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Concrete Patio Question - Any Experts Here? (Northeastern USA - Cold Weather Climate)

Warrior

Power User
We are looking to have a patio built on our newly constructed home (We closed in February). This is a new sub and lots of people are getting cement work done right now.

One of the "contractors" has poured about 5 patios here that I'm aware of. He is very reputable around this neighborhood and I've seen his work. It looks fantastic but not sure if he's licensed. He said he works/worked (dialect was strong) for a cement company and is now doing it on his own.

I think he works for a company and does his own thing on the side (nights and weekends).

He pins/dowels the slab to the basement concrete wall by drilling (1/2"?) holes and inserting rebar which extends into the slab when poured.
This will keep the slab from sinking as the grade settles.

I've been reading on this practice and there are those who say do it (including a post on Bob Villa's site) and those who say don't. Some municipalities require it and others don't.

Those who say "don't" either say it's not needed or it could damage foundation when slab is heaved due to frost.

Not sure what to do.

Also, many folks around here are not getting permits for cement patio's - including my next-door neighbor and a couple of others on my block alone (decks yes). I know our township requires one but his price is very tempting.
 

NeoSound

Fractal Fanatic
Stabilize the ground -

compress the ground with one of these to minimize settling - making sure the water drains away and doesn't seep under the concrete will further protect it from movement.
1592659183090.png



I would say don't attach it to the foundation, if the dirt isn't stable under the concrete and it settles then you may have a cave or a pit for water underneath, which will only cause more problems eventually.

I'm not a concrete pro but I have been around construction most of my life.
 

chumbucket

Inspired
Don't know what the weather is like there but I would wait until fall before getting any concrete poured. Dry hot weather is awful for the curing process. Mild rainy weather in the 50's is ideal.
 

Toopy14

Fractal Fanatic
Where do you live, generally speaking...ie., do you have cold winters, etc.? I presume so, since you said you have a basement.

If it’s a new build, I wouldn’t do anything for a few years until the ground settles. No matter how much compaction you do, newly excavated ground will still compact and settle over time due rain, snow, gravity, etc.

As for attachment to the foundation wall, I wouldn’t do it. The patio should float and have relief cuts in it. There should also be expansion joints between the patio slab and the foundation wall. If the slabs heave due to frost or settle, they may compromise the foundation. If cracks form in the foundation, then you will have all kinds of issues with water penetration. It will be a lot cheaper to repair the patio slab, if it cracks or heaves, then it will be to repair the foundation.

Typically, any structure, like a deck, attached to a house, has to have it’s own foundation. If it’s a floating deck, under a certain height or a patio slab, then you are not supposed to attach it the house, for the reasons I mentioned.

I would stay away from any contractor that says you don’t need a permit. That’s a huge red flag for me.
 

jimbop

Inspired
well in the UK...6" of compact hardcore.....a mesh and 4-6" slab wont move or settle in your lifetime.
if internal, run a flexcell or similar expansion around the perimeter.
it generates heat as it goes off so if its warm out, give it a little spray with water as it sets.
 

TG3K

Power User
I don't know that I'm an expert, but my dad was a prominent construction materials engineer and I grew up in a construction materials lab. I knew the difference between cement and concrete by the time I was about 5 years old, lol. I eventually worked for a number of years as a soil and concrete testing tech and civil/structural construction inspector. I've also done a fair amount of construction forensics, determining the cause of failures.

Whether the slab will settle or heave really depends on the soil type it's on and how the soil was prepped. Compaction is important, but getting the soil to the correct moisture content before compacting it is equally important. Just running a tamper on dry soil won't do the trick. And different soil types have different optimum moisture contents. Soil types vary a lot by region. What works here in the desert southwest might not work well at all in the Great Lakes region. You can even see profound differences in soil types (and behavior) from one end of town to the other. I'd suggest getting advice from a good local civil engineer or contractor, specific to the lot where your house is built.

Regarding pinning the slab to the foundation, I would recommend against doing it unless you KNOW that the soil below the foundation and the slab are both compacted to the same density, and that you're not on any type of expanding or heaving soil (typically clay). If one moves and the other doesn't, something will crack, most likely the slab since it's generally thinner. The only time I can recall seeing slabs pinned like that were on airport aprons (where they park commercial jets), and that was to pin slabs to each other. And each slab was sitting on very carefully compacted material. (In the case of this project, it was an 18" thick concrete slab poured on 4" of compacted asphalt sitting on top of 18" of compacted gravel base course sitting on 24" of compacted native soils.) Where I live, an expansion (or isolation) joint is typically put between the slab and the foundation in a case like you're describing. But your local codes should be the determining factor.

