How do I make a spa pad in a muddy spot behind my shed?

[stuartheth]

Hello,

We want to put a spa in here, behind our shed (ignore the crazy steel).

I have dug down 300mm and hit water (nieghbours on both sides have slabs and pounded blue metal.

How do i make a stable place to put 600x600 concrete pavers on which to then put a blow up spa (around 1000L).

Do i dig down 200mm, put a timber border, fill that with stones, then put geotextile, then put sand, then put concrete pavers on top of the sand?

The area i'd like to pave is 3m x 2m but i'm mostly concerned with how sloppy the ground is.

I want to avoid putting in full-on drainage.

Thanks,

[MitchellMc]

Welcome to the Bunnings Workshop community @stuartheth. It's wonderful to have you join us, and many thanks for your question about spa installation.

The first step to installing a spa base is to select a site with good drainage. Unfortunately, that's already ruled out in this location. Is there any possibility of re-thinking where it could go? 

Your steps for preparation are a method that is used, but you'll need to compact the aggregate before laying the sand. This ensures the spa doesn't subside when the ground compresses from its one tonne of weight. Please also check with the spa manufacturer that a poured concrete base is not required. 

I'm also concerned about how sloppy the ground is. At a minimum, I'd advise you to install Vinidex 100mm x 20m Socked Slotted Draincoil below the aggregate to try and direct some of that water to your stormwater drain.

Let me mention @TedBear to see if he has any thoughts.

Mitchell

[stuartheth]

Thanks Mitchell,

So if I dig down to the water table, bang in some slotted pipe and have it drain elsewhere, back fill with aggregate, then geotextile, then sand, I should be right to put some pavers on top and then stick a ton of water on top? 

lol - sounds like a casual but possibly successful plan? It’s only temporary really, it’s a blow up spa. 

[TedBear]

Hi @stuartheth, your question is pretty interesting.... the situation is that you plan to put water (contained in a tub) onto water (with mud). I don't therefore see that as a weight problem.  

Being an inflatable, with soft bottom, the weight of the water will be spread evenly over the area. If the density of the mud under it is reasonably even then at worst it may sink a little, but will that be a problem? 

Personally I would consider levelling the muddy area, put slabs down if you wish but consider also putting some rubber tiles or matting down over that.

This will give you a softer surface under the floor as well as insulating it temperature wise.

Perhaps some fine aggregate around the edges and some artificial grass over that (or not) to make a more pleasant approach than walking over a possibly muddy surface to get in and out.

The main issue will be if the underground water drains away and changes everything... hmmm.

[StevieB]

Hi @stuartheth. Fantastic to see that you've received suggestions from @TedBear.

@MitchellMc will be happy to help further when he's back on the site on Friday.

Stevie

[stuartheth]

Gday!

plan is to dig down so fence side is level with shed size. Then put a rectangle timber frame 3m x 2m (what kind of timber should I use?, do I need to put supports behind the timber?) then fill that frame with stone (what kind of stone should I use?) then a layer of geotextile (what even is that?), then sand leveled, (what kind of sand?), then 600x600 cement pavers.  Then rubber tiles (do Bunnings sell big ones?) then the tub. 

Looking for some advice.

thanks team!

[TedBear]

Hi again @stuartheth, I am a bit confused as to why you wish to do all that...   putting a timber frame into wet soil doesn't seem like a good idea to me because it will rot. Putting sand in it won't stop the water from rising back up and making it into wet sand (cleaner mud).

Putting drainage pipe in won't help either unless there is somewhere lower for the water to drain to, otherwise it will just seep back in. Can you stop  it's source?

If keeping the spa area out of the water is the outcome you are wanting to achieve, then you may be best to dig out the area a little (~300mm down should do), put some plastic edging around as a frame, either garden edging or cut up a sheet of corrugated plastic roofing plastic into strips (use tin snips) or even cut up some corflute - it's cheap and easy to work with.  Since you intend to then fill the area with sand, the frame won't have any load to bear, so something waterproof to define the edge should do.   I would then line the area with plastic sheeting (e.g.  https://www.bunnings.com.au/grunt-3-x-5m-150um-panda-film_p0811229 )and then fill it with ordinary yellow sand.   A bit like a wading pool in reverse (wet outside, dry inside).

You can use plastic edging pegs to hold the frame up until it is back-filled, or just dig the area a little wider that you need, create the frame inside the area (free standing), then back-fill on each side of it as you go around. Yellow sand inside, mud on the outside. You will then have an area that is easy to scrape flat and lay the slabs onto.

(I am not sure why you want slabs? I guess they will stop feet from digging up the sand below the Spa when people walk in it.) 

You can skip the rubber tiles if you like... that suggestion was only about not losing heat, but maybe that's not an issue. You said it's all only temporary.

(I hope I have understood the question...  i.e. that you want a dry, firm area to put the spa onto...  if that's not it, please let us know what I'm missing.)

[MitchellMc]

Hi @stuartheth,

A temporary blow up spa is slightly different from a permanent installation that needs to stay stable for many years. I like @TedBear's approach, and I wouldn't go to the effort of adding drainage if it's just a temporary installation that might be there for five years or so.

You can use any type of sand and aggregate. Geo-textile fabric is just drain matting that allows water to penetrate but not sediment. Here are our rubber tiles.

Mitchell