# Anchoring epoxy for rebars - how to estimate?



## miamicuse (Nov 13, 2011)

I cut open my concrete slab in order to have access for plumbing repairs below. Now that I am done I have backfilled soil, compacted, termite treated etc...and I need to put in some rebars to tie to old concrete to the new concrete I am going to pour.

It's not a large area so I have drilled about 16 holes 3/4" in diameter and going to use 1/2" rebars.

I need to anchor the rebars into the existing concrete using those two part epoxy that comes in tubes that you inject with a caulking gun. I have never done that before so could use some pointers.

(1) First, I need to figure out how much of this epoxy I need, or what mileage I will get from one tube. Strangely I do not see any quantity on these tubes except like 8.6oz or 10.1oz in weight. That tells me nothing. Looking online I found this product *8.6 oz. Quikrete High Strength Anchoring Epoxy* and in the product Q&A section their "expert" said "_A 8.6 oz. tube of QUIKRETE® High Strength Anchoring Epoxy yields 15 cubic inches of epoxy. One tube can fasten 18 5/8” bolts into 3/4” diameter holes at 6” depth. Yields will vary based upon waste, nonuniform hole dimensions, etc._" Well, if I do my calculation, the volume of a 3/4" diameter hole at 6" depth is 6*PI*(0.75/2)^2 = 2.65 cubic inches. If it yields 15 in^3 divided by 2.65 in^3 = 5.66 less then six holes. How did he get 18 holes? Or is he assuming you wouldn't fill up the entire hole with epoxy because the rebar takes up most of the room? But most videos I saw they bottom the nozzle into the hole and filled the hole, pushed the rebar in and the excess epoxy squeezes out as waste. In my case I have 3/4" holes as well, sixteen of them, 7" deep, and I am wondering if I can get away with one tube, or do I need two or more. I also read from another review that these epoxy tubes have a plunger inside that takes up half the height of the tube. In fact one review said all that came out was half a tube, about 4 oz, before they "bottomed". So I am more confused.

(2) What is a good product to use? I do NOT need it to be fast or rapid set. I can wait a few days before pouring concrete.

(3) Will a regular caulking gun work? Or do I need a powered one? I would prefer not to buy a new gun just to squeeze 1 to 2 tubes, but I also know once you opened these products you have minutes to work or it is wasted.

Thanks in advance for any comments or advice.


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## Nealtw (Jun 22, 2017)

I would put 5/8 rebar in the hole and dump the concrete in there.


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## ClarenceBauer (Mar 4, 2005)

I would use a pre packed epoxy it come in a sealed glass tube.
Drill hole for size of rebar insert glass tube put rebar in drill chuck insert behind epoxy tube pull trigger it mixes epoxy no mess no two parts mix.
Any tube left over store and use later.
I use to get the tubes from Hilti.


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## Nealtw (Jun 22, 2017)

I love solving problems, but usually you need a problem to solve. 
What exactly is the problem that we are solving by putting expensive goo in the holes?


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## concretemasonry (Oct 10, 2006)

How big of a truck are you going to drive over the "patch"?

Dick


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## miamicuse (Nov 13, 2011)

It's indoors so no vehicular loads. May be a big refrigerator or water heater or piano may go across it.


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## Daniel Holzman (Mar 10, 2009)

I am a little puzzled by this thread. Most residential slabs are not structural, they are simply there to provide a solid, easily cleaned walking surface, or to support a flooring material. Most residential slabs are about 4 inches thick, and often contain no rebar at all, usually just steel mesh for crack control. So why exactly are you going to the great trouble and expense of epoxying rebar in to tie the new slab construction to the old slab?

If you need structural support because the slab is doing more than providing a walking surface, you need to EXACTLY follow manufacturer instructions for the use of their two part epoxy. This means precise hole size, cleaning the hole, temperature range of the epoxy, curing process, everything. Typically each manufacturer has very specific tolerances for the hole size for a particular bar, so you need to purchase the epoxy first, then drill later.


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## Nealtw (Jun 22, 2017)

miamicuse said:


> It's indoors so no vehicular loads. May be a big refrigerator or water heater or piano may go across it.


If you compacted you don't need rebar and now that you have holes go for it but you don't need epoxy.


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## miamicuse (Nov 13, 2011)

Daniel Holzman said:


> I am a little puzzled by this thread. Most residential slabs are not structural, they are simply there to provide a solid, easily cleaned walking surface, or to support a flooring material. Most residential slabs are about 4 inches thick, and often contain no rebar at all, usually just steel mesh for crack control. So why exactly are you going to the great trouble and expense of epoxying rebar in to tie the new slab construction to the old slab?
> 
> If you need structural support because the slab is doing more than providing a walking surface, you need to EXACTLY follow manufacturer instructions for the use of their two part epoxy. This means precise hole size, cleaning the hole, temperature range of the epoxy, curing process, everything. Typically each manufacturer has very specific tolerances for the hole size for a particular bar, so you need to purchase the epoxy first, then drill later.


I am probably overdoing it but just wanted to not have issues.

My slab cut was made to access the plumbing below. However the plumbing wasn't directly below where I cut but offset from it. I made the cut based on an educated guess as to where things "should be". This means I had to dig sideways under the existing slab. Before it's all said and done my project mutated a bit, rather than repairing a short section of a leaking drain, I replaced a 6' piece, along with a wye and a portion of a branch line, ran two new soft copper lines to the adjacent manifold, and a new electrical conduit while I had the access. This means when I backfilled I could not practically compact the soil to the original degree of compaction because (a) part of the soil had to be backfilled "sideways", (b) the presence of the new drain, soft copper lines, electrical conduits mean I could not be pounding the dirt sideways without worrying about perturbing these lines. I am compacting as much as I can with water, and pounding with a 2X4.

My worry is the new and old concrete joint will not hold, if the soil under settles the weight of the new concrete might settle a small amount and tiles would crack. Having some rebars across the joint help prevent this if the old and new concrete separate from difference expansion & contraction and if the soil below settles.

If it's a contiguous slab I would have no need for rebars.


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## Nealtw (Jun 22, 2017)

If you can not compact sand, flood the area and let dry top up the sand and repeat. until sand no longer settles down, consider it compacted.


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## Koa (May 13, 2017)

Just buy several of the tubes of Simpson epoxy from Home Depot that fit in a regular caulking gun. Since it two parts, you get half a tubes worth. Take back the tubes you don't use. Simpson is a bit expensive but it's the right consistency and sets fairly quickly. Make sure to get one of their brushes and clean the hole and blow it out from the bottom of hole. Fill the hole about half way starting at bottom. You can also put a thin layer of epoxy on the rebar to wet it. Push in or scrape off excess. Any cheaper epoxy will work but you would need to add filler to make it thicker so it doesn't run out. The Simpson epoxy comes with two nozzles I think. When first using a tube squeeze out a little on a scrap board until epoxy is evenly mixing.


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## stadry (Jun 20, 2009)

*i'm w/daniel,,, the only reason there's a conc floor is to hold the bsmnt walls apart + provide a nice surface for your footsies rather'n dirt,,, if you used a 5/8" bit, that resultant hole will accept #5 bar,,, 5/8" is too large for a 4" slab but what's done is done,,, in hgwys, we epoxy 1/2 of the epoxy coated bar into the existing conc,,, fresh conc has the other 1/2 greased so, when temps cause the slabs to change size, smooth movement can occur,,, that won't happen in a bsmnt where the temp's constant

use #4 bar of you must & just grout them into place,,, save your epoxy $ for beer instead

as asked previously by dick w/tongue-in-cheek, what size truck ?*


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