Has anyone ever seen a basement slab that has no expansion joints. The home was built in 2016 and the seller said he was told by the builder that because the slab is installed on footers it didn’t need expansion joints. any thoughts or insight would be appreciated.
Morning, James. Hope this post find you well.
Maybe you are referring to isolation joint? You have an image?
What type of foundation. Deep or Shallow. Individual Footing or Isolated Footing. Combined Footing. Spread footings or Strip footings and Wall footings.
Control, expansion or isolation joint?
Expansion joints. An Expansion Joint allows the slab to move horizontally / vertically. Thus to impede mechanical damage if contact with parts of the structure should occur. IE: Foundation walls, Footings, or Structural Columns.
To answer your question. Yes.
Any images, James?
Around here expansion joint material is used in basements between the foundation wall and slab in lieu of cut or tooled joints out in the floor and it works well in most incidences.
If it is a larger slab, or with several corners, it will be cut or tooled for expansion/control joints.
Yes, many. Sounds like the builder didn’t want to pay for the concrete saw.
I’ve never seen control joints in the slab itself but as others have mentioned, there is an isolation joint at the perimeter
I have never seen the need for expansion joints in a residential basement, I think contraction joints is want the topic is about. Without exposure to the sun I don’t think the basement temperature would rise to the point where expansion would be an issue. Isolation joints around piers and isolated footings is a good thing. IMO shrinkage cracks have been the majority of the cracks typically homeowners see in their basement/garage floor slabs. In a rectangular foundation without foundation wall offsets theoretically a gap will be formed around the perimeter of the concrete slab due to concrete shrinkage as the concrete cures. But, realistically the subgrade the concrete is poured on is not frictionless. The friction plus any offsets in the foundations walls resists the movement of the concrete slab as it cures creating tension stresses in the concrete and shrinkage cracks develop. The best solution is to provide properly placed contraction joints or saw joints. On a rectangular slab try to cut the slab in equally spaced joints trying to make each section as square as possible not to exceed 20 feet. On an irregular shape foundation you have to be creative to ensure each section can shrink without restriction form any foundation offset. Anyone working in commercial construction on large slabs will always see special provisions in the contract and plans to address joint spacing, concrete mix design and temperature requirements to minimize random shrinkage cracks in concrete slabs.
The graphic below shows an irregular slab with predetermined contraction joints. The arrows represents how the concrete wants to shrink towards the center of mass.
YOU MAY HAVE TO CLICK ON THE PICTURES TO SEE THEM.
Exactly why I posted the link above. Inspectors have a BAD habit of using improper terminology, whether from ignorance or laziness, I don’t know, ~smh~
Considering a residential basement or slab concrete, for the most part concrete does not expand. Concrete shrinks after it’s initial pour.
Concrete: “When it first dries, concrete shrinks and undergoes structural alterations that make some of the shrinkage irreversible. Thus, even if it is later resaturated, the initial drying shrinkage isn’t fully recovered.” “However, concrete does indeed expand when it gets hot or when the moisture content changes.”
Accurately correct Randy, thanks for that.
Ok so it seems the biggest problem everyone is having with my post is the term I used and I apologize for that, and yes I was talking about control/contraction joints. I also think it is unnecessary to call someone ignorant or lazy and that is all I will say about it.
To go further on this the I posted prior to seeing the property and it was a question from the buyer realtor and I was mainly asking to understand why a builder wouldn’t put in the control joints. Further to this when the property was inspected it was discovered that the support posts were bolted directly to the concrete slab. Further it was discovered that the concrete slab construction is a “Waffle Slab”, more information can be found here; https://www.cornellengineers.com.au/beware-waffle-slabs/. Thank you to all of you who provided comments most of them were helpful.
Oh grow up!!
If you do not know details of something, you are ignorant of the facts.
If you do know the details of something and fail to properly utilize them, you are lazy.
It’s not my problem you don’t like the definitions of words in the English language!
A waffle slab is an engineered slab, which is a different animal from a standard poured slab. They have reinforcing steel and some may have post tension cables.
Mr Jonas I have grown up and will now avoid your input and comments as they seem to not be following the community guidelines.https://forum.nachi.org/guidelines. Thank you for your input and good day.
Randy, that is what I have learned through research, I also understand there are some people who like them and some who don’t. What I am trying to figure out is how to determine if this is the type of construction I am seeing. Is there something visual that will tell me it is a waffle slab or not. Most people that I inspect for, realtors and buyer alike are used to seeing steel support posts that sit on caissons or piers and not bolted to the concrete floor. It would be nice to be able to show them something that tells them it is a safe construction style.
Feel free to place me on “IGNORE”!!
James, A waffle slab is typically used on poor soil.