Is my engineer crazy??

[mlawrence17]

I've got an engineer designing a pool for me and here's what he's suggesting. It sounds feasible but I wanted to get a second (and third) opinion.

Basically the pool is a rectangle. 16' x 32'.....3' shallow / 6' deep. The problem is that my house sits 5' above ground level and I want the pool edge to be at the same level. So basically my pool will be mostly an above ground gunite pool. My initial plan was to form it up with plywood and shoot it with gunite 10-12" thick. Creating a structural shell. But after meeting with my engineer here's what he's suggesting.

Build the shell out of concrete block (w/rebar, filled with concrete etc...) then add some fill dirt for the slope, and pour an 8" slab. Then come back and hit the inside with 2" of gunite, rounding the corners, building the stairs etc. Then finally plaster it.

I'm not saying it's a bad idea...just not at all what I was thinking... but hey maybe it's good to think outside the box.
Thoughts???

 

[JohnT]

I would not go with dirt for the fill. Sand or gravel maybe.

 

[JamesW]

I think that your idea is the better one. What type of engineer is your engineer?

Since you're going to have an elevation difference, you might want to consider using a vanishing edge design.

 

[PoolGuyNJ]

Do NOT use block. It won't hold the water back. It will crack, leak, and possibly burst. There will be strength sucking voids.

Please get a real builder.

Scott

 

[Lershac]

I would ask to see his calculations

 

[duraleigh]

My pool, while IG with a vinyl liner, is constructed from concrete block. It doesn't leak.

an-unusual-pool-build-t10597.html

An AG concrete block pool will work, too, especially since you are apparently going to fill around it and then slope it down. (That five foot slope back to ground level seems problematic to me but that's not your question)

The problem (but it can be dealt with) that I see in your brief description is the "cold" joint that will occur where the floor will meet the concrete. I would suggest, if you choose that route, to pour a monolithic slab with rebar installed in the wet slab and protruding vertically to which you would anchor the block wall.

At that point, you can simply apply plaster to the block wall and concrete floor and wouldn't need gunite. Just how to round the corners without creating a cold joint may 'cause some problems but probably can be dealt with given enough thought.

Overall, just shooting the gunite into a plywood form sounds the most reasonable to me. Is the engineer suggesting block because of cost savings?

 

[PoolGuyNJ]

A liner pool is a different animal, construction wise. I was assuming he was plastering. Add to that his raised perimeter beam and it spells structural failure.

Scott

 

[bk406]

A liner pool is a different animal, construction wise. I was assuming he was plastering. Add to that his raised perimeter beam and it spells structural failure.

Scott

I agree with Scott here. Concrete block walls like Dave used for his vinyl pool is a different animal entirely. Using concrete block as a backer for a gunite pool is a disaster waiting to happen. You can do what your proposing, but you need to use a soild concrete structure, much like a wall for a basement foundation. You use that as the retaining wall on one side, and the pool wall on the other side.

 

[SCEADU]

I don't want to start a flame war here BUT!!!! I would seriously consider looking for a new engineer. As an excavator in the industry for 12 years, I did exactly what you are proposing almost 100 times in my career. I saw a wall built the way your engineer is proposing and that wall is now in a landill somewhere near Atlanta. Here is a project that I completed this year that is the same basic principle that you are trying to achieve just a little more elaborate. By the way, this design won me a slot in the Structure Stuidos Calendar for 2012. {Shamless Plug} :lol:

 

[SCEADU]

Afew more!

 

[no-mas]

SCEADU, you are shameless! Beautiful work, man!

 

[Lershac]

I would still ask to see the calculations. Its what engineering is about. If he can support his case with calculations I would consider it, but also consider the experience of guys in the industry basing their opinions on experience.

 

[bk406]

I wouldnt be so concerned with the calculation per se. Using concrete block is just the wrong material.

 

[SCEADU]

I would still ask to see the calculations. Its what engineering is about. If he can support his case with calculations I would consider it, but also consider the experience of guys in the industry basing their opinions on experience.

I am not going to take anything away from an engineer. I have met some that I thaought were crazy and their concepts have worked and made me eat me words.. I have also met some that I am astonished that are still in the bussiness. I know one that is spent some time in jail for Reckless endangerment when a deck colapsed and injured several people. Still I have found that all the schooling in the world can't make up for honest experience.

 

[PoolGuyNJ]

So you are agreeing with those, myself included, that are saying that using block is not the kind of practice that should be employed in this type of situation?

Scott

 

[duraleigh]

Hmmmm. Well, I am a little surprised that there has been so many strong opinions on this when we really didn't have all the info we needed. Looking at a previous post, it looks like OP is really interested in what amounts to an IG pool.[attachment=0:2lz2prvx]tem_blockwallpool.jpg[/attachment:2lz2prvx] Based on that rendering, I believe the pool walls could be built (theoretically) out of saran wrap since all outward force the water will apply to the wall and fill dirt would be transferred to the retaining wall shown some distance from the pool.

I used to put paper clips into the electrical outlets and touch them together while I was failing high school physics (my deskmate and I shorted out the entire classroom and, somehow, the lights as well) but a little bit of that stuff sunk in and I think I am correct.

Again, taking into consideration the above education level (or lack thereof), I filled my pool to the top with two of the concrete block walls completely unsupported on the back side and left them without backfilling for over a year with nary a crack of ANY kind.

I'm not saying that's the right thing to do.....just that sometimes ignorance and determination can overcome logic.

 

[JamesW]

It's important to remember that there are many types of engineer, such as chemical, electrical, civil, mechanical, geotechnical etc. Unless they have experience with building similar structures using similar materials, I would be cautious about using their plans.

 

[mas985]

Cinder block reinforced with both concrete and rebar should be just as strong as solid concrete. Countless retaining walls, building foundations, and Dave's pool should be proof of the strength. Also, since the block will be covered in both gunite and plaster, and the fact that plaster is really the water proof layer, I see no reason why this shouldn't work as the engineer suggested.

Not that this guy is proven expert but here is another opinion:

http://www.askthebuilder.com/439_Poured ... alls.shtml

 

[bk406]

Cinder block reinforced with both concrete and rebar should be just as strong as solid concrete. Countless retaining walls, building foundations, and Dave's pool should be proof of the strength.

Thats not really true. Using Dave's liner pool as a example is comparing the old proverbial apples to oranges.

Building foundations are made from SOLID concrete and rebar, not concrete cinder block (thats about the porest material you can use for a wall of this kind). The reason buildings are made from block is because there is a roof to hold it together. A wall like one is the above plans either needs to be a stone wall about 2 feet thick, a pinned wall system, or a solid concrete wall with a footing below the frost line.
You can see walls built out of anything; doesnt mean it the correct material.

 

[mas985]

Building foundations are made from SOLID concrete and rebar, not concrete cinder block (thats about the porest material you can use for a wall of this kind).

I have seen plenty of houses with foundations and basements make of block concrete, including the house I grew up in, so they are not ALL built out of solid concrete (see link I posted and pictures below). And yes it is porous but it really doesn't matter if it is coated with a material which is water proof and or has a water proof barrier. The point is that with rebar and concrete in the interior, it is as strong as a poured concrete wall.

Pictures of block foundations:

http://www.muehleisconstruction.com/id3.html
http://www.dornconstructioninc.com/Conc ... sonry.html
http://www.studiozarch.com/portfolio/pr ... ect19.html
http://www.drtenterprises.ca/block-contractors-gta.html