3 Things To Consider When Building A Gunite Swimming Pool

Most people think that a gunite swimming pool is just a gunite (concrete) pool.  There are a lot of variables when choosing a pool contractor.  You should be concerned with the structure, the mechanics, and the plumbing.  Most home owners are concerned with cosmetics, equipment, and colors, because they don’t understand the other stuff.  You don’t have to be a structural engineer to know if your contractor is going to do it right or not.  Remember to ask a few good questions, and listen for the right answers.

What kind of shell is it?

1.)  Is it a monolithic shell? This should be your first question.   A monolithic shell is where the floor and the walls are all sprayed at the same time.  Most contractors don’t do this.  Generally pool contractors pour the floor with a standard concrete mix design.  This is a cheap, easy way to get the floor in.  The materials cost less, but they are inferior structurally.  Regular concrete is more proned to crack, it is more water permeable, and even a good mix design is only half as strong as gunite or shotcrete.  This is a concrete shell, not a gunite shell.

They then spray the walls with gunite.  This makes a good wall, but it also creates a cold joint where the wall meets the floor.  A cold joint is where the concrete is not poured at the same time, there is no chemical bond.  It is a weak area in the concrete that is likely to leak or crack.  It runs around the entire perimeter of the gunite pool.  Some swimming pool contractors try to fix these problems by putting water stop at the base of the wall.  This helps with the leaking, but it is still a problem area.  Spraying the walls and floor at the same time is the way to prevent this.  The gunite floor is stronger, and there is no cold joint.

What type of rebar?

2.)  What size rebar are you using, what is the spacing on the rebar, what grade rebar are you going to use? Rebar is measured by diameter.  Rebar is numbered, and pool rebar should always be #3, #4, or #5.  Three is the minimum and five is the maximum.  They make it smaller and bigger, but it should not be used.  The number represents the number of eighths of an inch, i.e.. #3 is 3/8 of an inch.  Smaller bar is more common because it is easier to bend, and if spaced correctly it is as strong as larger bars.  When it comes to spacing, the closer the better.

Rebar is the cheapest insurance you can buy.  The spacing depends on soil conditions, slope, depth and several other variables.  Most people don’t use enough rebar.  The grade of your rebar is also important.  It is a measure of how pure and strong the rebar is.  Zero grade, 20 grade, 40 grade, and 60 grade are the most common.  The number stands for how many thousand psi of tensile strength the bar has.  20 grade bar is 20,000 pounds of tensile strength where 60 grade is three times that.  Zero grade bar looks the same, but has no guaranteed tensile strength.  People use it because it is cheap and easy to bend.  Never use less than 40 or 60 grade rebar for your gunite swimming pool.

Tell me more about the plumbing

3.)  What size plumbing are you going to use? When it comes to plumbing on your gunite swimming pool, the bigger the better.  Don’t let anyone use plumbing smaller that 2″.  Smaller pipes move the water quicker, which is dangerous and very inefficient.  Larger pipes move the water slower but more efficiently.

Just remember the bigger the better.

These are a few good questions to get you started.  Making a gunite swimming pool look good is pretty easy, but making a good gunite pool is more work.