Is a 1/4 inch expansion joint too thin for pool deck/coping?

[poolguy968]

Hi I am currently in the process of starting to build my new pool deck. Essentially the pool deck is going to be marble pavers attached with thinset on top of a concrete pad covering my entire yard. The concrete pad needs to be poured since my yard is originally all dirt.

Right now my contractor is getting ready to pour the concrete pad and he has compacted the gravel, put down rebar and also attached a 1/4 x 4 inch strip of expansion joint foam around my gunite pool shell. He says this is the kind of expansion foam he likes to use because it leaves a smaller gap between the coping and the deck.

However now I am reading that the correct expansion foam for pouring concrete next to the pool shell should be 1/2 inch thick. Then would it be problematic if my expansion joint foam is only 1/4 inch thick?

I’ve attached pictures of the specific kin of foam that my contractor used and also what the pool shell currently looks like with the foam glued on.

 

[ajw22]

1/4 inch is okay but may not last as long as a 3/8 or 1/2 inch joint.

Over time things may move, which is the purpose of the expansion joint, and the joint may close up. Whoever is the caretaker of the pool in 10 to 20 years may be grumbling at what you did as they need to saw the joint to open it up again.

Your contractor is not intending the be around when that grumbling begins.

 

[JamesW]

How wide is the deck?

Is the deck open on the opposite side or does it meet a wall?

Pictures of the whole pool and deck?

 

[JamesW]

The expansion depends on several factors including the width of the concrete, aggregate, temperature differences etc.

The wider the concrete, the more expansion you need.

I would say 3/8" would be minimum for concrete against coping.
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A typical value of thermal expansion and contraction of concrete is on the order of 10 millionths per degree Celsius, that is, very near the same as that for steel.

If an unrestrained slab or wall 30 meters long has a temperature variation from summer to winter of 38 degrees Celsius, the total thermal movement might be about 1.5 to 1.8 centimeters.

https://www.engr.psu.edu/ce/courses...cking/thermalexpansioncontraction/example.htm
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Thermal Expansion and Contraction of Slabs on Grade
By Concrete Construction Staff
Q. What is the rate of expansion and contraction for a concrete slab on grade due to temperature changes, and how much movement can be expected because of temperature change?

A. A general value for concrete's coefficient of thermal expansion is about 5.5 millionths/° F. If an unrestrained, 100-foot-long slab on grade was exposed to a 100° F temperature drop throughout its cross-section, it would contract about .66 inch (100 feet x 12 inches/foot x 100° F x .0000055). Since the slab is restrained by friction between the base and the bottom of the slab, the slab usually cracks instead of contracting the roughly 2/3 inch.

Since aggregate comprises a large percentage of the concrete volume, the coefficient of expansion for concrete varies depending on aggregate type. Typically it ranges from 3.8 millionths/° F for limestone to nearly 7 millionths/° F for quartz.

https://www.concreteconstruction.net/how-to/thermal-expansion-and-contraction-of-slabs-on-grade_o

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An average value for the coefficient of thermal expansion of concrete is about 10 millionths per degree Celsius (10x10-6/C), although values ranging from 7 to 12 millionths per degree Celsius have been observed. This amounts to a length change of 1.7 centimeters for every 30.5 meters of concrete subjected to a rise or fall of 38 degrees Celsius.

https://www.engr.psu.edu/ce/courses...ermalexpansioncontraction/thermalexpcontr.htm
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[poolguy968]

Thanks for the detailed replies!

So essentially the concrete I’m pouring is going to cover my entire yard (outside of the pool) from wall to wall. It will extend from the edge of the coping to my house foundation (which is wrapped in 1/2 inch thick expansion joint foam). The distance between my house and the pool is about 28 feet at its greatest width but that’s only on one side. On the rest of the sides it is more like 5-10 feet wide.

Basically the contractor has put 1/4 inch thick expansion joint foam all along the outside of the pool shell and then 1/2 inch thick expansion joint foam all along the bottom of my house and the bottom of the concrete retaining wall around my backyard. So there will be expansion joint foam on all sides of the new slab.

I’m not sure if this will be ok or if I need to maybe add an extra layer of expansion joint foam around my pool shell to make sure it doesn’t crack?

Also would you recommend wrapping expansion joint foam around my drainage pipes as well before pouring the concrete?

