# Doweling in a concrete repair



## twoply (Apr 11, 2017)

I'm looking for something somewhere that gives guidance for repairing interior concrete slab on grade. The mechanical contractors sawcut and excavated for some light unground work, and the patchwork crew is coming.

Look for what is the code, not what you think should be there.

I cant find anything about 4"-5" slab repair dowel spacing or sizes.

I've checked the concrete ACI book and they only talk about slabs 5" and thicker.

I'm just a little surprised that it's not anywhere. Am I missing something?

Thanks in advance!


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## steveray (Apr 11, 2017)

Project engineer or designer?


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## north star (Apr 11, 2017)

# ~ #

Which Section of ACI 318 are you referring to,
for the 5" dimension ?........Also, which edition
of ACI 318 are you using ?.......There is now a
2014 edition available.

*# ~ #*


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## Francis Vineyard (Apr 11, 2017)

May help to know the minimum Live Load, a parking deck or on expansive soil for applicable section of the code.


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## ICE (Apr 11, 2017)

What  steel is in the slab?


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## JBI (Apr 11, 2017)

If not prescriptive (detailed in the Code) then it is 'design in accordance with accepted engineering practice'.


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## Mark K (Apr 11, 2017)

Unless specifically designed to resist forces, and most slabs on grade are not, this is not a code issue.  I believe you will find a statement to this effect in either ACI 318 or Chapter 19 of the IBC.  If in doubt talk with an engineer.


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## conarb (Apr 11, 2017)

Doweling requires epoxy, Chapter 17 requires special Inspection for all epoxy doweling.  I have got some city inspectors to sign off my epoxy doweling on minor work, I have everything ready when they show up, air compressor with a blowing nozzle, brass hole cleaning brush, and epoxy gun set up and ready to go, some will sign me off if they see I know what I'm doing, but it's at their option.


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## fatboy (Apr 11, 2017)

Agree with JBI and Mark.....unless it must be engineered for some reason, move on along..........


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## Mark K (Apr 11, 2017)

Conarb

If slab on grade is not covered by the code then there is no need for special inspection of installation of anchors in existing concrete.  From a practical point of view you still need to install the anchors properly but it is not a code issue.


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## conarb (Apr 11, 2017)

Mark K said:


> Conarb
> 
> If slab on grade is not covered by the code then there is no need for special inspection of installation of anchors in existing concrete.  From a practical point of view you still need to install the anchors properly but it is not a code issue.


Mark:

If the slab on grade is part of a structure I think it is covered by code, otherwise why are ABs required to be suspended in place for inspection.


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## fatboy (Apr 11, 2017)

Slab on grade is usually part of a post tension foundation? Engineered? We don't see them around here. Footings, then foundation walls, the only slabs are basement floors, and garage/driveways, and they float, not tied to the foundation.


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## Francis Vineyard (Apr 12, 2017)

*1901.2 Plain and reinforced concrete. *Structural concrete shall be designed and constructed in accordance with the requirements of this chapter and ACI 318 as amended in Section 1905 of this code. Except for the provisions of Sections 1904 and 1907, the design and construction of slabs on grade shall not be governed by this chapter unless they transmit vertical loads or lateral forces from other parts of the structure to the soil.

Commentary:The structural concrete provisions of the code comply strictly with the provisions of ACI 318/318R, except for the modifications contained in Section 1905. Slabs on grade are another important exception. Slabs on grade typically only convey the gravity dead load of the slab and the gravity live load superimposed on the slab directly to the soil; thus, slabs are not considered to be the “structural concrete” that must comply with the design provisions of ACI 318. Slabs on grade, however, must comply with the durability provisions of Section 1904 and the minimum thickness and vapor retarder provisions of Section 1907.

The last sentence of Section 1901.2 clarifies that slabs on grade used to transmit “vertical loads,” “lateral forces” or both from other parts of the structure to the soil must comply with all the applicable portions of this chapter and ACI 318. In many cases, slabs on grade are used to transmit lateral forces due to wind or earthquakes into the ground. A common example is a typical pre-engineered metal building in which the shear at the bottom of the columns is resisted by placing “hairpins” around the column anchor bolts in the footing and extending the hairpins into the slab on grade.

