Hydrotherapy pool timber base project.

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Czar

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26 Jul 2015
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Location
Yorkshire
Hello, I am a complete novice to the world of woodworking, wood specie, soft & hard woods, their structural grades and intended construction use for the specie chosen for a particular construction role.

The reason I am writing this, is to share and hopefully offer awareness from my somewhat nieve blindness and trusting faith in timber suppliers, their knowledge and understanding of timber and chemical treatments, after all they are supposed to know what they are selling, and the advice given, right ? You'd think so, in my case, sadly not, what you want from the timber for the particular construction role, and my very first construction attempt.

This is my very first effort at any type of timber construction, thankfully nothing that is going to hurt anybody.

At the beginning of the year, I decided for my dogs health, to purchase a self contained Hydrotherapy pool, (hot tub without seats) once I had the dimensions and weights, I set about turning my garden into a building site, I must say this before anyone says, concrete, I do NOT like concrete, especially concrete bases, so armed with a head full of ideas, I decided that I wanted a finish base height level with my remaining lawn, this meant I had to dig down to lay a foundation base to support a timber frame base.

Let the digging commence.

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This is where the first of the issues dawned upon me, the timber will be below surrounding garden level, so with that realisation, I knew whatever type of timber I ordered would need protecting, anyway on with digging.

Once the digging was complete, down as far as the clay base level, a stone hardcore was used, compacted whacked flat, quarry sand was compacted and whacked flat on top of the stone hardcore to create a very solid level base from which to lay and support the commercial 18" x 18" x 3" concrete paving slabs, I hate concrete, but when they are free, mustn't grumble.

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Once the foundation base had been laid, I then turned my attention to the timber base, which would support the Hydrotherapy pool, whilst also needing to be chemically treated, as if you remember, the issue of below ground level was now more apparent after a very heavy down pour (14 hours continuously) oops the clay base was now doing its job, yes, my base was holding 1/2 inch of water across the entire base site, at least I know it's level.

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At this stage of my very first construction attempt, I'm now getting quite a few very different opinions on what I should do, given that the Hydrotherapy pool weighs 5 tonnes when full of water, most said I needed to contract the services of a structural engineer, which I thought was over the top, after all how many people sit their hot tubs on regular decking !!

Regardless of the advice to contract a structural engineer, I used my engineering (Motorsport) and common sense approach to work it out myself, albeit with advice from the timber supplying company, I ordered construction grade C24 with the class 4 ground contact chemical treatment, now what I wasn't aware of and had no advice that dependant on the different specie of wood and whether it's sap or heartwood and the moisture content, controls the % of chemical treatment ingress depth penetration.

This I wasn't aware of, and when my treated timber arrived, it looked very impressive, however, when I started to work with it, I became very suspicious to the treatment my ordered timber had been subject to, I also wasn't aware that treated timber is certified, given my concerns I contacted the timber suppliers and was told that chemical treatment doesn't ingress the timber fully, that said, I formed them my timber seemed to have just surface contact only with no ingress penetration.

Rather than argue, I contacted the chemical treatment manufacturers, they have been incredibly helpful and supportive, they asked for samples of my treated timber, the results of analysis confirmed my suspicions, the timber I was sold and was treated is not receptive to chemical treatment, and the company who treated the timber, should have known that the particular timber offered for treatment was not receptive, and would only have a surface coating, rendering the timber useless for my particular intention of ground contact.

Needless to say I am now in never ending talks, even with supported evidence to either get the timber replaced or a full refund, so I can continue with my project, very frustrating indeed, what I will say is, anyone purchasing treated timber or having timber treated, be very aware that varying timber specie, sap and heartwood have varying levels of % ingress penetration of chemical treatment,
 
Hello and welcome, The Hot tub that I'M familiar with sits beside the pool and I have not any experience in a therapy pool, but would presume, broadly speaking that they are similar in base requirements.
not knowing you're H/SPA, size and model etc, I Googled "laying a base for a hot tub" and got several hits.
The first recommendation is concrete at 4" on compacted hardcore with mesh,The loading is expected at around 120lbs per square ft, and as you would expect, suggesting the base be same size as the H/Spa and thereby hiding its sight.
There are plastic base systems, one named Handt-spa pads, laid in place of concrete, on compacted hardcore etc.
And I assume you have trawled through u tube as there are several how-to's on there.

Sorry to hear of the timber preserver situation.
Have to say, This is why so many better professionals try keep it all simple and straight forward.
Regards Rodders

https://www.youtube.com/watch?v=wIJoYWYvmlk
http://www.ezpads.com/
 
blackrodd":2el7yx3k said:
Hello and welcome, The Hot tub that I'M familiar with sits beside the pool and I have not any experience in a therapy pool, but would presume, broadly speaking that they are similar in base requirements.
not knowing you're H/SPA, size and model etc, I Googled "laying a base for a hot tub" and got several hits.
The first recommendation is concrete at 4" on compacted hardcore with mesh,The loading is expected at around 120lbs per square ft, and as you would expect, suggesting the base be same size as the H/Spa and thereby hiding its sight.
There are plastic base systems, one named Handt-spa pads, laid in place of concrete, on compacted hardcore etc.
And I assume you have trawled through u tube as there are several how-to's on there.

