Instructables

Laying a foundation for a tool shed or children's playhouse

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Picture of Laying a foundation for a tool shed or children's playhouse
This tutorial shows how to lay a strong 6' x 3' x 4" concrete slab a foundation for a small structure such as a toolshed or children's playhouse.  What's different from this foundation and a simple concrete slab is the inclusion of steel bolts embedded in the concrete that a 2x4 frame plate can attach to.  If you just want a concrete slab for other uses (grill, trash cans, etc.) just leave the bolts out in the last step.

I made it in TechShop.  You just need to take the WOD101: Woodshop SBU class in order to be qualified to use all the tools in the TechShop to make the concrete mold frame and stakes.  The really nice thing about TechShop is that you can buy the lumber next door at Lowes and walk right into the woodshop and cut it before taking it home.
 
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Step 1: Tools & Materials

Picture of Tools & Materials
IMG_20131108_094654.jpg
Tools you'll need:
- flat head shovel
- float or cement trowel
- curved cement trowel for creating a smooth rounded edge around the slab
- large flat bucket for mixing the mortar
- 2x4 about 2 or 3 feet long for tamping the concrete
- (2) 6' 2x4s and
- (2) 3' 4" 2x4s for the concrete mold frame
- several 1x2 stakes to secure the mold frame to the ground while pouring
- gallon bucket
- long (3' ) level
- (optional) bolt cutter to cut the wire mesh to fit inside the frame

Materials you'll need
- (6) 80 lb bags of Maximizer quick setting concrete mix (or the equivalent that makes a 3' x 6' x 4" slab)
- 14 gallons of water (2.33 galllons of water for each 80 lb bag) (or the equivalent for your concrete mix)
- (optional) 3' x 6' piece of steel wire mesh
- (11) 3" long 1/4" wide hex bolts
- (not needed right now for the foundation but for when you attach your frame) (11) 1/4" washers
- (not needed right now for the foundation but for when you attach your frame) (11) 1/4" nuts

Thank you for sharing your hard work.
The great thing about an effort such as yours (even if imperfect), is it does two things. First, it allows knowledgeable people who don't have the time or knowhow to make an Instructable to make improvement instructions.
And second, it encourages the rest of us to have the courage to attempt what you have done.

Bravo.

I meant improvement suggestions. Oops.

CHIEFGR8TWOLF8 months ago
I see you were following the instructions, but just to give you a heads-up. Rather than scraping the ground you want to dig at least 4 to 6 inches , compact the soil, and put 4 inches of gravel also compacted before pouring the concrete. You want to do this to get the proper support. This will also let water drain around it and into the soil without causing the slab to upheave during heavy rain or freezes. I read what papa2 said and he is correct, but you can fix that with pressure treated wood, painting the wood, or putting water sealent on it. No matter what you do though eventually wood will rot. duration and speed reduction is all you can truly hope for. Good luck, don't know what your climate is but if you get a heavy freeze you may see some cracks or even movement if this step was omitted.
papa29 months ago
Missing one important part !!! Between concrete and wood are no INSULATION ! The wood will start to rotten. In my country we use simple rubberoid. Otherwise good work !
chuckyd9 months ago
A few suggestions:

After going to all that trouble, you may as well have removed the organic soil and replaced it with compacted fill dirt. The organic soil will continue to move and settle for years to come.

Even with the temperature steel, the 3 1/2" slab seems awfully thin.

The anchor bolts should have an "L" on the bottom side to resist pullout. You can pull those bolt heads right out by simply tightening the nuts on the plates.

Wood in contact with concrete and within 18" of the soil should be preservative treated, else you will have a collapse in a few years.

I would have gone for a modular size, say 2' by 4', to minimize waste.

Great work, though, and thanks for paying attention to the amount of water to use in the concrete.
In a area that is subject to freezing for days or weeks on end a footing below the frost line and a layer of gravel will keep it from lifting then settling all wonky. It is also less likely to crack.
darwincam9 months ago
Nice job. It's difficult to tell what kind of wood you are using for your plate, but it's worth noting that one should use something rot resistance as the concrete will continuously wick moisture to the wood and cause rot. ps - concrete cures.
sircorvus (author)  darwincam9 months ago
That's a great point, I'll call that out in the last step and in the next Instructable I write which will cover the frame.
And...the anchor bolts should be of an "L" or "I" type. If the concrete begins to fail, the small hex heads will pull out IF there is sufficient force. That said with a small shed or storage area, most likely it would be fine given the number you have :-)
criggie darwincam9 months ago
Agreed - the normal method here is to use much longer bolts and wire them to the reinforcing mesh before the pour. You can use a scrap of tape to keep the threads clean of splatter.

Plus, depending on your local authority, a fixed structure like this may require some kind of permit, and roof drainage may be necessary.

Be aware of potential low spots too - don't allow the top of your floor to be below a puddle.

And if you have a young helper, get them to sign your work. Writing the year in a corner is a good idea too.
kinderdm9 months ago
Just curious as I don't see any in the pictures, but is any sort of underlay needed on this? Like say a bed of gravel for support or anything. I've never poured a slab before but I am looking to do a lot in the near future as we just tore out a deck and want to replace with a slab patio, in addition to a new shed and pouring a new pad for an existing closet sized shed.
enginepaul9 months ago
Nice; simple and efficient.
Not criticizing, just from my experience, I use 3" or 3"1/2 regular concrete. On larger sheds I thicken the edges, but have used a plain slab and then 2x6 pressure treated fir a\'footings' to spread the load with no failures here in California.
(the area freezes, but no snow) I always bolt for wind resistance.
sircorvus (author)  enginepaul9 months ago
Good point, I don't have to worry about earthquakes but good to know for those who do.

Wind resistance is a big problem here, but I bolted the plate mostly just to protect against marauding children :-)
Serega_Canada9 months ago
Good job, dont want to look like a smarty, but think that you had to leave some space between the shed and the fence, so that water and snow dont get trapped, other then that, good job )
sircorvus (author)  Serega_Canada9 months ago
Good catch, I don't have to worry about lots of snow in Austin but it's worth noting for those who do. Leaves also might be a concern. In the case of my shed, I'm planning for the roof to hang even with the fence which should keep out most of the leaves.