It was on a Saturday, the sixth of December in warm and humid conditions to be precise, that I met my Gripple. We were introduced by a good friend, and a happy meeting it was. I was captivated from the first moment by the sleek form and sheer charm that my Gripple displayed. It was a whirlwind romance as I showed my Gripple off to all and sundry. But alas it was a short lived affair, as my Gripple found someone else. I had fallen in love, and my Gripple had deserted me. O the tragedy, the heartbreak, and in a fit of anguish I vowed then and there that next time I would buy a box full. What, you ask, is a Gripple? Ah, not so fast. First we must start at the beginning.
It was on this fateful day that the Fremantle Community Garden Centre were having their Garden Festival, and I built a demonstration strawbale wall that displayed some of the principles of a load bearing wall using a tie down system. Just to add interest, I mounted the wall on a stumped footing system with garden sleepers as the bed on which the strawbales sat. It was only a small section of wall, done with a corner so that it was self supporting; a course of three bales with a corner return of two bales. This was taken to a height of five bales. Although the wall length was short, the integrity of the corner was what mattered, and that proved to be substantial.
The footings were twin stumps set beside each other, with a piece of 4"x2" Jarrah as a bridging beam. The stumps were set out as outriggers - i.e. they were set wider than the width of the wall. This was to give the wall extra stability as the ends were freestanding. In the exercise of constructing a building, the stumps would sit just inside the outer edges of the wall, with a much shortened beam connecting them. In fact, the mechanism for connecting the beam to the stumps would also tie down the the sleeper bed as well. If an insitu poured concrete stump was used, then a piece of allthread could be used to tie down both the sleeper bed and the connecting beam to the stump. Otherwise a very long coach screw would have to do the job. That particular answer lies according to the stump type.
So the stumps were sunk down 600mm or so, with about 100mm protruding above ground level, the cross beams coachscrewed into place, and two garden sleepers in parallel bolted to the beams. This gave a bed width of 16.5" which suited the 18"; wide bales just fine. In real life though a twenty inch wide bed would be the reccomendation. Any gap down the middle would be covered by galvanized flashing. No measurements are absolute, and the bales and footings seemed to get on just fine. Mind you, the spacings between the stumps were a bit lazy on this occasion. I would have to advocate no more than 1200mm between stumps for a full load bearing wall, taking into account render and roof loading. For those bothered by the slips between the Imperial and the Metric measurements, no apology is made. I am a child of the cusp, and am cursed by both systems 'til the day I die.
Under normal building circumstances, a damp course of tar paper or galvanized iron would be laid. Flashing along the edges of the timber footings should also be fitted. For the purpose of the exercise however, these steps were omitted. The main thrust of the experiment was the tie down system.
So Saturday arrived. A quick phone call to John Glassford for reassurance because, as I said to him, I'm trying this for the first time and it's in public! Trust me, he said. So off to the Gardens I go and start stacking bales. There was a good turnout of interested people, and I was kept busy describing and explaining all day. No wonder I was totally knackered at the end of it all. The wall raising itself was almost embarrassing in its speed and simplicity. The bales were simply stacked and pinned in a running bond with half bales at the ends of the second and forth courses, and U staples to hold the corner together. It was as simple as that. In fact it took less than twenty minutes, with another five minutes for halving two bales. Too quick - so it was dismantled and reassembled a couple of times so that people could have a go. The top plate was also very simple in its construction, and the reason for this is that the tie down system allows a basic spine arrangement that doesn't need crossbracing or hardpoints for the allthread tensioning system. The top plate consisted of a scaffolding plank about 8"x 1.5" with a spine of 4"x 2" Jarrah. In cross section it forms an inverted "T". The spine was located to the plank with a tek screw about every metre. This was simply to hold the timbers together and stop them sliding around. Just a small observation at this point - don't let anyone tell you that you need a power tool to put in tek screws. Bollocks. They go in very easily with a hand brace, particularly into seasoned Jarrah. In fact it seems to be the harder the timber, the easier it is with the handtool. Five or six turns on the brace and its home. To saw to length and assemble the two top plates took about ten minutes using the appropriate hand tools. They were then lifted into position and connected and crossbraced at the corner. The moment of truth had now arrived.
