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Concrete Floor Questions

tbz

tbz

Silver Member
Joined
Sep 10, 2010
Messages
1,250
Location
PA/NJ - Borderlands
So, If this seems like a dumb question, well its because I only know my trade's portion of the IRC, but working on building my new home and I am learning the finer parts of the sections I don't ever read lately.

So when you are lost, look for help, so a little clarification would be helpful, please.

I am putting down 2" foam over the gravel and foundation and then laying in 1/2" radiant heat tubing for in the basement concrete floor.

I am going to be using 4,000psi concrete with the fibers mixed in and from what I am reading on the WWW, says when using the fibers you don't need to use wire mesh.

Been about 20 years since my last floor pour and I am trying to verify this. I might still put the wire mess in place to just keep the tubing in place, but wanted to verify if there is an option to leave out the wire mesh when using fibers in the concrete mix, and what section of the 2018IRC for PA would I find this knowledge.

Thanks for the help - Tom
 
Similarly, not a requirement of our code North of the border either. However, I had a home owner overseeing their own build ask me this question once. I recommended keeping the WWM, but she was still undecided. I told her to talk with people who finish concrete floors for a living and see what they said. Overwhelmingly, they said that they only do a job if the WWM is used.
 
tmurray said:
Similarly, not a requirement of our code North of the border either. However, I had a home owner overseeing their own build ask me this question once. I recommended keeping the WWM, but she was still undecided. I told her to talk with people who finish concrete floors for a living and see what they said. Overwhelmingly, they said that they only do a job if the WWM is used.
Click to expand...
Interesting to hear that, the information I keep hearing is with the heated floor system being radiant and sitting on 2 inches of foam insulation that the fiber mesh additive adds a lot more strength, flexibility and air, greatly improving the slab and the metal wire works, but is nothing more than something to tie the tubing on to.

The only reason I want to keep it, is for the tubing layout.
 
Just like the mesh is not required, but good trade practice...

R506.2.4 Reinforcement support. Where provided in
slabs-on-ground, reinforcement shall be supported to
remain in place from the center to upper one-third of the
slab for the duration of the concrete placement.
 
Mesh or rebar only helps if it is raised to approximately the middle of the slab. Best practice is to support it on chairs. Some concrete contractors lay it on the vapor barrier or ground, then pull it up with a rake as they spread the concrete. Many just lay it on the vapor barrier or ground and leave it there.
 
You don’t think the radiant tubing tied to the mesh might cause problems? Galvanic corrosion or friction wear?
 
e hilton said:
You don’t think the radiant tubing tied to the mesh might cause problems? Galvanic corrosion or friction wear?
Click to expand...
Depends on the pipe material. Locally, I have only seen PEX used for radiant tubing (no galvanic corrosion issues). Once encased in concrete, friction wear is non-existent.
 
The home is in the mountains of PA, ground is hard shale pretty much can't dig without hitting rock.

Footings will be set 42" deep with the walkout basement, poured concrete walls, thus slab will be inside walls with 2" insulation under and around the wall edge.

This picture shows a typical installation with the plastic PEX pipe strapped to the WWM.

most of the people I have been conversing with are strong on the fiber additives for heated floors.

maxresdefault.jpg
 
Just my two cents along with steveray and ICE. First, I have never been a fan of fibremesh, it doesn't do well in shear or "hold cracks together. WWF rolls are almost as worthless because of the typical installation ("hook" with the rake and pull it up, about as precise as a shotgun in water). For years I would specified W2.4xW2.4 WWF flat sheets (W2.4 is the lightest ga. for flat sheets and can be set on chairs) with better but not great results. Like ICE I've been using "real" reinforcement for about 20 years but I specify #3 at 18" EW (the 18" permits "stepping" in the grid without pushing the bars down) set on "real" chairs (would recommend sand chairs on foam). Back to the OP, I would tie the PEX to the rebar (in the center of the slab), I would also use foil faced poly ISO for your insulation. Just my thoughts.

Ken
 
tbz said:
Interesting to hear that, the information I keep hearing is with the heated floor system being radiant and sitting on 2 inches of foam insulation that the fiber mesh additive adds a lot more strength, flexibility and air, greatly improving the slab and the metal wire works, but is nothing more than something to tie the tubing on to.

The only reason I want to keep it, is for the tubing layout.
Click to expand...
Just to clarify, she ended up going with both the fiber reinforcement and the WWM.
 
