The dark color gets HOT. Expect to where flip flops. Utah is a large state with different climates ranging from hot desert to mountainous. Where in Utah?

Scott

We had a blue stone walk to our pool at our old house in MA. It was very, very hot...I constantly worried about kids burning their feet on it. I would never do that again for that use, even though it is beautiful.
Judy

You have asked a very interesting question, one in which I have invested literally hundreds of hours. Let me explain.

I am in the process of finishing up a high end home in which the architect specified Virginia Blue-Black Slate for both the pool coping and deck. Suffice to say I was concerned enough that I decided to invest the time to find out just how hot this stone would get.

Cut to the chase it gets exceedingly hot and the reason isn't only or necessarily primarily the color. We ended up getting bluestone. It gets warm but not so hot to be unbearable.

Here is some information to get you started down the road to make your own decision.

First, pick up a couple of pieces of bluestone along with some other material so you have something to compare to. Some material (I think limestone but can't quite remember) stay extremely cool.

As I said it isn't just color, but something called specific heat. Certain materials hold heat better than others even if they are the same color. I won't go into the details of how material absorb and re-reradiate heat but suffice to say that a material gets hot when it can't shed the heat it absorbs. So the less heat a material absorbs, the cooler, but if two materials absorb similarly the one that re-radiates more will be cooler. In addition if you can shed the heat another way, that also can be used to keep the patio cool.

But back to a simple method for you to decide for yourself. Lay the material out in the sun and see how hot they get. Try walking on them. If you want to quantify each material more exactly buy a digital thermometer with a surface probe for about $100 (a great investment) and measure the surface temperature of each material. Then walk on it and see how it feels.

Could you stand on the material at that temperature, walk quickly or would it cause pain? I don't have my notes here but I quantified the temperatures from about 100 to about 115 ie from comfortable to painful to dangerous. My take was that bluestone was the upper end of the range in which I would feel comfortable walking on the material without shoes.

That said a few caveats.

First, measuring the temperature in free air isn't quite correct as some heat will be conducted to the ground below lowering the surface temperature. However my experience shows that the effect is small.

Second, you have any number of alternatives to reduce the temperature of the stone. You could throw water out of the pool once in a while (the energy absorbed when water convert to a gas is enormous). You could spray the patio with a hose, install some pop up sprinkler heads to wet the patio automatically (cheap) or install a misting system. Alternately you could run a line with holes in in and "wash" the patio with a sheet of water once in a while. It all depends on what your installation looks like and if you are willing to tolerate water or spray. If so the problem is easily resolved.

If not the other option is to install pipes, probably flexible pex, under the patio. Depending on your situation this may be very desirable in that it allows you to use the patio as a solar collector but to do so is neither simple nor cheap (unless you possess a level of engineering expertise).

The problem is that it doesn't work to just run pool water through the tubes because the temperature differential between the stone and the water isn't enough to remove very much heat. Instead what you need to do is circulate cold water by installing a water to water heat pump (like the geothermal people use). These put out cold water, almost to freezing, which is circulated in the pex tubing under the patio, generally in the slab or sand if you sand set. The water warms up and is returned the heat pump which sucks the heat out and uses it to heat water drawn from the pool. The cold water goes back to the slab and the hot water is used to heat the pool.

A double win, cool patio, warm pool.

The problem of course is it isn't cheap unless you know how to run your own pex before they install the patio (in which case it is very cheap) and install your own heat pump. Also not so good for climates where the same days the patio is getting too hot are the ones you don't really need or want more heat in the pool.

Bottom line. Buy some material and see for yourself. If you are in love with Bluestone and have a situation where you can rig a way to periodically wet the stone or don't mind doing it manually then the problem is manageable, but it does require some degree of attention to the design.

My take is that except for the warmest climates bluestone works fine if you have a well thought out plan for getting rid of the heat. That is why it works in New England (plus its available there). But there are going to be days that keeping it wet is going to make all the difference. Design a solution in to handle them.

One thing I think you missed was the effect of rabid hot/cold temp changes to the material speeding the erosion process. Some materials are more resistant to the uneven and sometimes rapid expansion and contraction cycles than can occur when cool water hits the deck surface.

Scott

I can't see this being a problem. We are talking about surface temperatures of around 109-111 F which for stone isn't very not. Furthermore the volume of water is low enough compared to the thermal mass that the stone doesn't change temperature all that quickly.

This isn't like dousing a rock that is in the middle of a fire with water but more like washing down your driveway with a hose. Its well within the design specification for how the material is intended to be used.

If it weren't then people with bluestone coping around their pools would have experienced failure of the material since coping is frequently wetted from splashing. That the material has been used as pool coping for at least 50 years without such a problem is pretty strong evidence its robust enough for the task.

But it can never hurt to check.

wow, thank you for the information. I can tell you have a lot of knowledge on the matter. I live in Salt Lake City and it does get very hot in the summer, but I love the look. Is there anything that looks similar that doesn't retain the heat quite as much? I have looked at some sandstones, but they have a lot of orange in them, this is not the look I had in mind. Does granite do the same thing as blue stone? Is the price much more? I really appreciate your time.

I have a little over 2500sqft of bluestone patios in the yard. "Full color" two-inch thick bluestone dry set over 6" to 8" of stonedust. When installed some stones were darker than the "pure" bluestone, which is a more consistent and lighter blue-gray color.

The darker "full color" stones have lightened over the years, and they were indeed hotter under foot in year one compared to recent years. The patios are south-facing, so they get the full brunt of the summer sun. We're outdoors and barefoot all the time, no problems.

Out by my pool I have maybe 300 sqft of the lighter blue-gray bluestone (not full color) dryset over stonedust, it's in a garden off to the side of the pool. Again it gets full sun, and it's never been uncomfortable underfoot even when first installed.

