Because we are new to landscaping it seemed like a good idea to buy two ready-made large circular timber decking tiles to position down the garden for seating areas ( diameter around 180 cm/ 5ft 9inches). The problem is there is no advice on the company website on how to lay these and what kind of base is best. The garden is currently fairly flat and laid to quite chunky limestone gravel. We haven't bought them yet in case the process is too tricky. Any help gratefully received.
You probably need to protect the deck wood from contact with the ground. If the limestone provides excellent drainage, then it may be OK to lay them right down on the limestone. Otherwise you may have to set some kind of concrete piers.
How are the boards held together? If you just propped it up by the ends of the structure, would it hold? Lets just say you put 4 'legs' on one of these. Would it sag? Break?
This picture is about the worst case scenario.
If you can find out the size of lumber that attaches the boards together that may answer the rest of the questions. How strong are these supports (I have drawn them in black)? How often do they need to be supported? Are they a lumber that is approved for contact with the ground? (resistant to local pests, fungi, damage from constant moisture) If the black boards are OK in contact with the ground, then the limestone base will be enough. No need for piers or additional boards.
If the limestone is not good, level support, then use the piers. Then add the blue boards.
If the limestone drains well, and can be made perfectly smooth and level, but the black boards should not be in contact with the ground, you should provide some horizontal boards (drawn in blue) that are strong enough to support the weight of people walking around on these, and are approved for ground contact.
OK, I found the web site.
It does specify that the boards I drew in black are pressure treated, so I would hope that means they are OK with ground contact.
You will have to be very careful to make sure the limestone is absolutely smooth and level under each board, but it seems you could set these right down on the limestone.
I also see a possible problem.
Zoom in on the picture you included and look at the large circle.
Start at the top and count the boards. See the 3rd board? Follow it out to the right, to the edge.
There is no support under the ends of these long pieces.
What did they use to connect the boards?
I would be suspicious about the price, too. That seems awfully cheap!
I could not buy the local materials here (California) for that price, and do a proper job, with the right lumber. I haven't allowed anything for labor- I was already out of money just 'buying' the materials.
Call or go to whatever lumber yard is closest and see what they would sell you if you wanted to build these yourself. What quality of lumber, what price. Find out how long one of these boards is OK overhanging, with no support.
Thanks- I can't believe your amazingly detailed and useful response. I am now armed with the right questions to ask when I call next week. We don't have the cash to do a full landscape job yet but I don't want the boards to break in a few months. I will let you know the outcome and post some pictures if we do go ahead. I too felt this was very cheap but possibly good enough for a couple of years.
I am in the construction trades, and have been part of crews building quite a few things, and built my own deck, among other projects.
Anyway, I thought of another way this could work:
If you made a very gentle mound out of the limestone chips, then leveled out the top this would ensure good drainage. Then add just enough more to fill the spaces between the boards that I have drawn in black. The actual deck boards would then be fully supported by the limestone chips, and the connecting boards would be 'sunken' in the chips. There would be no free ends unsupported.
My concern is that this pretty much buries almost all the wood in a material that will hold some water, (even slightly elevated) and greatly reduce air flow. The wood will rot much faster.