It is specifically stated in ACI 318 Section 1.4.7 that it does not govern the design and construction of soil-supported slabs, unless the slab transmits vertical loads or lateral forces from other portions of the structure to the soil. This does not preclude the application of any ACI 318 provision that would ensure the proper strength, durability, and abrasion resistance of concrete slabs on ground. Slabs on ground may be plain concrete without any reinforcement or may contain shrinkage and temperature reinforcement in the form of reinforcing bars or wire mesh.


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## conarb (Apr 12, 2017)

Francis said:
			
		

> The last sentence of Section 1901.2 clarifies that slabs on grade used to transmit “vertical loads,” “lateral forces” or both from other parts of the structure to the soil must comply with all the applicable portions of this chapter and ACI 318. In many cases, slabs on grade are used to transmit lateral forces due to wind or earthquakes into the ground.



In areas of expansive soils building slabs are all structural, there was a time that we used post-tensioned slabs on grade but homes heaved as much as 3" from one end to the other.  Today most slab homes and buildings here are monolithic pours with the rebar going from the footings through the slabs, even garage slabs are now monolithic pours.  There was a time back after WWII that FHA required stem walls in garages so occupants could "hose out' their garages, it also helped with the requirement that garage slabs be at least 4" lower than the home floor so gas leaking from cars couldn't run back into the houses, builders building anticipating FHA financing built stem walls in their garages so their slabs did float free.  A friend builds in Houston with very expensive soils, he builds with bell-bottomed piers and cardboard cartoons under his structurally reinforced slabs.  *Here is an example of carton forms.*

In my 60+ years building I have never built a slab that wasn't reinforced so anyone cutting into one of my slabs is going to cut into steel, and in most of those cases the engineer has used the slab as a diaphragm that he has carried loads from the roof to the earth.


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## fatboy (Apr 12, 2017)

Agreed.......different areas, different requirements.......apples and oranges.......


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## ADAguy (Apr 13, 2017)

1. is there a membrane under the slab?
2. Does existing slab have 6x6x10x10 wire?
3. Depth of water table?
4. Any freeze/thaw concerns?
5. Depth of underslab excavations?
6. Any soils report?
7. Use of building?


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## ameliasolis (Jun 18, 2022)

twoply said:


> I'm looking for something somewhere that gives guidance for repairing interior concrete slab on grade. The mechanical contractors sawcut and excavated for some light unground work, and the patchwork crew is coming.
> 
> Look for what is the code, not what you think should be there.
> 
> ...


I cut a decent portion out of my slab and I have some questions about dowels.

Area:

1) The slab is 4" in most areas. Should I use 3/8" or 1/2" rebar/smooth round steel? (I am personally leaning toward 3/8" so there is no chance of cracking)
2) Should I drill the holes just 1/8" larger than the rebar?
3) What type of epoxy(or whatever) should be used to hold the rebar? ..or perhaps no epoxy and just form oil/grease
4) How deep should the hole in the existing concrete be and how much should the rebar stick out.
5) 16" OC or 24" OC?

Thanks!


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## ameliasolis (Jun 18, 2022)

ameliasolis said:


> I cut a decent portion out of my slab and I have some questions about dowels.
> 
> Area:
> 
> ...


thanks in advance for any help


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## ICE (Jun 18, 2022)

Without an understanding of the details such as what, where, how and why, here is a generic response. (in no particular order)

#1.  1/2" deformed rebar
#2. #4.  5/8" hole six inches deep
#5.  12" on center staggered in trenches and 16" on center field
#4.  20" or width of trench whichever is less
#3.  Simpson Set-XP epoxy
​


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## ameliasolis (Oct 13, 2022)

Francis Vineyard said:


> *1901.2 Plain and reinforced concrete. *Structural concrete shall be designed and constructed in accordance with the requirements of this chapter and ACI 318 as amended in Section 1905 of this code. Except for the provisions of Sections 1904 and 1907, the design and construction of slabs on grade shall not be governed by this chapter unless they transmit vertical loads or lateral forces from other parts of the structure to the soil.
> 
> Commentary:The structural concrete provisions of the code comply strictly with the provisions of ACI 318/318R, except for the modifications contained in Section 1905. Slabs on grade are another important exception. Slabs on grade typically only convey the gravity dead load of the slab and the gravity live load superimposed on the slab directly to the soil; thus, slabs are not considered to be the “structural concrete” that must comply with the design provisions of ACI 318. Slabs on grade, however, must comply with the durability provisions of Section 1904 and the minimum thickness and vapor retarder provisions of Section 1907.
> 
> ...