My pool patio is about 1800 sqt of 16" slate, mortared down. It's never been uncomfortable hot underfoot either.

So the only issue I've ever had with heat was with the "full color" bluestone which had darker shades in the mix than the "pure" bluestone. But again, those darker colors bleached out over the course of a couple of years and now the full color mix has no heat problems.

Slightly off topic but am I correct that you mortar set rather than sand set the stone around the pool because you were concerned about stuff getting in the water or was there another reason?

I'm asking because I'm trying to decide which way to go.

No, that's why I did it. All my other patios are stone, dry set over stone dust. I'm in CT with freeze/thaw and haven't had anything heave, the stone dust provides excellent drainage.

But yes, out by the pool I wanted no stone dust migrating from the dry set joints into the pool, or ants tunneling, or weeds sprouting up, so I did stone tiles mortared over a concrete slab. Nice and clean.

Grouted with a grout bag instead of a float so the cleft of the stone wasn't a problem grout-wise.

Do you find yourself feeling the need to wet it down on a hot sunny day or do you just live with it?

The reason I ask is that I've looked at all kinds of way to keep it cool and have narrowed the options down to either just letting it get hot or spraying it with water once in a while. If just letting it be isn't that bad, then obviously its the easiest, but if not then I've got a couple of options I'm thinking of plumbing in to wet the thing down automatically.

What can you tell me about actually living with the patio?

BTW I really appreciate the help. There is no substitute for actual experience.

The only overly hot issue we had was maybe the first two summers with the full-color bluestone patio, that patio faces directly south and it's on the south side of the house. After a couple years of sun exposure the darker stones have "bleached out" so to speak. The entire patio is a more muted blue-gray instead of the more varying and sometimes darker "full color" that it was after initial installation. Since it has "bleached out" it doesn't absorb as much heat, it hasn't been uncomfortable at all. It's warm certainly, but not hot. There is moss and some creeping thyme in some of the joints, if it was too hot I think it'd roast the moss.

I did the pool patio a couple of years after the bluestone patios. With the heat in mind I thought the same as you, and had plans in mind to install a perimeter sprinkler system around the pool patio. Something along the lines of yard sprinkler heads that would mist the stone patio a couple of times during the day as needed. There's been no need for it so I never followed through with the installation.

When we have large crowds over the adults usually take the chaises and chairs and the younger kids ether lay right on the stone, or they lay on towels laid out on the patio.

We used to moan for the first two years over the heat of the full color bluestone, but since it's bleached out we've had no complaints about it. We've never had any issues with the other "blue" bluestone nor have we had any complaints about the slate pool patio.

We're outdoor people, so we use it every day.

I'd say to be on the safe side plan for perimeter sprinklers. All you'd need to do is invest in a roll of black plastic pipe and install that when you do the patio rough-in. Then if needed down the road you can plumb the pipe to a water source and add sprinkler heads.

I really appreciate the real world feedback. I'm going to go ahead and put in some pipes for sprinklers but unfortunately its a lot more complex in my case because the way the patio is laid out I need to have the heads in the stone not just in the perimeter.

Because of this I've looked at alternatives to pop up heads like using a long tube with holes in it that would flush the patio with a wash of water or using pressure misters that would kick out a fog. The problem I keep coming back is how to get the water onto the stone without wetting the people too badly.

I've really got two patios. The lower one sounds like yours with chaise lounges and such down near the pool. Here the problem is getting the stone wet with all the chaises and chairs around. Wetting the people isn't such a big deal because they are probably not in street clothes anyway.

The upper one is where the long dining table is. It can get wet, but I can't quite figure out how the water should get onto the stone without annoying the people. Some may be in bare feet and bathing suits but it only takes one in slacks with socks and shoes to kind of mess the whole thing. That's why I'm thinking of the sheet of water idea rather than sprinklers. With the sheet water just washes over the stone without getting up into the air.

The problem is the stone is uneven so the amount of water needed to wash neatly over everywhere is not insubstantial, which brings me to the idea of the mist. If I can blow the mist across the stone then I have the advantages of the sprinklers without the problems of the washer (because the mist won't wet anyone).

What I don't know is how far I can throw the mist. Luckily I have a long bench I can hide the mister tube under so I've got a low mounting place.

I'll just have to run a bunch of pipes so I can do anything I guess.

Any suggestions?

mongoct please come back, I need the advice of someone who has been there!

I don't have a problem anymore with a hot pool decks because I wear my Barefoot Feet when I go to a pool. The best part is that they are made of neoprene so I can walk right into the water with them on.

sbedelman, any chance you can update on your experience with bluestone and the cooling solution you went with? I am considering the options listed and it would be great to hear your results.

We are building a new PATIO and have had two different opinions about Quartzite verses Pennsylvania Blue Stone used on outside patios. One of our local dealers told us that Quartzite stays about 15 degrees cooler than the Blue Stone during the very hot summers down in the south. Another dealer said that may not be true depending on where you get the Quartzite from.

The Quartzite we plan on getting is from Brazil. Can anyone tell me is there any truth to Quartzite staying cooler ?

Or… is there any Website that may have detailed data like this you can send me the link to?

Thank you very much,

Dale Baton Rouge

Hi all—I used my concrete slab for my porch and formed concrete pavers for my pool coping. It looked great for about a year, but now cracks and sealers are causing an issue and I would like to replace it with bluestone. The pool and stone sellers here are discouraging me due to the heat here in South Carolina. After reading helpful comments (sbedelmen in particular), I am back to considering it! My porch is covered, but not the coping. It gets very hot afternoon sun, and hits most of the porch all afternoon. Any thoughts based on my location and orientation? Many thanks in advance!