Owner Building a Strawbale House
in the Bega Valley,
NSW,
Australia.



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Mobile Scaffold Tower

As we were putting the first roof up it became clear that we needed a better way to work up high than several (some rickety) ladders, none of which reached the highest point we need.

Our strawbale walls will need rendering and for the obvious reasons it would be good if the render goes all the way to the top of the walls and doesn't just stop at our highest ladder height. We will also need to reach fairly high to put in the ceiling lining boards in the cathedral ceiling in the living area. Not to mention getting the next lot of eave bits and pieces in place.

We checked out ladders in our local hardware store. To get an "A" frame ladder that would let us work on things 4 metres up meant a 'tradesmans' ladder not a "domestic" ladder and that meant a more than $500 price tag. If we wanted a platform to stand on to render walls that meant two of them and a plank. At over $1000 that seemed a fairly costly and didn't give us a particularly wide platform to work from.

Clearly we needed scaffolding. A mobile scaffold we could wheel around easily from spot to spot as we were working was required. Fixed scaffolding seemed too cumbersome for all the relatively short jobs in each location, as we'd either need lots of it or spend plenty of time erecting and dismantling it in each spot.

So we started looking at prices of scaffolding. If we were in a big city (or at least closer to one) there seemed to be some second hand ones available. Again we're talking more than $1000 for a basic module and the higher you want the scaffold the higher the cost.

In the meantime we were putting together the order for the steel for the house frame, so we got a quote on some galvanised pipe seconds. The price was good, so the decision was made to build that mobile scaffold ourselves.

If you decide to build one yourself hopefully you can use our experience to make it faster, simpler and cheaper.

Requirements

Before we started work we talked about what we needed and did some searching on the Internet. We came up with the following list:

  • Safe;
  • Maximum working platform of at least 2.5 metres (so 4m bits would be about in front of our faces as we worked);
  • Come apart enough to fit through all our doors and allow us to use it under the lowest ceiling level;
  • Mobile over building site (dirt etc) and stable in use;
  • Weight carrying capacity for at least one person and about 50 kg materials (eg buckets of render and tools), preferably capacity for two people;
  • Individual pieces light enough for two people to lift easily and transportable in a box trailer.

Design

We designed it in roughly three modules or levels. The base level goes to about 1800mm high (including wheels). The next level extends the possible working height of the platform to 2700mm. The top level is a set of safety rails, which also fit straight onto the base level when needed.

The base level is fully welded together. This makes is more difficult to transport, but it fits in our trailer and fully welding these joints provides the cross-bracing for the whole structure. The next levels come to bits. Welding them together would have made them too heavy to lift up and down.

We deliberately made the safety rail level different from the extension level. This will hopefully stop it being used to get just that bit higher (and then not have a safety rail). It also makes it easier to climb onto the platform under the railing, giving you plenty to hold onto while you do it.

The area of the scaffold is 900mm by 1800mm, partly because it will fit through our doors and partly because its convenient for the sizes that materials are supplied in.

The working platform is made from four cleated planks with bits of board screwed to the outside edges to create a toe board. The cleats stop the planks sliding off and giving a worker an exciting ride to the bottom and the toe board stops tools rolling off the edge onto unsuspecting passers-by. The platform can be set at 300mm intervals from about 300mm off the ground to the maximum of 2700mm. We designed the long cross rails so that we could work at any height without them getting in the way.

From our research the maximum working platform should not be more than 3-4 times the size of the minimum base dimension (in our case 3 x 900mm = 2.7 metres) unless you install outrigger supports, which we chose not to do.

The levelling of the structure when its on uneven ground is provided by creating a screw down mechanism to attach the wheels. Four "deep" nuts are welded directly to the bottom of the scaffold pipe in each corner. An ordinary nut is used on each wheel thread to lock the height in place by tightening the nuts against each other.

Materials List

What we used and some approx costs...

  • Four 1.8 metre planks of wood, each 200mm wide by 50mm thick, Douglas Fir used (but any suitably graded soft wood should do, oregon, pine, etc.)
  • 5.4 metres of wood for the toe boards, we used 90x20mm treated pine decking
  • Eight 200mm lengths of angle iron (we used 40x40mm), or blocks of wood, to use as cleats holding the planks between the runners
  • Pipe - used for the bulk of the scaffold structure, galvanised is good (to suit outdoor use). We used 51mm OD (46mm ID) galvanised steel pipe seconds - so some had bad seam welding).
    • four 1550mm uprights
    • eight 900mm uprights
    • twenty 830mm runners
    • eight 1730mm horizontals
    totaling around 44 metres of pipe, or about eight 6 metre lengths
  • Eight 250mm joiners of smaller diameter pipe. We used 43mm OD galvanised steel pipe seconds
  • Eights nuts & bolts to "pin" the joiners, we used 1/2 inch UNC because we had them, and some steel rod to make a handle on the head of the bolts
  • Eight nuts and bolts to connect the movable horizontal rails, we use some old 7/16 inch BSW head bolts and some steel rod to make a handle on the head of the bolts
  • Wheels - think about spending real money on serious casters. These wheels need to take the weight (the scaffold itself will weight in at about 150-200Kg, plus one or two people, plus materials and tools plus dynamic loading), and you need to be able to roll it about without giving yourself a hernia, and you need to be able to securely lock the wheels in place so they don't roll around once in place. We used 200mm casters with a 250Kg load limit (each caster) at just under $100 each. We initially priced proper scaffold wheels with a levelling mechanism built-in. At more than $400 each we decided to build our own levelling mechanism onto the cheaper wheels.
  • Levelling adjustment - you need a screw thread height adjuster on each corner (usually between the wheel and the scaffold). Old Acro-prop adjusters are great, we couldn't get any so we bought some 1 1/2 BSW all-thread rod and some seriously big nuts. The four "deep" nuts were about $25 each.
  • Miscellaneous steel plate - we use 10mm plate to weld onto the all-thread rod and bolt to the casters

We spent $80 on wood, $165 on galvanised pipe, $432 on casters, $176 on all-thread rod and nuts. Everything else we already had lying about, so we spent $853 to get our scaffold. We also spent about a week building it.

