# Square footage of tile needed for negative edge spa

#### VacaAtHome

##### Member
Does anyone know how to calculate the square footage of tile needed for a 360 degree negative edge spa? Our spa is 7 ft in diameter and raised about 8 inches. We were only planning on installing tile on the top edge and around the outer part.

#### jblizzle

TFP Expert
Welcome to TFP!!!

It depends on what you need to cover and the size of your tile
Your question does not require all the information required to answer you.

Circumference x Height (or width) = Diameter x pi x Height = 7ft x 3.14 x 8/12 ft = 14.65 sq ft plus the top width plus breakage plus they may not be 8" in height.

Usually waterline tile is 2 rows of 3" tiles or more rows if smaller tiles are used.

#### VacaAtHome

##### Member
Welcome to TFP!!!

It depends on what you need to cover and the size of your tile
Your question does not require all the information required to answer you.

Circumference x Height (or width) = Diameter x pi x Height = 7ft x 3.14 x 8/12 ft = 14.65 sq ft plus the top width plus breakage plus they may not be 8" in height.

Usually waterline tile is 2 rows of 3" tiles or more rows if smaller tiles are used.
Thank you! We are using 7/8” x 7/8” glass tiles. Do you know if it’s necessary or recommended to have glass tiles on the inside of a negative edge spa?

#### JamesW

TFP Expert
πD1h + π(D12 - D22) ÷4 = area.
D1 = outer diameter.
D2 = inner diameter.
h = height in feet.
Assuming D1 = 9 feet, D2 = 7 feet and h = 0.67 feet, the area should be 44 square feet.

Last edited:

#### jblizzle

TFP Expert
I am assuming your spa will be plaster or pebble? You can have dry plaster and I don't think most pebble products are supposed to be above water either. So, you need to have tile at the waterline.

So I am still not clear on what surfaces or dimensions you actually need or want to cover in tile to be able to estimate the amount of tile you need. Seems that your builder would be doing this for you.

#### jblizzle

TFP Expert
@JamesW, but they would order at least 15-20% more than that right?

Plus your equation does not include the waterline tile at D1

#### JamesW

TFP Expert
Ok, they said only the outer part. If you're going to do the inner part, you would add πD2h.

OP, is the 7 foot measurement the inside diameter or the outside diameter?

And, yes, you would want a certain amount of extra for cuts, breakage and future repairs.

#### VacaAtHome

##### Member
Ok, they said only the outer part. If you're going to do the inner part, you would add πD2h.

OP, is the 7 foot measurement the inside diameter or the outside diameter?

And, yes, you would want a certain amount of extra for cuts, breakage and future repairs.
I just checked the exact measurements on the gunite. The height of the spa is 18 inches above ground, the outside diameter is approximately 9'2", and the inner diameter is 7'. I think our pool builder is only planning to tile the top surface and the outer part, not the inner part. Unfortunately, our builder has not been the most communicative/responsive with us and has quoted us for various square footages, so I thought I would seek advice on this forum At ~\$40/sq ft, I just want to make sure we're in the ballpark for the amount needed and not way over! With these new measurements, I calculated roughly 68 sq ft.

Jblizzle, we're getting pebble on the inner part, but since this is a negative edge spa, I was just curious if it's still recommended we install waterline tile on the inner part, or is this unnecessary since the water will be overflowing the top?

#### jblizzle

TFP Expert
I guess the water should always be at the top with a negative edge. Se perhaps that is not needed.

#### JamesW

TFP Expert
With D1=9.17, D2=7 and h=1.5, I get 70.8 square feet. That's the top and outside.

I would think that you would sometimes use the spa as a spa sometimes without overflowing so that you can heat just the spa.

In that case, I would recommend a waterline tile around the inside perimeter.

Get extra tile and store it somewhere because there will come a time that you will need to do a repair and the tile will probably not be available at that time.

Will the tile in the pool match the tile in the spa?

#### jblizzle

TFP Expert
Certainly will be a lower water level as people climb out of the spa, at least until the circulation pump is turned on to refill it.

#### MinerJason

Bronze Supporter
I just checked the exact measurements on the gunite. The height of the spa is 18 inches above ground, the outside diameter is approximately 9'2", and the inner diameter is 7'. I think our pool builder is only planning to tile the top surface and the outer part, not the inner part. Unfortunately, our builder has not been the most communicative/responsive with us and has quoted us for various square footages, so I thought I would seek advice on this forum At ~\$40/sq ft, I just want to make sure we're in the ballpark for the amount needed and not way over! With these new measurements, I calculated roughly 68 sq ft.

Jblizzle, we're getting pebble on the inner part, but since this is a negative edge spa, I was just curious if it's still recommended we install waterline tile on the inner part, or is this unnecessary since the water will be overflowing the top?