The tie down system used was simply a variation on a theme - fencing. High-tensile fencing wire 2.5mm diam. was cut into lengths that formed a complete loop around the height of the wall. A rachet type inline fencing strainer was attached to one end of the wire, and the other end threaded through the axle of the tensioner. A spanner was then applied to the strainer and the wire tightened. Four tie downs were used, two per wall about two metres apart. The rachet gismos were alternated either side of the wall to compensate for their tendency to pull slightly in the direction of the rachet. Tensioning was done incrementally so that the load was evenly spread over the top plate. We gained a compression of the bales of about 3 inches. At this point the wall was acting as a single unit, was very stable and almost unmovable when pushed at the corner. The system worked like an absolute charm.
It was at this point I could sit back and relax. Although I couldn't see any reason why the system wouldn't work, one doesn't normally carry out experimental work under the scrutiny of the enquiring public. So there was a sense of relief when it all tied together as well as it did. It was then that Dave Moore, good friend and draughtsman extrordinaire introduced me to the Gripple. The attached diagram shows the technical attributes of the Gripple, but gives no idea of the charm. They are cute with a capital C. As you can see from the drawing they are an inline fence strainer that works on a continuous feed system. The ends of the wires are fed through the Gripple and tensioned using the gripple tensioner, but can't pull back out. To remove the Gripple you cut the wire just behind it and pull the remnant forward. Although they are a very small unit they can take very high strains, and are very popular in the vineyard industry where they carry high loads and can be retensioned when necessary. They are also not expensive at about $25.00 for a pack of twenty. On top of that they have all the character and personality that a tamagotchi lacks. Get hold of one and you will see what I mean.
So, an analysis of the tie down system as used on the experimental wall. Obviously the Gripple would take pride of place over the larger, more expensive and clunkier rachet device. I would recommend using one on each side of the wall as this evens out the loads and removes the tendency to pull. The top plate doesn't need an outrigger where the wire goes over the top as it cuts into the bales, straightens out under tension and actually forms a slightly triangulated tensioning unit. Multistrand steel cable may also be preferable to fencing wire as the wire can snake around a lot off the roll and possibly poke someone's eye out, but I am not sure about its compatibility with Gripples. If you do use the wire keep the end bent over to avoid that problem. Place the tie-down points every three to four feet. The top plate itself works perfectly. You don't need to cover the whole top of the wall, just spread the load over one third to one half, and centre it.
Regardless of the footings used, I would recommend starter bars just at the corners and wall ends. This simply means that the bottom course bales can be shoved up tight. Because the stacked bales become somewhat unsteady over five bales high, it is a good idea to temporarily prop them, fit a section of top plate and nominally tension it. Staples for the corners from the third course up are advisable as the corners give much structural strength. The wire or cable used in tying down can either attach to hold downs either side of the footing or loop right under it. A properly engineered stumped and suspended footing system of timber or concrete will work as well as anything else, and also allow suspended timber floors. The entire system is simplicity itself. No starter bars other than the corners, no allthread up through the walls, no chicken wire to hold it all together, no complicated ladder top plate. Simpler and cheaper. With a couple of variations it is a similar system to the one used by John Glassford of "Huff-n-Puff" when the load bearing tests were performed in N.S.W. earlier this year. As a load bearing system the roof would connect directly to the top plate, and I can't see why the system in principle can't be used in an infill situation if that is the way you decide to go.
So all in all it was a successful day. The tie down system worked a treat, lots of people turned up and asked lots of questions, and I fell in love with the Gripple. I hope one day to meet another. If you too come across your own Gripple I think you may feel the same.