Construction Process

The basic construction of the scaffold is fully-welded pipe. The added height sections use a pin held by a bolt, and the safety rails bolt in as well. The casters are connected to the scaffold with a threaded rod, to allow independent height adjustment, for leveling.

The pipe joins are welded (using a MIG welder, but you cam use any welding method). The pipes should be carefully notched for the strongest joint (not just 45 degree straight cuts or cut off square), tack welded into place, and lastly fully welded. Start welding the square, flat, end pieces, then join the end pieces (again triple check it is all square).

After you have the basic bits welded together you can drill some holes and weld on some exterior nuts, plus weld some rod onto some bolt-heads (as small handles). The exterior nuts pinch some pins inside the pipe. The pins are really just the next smallest size of pipe welded into the pipe above, and slid down into the lower pipe (where the bolt is waiting to clamp it into place). This connection isn't the strongest, but is all that is required to reduce movement (the weight is taken by the pipe-to-pipe ends meeting, weight from above). The upper section of pipe has several holes drilled in it (exact location is not important); the pin (smaller tubing) is about 250mm long with 100mm inserted into the upper section; this is clamped to ensure the ends up away from the bolted side (note G-clamp presses small dolt into a welding hole to push the pin over to one side of the upper pipe); then you weld into the hole (called a plug-weld or a rosette weld); keep welding the holes; grind the excess metal off; wire brush and finally paint with a zinc-rich paint.

The scaffold planks are simple. Cut to the length of your scaffold (not longer, it is a safety hazard to have them hang over the ends). Add a cleat of some sort (a block of wood, or in our case some angle-iron) to the bottom of the plank at each end, just inside the scaffold (to stop the planks sliding out of the ends), and screw on some toe-boards (again, a safety thing) all around the platform.

The horizontal safety rails (which are 1800mm long, and go between the end sections) are connected with a bolt at each end. We drilled a horizontal hole through the vertical pipe of the end sections, and put a bolt through this hole. Just inside each end of the bolt-on rails we welded a short section of 10mm plate steel, which we had previously drilled and tapped a threaded hole in. The bolt screws into this (straight down the centre of the safety rail tube). You can drill multiple holes in the end secions, we drilled one at each plank cross-rail (every 300mm) so that we could adjust the safety rail to suite requirements.

The casters are made by welding a flate piece of steel plate onto the end of a 250mm section of one and a half inch all-thread rod. The purchased casters bolt onto the steel plate (drill and tap holes as required). The "deep" nuts are welded onto the bottom of the vertical pipe (at each corner of the base section of scaffold) - before you do this ensure the pipe ends are square, so your threaded rod will go up the centre of the pipe! Then thread the standard nut onto the all-thread, and then screw the all-thread up into the deep nut. Adjust as required for terrain.

Ta Da!

The finished thing.... with two levels in use and with all the modules in use. The second it was completed we started using it. There are so many jobs around the site that the scaffold has already made much easier.

In hindsight if you're thinking about a mobile scaffold (and especially if you are close to a major centre or can arrange your own transport and avoid freight costs) you should probably get a quote on a second-hand one to meet your requirements. We are very happy with our scaffold but building it ourselves was not as cheap as you might expect. The things we'd think about to improve next time include:

  • Time to construct - It took us a lot longer to construct than we expected. Using round pipe meant lots of time consuming notching before the bits could be welded together. There were also lots of fiddly bits involved in welding nuts onto pipes or tapping threads into holes to make the bolt together connections.
  • Speed of erection - The bolt together connectors are fiddly to use when changing the height of the scaffold. This is a pain if you are working on a wall that changes in height and you need to change the scaffold height every time you move it. A connection mechanism that is faster to use would be good.
  • Levelling mechanism - We use this much more than we expected. Every move around the outside of the building means resetting the feet levels. We're already thinking about adding hand grips (a kind of wheel like structure perhaps) to the lock nut so it is easier to turn. With this addition we'd be able to screw it down against the wheel plate and then use it to screw the whole foot down against the soil. At the moment we don't have enough leverage so someone has to hold the corner of the scaffold up while someone else screws the plate down. This addition would also mean we wouldn't go looking for our big shifter every time we move the scaffold.
  • Transportability - Our solution also doesn't break down into the small easily transportable bits like the commercial ones. We didn't solve the problem of removeable cross-bacing in our solution, so if you want one that breaks right down into pieces you'll probably need to purchase commercial angle connector bits that are available for scaffolding. These might also fix the speed of erection problem, but expect each connector to be reasonably pricey (perhaps $20 to $50 each, and need about 20 for our size scaffold).