Negative Edge, Vanishing Edge, Infinity Edge Pool Weirs & Walls

Paolo Benedetti discusses Negative Edge, Vanishing Edge, Infinity Edge Pool Weirs & Walls, design and construction considerations and the realities of routine maintenance vs. construction defects.

The Weir - The point of spillover...
The "weir" is the actual crisp edge that the water spills over. The material and design details that comprise this edge are critical.

Ceramic tile is the least forgiving when installed as a weir. The greater the variance in the surface of the tile & grout joints, the more water will be required to flood the edge. This also requires that the installer be "dead on" with their installation. Water will ALWAYS sit level inside the pool. If the tile is not installed level, the water will be a dead give-away!

I prefer to use polished natural stone. Though our specifications call for +/- 1/32" (a total of a 1/16" difference between highs & lows), natural stone can be further polished to ensure absolute perfection.

The grout joints will also contribute to variances in the weir elevations. Wider grout joints tend to have greater variances in their depressions. Additionally, they have a higher incidence of cracking.

NOTE: GROUT WILL CRACK - so, cracked grout, in and of itself is not to automatically be considered a construction defect!

Flowrates - low & slow is the goal!
The backside of vanishing edges are not supposed to be grand cascading waterfalls. Actually, the designer's goal is to flood the edge(s) using as low of a flowrate, and therefore as little energy, as possible.

This is not to say that they cannot be designed to be cascading waterfalls. However, if the owner desires a "waterfall" effect from the vanishing edge wall, then additional expenses and costs will need to be factored into the project.

A waterfall effect will require a material or weir that causes the water to break tension from the wall. It can be a simple change in the weir detail to create a large cascade effect. Or, an irregular material (e.g. ledger stone) can be installed on the outside face of the vanishing edge wall, to cause the water to splash free from the wall.

The cascading effect will require additional pumps & plumbing. Both effects will require a wider catch basin, as the splashing water will easily clear the width of a normally sized basin. Depending on the height of the vanishing edge wall, the width of this basin can be substantial. All of this translates to an additional project cost.

Choice of Veneers
What ever material is chosen to veneer the outside face of the vanishing edge wall, special construction techniques must be employed. Since the vanishing edge wall is in effect a giant dam, waterproofing is paramount. The waterproofing program should begin with the concrete itself and then include additional layers of protection as construction progresses. A competent
designer or builder will be intimately familiar with the options available.

The installation of the veneer material will require movement joints throughout the material. This means color matched caulking joints both vertically & horizontally through the material. Since this surface is repeatedly put through wet & dry and hot & cold cycles, the material must be able to expand & contract with these extremes. Failing to provide these joints will cause the material to crack or delaminate.

Efflorescence - French for "to flower out"
Whenever you have wet cement surfaces exposed to air, you will get efflorescence. It is a chemical reaction of the salts within the cement products hydrating & leeching towards the surface. The more the surface is subject to wetting & drying cycles, the greater the efflorescence to be expected.

Any cement product can contribute to efflorescence - concrete, mortar, thinset & grout. Even the labels on epoxy grouts contain a disclaimer about efflorescence.

There is no easy solution to preventing efflorescence. The key is to control the migration & penetration of water into & through the cement products. I say "through," because concrete contains microscopic capillaries through which water can migrate. There are chemicals and processes to control the water migration and saturation. The specifications just need to be defined and included in the project specifications - and, yes, they do add to the cost.

So, the presence of efflorescence is not a construction defect. It might indicate that the designer or builder did not include a waterproofing & migration control program (which you probably did not pay for either). This will result in the unsightly development of efflorescence and reoccurring maintenance expenses to remove it.

The caulking joints will also require periodic removal and replacement. The frequency of the maintenance of these joints will depend on the wall's exposure to the sun, temperature extremes, proper installation & joint preparation and the veneer materials. Materials with a high expansion index will place greater stress upon the caulking (mastic).

If you hire a knowledgeable designer & specifier, they can discuss the additional costs, help you weigh the maintenance and cleaning costs and the negative long terms costs and ramifications of not taking these simple precautions.


Paolo Benedetti - Aquatic Artist"Creating water as art."™Aquatic Technology Pool & Spa©www.aquatictechnology.com