Hi,

I am working on a basement remodel and have recently trenched approximately 120' lf (1' wide) of the existing basement slab for plumbing. Since most of the flooring under the trenched areas will be tile, I had planned on doweling into the existing slab on either side before I pour back.

My question is regarding the type of dowel and spacing I should be using.

- Should be I be using actual dowels, or will rebar suffice? I had hoped to use #3 rebar (partly for the next bullet point)
- I'm worried about spalling the concrete if I drill (4" sog), and with the trench being 12" wide I'm reduced to drilling at a slight angle. Will this be an issue?
- Is #3 bar enough? What should my spacing be?

Thank you for any help!!!!


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## Msradell (Oct 13, 2022)

ameliasolis said:


> Hi,
> 
> I am working on a basement remodel and have recently trenched approximately 120' lf (1' wide) of the existing basement slab for plumbing. Since most of the flooring under the trenched areas will be tile, I had planned on doweling into the existing slab on either side before I pour back.
> 
> ...


Rebar is sufficient and is actually what is used in most cases. #3 Bar will be fine since you really are doing it for strength as such, you just want to keep the 2 slab sections together. Drilling at an angle will not be a problem and you can actually bend the Bars to make them flat after you epoxy them into place.


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## ameliasolis (Nov 21, 2022)

Francis Vineyard said:


> *1901.2 Plain and reinforced concrete. *Structural concrete shall be designed and constructed in accordance with the requirements of this chapter and ACI 318 as amended in Section 1905 of this code. Except for the provisions of Sections 1904 and 1907, the design and construction of slabs on grade shall not be governed by this chapter unless they transmit vertical loads or lateral forces from other parts of the structure to the soil.
> 
> Commentary:The structural concrete provisions of the code comply strictly with the provisions of ACI 318/318R, except for the modifications contained in Section 1905. Slabs on grade are another important exception. Slabs on grade typically only convey the gravity dead load of the slab and the gravity live load superimposed on the slab directly to the soil; thus, slabs are not considered to be the “structural concrete” that must comply with the design provisions of ACI 318. Slabs on grade, however, must comply with the durability provisions of Section 1904 and the minimum thickness and vapor retarder provisions of Section 1907.
> 
> ...


Hello all,
Sometime back in the late 70s, the concrete floor in my flat was channeled out for central heating pipes.
The concrete covering the pipes has broken down and there is virtually nowhere where it's actually still attached to the existing floor (in fact some bits are just a trench with a loose filling of gravel sized pieces).
Whats the best product to use for repair? My main concern is getting a good strong bond to the rest of the floor.
I was considering the screwfix floor repair compound but i don't think 5kg will go far, could get quite expensive.
Thanks.


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## redeyedfly (Nov 21, 2022)

ameliasolis said:


> Hello all,
> Sometime back in the late 70s, the concrete floor in my flat was channeled out for central heating pipes.
> The concrete covering the pipes has broken down and there is virtually nowhere where it's actually still attached to the existing floor (in fact some bits are just a trench with a loose filling of gravel sized pieces).
> Whats the best product to use for repair? My main concern is getting a good strong bond to the rest of the floor.
> ...


How do you keep finding these slabs?  And how do you remember that you have this thread out there that you pop in from year to year and ask slab cutting/patching questions?  


Pics would help to get a sense of the scale and dimensions of the problem.


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## brokenkeys (Nov 22, 2022)

redeyedfly said:


> How do you keep finding these slabs?  And how do you remember that you have this thread out there that you pop in from year to year and ask slab cutting/patching questions?



I'm guessing you won't get a response, or at least one that makes sense, so I'll give it a shot; uncanny valley. 

It is weird. too weird.


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## Paul Sweet (Nov 22, 2022)

Ameliasolis, you would be best in finding a similar site in the UK, because many American building practices are different than European practices.


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