If the wire is NOT lifted into place it does nothing for the slab. Some concrete guys don't like the fiber in the concrete mix due to it some times clumps and is a little harder to finish. I've used just fiber in slabs for drive ways and some are 20 yrs. old now and very few have significant cracking. I would suggest to use the wire & fiber. If you get a finish with little hairs, most of the time a propane burner will take care of it.
 
my two cents. forget the fiber,

the wire mesh shall be set on metal chairs, then the radiant tied to the WWM. That is what I would do at my house.
 
Paul Sweet said:
Mesh or rebar only helps if it is raised to approximately the middle of the slab. Best practice is to support it on chairs. Some concrete contractors lay it on the vapor barrier or ground, then pull it up with a rake as they spread the concrete. Many just lay it on the vapor barrier or ground and leave it there.
Click to expand...

No Soup for you said:
my two cents. forget the fiber,

the wire mesh shall be set on metal chairs, then the radiant tied to the WWM. That is what I would do at my house.
Click to expand...
What have you got against reinforcement?
 
khsmith55 said:
Just my two cents along with steveray and ICE. First, I have never been a fan of fibremesh, it doesn't do well in shear or "hold cracks together. WWF rolls are almost as worthless because of the typical installation ("hook" with the rake and pull it up, about as precise as a shotgun in water). For years I would specified W2.4xW2.4 WWF flat sheets (W2.4 is the lightest ga. for flat sheets and can be set on chairs) with better but not great results. Like ICE I've been using "real" reinforcement for about 20 years but I specify #3 at 18" EW (the 18" permits "stepping" in the grid without pushing the bars down) set on "real" chairs (would recommend sand chairs on foam). Back to the OP, I would tie the PEX to the rebar (in the center of the slab), I would also use foil faced poly ISO for your insulation. Just my thoughts.

Ken
Click to expand...

Ken IMHO is spot on!
 
Holds the tubing at the bottom of the concrete away from any rebar or WW that may be used to control cracking in the slab.
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No, nothing against rebar at all. It would be great but probably overkill for the basement slab.

If the wire mesh is installed on chairs as it should be, (not pulled up by the old hook method) I would say that should be sufficient for a typical pour.

But hey, rebar would be great, why not.......... Its only time and money....... and not ours... HAHAHA :)
 
Years ago one developer used copper tubing to heat the slab on grade. There were numerous corrosion problems and most owners ended up abandoning the slab heating.

Fibers have their place in dealing with initial shrinkage cracks, but are not effective in dealing with cracks resulting from long term shrinkage, poor subgrade, or loads on the slab.

The use of foam on gravel will likely result is a soft subgrade which will result in cracks. In order to get a level bed for the foam place it on sand. The use of a more substantial slab will help. In addition not all foam is equal. You want a stiff foam.

Current thinking is to place a vapor barrier directly under the concrete. This is to deal with moisture migrating from the ground into the house resulting in mold.

Use a low slump concrete mix with as little water as possible. It is the water that causes the shrinkage cracks. Water reducing admixtures can help.

Inevitably concrete cracks either from shrinkage effects or from loads placed on the slab. What you can do is to control the size and spacing of the cracks. Wire fabric is basically ineffective because it ends up on the bottom of the slab and because it does not provide enough steel to control the size and spacing of the cracks.

My practice has been to specify a 5 inch slab with #5 rebar at 12" oc. each way. I realize that some will be threatened by this recommendation but after looking at many slabs over the years these lesser slabs often have cracks that cause problems. In addition the amount of reinforcing is based on data from an ACI publication. This works. You can try to save some money but is it worth it? I would be concerned that any substantial cracks would result in failure of the heating tubing which is not easily fixed.

Use rebar located on supports. Inevitably the wire fabric ends up at the bottom of the slab even if supports are used. Attempts to pull wire mesh up to the middle of the slab are ineffective. Use typical reinforcing supported on chairs or special concrete blocks. The workmen placing the concrete should not be able to displace the reinforcing.
 
Is using poly jacking a good idea? It seems this technology can help protect the floor from the soil's dampness and make it not as cold. It also can help save money on floor heating.
My house needs a major renovation, and I want to make general estimates before calling any contractors. I don't know much about construction, so I'm doing my research now, not relying on someone's opinion completely. I just want to know what I want from the concrete constructors from my town I will hire.
I want the house to be as dry as possible because the soil in this area is very wet, and it causes mold in houses.
 
It appears that you are talking about an existing building. Do you have moisture problems? If you do not, then your concerns may be leas. What is the source of the water? If the water is from runoff, then installing drainage around the house may be effective.

Consult with an Architect. They generally have more awareness of water issues.

Poly jacking will raise your floor and likely cause other problems.
 
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