Base Slab question

[NCMan]

Re: Base Slab question

Just do the best you can and just let it thin out a bit as you get close to the edge.

[iluvpizza]

Re: Base Slab question

NCMAn, I saw the pic of your slab (btw great oven). I can i put gravel into the footers, but since mine are going to be deep, how can I put 3-4 inch of gravel on the central part (the one that will stay under the middle part of the slab) without it falling into the trench?? any suggestion??

[NCMan]

Re: Base Slab question

The way I do it is to put gravel everywhere under the slab. I also recommend a layer of plastic for a vapor barrier over the gravel but that is up to you. There are different ways to prep and pour a slab and just as many opinions about it. My theory is you only get one chance to do it right and it's what supports your whole project. I recommend you take photos at each step along the way and ask some of the knowledgeable folks on here for opinions and help. Many are more than willing to help if and when they can.

[iluvpizza]

Re: Base Slab question

To be honest with you NCMan I had in my mind what a monolithic slab is but I did not know that it is called like that....
From there my previous question: do I put the gravel only at the bottom of the footers (this is what hold the structure) ? what for the middle portion of my slab? Do I pour concrete on the ground without any filling?
Yes I will do the cement by myself...

[jeeppiper]

Re: Base Slab question

I did a monolithic foundation for my build. I live in Pennsylvania and our freeze line is 36" (according to our zoning office). The guy at the zoning office recommended to me that I should use a monolithic foundation and helped me spec it out.

My footers were 1 foot wide x 3 feet deep and ran the length of the slab. The slab itself was 6 inches sitting on 4-6 inches of compacted gravel and rebar throughout. I rented an auger from home depot to help dig the footers. I plunged multiple holes and then just had to dig the dirt between the holes. Although a back-hoe would have been better, for me this was a big help and saved me about 70% of the back-breaking digging.

I had a truck deliver the concrete which worked out to be 2 cu. yards.

It was a real pain, but I am glad I did it because I now have complete faith that my oven will outlast the Pyramids of Giza! I attached a picture showing the monolithic foundation.

[NCMan]

Re: Base Slab question

I'm not sure you understand what a monolithic pour is. Maybe you do (?). I would go that route, if it were mine. All you need to do is set your forms. Stake them in good, because you'd be digging right inside them. Once they are set, simply dig a trench (a shovel wide is enough) around the inside of the forms until you are 24" down from final grade (top of form). The downside of a mono pour is it takes all the concrete at once. Will you be having a truck bring the concrete or mixing it yourself? The alternative is pouring your footers, laying block and then prepping and pouring a slab. Photos would help alot. There are lots of others, but if you look back at my build, in the early stages, I did a mono pour. Maybe that will help. In the end, there are a few ways it can be done.

[iluvpizza]

Re: Base Slab question

I was thinking of a monolithic but that is why a 53 cubic ft of dirt to dig (and then cement to pour...) looked to me a little too much and I was looking for alternatives...

[NCMan]

Re: Base Slab question

Kensington, MD... DC area..
After better home works I find out that the frost line is more 24" than 30".

So if I understood, I should start digging for my base slab the famous 5.5" and then dig a perimetral trench deeper than 24" from ground level (always granted that I will still not be in the fill). After laying a layer of gravel stones into the trench, I will be poring in cement to reach the bottom of my base slab (possibly using vertical rebar to make the perimeter more solid.
Now what? Should I then cover everything with gravel and proceed with the slab? Or should not put any gravel and pour the slab over the entire area (covering the perimeter of cement and the central area or dirt)?

Thanks

The footing itself should be at least 8" thick. I would recommend using two horizontal (not vertical) #5 (5/8") rebars in your footing. Be sure they are towards the middle of the footing when you pour. It's best to use rebar chairs and tie rebar to them, if you are not real experienced w/it. Are you doing a monolithic pour or pouring a footing, laying block,etc? I'd go w/a monolithic, if you can, especially w/only having to dig down a total depth of 24", plus a little for gravel.

[iluvpizza]

Re: Base Slab question

Kensington, MD... DC area..
After better home works I find out that the frost line is more 24" than 30".

So if I understood, I should start digging for my base slab the famous 5.5" and then dig a perimetral trench deeper than 24" from ground level (always granted that I will still not be in the fill). After laying a layer of gravel stones into the trench, I will be poring in cement to reach the bottom of my base slab (possibly using vertical rebar to make the perimeter more solid.
Now what? Should I then cover everything with gravel and proceed with the slab? Or should not put any gravel and pour the slab over the entire area (covering the perimeter of cement and the central area or dirt)?

Thanks

[NCMan]

Re: Base Slab question

I also meant to ask you....what part of MD.?

[NCMan]

Re: Base Slab question

One last question: I know that the freeze line should be at 30 inches where I live, do I have to dig the entire slab down to that dept? it looks to me a huge amount of dirt (and cement..)if I want to do a 62x62 base slab...
Any suggestion?

No, just the perimeter. Also remember, that 30" mark is from final grade. If your final grade will be lower or higher around the perimeter, adjust accordingly. For example,if there is a way you can raise up the grade later, you wouldn't have to go so deep. Also, you need to be on solid undisturbed soil, not fill. So, in theory, you might dig down 30" in one spot, but still be on fill. So, it's 30" from final grade and be on solid ground, also. Personally, I like to go just a bit deeper and add a few inches of clean gravel, if you can. Are you planning on any rebar?

[iluvpizza]

Re: Base Slab question

One last question: I know that the freeze line should be at 30 inches where I live, do I have to dig the entire slab down to that dept? it looks to me a huge amount of dirt (and cement..)if I want to do a 62x62 base slab...
Any suggestion?

[iluvpizza]

Re: Base Slab question

thank a lot for the answers! I think that there is good dirt underneath the patio but I do not want to lift up bricks to confirm it. I will have to find another spot for my oven

W la pizza W

[NCMan]

Re: Base Slab question

I also agree. Being from there originally, if my memory serves me and they haven't changed the code, the frost line is 30" in most of the state, except for the western part, which is/was even deeper. Smart move to excavate and do it right. That's alot of time and expense to chance not doing it the right way.....if you can. There are alot of knowledgeable and experienced folks on here to help when they can. Best of luck w/your build.

[Les]

Re: Base Slab question

Ditto w/ Gulf - No! You live in Maryland, you have serious problems with freezing. Many have built on a bed of crushed gravel, many have taken the safe route of pouring DEEP footings per your code.