Sorry to hear of the timber preserver situation.
Have to say, This is why so many better professionals try keep it all simple and straight forward.
Regards Rodders

https://www.youtube.com/watch?v=wIJoYWYvmlk
http://www.ezpads.com/


Thank you so much for you're reply, my dogs Hydrotherapy pool is very similar to a hot tub, it has everything without the moulded seating arrangement, with the addition of 5 two stage swim jets, the pool base footprint is 3m x 2.4m

although I have trawled the Internet, sadly there isn't any other solution to the timber construction base I am pushing forward with, as I have a perfectly level paving slab base, albeit be 8" below the surrounding garden lawn, I have to get the pool to lawn level, as my base holds 1/2" of standing water, due to the clay, this does soak away reasonably quickly, thankfully.
 
The only way to keep the water from laying on you're lovely new base is to either dig and make a sump beside the base,
and or pipe it away a short distance.
You don't want to dry the clay out under the base completely, as it will shrink and could cause splits etc in really dry weather, I would think it would stay damp enough.
But as the clay sounds to be an issue, just lay a 4" sloping pipe to get that amount of water away, You could use this to drain the changed water, should you not wish to drain directly on the lawn.
Do you know how deep the clay is in you're immediate area/garden?
Sometimes it can be in quite small depths or bands and I had the situation once that it was easy to dig down through the clay belt and soakaway.
I have seen a timber base on u tube that is similar that I imagine you are constructing.
Good wip there and thanks for posting
Regards Rodders
 
blackrodd":3ppx7nnz said:
The only way to keep the water from laying on you're lovely new base is to either dig and make a sump beside the base,
and or pipe it away a short distance.
You don't want to dry the clay out under the base completely, as it will shrink and could cause splits etc in really dry weather, I would think it would stay damp enough.
But as the clay sounds to be an issue, just lay a 4" sloping pipe to get that amount of water away, You could use this to drain the changed water, should you not wish to drain directly on the lawn.
Do you know how deep the clay is in you're immediate area/garden?
Sometimes it can be in quite small depths or bands and I had the situation once that it was easy to dig down through the clay belt and soakaway.
I have seen a timber base on u tube that is similar that I imagine you are constructing.
Good wip there and thanks for posting
Regards Rodders

Once again thank you for you're advice, very much appreciated, would you by any chance be able to find the YouTube link you mention ?

Given the location of the base in my garden, I now can't dig in pipe work to drain off the 1/2" standing water which only collects whilst it rains very heavy for a few hours, I did think about a sump and pump, that said, I don't want to disturb the base now, so to combat the standing water issue, which isn't really that much of a problem, my timber base will be completely sealed in Firestone 1.52mm rubber EPDM, I have discussed this at length with Firestone technical, and yes it will work, here is such a base, on a much much larger scale than my 3m x 3m base.

Photo courtesy of Firestone Rubber company.
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Be aware when purchasing treated timber, it may seem treated externally, however when you cut it, not all treated timber is what it may seem, here are images of my C24 class 4 ground contact treated timber, which should have been good for 15 years!!

This is 6" x 2" C24 graded timber, treated with class 4 ground contact, it turns out to be Spruce timber, which is non receptive to ingress penetration, at best all you will ever get is an envelope covering.
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This is 4" x 4" C24 graded timber treated with class 4 ground contact, and is heartwood, (from the centre of the tree) and heartwood is very very poor at ingress penetration of chemical treatments.
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If the spruce you refer to is western white spruce, which it does look like in you're pic, you're right, it's truly horrible timber for any use, sold by many sheds also Wickes. Most of it is twisted or bowed, and it is so dense.
Sounds like these people are just dipping and not pressure treating
The knots and part fly out like bullets when you are trying to work it on a planer or spindle, Jolly painful, as my gran would say!
Please keep the WIP going and keep chasing up after those suppliers.
Regards Rodders
 
It's been a while, for those following my journey, the first batch of truly dreadful timber was replaced, with excellent carpentry grade timber, however, by the time the replacement timber arrived, it was too late in the season weather wise, so the project stopped.

Sadly on November 11th 2015 I had to make the decision, nobody who has a pet finds easy, I had to set my beloved Samoyed dog of 12.5 years, free to journey over the rainbow bridge.

Although the project stopped and then became redundant, I have had time to reflect, so the project will once again continue in memory of my late Samoyed dog.

Having had lots of time to think about the best way to construct the deck base, at first I was going to fasten the timber together with the Spax screws already purchased, that said, I have been lucky enough to visit New York, whilst there, I stumbled across a beautiful shop, Miya Shoji, a traditional Japanese furniture craftsman.

Having seen and spoken to the craftsmen about the simplicity of how the Japanese construct not only furniture but homes and temples alike, without a nail, screw or other metal fasteners anywhere, this got me thinking, why couldn't I or anyone apply this technique to construct a deck base ?

I think I am going to give it a go.
 
Having spent a good deal of time in Japan, one of the things on my project list is to construct a Japanese hot tub. They are brilliant. In Japan they are made of Hinoki, which so far as I can tell, is not available in the UK, at least not in the dimensions required (I have not searched very hard yet). Western red cedar seems to be a sensible alternative. Construction is quite straightforward.

Good luck with your project.
 
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