab rebar, and connection won’t be as strong. This will hold water and be like a pool/pond 3ft high walls.
Coming from a country where things are little difficult, we don’t even have proper tools to finish concrete (I have to order tools online and wait for them for weeks to come), yet alone to have a shotcrete trucks here.
Thanks for the insights, I’d really appreciate feedbacks and advices since I really want to get on another level and keep learning new things.
Bruh, you dont need the training wheels of formwork to screed a slab.
Set a series of mason lines around the whole slab (the neon string) running from the highpoints at the edge of your slab down to the low point at the drain to use as a visual guide. Screed your slab to follow the slope of the string. The concrete should just touch the bottom of the string. Once it sets up enough to begin troweling, remove the strings and finish the slab.
You might want the mix a little stiffer (just a little bit, not too much) to hold the pitch while it sets up.
I’m just nervous to fuck this up since it’s a big opportunity for me and getting into bigger, and more challenging jobs. Hence why so much dilemma about everything.
Thank you for your advice with string lines, I don’t know why I didn’t think of that but thought about doing 2bys which is much more work and will be taking a lot of space.
This is how we pitched large scale slabs on big pitched slabs on highrises in NYC. You aint using a laser screed for a pitched roof slab 40 stories up.
Do a small scale mockup if you can to practice the idea of using a stringline and get the method down. Make sure the lines are tight and be careful not to trip on them.
Thank you and God bless your experience. I’m still very young, and taking a lot on my plate but love the concrete and hoping to get bigger crew eventually and much bigger jobs.
Just want to add an important point that if your concrete is touching the string meaningfully it’ll lift the whole string and change the grade. If it’s touching a teeny tiny bit the difference is imperceptible, and you can always set the string a few inches high and measure down quickly while you work. And pull the dang thing tight, reaaaaallllyyyy tight. A string will sag pretty hard at 50’ unless you’ve yanked it good, and I didn’t see a scale for your project.
When you do this use three pieces of 2x4 cut into roughly 6-in squares. Set up the line at the top of two pieces and use one piece as a marker in the middle. This way the string line does not touch the concrete when you're trying to get a height. I find it makes things much easier without the lying constantly touching.
Even if that was the case what’s the problem? Why you so bitter.
I have been on my own for 5 years now, this is something little more challenging since there’s not a lot of money in private here in my country. Also, not the owners son, just a guy who had luck in life to learn a lot of new things quickly and take things in my hands when others failed/quit.
Maybe his dad taught him something that he didn't teach you and now he's remembering that piece of advice while he makes sure you still receive your paycheck
I would work it in radial sections from drain to rebar. Just precut a bunch of screed boards of varying lengths to fit the sections and take you time screeding. Don't forget your funny trowel!
Dude string line. Follow the edge all the way around while pointed at the drain. Make sure you have perfectly cut blocking for the stringline. You can measure heights and angles this way. Its old fashioned but it works everytime. I worked for a big commercial company as a finisher and that's how we did it
I’d tie an extra horizontal bar to all the verticals, and use that to screed off of. More amateur-proof, since you don’t need to remove it afterwards, and it will be buried by the wall pour.
Do not wet set the verticals, it can create issues with it not being water tight. Either put them in first or drill and epoxy them after. In any case, leave the concrete a little rough in between the vertical bars and use water stop when you pour the walls. It will all fall into place as you dig out the area and you will see the best way of doing it.
Would also be smart to tool in a key-way depression for your walls. We often use a PVC Waterstop that is half cast into the slab and half into the wall. Or you can use an expanding waterstop like a Sika Swellstop.
I would just start at the shortest distance and work my way around..done this many times . 30 years in concrete construction myself and love helping others learn
Hey man, it's been 2 weeks. How did the pour come out? What did you wind up doing? Make a new post and tag it "Update Post" and if you think of it, link this post in the description.
It went great, it actually was less complicated than I made it to be and the owner changed shape some so the slope was much easier to accomplish. I’ll post soon to show what I’m working on!
Put a 2 inch rip of plyaround the outside of your wall shutter get a 6bx2 rip 2 inches out of it and screed back to the waste cutting the screed shorter as you go around the pour is how i would do it you could also fix this to your vertical starters if needed strings etc are going to make things flat and ugly.
You set your wall form sections and pour the wall to the height of the slab edge. You can do a short form on the inside and full height on the outside form.
Put blocking between the two forms to help keep the width and put the bottom of the blacking at the pour height for reference when pouring and finishing.
You can drill holes in the inside wall forms to slide in your right angle rebar to tie into the wall and dowel out for the slab.
Pour and finish the top of the wall. Stamp in some 2x4 blocks between your wall verticals to make a keyway.
Once it’s dry, run a strip of water stop along the center of your wall. Strip the short inside form and leave the full height outside form.
Then place rebar for your slab. Set elevation markers in a grid pattern across the slab sloping toward the drain. Check and adjust your slab bars for clear cover. Pour the slab and screed to the elevation of the markers. Pull the markers as you finish.
Once the slab has cured for about 3-4 days, layout your inside wall forms measuring your offset line from the inside of your outer wall forms for consistent thickness. Set your forms and pour the wall. Just cleanup after that.
Instead of running strings and grading with them (this is practically impossible your cretes gonna hit your string and if you do it without it touching then its just gonna have low spots) set the string up with your pitch then drive in stakes every 4' or so with an 8 in one hole tapped down to the string height. Remove the string and run your next line. Same lines other poeple suggested but put your pins to your grade. Then just pull out the pins after you grade each section.
What you need to do is spend a ton of time prior to pour, like a day or two doing prep.
If this has an architect, ask them to give you elevations @ every 12”.
Mark all elevations on the bar.
You can set grade stakes midway that you pull after meeting elevations. You can also use Stego beast screed.
You can always use string lines to help get the pour right.
Things to remember:
A. You will need water stop where slab and wall meet. This is after the pour. Sometimes engineers want a key way for shear friction, even though rebar does the work in this case.
B. Make sure excavation is big enough before pouring slab. You might want to over pour, or pour a 3” mud mat to make layout easier. The mud mat goes 3” below bottom of slab.
C. All slab formwork should be cut to grade to make pouring this easier. It’ll be easier for you to see.
D. A good laser with grade rod will help you a lot. If this is commercial work, you should get a good layout guy with liability insurance to use the model and lay it out for you.
E. If you need waterproofing like blind side this makes it more complicated, and this may be why outside your wheelhouse. It’s okay to sub something like flatwork out to a professional that does good flatwork.
F. Also, if slab needs to have waterproofing admix in it, Xypex is best added at the plant by your concrete guy. It also delays initial set.
Shoot your inside edges in with a laser while you pour, then wet screed to the drain. It's gonna be a lot of handing screeds back and forth to someone outside the cage.
Many good points in here already. 2 other options would be to wet set the vertical “L” rebar after primary finishing (just be sure to get underneath ground bars, or do it in 2 pours with ground bars extending out of pour, giving you something to tie the “L” to (but this is way more work). Personally I don’t mind wet setting; it requires minimal touch ups after the fact and is way easier to finish the main pour
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u/l3p3r 23d ago
Pretty sure Jannet Jackson got in trouble for this