Monolithic slab preparation a DIY job?

[Paul_VR6]

Very timely thread as I am in the planning stages for my build and due to some constraints a mono slab with a metal, pole or stick built on top may make the most sense.

I haven’t seen it used much here at least for smaller buildings (southeast pennsylvania) but interested in how its working for people in a similar climate. We have **** soil, clay and poor drainage, so I don’t know how that plays in. Also if there are any concerns for driveways and aprons that **** up to the slab.

 

[lakeroadster]

Question: On a monolithic slab are the control joints cut all the way to the edge of the foundation?

If the answer is yes, when the concrete cracks, does it crack all the way through the thickened edge?

Is that why re-bar placement is so crucial in the thickened edge portion?

 

[850xpeps]

Question: On a monolithic slab are the control joints cut all the way to the edge of the foundation?



If the answer is yes, when the concrete cracks, does it crack all the way through the thickened edge?



Is that why re-bar placement is so crucial in the thickened edge portion?

No just control cut like any other slab. Mindful of door and drain layouts.

I’ve seen large slabs without control cuts fair perfectly fine. Small shrinkage cracks hardly noticeable.

 

[gtae07]

I did all my site prep myself, with a skidsteer, shovel, pickaxe, and plate compactor. Leveled and squared the forms with tape measure, string, and a water level.

Inspector said it was the cleanest and most to-code rebar work he'd ever seen

One thing I found really useful was anchor bolt holders--I needed 5/8 J-bolts every 18" due to the hurricane winds and I didn't want to be stabbing them in wet. The holders let me set them in place before the pour at perfect spacing; inspector said he'd never seen them before but thought they were "really cool".

However, around here there's no such thing as a frost line. I think most residential (and even a lot of commercial) construction is done as mono slab, unless you're somewhere in a flood zone and your building is on stilts.

 

[850xpeps]

I did all my site prep myself, with a skidsteer, shovel, pickaxe, and plate compactor. Leveled and squared the forms with tape measure, string, and a water level.



Inspector said it was the cleanest and most to-code rebar work he'd ever seen



One thing I found really useful was anchor bolt holders--I needed 5/8 J-bolts every 18" due to the hurricane winds and I didn't want to be stabbing them in wet. The holders let me set them in place before the pour at perfect spacing; inspector said he'd never seen them before but thought they were "really cool".

However, around here there's no such thing as a frost line. I think most residential (and even a lot of commercial) construction is done as mono slab, unless you're somewhere in a flood zone and your building is on stilts.

Those anchor bolt holders are interesting. I think it would be annoying as hell to screed a slab though lol if J bolts are required o would wet set them for that reason.

Our code is 4’ for anchor points of a wall. Your wind must be a little higher than ours lol common practice is drilling in wedge anchors.

 

[matt_i]

One potential problem with the pre-set bolts is that concrete splash can stick to the threads. I recall a slab my grandfather had poured and all 5 grandsons were employed as free labor to help frame and set up walls. All of the bolts had some kind of concrete stuck to the threads. Very tough proposition to get the threads cleaned. A few hours' work could be saved with a few minutes' prep. Either some wraps of duct tape or greasing the threads is an alternative but messy way.

 

[ConCretin]

Question: On a monolithic slab are the control joints cut all the way to the edge of the foundation?

If the answer is yes, when the concrete cracks, does it crack all the way through the thickened edge?

Is that why re-bar placement is so crucial in the thickened edge portion?

That is a good question, lakeroadster. I can only tell you how I’ve approached the issue. Since the goal of control joints is the avoidance of random cracks, I typically cut all the way to the edge and down the face, increasing the depth of the saw as much as possible. I assume the crack goes all the way through the haunch. I don’t want a crack getting started in the haunch and shooting off across my slab.

For those who don’t know, control joints are especially important in a monoslab because the haunches at the edge restrain the slab from shrinking inward increasingly the liklihood of shrinkage cracks.

The rebar in the bottom of the thickened edge will keep the control joint cracks from opening up but just as importantly, they resist the tension that develops in the bottom of the section as loads are applied to the top. Building loads are pretty manageable but you also need to consider vehicle loads in the area you drive over.

 

[850xpeps]

One potential problem with the pre-set bolts is that concrete splash can stick to the threads. I recall a slab my grandfather had poured and all 5 grandsons were employed as free labor to help frame and set up walls. All of the bolts had some kind of concrete stuck to the threads. Very tough proposition to get the threads cleaned. A few hours' work could be saved with a few minutes' prep. Either some wraps of duct tape or greasing the threads is an alternative but messy way.

Can dip the threads in diesel fuel or spray pan on them. Usually if you spin them off the next day there is no issue. Wire brushes make short work of cement in the threads and much easier when it’s green.