 

[Dirk]

There's going to be another layer of foam on top of that one, like backer rod, and then an elastic joint compound on top of that, right? Both installed after the coping and pavers are in. You know about all that?

Personally, I think 1/4" is too small. 1/2" is better (less risky), and when filled with the correct expansion joint compound can be disguised to look like grout. I just replaced mine, and sprinkled sand on it. When set, it looks pretty good, and is semi-solid, so when stepped on it doesn't feel like stepping on something soft.

That's the original grout between the two stones, and the new "sanded" expansion joint compound between the stones and the concrete.



There will be virtually no difference, aesthetically, between a 1/2" gap and a 1/4" gap. No one (with maybe the exception of your contractor), would look at either one and think one looks better or worse than the other. That's not a thing. But the 1/4" gap might someday become a problem, so why risk it? My deck is moving differently than my coping is, just in about 10 years, and the gap has changed. So that is a thing. As pointed out, this contractor won't be around if you later have a problem with the gap. In fact, he won't be around 5 minutes after your deck is done, so who cares what he thinks about how it looks! (Only half joking!)

Nit pick (few things to check on before the pour): that end of that one chunk of rebar in the pic looks to be too close to where the concrete will end. I don't know what the recommended clearance should be, to correctly encase the rebar, but that doesn't look like enough. You might check that all the way around the pool. The rebar looks to be too close to all those drain pipes, too. No concrete expert here, but that doesn't look right to me. And isn't the rebar supposed to be elevated off the gravel? Not laying on it? Do they lift that during the pour? Or are there supposed to be dobie blocks installed now? (Maybe they're just not done yet?) @JamesW?

And is that your bond wire in one of the pics? Has that been properly attached to the rebar? I think there is a spec (code) for that.

Have you made sure the slope away from the pool is correct? There needs to be one. I think there is a spec for that, too. If you use the bottom of the spa tiling as a visual guide, it almost looks like there is no slope, or that it's actually going the wrong way (at least the gravel level looks that way).

Is this getting inspected before the pour? You wanna make sure this is done right, and all to code. Has your contractor done pool decks before? Not everybody that knows how to lay down a slab knows how to pour a pool deck.

 

[JamesW]

The distance between my house and the pool is about 28 feet at its greatest width but that’s only on one side.

28 feet x 12 inches/foot x 100° F x .0000055 = 0.1848" = 3/16" movement.

I would go 3/8" to 1/2" due to the width of the concrete.

On the rest of the sides it is more like 5-10 feet wide.

10 feet x 12 inches/foot x 100° F x .0000055 = 0.066" = 1/16" movement.

Expansion Joints and Coping - Further Reading

www.troublefreepool.com

The whole point of the expansion joint is to separate the top of the shell, mortar bed and coping from the deck. Any time the deck impinges on the back of the coping and mortar bed, damage is almost certain to occur. I like to see a gap that's ½-inch wide between the deck and the coping. The gap should extend downward through the entire depth of the slab, usually about 4 inches.

Mind the Gaps: Perfecting Control and Expansion Joints

Understanding the purpose and importance of control and expansion joints is a basic matter of education, dedication to quality and on-site awareness.

www.aquamagazine.com

EXPANSION JOINT FOAM BETWEEN COPING AND PAVERS

When my pool was built, I was required to keep an expansion joint between the coping and my deck pavers. The joint was 1/4 inch and was filled with foam 4 inch by 1/4 inch (this foam was also required). I have a contractor fixing some stuff and he pulled up the foam and is replacing it with a...

www.troublefreepool.com

https://www.wrmeadows.com/data/325.pdf

 

[poolguy968]

Thanks! I did end up wrapping a second layer of 1/4 inch thick expansion joint foam around my gunite shell just to be extra safe. I also told the contractor to trim back the rebar that’s too close to the edge. He also said he will be lifting up the rebar as they pour the concrete next week.

I do have another kind of related question though: Before the concrete is poured, should I also wrap my plastic pipe risers/stub outs with expansion joint foam as well? Right now I have some pvc pipe risers as well as some abs pipe risers that will be encased within the concrete and I haven’t wrapped anything around them. The contractor says he usually doesn’t wrap anything but then again he will be gone as soon as the job is done so I wanted to double check with you guys what is the best practice here?

The other thing is, should I also wrap expansion joint foam around the outside of my skimmer lid/box that’s going to be in the middle of the concrete slab?