Niels’s DIY Hexagon Hot Tub Build: The Netherlands (Case Study)

Last updated: September 2026

Niels first got in touch with me in January 2022 about the possibility of me designing his DIY hot tub. Of course, the answer was yes.

Niels wanted to build a hexagon-shaped hot tub. The challenge was that he wasn’t sure about the plumbing side of things, and parts availability in the Netherlands wasn’t great. Don’t worry, I said. I can export everything you need and sort you out with a plan and a design.

What was also unique about Niels’s plan was that he wanted to include a fire pit for heating. I’d done one project like this before, with Francisco in Chile, so I knew what we needed to do.

Let the design commence

As with any of my custom design projects, we went back and forth with the design until Niels was totally happy with it.

From there it was on to the plumbing layout. That tends to involve less back and forth, and I usually put it together with little input from the customer, apart from the control room location, of course. If you’re curious how that process works, I’ve explained it in my custom hot tub design process.

Parts shipped

About six weeks after the design was complete, Niels was ready to order the parts, so I exported everything he needed to him in the Netherlands.

All gone quiet

When I first started doing these projects, what feels like a lifetime ago, I always used to worry when things went quiet and I didn’t hear from a customer. Now I know “that’s life”. Things happen along the way with these builds, and it’s become normal.

So I thought nothing of it when I didn’t hear from Niels for some time. If you’re wondering how long a build like this really takes, have a read of How long does a DIY hot tub build take?

Fast forward to August 2023

Niels got back in touch and sent me a lovely email update. I’m going to share some of it with you below, in his own words.

“What should have been an approximately 6 month project turned into a project over a few years. I remeber contacting you in late 2021, and here we are in 2023 and still not done. I’m making progress now and i’m committed to get it done now in a few weeks but probably a few months now.

As you may know i’m what of a water pool enthousiast which is why i contacted you. […] my whole live i’ve been a little obessed with swimming pools and huttubs, i even built a DIY sun heater for a stander intex pool.

Ok now to the part where we connected. I contacted you becouse the previous prebuild jackuzzi was broken and leaking from places i couldn’t reach. […] So after some e-mailing between you and me i had a picture of how i was going to do it.”

The dig and the base

“So i started to dig a hole in the ground which would cover the hottub plus a bit to spare becouse we have to fit the insulation and plumbing (pictures -3, -4, -5 and 1). At foto 1 you can see how deep i dug and where our ground water level is at. On top of this i threw 17,5 cm of rubble grit ( pictures 2-4 ). After that i wanted to insulate my tub, […] i asked [an insulation specialist] for some advise of which insulation i could use, with the possibility of getting wet. I don’t expect it to be but just to be sure. He asured me to use PIR plates which of course i did (pictures 5-8). I used 8 cm plates by the way. After that i threw a base of 17.5 cm concreet on top and with that my base was completed. […] So the “shovel” was put in the ground at 2 april. Then i did the rubble grit and insulation myself.”

Where Niels dug, you can see the groundwater. If you’re building in-ground on a site with a high water table, plan for it from day one. My guides to installing a hydrostatic relief valve, insulating a DIY hot tub and DIY in-ground hot tub groundwork cover the base in more detail.

The first “wait moment”

“When we poured it was 28 of july. Which already made a delay of 3 months. […]”

After the pour, life got busy and the build paused for a while. Once things settled down, Niels picked up where he’d left off.

The walls

“[…] So i asked a friend if maybe he would help me, and he said ofcourse you build my computer so i will help you build your hottub. So we got together on 2 saterdays, the first we build the first layer of bricks onto mortar so we had a level first base. And the second saterday we did the second and third layer (pictures 9-15). Then i had a little wait becouse it was a little hectic at work and i had to do some (a lot) of overtime hit our deadlines.”

Getting that first course level is the most important part of any block or brick build. There’s more on it in building a cinder block hot tub and hot tub wall construction options.

