Waterproofing, Grout & Tile Adhesive

One of the most popular questions that I get asked about building DIY Hot Tub concerns the waterproofing, grout, and adhesive that should be used in the build. In this article I will look at exactly what you need to waterproof your concrete or block structure and then we will look at what grout and tile adhesive options are available.

Before we get going, I think it is pertinent to point out that out of all the Hot Tubs and Plunge Pools I have helped people build – very few have leaks from the structure. Nine times out of ten the leak is in the plumbing and not the structure itself!

Preparing the surface

The first port of call is preparing the surface. That can come in different forms depending on what method you have used for your structure. In this article, I am going to deal with two options, block built and concrete pours.

Block Surface Preparation

If you are building out of block, then you will need to prepare the surface. Blocks themselves can be porous so we need a way of sealing these. What we are going to do it to render the surface with a waterproofing render mix. How do we do this? Well, we add into our regular mortar mix waterproofing agent.

This waterproofing agent can come in various forms, but they all do the same thing. What they do is actually reduce the amount of air in the mixture. It is the air in the mortar mix that allows water through. Reduce the air in the mix, and you improve the waterproofing capabilities.

Here are a few of the agent you can use.

Interestingly, they seem to be a lot less popular in the USA. They are very common in Europe and there are lots of brands. Below I have found an additive that is used for Chimney construction but its properties are desirable in our hot tub and plunge pool builds

In Europe from B&Q

Water Proofing Agents

In the USA


This step is not essential and is just a precautionary measure in terms of the additive. If you can’t find the additive locally, then you can concentrate on the next stage which is sealing the concrete.

Sealing the Concrete

Once we have rendered the surface, or if you are in a poured form, the you will be in the same position at this point. This is where we need to seal the surface of the concrete.

There is no shortage of chemical sealants – a quick search on Amazon for “Concrete / Masonry Sealant” will give you lots of options. At this point, do NOT go for a rubber or latex based one – this is not what we are looking for as this can cause problems with adhesion later on when we come to tile.

What I actually did on my own tub was mix up a PVA wash which worked quite nicely. PVA glue combined with water then a couple of coats and let it dry – cheaper alternative than the chemical equivalent and also really easy to apply.

Now for the Water Proofing Layer

Once your sealant has dried, the next step is to use a waterproofing layer. Normally, these are paint on products. In the USA, something like Hydro Ban is a good option. This is a green color and you paint it on in one direction let it dry, then paint another coat on perpendicular to it. When it is cured it goes from a light green to a dark olive colour. It is not the cheapest product around, but it is very good.

waterproofing grout tile adhesive

In Europe, something like Ardex S7 is a great product for adding a water proofing layer. They both work in a very similar way and the Ardex S7 is a mix then pain on solution too.

waterproofing grout tile adhesive

The whole purpose of these last two steps is the create a fully waterproofed structure before you even get to the grout and tile stage. On its own, the grout and the tiles should be enough, however, with the additional steps taken we can ensure we have a perfectly water tight vessel.

Do I need a separate Grout and Adhesive?

In short, you do not. When I built my own hot tub, I used a combination mixture which was an adhesive and a grout in one. It was of course swimming pool grade. I actually picked this up in the local hardware store.

Interestingly, when I was researching for this article, it would seem as though they don’t carry it anymore. Guess there was just not the demand for it. It was a generic branded “swimming pool grout and adhesive” nothing special really.

That said, my usually “go to” company in Europe is Ardex – I’m not affiliated, they just have good products! They have the Ardex X10 which is a swimming pool grade tile adhesive and the Ardex F4 which is the swimming pool grout.

waterproofing grout tile adhesive

waterproofing grout tile adhesive

For the USA market, there is really no shortage in pool grouts and adhesives. The market is so much larger than in the UK and Europe. A quick google and Home Depot have a huge range themselves from companies such as Polybend, Prism, Mapei just to name a few.

The main point here is that it needs to be swimming pool grade, not wetroom or bathroom grade, swimming pool grade.

Sealing Around the Jet Wall Niche, Skimmer and Inward Suction Drains

I’m adding this last section as it is another question that crops up quite often. Below is an image of the physical wall niche that we use in our builds in the upper left corner and the background is the wall niche inside of the wall before tiles.

waterproofing grout tile adhesive

The idea of the wall niche is that it sits flat with the surface. You can however, mortar over the surface of the niche if you wish. The nice is only there to give the get holder something to butt up to (and it does not seal to that at all – it is just a screw in). A flat surface is just fine so totally up to you.

What I did, and what most people do is leave a gap for the tiles so you are positioning the wall niche so it is going to be level with the surface. A lot of questions come my way about this wall niche and how to seal around it. I, as you can see below, used mortar with waterproofing additive and made sure there was lots around the niche as you can see. The other alternative is to use an epoxy putty to make sure you get a good seal around the niche itself. This is the same for the inward suction pipes too.

Wall Niche

Products like Jenolite Epoxy Putty Stick and JB WaterWeld will do the job just fine as they are designed for under water use. Both of these are available on Amazon in both the USA and Europe.

Hope you found this article on waterproofing, grout and tile adhesive useful!

Happy Hot Tubbin’