Some unlicensed contractors do great work, some are hacks. The same is true for licensed contractors, but if a licensed guy screws something up, he's generally got insurance and other things in place to protect you, the buyer. If "Side Hustle Sam" screws up, the buyer is often left holding the bag. I've used both types of contractors for work around my house, and so far haven't had any hack jobs done. Licensed or not, often word of mouth is a good way to find out who does good work and is familiar with local conditions.

Don't know what the weather is like there but I would wait until fall before getting any concrete poured. Dry hot weather is awful for the curing process. Mild rainy weather in the 50's is ideal.
Mild damp weather is ideal, but there are lots of ways to successfully pour and cure concrete in hotter (and colder) weather. I've been on pours in freezing mountain temps and in the middle of summer in the desert. Here again, a knowledgeable local guy should know how to deal with the local conditions.
 
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Warrior

Power User
Great advice folks.

I'm in southeastern Michigan (Near Ann Arbor) so we have cold winters.

The contractor works for a company doing the same thing for his day-job and has been doing his own work on the side.
He told me he is considering going full-time on his own.
He did my next-door neighbor's patio last year (new construction) and just completed one 2 doors down. He just sealed it this morning.
He's done several others in the neighborhood. Only time will tell, I guess, but his work looks very good.

The construction supervisor told me the ground here has lots of sand but I know there's a lot of clay - at lest on the surface.

Not sure if this picture helps but here's a photo after the footings were poured.

IMG_2063 (1).jpg

I buried PVC for the gutter downspouts and it was the hardest dirt I've ever dug.
I also dug holes with a post hole digger - to act as French drains - and had a hard time getting to just 24".

I reached for estimates to some other companies. One of them that does a lot of very high-level called me yesterday.
They told me we were out of their service area so I asked them about pinning the patio to the basement wall - is that the "right way" to do it - and they told me that's how they do it.

Not sure if it is the "right way" to do it but coming from a company with their level of experience and high-level of work, it does give me some confidence in the practice.

I do understand the advice of waiting a few years to allow the ground to settle and I agree it is very good advice.
However, I know we're just not likely to wait that long. They backfilled in September of last year so it's been 10 months.

The area at the top of the photo is where the patio will be. The final grade is a little higher than shown here.

IMG_2225.jpg
 

Tahoebrian5

Fractal Fanatic
I’m a structural engineer. Best practices for patio slabs is to let them float separate from your foundation. As mentioned above, subgrade prep, sufficient rebar, and control joints are usually sufficient to keep it from cracking.
 

TG3K

Power User
...As mentioned above, subgrade prep, sufficient rebar, and control joints are usually sufficient to keep it from cracking.
You're right, but the three rules I've learned about concrete:

1. It's almost always gray
2. It gets hard
3. It cracks :D

The control joints are there just so you can tell it where you want it to crack, lol. But done right (like you described), the cracks will just be cosmetic, not structural.
 

Tahoebrian5

Fractal Fanatic
You're right, but the three rules I've learned about concrete:

1. It's almost always gray
2. It gets hard
3. It cracks :D

The control joints are there just so you can tell it where you want it to crack, lol. But done right (like you described), the cracks will just be cosmetic, not structural.
Right, was trying not to get overly technical but in the spirit of conversation I’ll add to your comments.

yes all concrete cracks, the idea as you mentioned is to control the location and size of the cracks. Interesting factoid.. most rebar in slabs is considered “temperature“ steel, meaning the ratio of steel to concrete is optimized to keep the micro cracks that occur during expansion contraction due to temp fluctuations small enough that they don’t become a nuisance.

How well the slab holds up during curing is mostly due to experience and craftsmanship of the installer. If the top cools at a different rate than the bottom it can cause curing cracks. some contractors use blankets over the top to help out. Then there is the whole sand vs gravel base and some builders successfully pour directly on vapor barrier.

in general if the builder is experienced that is a good sign but I would definitely not pin it to your foundation.
 

jimbop

Inspired
ive seen frost heave in footings, not in a reinforced floating slab.
i was a brickie/builder for 40+ years, done hundreds of extensions.
no cracking either if you have expansion joints on the perimeter or every 3M if slab is large.
 

Warrior

Power User
Thanks, everyone for your opinions and advice.
We've decided to spend a little more and hire a contractor that pulls a permit, who's workmanship looks much better and who will pin the slab to the wall if we want - but doesn't recommend.

We are not pinning it to the wall.

He said he knows of only 1 county in Michigan that requires it.
 
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