Fibreglass Hot Tub Refurbishment – Case Study

Not every DIY Hot Tub project that I work on is a new design and build. I do a lot of “rescue projects” where tubs and pool are either partly done or partly designed and the customer needs help to finish things off. The other line of work that I do is refurbishments and help people get non-working tubs back in action. 

This project is more of a hybrid between a refurbishment and a new build than anything. Mark came to me wanting to remove his fibreglass hot tub that had seen better days and replace it with a poured concrete tub but keep most of the plumbing he already had.

Let’s see how he gets on as we follow his progress in this case study.

The Background

The background to this project is pretty straight forward. Mark has a beautiful indoor pool and hot tub at his home. Both are 20 years old and the while the pool was in good shape, the hot tub had definitely seen better days.

What he wanted to do was rip it out and then replace what was there with a poured concrete tub. Pretty straight forward right? Let’s see if this is the case!

The Plan

The plan – Mark had a very clear idea of the size and the dimensions that he wanted for the tub to fit in the void that was left. What he needed assistance from me with was the plumbing payout.

One of the problems with the old tub was that as it was a spillover tub, when the pumps stopped, the water would drain back into the pool. 

Somebody had either forgotten a Hartford loop or a one way check valve on the lines, that was going to be pretty easy to fix.

He sent me some pictures of the existing pipework that was there and he had already labelled up exactly what each of the pipes does. The plan was to use the existing kit that he has on his pool pad as most of that was working. 

What we would need to do is get a new jet pump but that runs to and from the tub have all been working just fine so we were going to use them.

Mark also wanted to do away with the dipping pool that was at the end of the overflow and replace that with a slide – something he was sure his grandkids were going to enjoy.

With a plumbing design done, parts ordered, it was time for Mark to get to work.

Let the Work Commence

The first thing that Mark had to do was to remove the existing fibreglass hot tub. This was not too much of a problem and it came out of its housing quite easily.

When the tub was removed, it was not deep enough so Mark had to dig down about another foot to so to give himself enough space for a poured base and also some formed seating.

The Base

Next step was to get the damp proof membrane in there so that he could keep dirty water ingress out and then it was time to plan for the base. The rebar went in as you can see below.


You can clearly see here the the existing pipes that we are going to tap into. Mark has labelled them ready for us to use.

With the base in place, the next stage was to pour the seats. Rather than show you lots of individual pictures, here is a montage of this stage. As you can see, there was quite a lot of form work to be done before he could pour and Mark had already put the plumbing in situ too.

A quick note on the plumbing, as I mentioned earlier the tub was draining back into the pool when not in use so what we did was put a couple of Hartford loops in place to make sure that this didn’t happen again.


You can also see on the picture above that mark was insulating the backs of the seats too before he formed them up and poured.

The Pour

Below you can see the main pour for this – again plenty of bracing on the forms as there is quite a bit of weight to hold back with the poured concrete.

With the seats all formed up, it was time for Mark to turn his attention to the slide that he wanted to create for his grandkids. 

The Slide

Here you can see the pour for that, check out the lilo in the pool being used to hold all this up – genius!

After the concrete had cured, Mark needed to turn his attention to the waterproofing coat and the tiles. He did run into a little bit of a snag in that he didn’t use a cementitious waterproofing agent first and had to pull his tiles back and redo them. Looks good though.

Job Done

And here we have it – the finished product complete with grandkids! All working fantastically and Mark is really pleased (as as the grandkids) with the end result. Really nice job Mark!

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi


Hi, Andi here. I own 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.

Today, I've helped over 1000 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

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