Concrete types, reinforcement, etc

[ubarch]

Hello,

Just poured the top tray portion of my stand. I realize it's too late to go back, but if anyone sees any fatal mistakes I might have made, then maybe you can tell me and instead of building an oven I'll tell people that the stand is our kid's bedroom.

Pictures are in this thread:

http://www.fornobravo.com/forum/21/o...a-13648-2.html

Some concerns I had:

Was it OK to use ordinary Sakrete? I didn't buy the "5000 plus" variety.

Is the placement of the rebar reinforcement OK?

I finished up around 9:00 pm when the concrete hadn't set yet, and woke up at 7:30 to hose the slab down. I'm at home today so I can keep it wet. Any suggestions on how to help the slab cure?


Thanks!

[Muscats]

Re: Concrete types, reinforcement, etc

Ubarch;

I notice you didn't get any replies on your questions, so here goes;

Ordinary Sakrete should be fine (if its the same as our general purpose cement here in Australia) Sakrete is a brand name isn't it, your bags say high strength so that should be OK

Your rebar looks good too, some people worry about getting it exactly in the middle of the slab however for the purposes of a WFO having the reo a bit low in the slab is actually better as the force on the slab is to bend in down in the middle and therefore stretch it along the bottom edge.


Best way to cure it is to keep it wet, so spraying it is great. I cover mine in a plastic sheet after spraying it to prevent the breeze from evaporating all the water.

Paul

[ubarch]

Re: Concrete types, reinforcement, etc

That's good to hear. Yes, "Sakrete" is a brand name of concrete.

As for curing, I was able to keep it pretty wet throughout the day after I poured the slab. The next day I got only a couple sprays in, and yesterday I had only one. Is this adequate? I'm not noticing any hairline cracks, or "dusty" finish.

[Muscats]

Re: Concrete types, reinforcement, etc

Curing depends on the weather conditions. If it is dry and windy you need to make an effort to keep it wet, if it is raining you donr need to do anything. The main theing is to stop wind drying it out between spraying it. The experts suggest keeping it wet for a week. I spray mine once a day and cover it with plastic to keep it damp and that seems to work

[SteveP]

Re: Concrete types, reinforcement, etc

I used numerous 80# bags of Sakrete for both my oven foundation and hearth slab. I didn't see your photos, but rebar with Sakrete is plenty sufficient. You need to keep the surface of the concrete moist for 5-7 days to ensure proper hydration. you can lay old towels or blankets on the slab and spray to keep moist to ensure that the cement has enough water to continue its hydration.

My oven is about 2 years old, and I look at the underside of the hearth slab occasionally to see if any cracks appear. So far, no noticeable cracks.

[ubarch]

Re: Concrete types, reinforcement, etc

Hmm. I don't think I was able to keep the slab consistently moist for 5-7 days.

Water is a catalyst for concrete curing, though. Shouldn't I be able to re-soak the concrete to strengthen it? I'm going to defer oven construction until the spring, so the slab has all of fall and winter to cure. There's plenty of time for me to get wet again.

What do you think I should do?

[Muscats]

Re: Concrete types, reinforcement, etc

I remember reading that concrete continues to cure and harden for years (some people say hundreds of years), so the longer you leave it the harder it will get but there is no need to get caught up with long term curing, it will achieve the majority of its curing and hardness within 28 days

[Neil2]

Re: Concrete types, reinforcement, etc

"Shouldn't I be able to re-soak the concrete to strengthen it? "

No. The curing process needs water continuously from the initial pour for at least a week. If it dries out completely before the curing is finished, the curing process stops and can never be completely re-started.

Most people, if they have any experience at all with concrete, are used to pouring slabs on grade (sidewalks, patios etc). In this type of pour there is some margin for error because the curing concrete may be able to "draw" moisture from the subgrade. With a suspended slab, however, the curing concrete must be supplied with moisture, either from the atmosphere (if it is humid) or from providing it with water continuously for at least a week.

This is a simple but very important thing to do. Unless you are prepared to provided the curing concrete with lots of water for at least a week, postpone your pour until you can.

[ubarch]

Re: Concrete types, reinforcement, etc

Well, how do I tell if I cured my slab correctly? I read online about micro-cracks and a "dusty" finish, and my slab has neither of those.

[Neil2]

Re: Concrete types, reinforcement, etc

"Well, how do I tell if I cured my slab correctly? "

There is no way to tell for sure based on appearance.

[azpizzanut]

Re: Concrete types, reinforcement, etc

Hello ubarch,

You could use the "Hardazell" test to see if the concrete has cured.

Cheers,

[ubarch]

Re: Concrete types, reinforcement, etc

I do not recommend that you Google that term.

Come spring, I plan to pile some 80lb concrete bags on top of it for a week or so to see if any cracks appear. I might buy a few refractory bricks, get a notion of the density, estimate the volume of the oven, then use those terms to get a rough picture of the oven's weight, and finally put 1.5x that estimated weight on the stand.

[Tscarborough]

Re: Concrete types, reinforcement, etc

I seriously doubt you need to bother with that. I don't remember exactly what the numbers were but when I did the weight calculations for my oven the numbers were ridiculously low for the strength needed for the stand and slab.

[Muscats]

Re: Concrete types, reinforcement, etc

I do not recommend that you Google that term.

LOL. I know what you mean I lsearched for it and got a lot more than I expected.

[Muscats]

Re: Concrete types, reinforcement, etc

Come spring, I plan to pile some 80lb concrete bags on top of it for a week or so to see if any cracks appear. I might buy a few refractory bricks, get a notion of the density, estimate the volume of the oven, then use those terms to get a rough picture of the oven's weight, and finally put 1.5x that estimated weight on the stand.

I think you are really worring too much about the slab. If you mixed the concrete according to the instructions on the bag and you put some reo in the slab you should have no problems. Has the slab hardened now? I.e. does it have a hard surface? can you take some photos of the surface?