The Birth of the Power Trowel

Very early on in our careers as straw bale builders, we realized that being able to pump plaster would be important if we were going to attempt multiple projects. Bodies and spirits just wouldn't be able to keep up with endless hand plastering. So we bought an ancient pump and started spraying.

Oh, how I remember the days of the sprayer nozzle! The comforting farting sound, the reassuring overspray sticking everywhere, plaster in our eyes, noses, lungs, hair, shirts, and sometimes even ending up on the new roof of the house we were plastering (do not trip while spraying!). The nozzle end was a tiny opening, just V to 5/s inch, so if a tiny pebble made its way through the screening and into the nozzle, it could (and did sometimes, much to our chagrin!) jam up and create back pressure, even to the point of exploding the hose! Luckily no one has ever been in the way of the hose at the time, but what a sorry mess it makes!

We talked often about improving our lot in life. I had read about trowel ends for plaster pumps before, and this kind of fitting seemed like it would be cleaner and easier to use, but they seemed impossible to find. So as often happens in life, I set about to make my own. These are the steps I followed:

• Make a 30 degree (approximate) bend in the 1-inch pipe, leaving an 11-inch section of the pipe straight at one end. Use an acetylene or propane/oxygen torch and wind a coupler onto the threads, or they will get bent!

• Grind a flat face roughly % inch across along the straight, 11-inch section. This is where the trowel will attach.

• Grind a slot through the pipe where you have ground it flat, 3/s inch wide by 5 inches long, centred 5 inches from the bend. This is where the plaster will exit.

• Place the flat face on the workbench with bend up and weld on 4 reinforcement bars flush with the face. Use the 3/s-inch square bar. These are necessary to support the trowel attachment, as the trowel material is not strong enough by itself.

• Weld on the handle. Shape to taste from 3/s-inch round bar, remembering that heavily gloved hands will be trying to hold the handle.

• Lay out the trowel face. An aluminum hawk makes decent material. Our trowel is 12 inches long by 6 inches wide, with a 3/s-inch-by-4-V inch slot. Bias the slot towards the end of the trowel by V to 1 inch to allow closer application to ceilings.

• Use a drill and saber(jig) saw to cut the trowel out. File off sharp edges.

• Fasten the aluminum to the steel pipe with polyurethane caulking and annealed steel wires twisted tight with pliers. Our earlier experiments using lexan for the trowel and held on by 20 machine screws failed, lasting only one or two homes.

The rest is basic plumbing. Use Teflon tape on all threads and heavy-duty hose clamps. As we're reducing the hose down to 1 inch, a full-size quick-connect is necessary at the upstream end of the s-foot hose to allow for proper cleanouts.

Thus was the birth of the power trowel. It was a big success! It worked! No more overspray! We won't kid ^

19.17a you we still make a mess when we plaster, but a least it's a bit more controlled now. The power trowel needs two operators (or one if that person is truly a power-power troweler): one is the hose holder, the other holds the trowel end up against the wall. The trowel can be moved either sideways across the wall, or more popularly, up the wall. There is quite a knack to this grueling job, and those who are quite talented at it actually seem to dance together as they pass the power trowel back and forth, weaving gracefully around scaffolding, rocks, and slow hand trowelers.

Power trowel advantages:

• tends to fill hollows, somewhat self-flattening

• less clogging by far

• blow-off valve works

• less back pressure

• less loss of cement paste and water to atomization, resulting in longer working times

• no more overspray on windows, ceilings, and people (although we do still drop almost as much on the ground or floor)

Power trowel disadvantages:

• overhead areas are difficult

• does not quite reach ceiling, trowelers often have to push the mud up the last 3 or 4 inches

• occasional air pockets between coats

• somewhat more effort for the nozzleperson

The power trowel has made life as plasterers easier, cleaner, and quieter.

— Peter Mack A version of this article appeared in The Last Straw, no. 42. ■



19.17a - b: Pumping the plaster through the 'power trowel' takes about half the time of applying it by hand. Burt and Andrew both make it look easy.

water at the nozzle. Both are suitable for straw bale walls although gunnite might be overkill.

Despite being faster than hand plastering, spraying is not necessarily less physical work. Feeding the hungry machine can take up to three dedicated mixers, and the person spraying will have to be followed by at least two trowelers.

You will need to prepare your site thoroughly for a machine application. Larger homes should have sand piles deposited on opposite corners ten feet away. The hoses are heavy and the machine is stationary, so make clear paths for k moving the hose around die site. Scaffolding must be provided where necessary. It is critical to tape and cover elements you don't want plastered, since sprayers are less than completely accurate!

Plaster spraying outfits tend to be expensive to hire. If you are hand plastering with volunteer labor, your savings are significant. However, with a sprayer, die reduction in time and effort is equally significant, and a hired s spraying crew will be

| cheaper than a hired handplastering crew.

19.18: It's so easy You could hire a spraying outfit to apply your shadow only a base coat, which would take care of the could do it! The most labor-intensive aspect of hand application. plaster should be Or you could have a specialty top coat sprayed. stiff enough that You might hire a sprayer for the exterior and do it doesn't easily the interior by hand.Any combination of options run off the hawk. is possible.

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