The Floor

With the foundations laid it was time to get on with the floor!    I stood inside the decagon and tried to imagine what this whole structure would be like and I found myself thinking "its an awfully small space..." So I decided to make it bigger,  I laid out the floor joists with a half metre overhang giving a new overall diameter of three metres.   Structurally this isn't a particularly great idea, it creates the opportunity for a lot of movement in the floor but it did result in the foundations becoming almost entirely invisible so now the observatory appears to float above the ground with no visible support which is a pretty cool effect.  It later turned out that - again - this was a decision that would have serious consequences later down the line:  There are quite a few commercially made products that have two metre diameter domes: oil stores, sceptic tanks, geodesic green houses to name a few.  Small composite manufacturers will happily lay up two metre diameter hemispheres for you in fibreglass... but not so with three metres.  There are very few commercially made products with three metre diameters and the few that are available are hugely expensive to the point of out costing the rest of the build by an order of magnitude.  This decision basically committed me to building my own dome from scratch and that (as we will see) was not easy.

I had a friend over to help and together we set about laying in the floor joists and cutting all those awkward joints I illustrated for you in "The Design"  and after a few hours work this is where we were:

The "Pole star" stage

Then we had a tea break.  

I had planned to use the 18mm plywood that had formed the sides of the Observatory mk 1 to make the floor. The plywood itself would have added significant strength to the structure however it turned out that most of this plywood was not in good condition and (because it had been nailed to the timbers rather than screwed) most of it was too badly damaged to reuse.  So the tea break discussion focussed on what to do next.  Again the easy way out of the problem would be to just buy new plywood but a quick call to the local timber merchant revealed that sufficient plywood would cost a couple of hundred pounds and I wasn't keen on that!  Then Ryan's eyes alighted on the pile of pallets that I had recently collected for firewood.   "Why don't we use those?" he said.  Well why not indeed, wasn't that "The Plan" after all?

The first of many such piles to be converted to building materials

Well, I don't know if you have ever tried to dismantle a pallet without breaking the wood but it is not easy!

It is very annoying when this happens!

The rest of the afternoon (and most of the next week, ah who am I kidding, most of the next year!)  was spent trying work out an efficient way to separate the deck boards from the runners without breaking them.   I'm not sure we ever found a really good method but a Gorilla bar turned out to be good enough and if you have enough pallets then you can get away with breaking a few planks along the way, it is all useful. If I can't build something from it it can always go in the wood burner to keep me warm!

After I broke up a lot of pallets Ryan came over again the following weekend and we set to laying up the floor:

Looking good!

While this is going to give it an undeniably great look it was clearly going to take a long time to do, which isn't a huge problem. What was a big problem was that the spacing between the joists was too wide to support the planks sufficiently at the outside edges and they bowed alarmingly under loading.

This is the problem with repurposing materials for jobs they were not designed for and modifying your design criteria on the fly.  The joists would have been fine with the planned-for structural plywood floor but it was clear we needed some serious reenforcing if we were going to get away with using pallet wood instead.

Fortunately some of the runners from the pallets were a good size to make the extra joists and more carpentry ensued:

Lots more wood added to the pole star

Here you can see the extent of the reenforcing needed, each original radial joist has had an extra piece of timber on both sides to allow sufficient timber to attach the boards to and each "wedge" has had an extra radial joist added.  We also added plywood cross ties underneath the joists to provide some measure of load sharing to reduce the flexing at the outside edge.

Tests showed that the new arrangement provided adequate support for the pallet deck boards and we really started to motor along by the end of that day we got to here:

Notice the extension at the far side of the central ladder, this is to become a storage pod later on.

This was pretty slow going because every plank had to be laid in place, marked up, taken up, cut to shape, replaced and fixed in position.  There are ten wedges and two ladder section, each section contains sixteen planks so that is around one hundred and ninety two planks, each end had to be marked and cut at both ends, so that's three hundred and eighty four cuts, and that's just the first layer, we did a second layer to add strength... seven hundred and sixty eight individually measured and cut piece of wood. 

about two weeks after we first started laying the floor the first layer was complete and looking good

Layer one done!

It was now that I had a floor that I could walk around on that I recognised how annoying it would be to have things stored on that floor so I added further extensions to the joists to allow the construction of two storage pods to keep all the ancillary equipment in.  I am very please I did this and I heartily recommend that if you build your own observatory you give some serious thought to where you will store things when they are not in use,  it very quickly gets tedious tripping over boxes in the dark!

Having by now gotten quite good at the process of laying the floor the second layer went down fairly quickly, here we see my son helping me glue the boards of the second layer in place:

And with that done we were ready to start building the walls!