Garden decking.

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Hello, I'm a newbie to the forum and a relative novice to DIY, especially garden related projects, i am looking to construct a timber decking area in my garden 3.0m x 3.0m to support a hydrotherapy pool for my dog, I want the deck board finish height to be flush with my lawn.

So far I have dug out the area and down 15 inches, compacted the soil/clay ground till that was level, tipped in old broken up stone roofing slates mixed with other quarry stone crush, compacted that level, compacted 1.5 tonnes of quarry sand over the stone crush till absolutely solid and level.

All the time not really knowing what I was doing, had it not been for Google and YouTube, I still don't really know if what I've done so far is correct, after watching many YouTube clips on laying block paving, I thought this was my next step, I must also say, as I hear some of you shout, why not pour a concrete base, I do not like concrete anywhere in my garden.

I was lucky enough to be donated as many as I needed 18" X 18" x 3" paving slabs, so this is what I laid onto a bed of sand, on top of the already mentioned foundation base, after much adjusting with a pavers rubber Mallet, I then used the whacker plate to compact this, to settle or unsettle any suspect paving slabs.

Just 3 needed to be lifted and reset, I now have a 3.0m x 3.0m absolutely dead level paved area, that does not move in any direction, as it is locked in around the outer edge with a locking stone perimeter, this paved area has been laid for 6 weeks now, and endured lots of rain, at one point we had rain constantly for 14 hours, this is when I discovered a slight issue, non of the pavers moved, that said, the hole in which they lay is now 8 inches below my lawn, and after 14 hours of rain, the pavers ended up being submerged under 10mm of water, which did drain away slowly over 2 hours.

I did not give any thought to drainage nor did it even cross my mind, and I don't want to undo any of my hard work, so I still intend to press on with the timber construction, it is at this stage I got so many conflicting advice on what I should do, so what I have done is use Google again, and ordered the following, which has now arrived apart from the fasteners.

C24 6 x 2 treated with class 4 ground contact which came in 4.8m lengths, this will form the substructure frame, simply placed directly onto the paved area, this substructure frame will then be topped off with C24 5 x 2 again treated with class 4 ground contact treatment, all fixing screws are A4 stainless steel by Spax.

Hopefully this will be enough to support my dogs hydrotherapy pool with a wet weight of 5 tonnes, can anyone see any further pitfalls or mistakes before I build the timber frame ?

Many thanks.
 
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Here are a few photos of the foundation base;

Starting the dig.
image.jpg3_4.jpg


Compacting the stone roofing slate and quarry stone crush.
image.jpg1_11.jpg


Stone crush and quarry sand compacted ready for bedding sand.
image.jpg5_4.jpg


Laying the paving slabs.
image.jpg13_1.jpg


14 hours of rain, submerged under 10mm of water, oops.
image.jpg9_2.jpg


Resetting the ones the whacker plate disturbed.
image.jpg2_5.jpg
 
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Lucky dog :D I'm not quite sure what you're asking, the base will take 5 tons, no problem. The buried timber won't last for ever...
Don't you need warm water for the hydrotherapy? Looks a tidy job anyway!
 
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Lucky dog :D I'm not quite sure what you're asking, the base will take 5 tons, no problem. The buried timber won't last for ever...
Don't you need warm water for the hydrotherapy? Looks a tidy job anyway!

I was simply asking if anyone can see any pitfalls to my DIY construction, as this is the first time I have undertaken such a task, yes he's a very lucky dog, and yes his hydrotherapy pool is heated with swim jets too, the water will be a constant 30°c

Thank you for your kind words.

Here is the lucky dog.
imagejpg1-2.jpg


Here is his pool under its cover in the garden.
image.jpg4_3.jpg


And here is what it looks like uncovered, library photo.
image.jpg1_7.jpg
 
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I would like thoughts on the proposed idea, as my timber frame will suffer from constant wet dry cycles, and during the rainy season, my frame will be almost completely wet from standing in 1/2" + water.

Having had the original ideà to cover the deck top face with Firestone EPDM lapped over the edge by 3" to protect the Celotex insulation board, yesterday I spoke with Firestone technical, and they suggested the following as an idea.

Why not wrap the whole timber frame in EPDM, this will stop any of my timber frame from coming into contact with water from below or above, and it wouldn't matter how deep the standing water became.

The timber for the frame, is stored away from any water contact and has now dried out completely.

Wrapping the whole timber frame in EPDM seems a good idea to me, thoughts please.
 
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The only thought I had for this was that the waterproof box (which is what you are making) may become unstable when it is submerged, i.e. it will want to float... as long as the weight of it is more than the weight of water it displaces then you will be fine.

I have no further comment on the proposed as I don't know enough about EPDM to say if it will be a good or bad idea...

Andy.
 
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The only thought I had for this was that the waterproof box (which is what you are making) may become unstable when it is submerged, i.e. it will want to float... as long as the weight of it is more than the weight of water it displaces then you will be fine.

I have no further comment on the proposed as I don't know enough about EPDM to say if it will be a good or bad idea...

Andy.

Thank you Andy, not long after you posted, Firestone technical contacted me, as I requested a call back to discuss other technical aspects, so I asked about the possibility of floatation issues, and as the EPDM is breathable besides being watertight, and the given bearing weight of 5 tones, there will not be a floatation issue.

So based upon technical fact, lots of common sense, I am going to wrap my timber completely in EPDM, let's see what happens.
 
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Haven't quite followed what the timber is doing, so hope my advice makes sense.

Wrapping timber generally makes it worse, water still gets in through joints and the protection then stops the timber drying (so it is wet all year rather than for x weeks or months).

Best to rely on the pre-pressure treatment, make sure to retreat cut ends and squirt treatment down drilled bolt holes etc. Sit the timber on packers rather than direct to a slab, try and avoid where possible the timber sitting hard against a flat surface as water will be held between the two surfaces.

The biggest problem with pre-pressure treatment is making sure it has been done properly.
 
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Haven't quite followed what the timber is doing, so hope my advice makes sense.

Wrapping timber generally makes it worse, water still gets in through joints and the protection then stops the timber drying (so it is wet all year rather than for x weeks or months).

Best to rely on the pre-pressure treatment, make sure to retreat cut ends and squirt treatment down drilled bolt holes etc. Sit the timber on packers rather than direct to a slab, try and avoid where possible the timber sitting hard against a flat surface as water will be held between the two surfaces.

The biggest problem with pre-pressure treatment is making sure it has been done properly.

Thank you Aron Searle, advice much appreciated, to bring you up to speed, I have dug out a 3 x 3 metre area below the level of my surrounding garden, this area was filled with stone crush hardcore, levelled and compacted, topped off with bedding sand, and the whole area paved with 18" x 18" x 3" pavers.

The timber to construct the decking is C24 grade softwood 6" x 2" which has been treated with class 4 ground contact, this will sit directly onto the paved area, and will now be wrapped in Firestone EPDM, all fixings are by Spax, M10 x 160mm A2 Stainless Steel full tread countersunk and M8 x 140mm Hi Force washer head A2 Stainless Steel.
 
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At long last some of the screws I ordered from Spax have landed, these are M8 x 120mm A2 Stainless Steel cylindrical deck, path and walkway dedicated fixings.

image.jpg1_12.jpg


image.jpg6_5.jpg


image.jpg5_5.jpg
 
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Update,

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!!

So all my treated timber, is not fit for purpose, I'm hoping the timber suppliers are going to replace it at the very least.

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.
image.jpg2_7.jpg


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.
image.jpg3_6.jpg
 

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