The area on top will be about 27.5 square feet. Still not sure what to tell you about the outside without knowing the height from the waterline to the top of the spa wall, but you'll want the tile on the outside to extend about 3 inches below the waterline. If we assume it's 18" to the waterline and extend the tile 3" below the waterline, the area around the outside would be 50.4 square feet, for a total area of 77.9 square feet.

Is the top of the spa wall slanted inwards significantly, or just a little? If it's a significant slant (several inches of vertical drop) then you likely don't need any tile on the inside, otherwise it would be a good idea to put at least a few inches of waterline tile on the inside. Adding a standard 6" of waterline tile on the interior would be another 11 square feet.

And as mentioned previously, you'll want to have at least 10% more tile than the area to be covered to account for waste.

#### VacaAtHome

##### Member
The area on top will be about 27.5 square feet. Still not sure what to tell you about the outside without knowing the height from the waterline to the top of the spa wall, but you'll want the tile on the outside to extend about 3 inches below the waterline. If we assume it's 18" to the waterline and extend the tile 3" below the waterline, the area around the outside would be 50.4 square feet, for a total area of 77.9 square feet.

Is the top of the spa wall slanted inwards significantly, or just a little? If it's a significant slant (several inches of vertical drop) then you likely don't need any tile on the inside, otherwise it would be a good idea to put at least a few inches of waterline tile on the inside. Adding a standard 6" of waterline tile on the interior would be another 11 square feet.

And as mentioned previously, you'll want to have at least 10% more tile than the area to be covered to account for waste.
I included some photos of the spa. The 18 inches I measured was from the bottom of the basin (or whatever that area is called that the water spills into) to the top of the spa. I would say it has a significant slant. More than I’d like, but I’m ok with it if that’s what makes the negative edge operate best!

#### Attachments

• 251.3 KB Views: 32
• 497 KB Views: 29

#### VacaAtHome

##### Member
With D1=9.17, D2=7 and h=1.5, I get 70.8 square feet. That's the top and outside.

I would think that you would sometimes use the spa as a spa sometimes without overflowing so that you can heat just the spa.

In that case, I would recommend a waterline tile around the inside perimeter.

Get extra tile and store it somewhere because there will come a time that you will need to do a repair and the tile will probably not be available at that time.

Will the tile in the pool match the tile in the spa?
With D1=9.17, D2=7 and h=1.5, I get 70.8 square feet. That's the top and outside.

I would think that you would sometimes use the spa as a spa sometimes without overflowing so that you can heat just the spa.

In that case, I would recommend a waterline tile around the inside perimeter.

Get extra tile and store it somewhere because there will come a time that you will need to do a repair and the tile will probably not be available at that time.

Will the tile in the pool match the tile in the spa?
I also thought we should install some waterline tile in the inner part for that reason! Do you have any recommendations how much? 6"? I can discuss with my pool builder.

Our waterline tile for the pool is different (see attached pics of pool waterline tile and spa glass tile). It is NPT Simulated Quartzite in Grey. I was planning on using Custom Building Products Prism Grout in Delorean Gray since I saw this on a sample with the glass tile we're using, and I thought it helped in matching the two tile types. I'm open to other suggestions if you have any!

#### Attachments

• 440.9 KB Views: 10

#### MinerJason

Bronze Supporter
That's enough of a slant that you shouldn't need waterline tile on the interior if you don't want it. It also means it'll take slightly more tile for that section. The waterline should fall pretty close to 3" below the outer basin wall. If you want to save on tile you could only tile the outer wall to 3" below the waterline, but it might look better to tile all the way to the bottom of the basin. How tall is the outer basin wall?

#### JamesW

TFP Expert
The slope makes the top closer to 29.9 square feet.

With the slope, you might not need any interior perimeter tile. You might do a few inches, but that's up to you.

#### VacaAtHome

##### Member
That's enough of a slant that you shouldn't need waterline tile on the interior if you don't want it. It also means it'll take slightly more tile for that section. The waterline should fall pretty close to 3" below the outer basin wall. If you want to save on tile you could only tile the outer wall to 3" below the waterline, but it might look better to tile all the way to the bottom of the basin. How tall is the outer basin wall?
The outer basin wall is 9". I think I'd prefer the glass tile to be installed all the way to the bottom of the basin.

#### MinerJason

Bronze Supporter
So with an estimate of the slope on top from the photos, and now having a pretty good idea of where the waterline is in relation to it, the minimum tile you'd need is approximately 65 square feet (assuming 10% waste). Tiling the outside wall to the bottom of the basin would add about another 16 square feet for a total of 81 square feet. Adding 3" of waterline tile on the interior would add about 6 square feet, for a total of 87 square feet, or adding 6" would be an additional 12 square feet for a total of 93 square feet. I think the tile on the interior is totally optional, and it might even feel odd to lean back against two different materials when sitting in the spa.