[Ginfamous]

Building a 12'x8' shed with a concrete slab floor. I've put down 4" of gravel and laid my form in place and the form is too short to make a 4" slab. Can I stack 2 forms on top of each other to achieve the height needed for my slab? Or do I need to completely remake my form?

 

[Nealtw]

How thick did you want it and what did you build it with. You can raise a 2x4 frame to 5" and it would be fine.

 

[Ginfamous]

How thick did you want it and what did you build it with. You can raise a 2x4 frame to 5" and it would be fine.

I want a 4" thick slab with up to 6-8 inches at the edges in order to support the weight of the walls and roof.
I used 2x6's but forgot to compensate properly for the depth of the thicker outer edge of the concrete to support the walls so at that depth it only makes like a 1"-2" thick slab. You think it would be fine to build an additional 12'x8' internal dimension frame out of 2x4 and secure that on top?

 

[Nealtw]

I want a 4" thick slab with up to 6-8 inches at the edges in order to support the weight of the walls and roof.
I used 2x6's but forgot to compensate properly for the depth of the thicker outer edge of the concrete to support the walls so at that depth it only makes like a 1"-2" thick slab. You think it would be fine to build an additional 12'x8' internal dimension frame out of 2x4 and secure that on top?

I would do it with 2x4s and raise it to the level you need, an inch or two off the ground is fine.
brace it like this.

 

[Ginfamous]

I would do it with 2x4s and raise it to the level you need, an inch or two off the ground is fine.
brace it like this.
View attachment 639213

Ok. The bracing pictured, is that also done with 2x4s? Also, I was thinking of using a few scraps of 2x8 to connect the top form to the bottom form. Would this be necessary with the bracing you suggest?

 

[Nealtw]

Ok. The bracing pictured, is that also done with 2x4s? Also, I was thinking of using a few scraps of 2x8 to connect the top form to the bottom form. Would this be necessary with the bracing you suggest?

set your frame in place, drive 2x4 stakes beside it, lift the frame to height and nail it, use your level as you go around and nail the frame to stakes and then place the back up braces to support it for the weight of the concrete.

 

[Ginfamous]

set your frame in place, drive 2x4 stakes beside it, lift the frame to height and nail it, use your level as you go around and nail the frame to stakes and then place the back up braces to support it for the weight of the concrete.

But, if doing that, won't the concrete spill out the bottom of the form?

 

[Nealtw]

But, if doing that, won't the concrete spill out the bottom of the form?

We do an 8" footing with 2x6, if the concrete is running out under there is something wrong with the mix,.
After you have your form in, you can always throw dirt or gravel on the outside to lesson the gap.

 

[Ginfamous]

Ok.

We do an 8" footing with 2x6, if the concrete is running out under there is something wrong with the mix,.
After you have your form in, you can always throw dirt or gravel on the outside to lesson the gap.

Attached are a couple of pictures of the current state of the foundation. If I understand correctly, your suggestion is to simply raise the entire form by a couple inches to achieve the desired slab. As you can see, the surrounding area is not level, which isn't a problem over all just something we have to work around. The first corner is really my one concern as we were not able to dig it as deep as we would have liked.

 

[Nealtw]

Ok.

Attached are a couple of pictures of the current state of the foundation. If I understand correctly, your suggestion is to simply raise the entire form by a couple inches to achieve the desired slab. As you can see, the surrounding area is not level, which isn't a problem over all just something we have to work around. The first corner is really my one concern as we were not able to dig it as deep as we would have liked.

Is the top of the form level now all the way around?

 

[Ginfamous]

Yes

 

[Nealtw]

Yes

So if you had built the form with 2x10 you would be in good shape. Just add to the top and add taller stakes.

 

[dj3]

Regarding your photos: You have re-bars holding the form, but you need to use stakes nailed to the forms. You want the form to be stationary.
1x3 or 1x4 stakes are fine, metal stakes are also fine. Use double head nails or screws to fasten them.

 

[Ginfamous]

It was decided to go with raising the form to meet the height we needed for the slab. And yes, the form is currently being held in place with rebar. The area we are working in is still high traffic so we are keeping the trip hazards low until we are ready to pour the concrete. Thanks everyone for the input. ☺

 

[jomama45]

Seeing as your steel stakes are already below the top of the form, I'd suggest adding a 2x4 flat on top, screwed into the 2x6. If you need to go higher/ thicker, add a 1x4 into the mix. Using a 2x4 in this way will mean that you won't have to bother with bracing, most likely......

 

[Ginfamous]

Being that it was our first big pour it was rough, but it seems like it went well over all yesterday. We did misjudge the set time of the first 4 feet so didn't get the J bolts in place properly in that section but oh well. Nothing a drill can't fix later. Thanks for all of the advice!! 😊

 

[huesmann]

Hopefully you covered it up immediately after that photo was taken.

 

[Ginfamous]

We had it covered over the first night, it's been raining pretty steady since early morning yesterday. We were going to spray it with acrylic curing and sealer, but according to the bottle it is too cold and rainy here for that. Everything we've read so far has indicated that leaving it open to the rain is just as good as watering and covering. Did we misunderstand something and need to alter our curing treatment?

 

[huesmann]

I guess it depends what kind of surface you want? I would think rain could leave it pitted.

 

[jomama45]

We had it covered over the first night, it's been raining pretty steady since early morning yesterday. We were going to spray it with acrylic curing and sealer, but according to the bottle it is too cold and rainy here for that. Everything we've read so far has indicated that leaving it open to the rain is just as good as watering and covering. Did we misunderstand something and need to alter our curing treatment?

No, don't change anything. Cold/wet/damp are the perfect recipe for strong concrete. As long as it wasn't allowed to freeze for the first 2-3 days (surface temperature, not necessarily air temp) you'll be fine.