The control room

“Which brings me to today. I have vacation now (5 weeks of which 1 already has passed). And i’m planning to do a work vacation as they call it. try to get as much done in and around the house so i can start clean when i have to start work again.

Yesterday and today i dug the whole which will be the compartment where the pumps etc. will be […] (pictures 16-19). After i kind of leveled the base of this i put in some leftover tiles, i will be adding 10cm of concrete here to bring it a little bit up. You can see i have a pvc pipe in place which will act as a overlow. If any or ever something will leak the water has a place to go. It’s connected to our local rainwater disposal network.”

A drain in the control room floor is a really good idea. If anything ever leaks, the water has somewhere to go instead of sitting around your pumps and electrics. See hot tub control room design considerations for the rest of my checklist.

So, as you can see, it’s been quite a journey for Niels, but progress is being made.

September 2026 update: Niels is tiling!

Niels has been back in touch with a fresh batch of photos, and I’ll be honest, I’m really pleased with what I’m seeing. The last time we caught up he had the base down, the first few courses of the walls laid and the control room dug out. Now it actually looks like a hot tub.

The shell is tiled

The whole hexagon is now tiled. Niels has gone for large-format dark grey tiles on the walls and a stone-effect tile on the seats and floor, and the two work really well together. The bench seating steps down to a hexagonal footwell in the middle, and seeing the shape I drew for him come out of the ground looking like this is exactly why I love doing these projects.

You’ll spot the little black tile levelling clips still sitting in the joints. If you haven’t used a levelling system before, they’re well worth it on big tiles like these because they stop one tile sitting proud of the next. On a surface you’re going to be leaning back against, the last thing you want is a lip. Once the clips come out, it’s on to grouting. If you’re at that stage yourself, have a read of choosing hot tub tiles and waterproofing, grout and tile adhesive.

Jets and fittings in

The jet fittings are in, set into the walls at back height in threes and pairs around the seats, with fittings low down in the footwell too. This is where the design work pays off. Every one of those positions was on the plumbing drawing long before a single tile went on, so on the day it’s simply a case of following the plan rather than guessing. There’s more on getting jets right in my DIY hot tub jets guide.

There’s also a raised corner seat next to the skimmer, which you can see in the photo below. It’s a nice touch and gives a different height option if you just want to perch and cool off for a bit.

The skimmer

The skimmer mouth has been cut into the wall at the waterline, with the skimmer body sitting behind it and the basket on top of the wall. A skimmer is one of those parts people are tempted to leave out on a DIY build, and I always tell them not to. It takes leaves and anything floating off the surface before it ever gets near your filter, and with ferns and trees right next to Niels’s tub, it’s going to earn its keep. I’ve covered the whole job in how to install a skimmer on your DIY hot tub.

Plumbing on the outside

Walk round the back and you can see the plumbing coming together, with the grey PVC manifold running along the outside of the wall and the flexible pipe waiting to be connected up. It’s all heading to the control room Niels dug out last time, which is exactly where it should be.

The coping going on

The last few photos show Niels dry-fitting the coping, laying the big grey tiles loose around the top of the walls to check the cuts and the overhang before anything gets stuck down. That’s exactly the right way round to do it. On a hexagon, the corners are where the cuts get fiddly, so it pays to lay the whole lot out first rather than find out on the last piece.

So, from a hole in the ground in April 2022 to a tiled, plumbed shell with the coping going on. It’s taken longer than Niels planned, but that’s DIY, and I’ll take steady progress over a rushed job every time. I can’t wait to see it full of water, and I’ll add the next update here as soon as he sends it.

Planning your own custom build?

If you’ve got an unusual shape (a hexagon, say) or an unusual heat source in mind, start by sketching it in the free Tub & Pool Designer Pro software. I can then turn it into architectural CAD and a 3D plumbing design. If a standard size suits you, my DIY hot tub plans come in metric and imperial, with CAD drawings, the plumbing layout, a parts list and the video course.

Got a question about Niels’s build, or your own? Drop it in the comments below. I read them all.

Cheers,
Andi

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Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi