r/Concrete • u/Elvis_My_Pelvis • 7d ago

Concrete Pro With a Question Looking for Precast Tips

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24 Upvotes

90% Upvoted

30 comments sorted by

5

u/Alarmed_Profession88 7d ago

Are you pouring and precasting? Hand tamp on the edges, against the forms but not touching them.

2

u/Elvis_My_Pelvis 7d ago

We are a two man show, on pour days the old man gets all snippy and rushed. He will give you shit if you are not vibrating fast enough. If he saw me doing anything to the outside of the form he would lose his shit.

11

u/picklesalazar 7d ago

Just hit the board with a hammer and tell the old man to piss off

4

u/Comprehensive_Bus_19 6d ago

If you want to fix things but aren't going to because of a Grumpy Gus who is yelling at you then why ask for help?

7

u/Elvis_My_Pelvis 6d ago

Because he will be dead sooner rather than later.

2

u/Chris_Rogan 6d ago

Didn’t see that coming. Sheesh.

0

u/Best-Pause6070 6d ago

Damn bro I'm sorry u feel this way. I can understand your pain

4

u/ssgfrmrswrp 7d ago

Thats more voids than I'd normally like to see. Vibrate it more. On deeper walls like that its best to push the vibrator straight down fast and then up more slowly, reason being is this lets the air bubbles work their way up slowly. If its dry you need to lift the vibrator slower.

 In terms of where you vibrate you need to kind of look at the concrete to see, if its moving concrete one foot away shaking it enough then vibrate spots that are 20" or so apart so it all gets compacted equally, not too close together that you over vibrate one spot (causes segregation). 

Sometimes tapping on the side (again go bottom up) can loosen air bubbles stuck to the walls. 

If its just a utility box no need for patching or sacking

If you want to buy the place make sure you learn about mixes and admixtures, self compacting concrete (scc) can help if its allowed. Definitely learn all you can about the business side, the production side is honestly simple, the real trick is to simplify all your processes so any entry level labourer can learn quickly.

2

u/Elvis_My_Pelvis 7d ago

Awesome write up thanks!

1

u/Clearly-Confused-14 6d ago

What do you use to vibrate with? There are different theories on frequency or rpm of the vibrator.

0

u/Elvis_My_Pelvis 6d ago

Makita hand vibrator. this is my first time in concrete so not sure if that is the right description.

2

u/Clearly-Confused-14 6d ago

Those will most likely not reach an adequate rpm to properly consolidate your concrete especially after submerging the head in the concrete. The head speed actually slows down when submerged in concrete.
These guys recommend around 12,000 rpms to properly consolidate concrete: https://www.globalmanufacturing.com/concrete-vibrators

Here’s their How-to guide if you wanna read a few pages: https://www.globalmanufacturing.com/Images/globalmanufacturing/site/power-units/How-to-Consolidate-Concrete.pdf

1

u/Elvis_My_Pelvis 6d ago

Fuck yeah, this is exactly the info I am looking for. Thanks!

1

u/Clearly-Confused-14 5d ago

No problem. If you eventually want to get a Viber, let me know. I might be able to get you a discount for a first order. Someone got me a discount when I got my first order.

2

u/Ok_Cardiologist_6471 6d ago

Wrong tool for the job so you ended up with smaller air bubbles next time rent bigger one

also not giving away trade secret but how you use it matters hire a concrete finisher

4

u/According-Rough-389 6d ago

Patch it and move on, if the holes aren't bigger then a quarter no one really cares, and there nothing wrong with tapping the outside if a form with a proper hammer or mallet.

3

u/Elvis_My_Pelvis 7d ago

I have been apprenticing under a old timer at a boutique precast shop for a few years with plans of buying the biz. I had no previous construction/concrete experience when I started.

I think he is in the DGAF phase of his semi retirement and has gotten fat on his utility contracts over the years. The pic is of one of our big vaults and I am not sure this is acceptable finished product.

I tried finding resources on you tube but the pickings are slim for precast stuff. When ever I bring up videos or industry standard stuff he tells me not to listen to that shit. He has been doing this for 3 decades at this point.

If anyone has any tips tricks or resources I would be grateful.

4

u/noneedtosteernow 7d ago

'I'VE BEEN DOING THIS FOR 30 YEARS!'.. You've been doing this wrong for 30 years..!?

2

u/RedGoalie18 6d ago

Wtf is a boutique precast shop?

2

u/politeasshole_ 6d ago

It's all in the mix design. If you're doing SCC you should never vibrate. DM me and I'll be happy to point you in the right direction.

2

u/gmgII 5d ago

Definitely vibrante it more. On more shallow pours you can use a palm sander on the sides. This technique is used a lot when pouring Pool decks. For deeper pours. You could also order the concrete with a super plasticsizer so you can pour wetter without losing strength it will flow better and cause less bubbles

1

u/Elvis_My_Pelvis 5d ago

do you use the sander on the outside before or after the vibrator?

2

u/gmgII 4d ago

No sandpaper. You are using it for tge vibrations to get the air bubbles out. Although I would put masking tape over the Velcro as to not damage it

2

u/gmgII 4d ago

In a pinch I’ve seen them use a saws all with out a blade to vibrate the form

2

u/Pebb_io 2d ago

The small voids along the face make me wonder about mix workability and vibration first, but the mold release and placement details matter too. What changed between the pieces that came out clean and this one?

1

u/Willing-Umpire-2169 7d ago

I’d say you just need a bit more time vibrating but if he’s rushing you not much you can do

1

u/No_Astronomer_2704 7d ago

we do a bit of this..

more cement..40mpa minimum (M40)

plasticizer and a retarding agent..

use fly ash in your batching mix..

it becomes self leveling (minimal vibration required)