Ramp next to pump

Merry Mudders

(Stucco Pumping Iron)

by Habib John Gonzalez – British Columbia, Canada

This article, under the title “Stucco Pumping Iron” appeared in TLS#33 (Plaster special issue). [See note at end of article.]

The system I’ve been using for helping owner/builders stucco their bale homes comes from New Mexico. Folks there hire the stucco pump and operator, rent a big (125 cubic foot per minute) compressor with two 50-ft. lengths of air hose with Chicago fittings, two mortar (paddle type) mixers and enslave seven or more friends to help. Two people run the mixers, one runs (literally) the wheelbarrow, three trowel the mud, and one helps me with the hoses. This method worked well for the projects around here.

Experience shows us that nine to twelve workers make the jobs run smoother, with less burnout from the heavy work of mixing and wheel barrowing the mud. It is easier for the trowellers to keep pace with the spraying if there are more hands to help.

If you hire the four legendary Merry Mudders to mix the materials, we usually spray about 2,000 square feet/185.81 square meter of wall per day. These hard-working apprentices are the building and spraying crew for Sustainable Works.

Since most of the trowellers will be inexperienced and tend to overwork the material to make it look “professionally” finished, there is less stress and work if the owner/builder uses a hand-rubbed finish to the walls. As the brown (second) coat begins to harden, the crew rubs the walls with heavy damp sponges, rubber gloves or burlap rags. The trowel marks are removed and the wall takes on a soft porous “sand” finish, like a traditional adobe building. It is beautiful and easy to do.

The equipment rental, stucco materials costs (use prescreened mortar sand to avoid pebbles jamming the spray nozzle which makes me cranky), and prep work are added to the price of the spraying. I helped an architect friend do his load-bearing cottage in Sandpoint, Idaho, and he calculated his cost was half of a commercial job.

When you have evaluated doing your job this way, please let me know what you decide, and we can take the next step from there.

Masking

An important job before spraying is to mask carefully everything you do not want stuccoed with 2-mil. plastic. Where fine, straight stucco lines are desired around posts, window and door bucks, and such, use duct tape to hold the plastic in place. Otherwise, careful stapling will do.

Sifting

In the 1999 season, we introduced a homemade screen to sift the stucco mix as it pours into the wheelbarrows. Owners build a 2×4 frame, large enough to cover most of a wheelbarrow with a brace in the middle to keep the 1/2-in. hardware cloth (galvanized screen) from collapsing with the weight of the mud. This screen catches rocks, sticks, and dry lumps of unmixed materials before they reach the stucco pump to cause clogging stoppages. This saves heaps of time and work clearing the pump, hose and nozzle. I remain a happy camper without all these dramatic “lock-ups” plugging up the works.

A Ramp

The 18-gallon/68.117-liter hopper on the pump is 32 in./81.28 cm high, so we need a ramp and table for the wheelbarrow operators to be able to dump the mud into the machine.

The ramp is generally 16 ft. long and 20 to 24 in. wide. It is built strong enough to carry an adult and a full wheelbarrow of material – about 400 lbs./181.4kg, depending on how well in shape the operator is. A bale or two placed under the ramp keeps it from flexing as the barrowers run up to the table. The well-braced table is built of 2x4s and scrap plywood, 32 in. high, 32 in. wide and 32 in. long.

Buckets

Have lots of 5-gal./18.92-liter plastic buckets on hand (a dozen or so) to measure sand and water and to soak trowels and sponges at the many work sites along the walls. Additional supplies to make life easier are: eight large cellulose sponges for rubbing the brown coat, at least four heavy wheelbarrows to empty a full load of stucco from each mixer (frees the mixer for immediate refill), and three large heavy-duty garbage cans for water (dipping water for the mix is much faster and accurate than waiting for a garden hose).

Estimating Materials

In stick-frame construction, one bag of mixed stucco covers about 80sf./7.43m2. Stucco covers about 35sf/3.25m2 of bale wall due to the thick layer applied, absorption of material by the fibres and the irregularities of the wall surface. One bag of stucco mix (a commercial cement lime stucco product) has a volume of one cubic foot. Measure the length and height of the exterior and interior walls to determine their total area. This figure is the total area per 1/2-in./1.27-cm coat of stucco.

Divide this figure by 35sf/bag to get the number of bags of cement (or stucco mix) needed per coat (scratch and brown). If you are spraying two coats of stucco, multiply this figure by two.

The first or scratch coat is mixed with sand at a ratio of 3:1.

This converts to shovels of material as follows: one bag of stucco mix equals seven shovels in volume, therefore the scratch coat is mixed with 21 shovels of sand per bag of mix. The second or brown coat is mixed at a ratio of 4:1, or 28 shovels of sand per bag of mix.

To calculate the total amount of sand needed, we use the brown coat ratio and multiply the number of bags of mix by four. This gives us the amount of sand in cubic feet; sand is sold by the cubic yard, so this figure is divided by 27. Order the sand by the next greater dump truck load; if you need 7 cubic yards for the project and the supplier has a 10-yard truck, get 10 yards since sand is cheap and a lot can be lost in dumping, and during building.

During the work, water and sand will be added by pre-measured buckets to keep the density of the mix consistent. This avoids wet mixes running off the walls or dry mixes plugging the pump and hose. Anyone seen randomly adding material to the mixers (i.e., “eyeballing” a little extra water or sand) will be drawn and quartered and then considered for serious punishment!

Cold Weather Work

As the daily temperatures drop in the fall, the experts from the Portland Cement Association say to heat the stucco mix water when the daytime temperatures reach 4oC/39.2oF. The other strategy is to enclose the building while stuccoing and for a few days afterwards.

The PCA Stucco Manual states “Water heated to 130oF to 140o F/54o C to 60o C and combined with cold but unfrozen sand will produce plaster in the 70oF to 100oF/21oC to 38oC temperature range. Heating water to raise the mortar temperature has the effect of accelerating the plaster set which protects against early freezing.”

The water can be heated using a large residential water heater to fill the buckets at the mortar mixers.

Another very useful heater is the propane-fired demand water heater; this only burns fuel when a hot water tap is turned on, there is no tank to be constantly heated. Boche and Paloma are two popular makers of demand water heaters.

A third option is to find an old metal trough or several heavy 45-gal./170.29-liter drums which will be heated by a wood fire below. The warm water will be dipped out by the mixing crew.

To ensure against a cold snap, it is helpful to have enough tarps, plastic sheeting, and similar materials available to hang from the eaves to enclose the whole building. This allows the stucco to cure without the threat of spalding (flaking caused by severe frosts).

Lubrication

Buy two large bottles of Joy dishwashing soap. Old Russian plasterers told us a little bit in each mix acts as a lubricant for the pump and they are right!

A Review of Stucco Options

After reading the stucco handout, a contractor still asked what kind of interior finish I trowel onto the bale homes. Here is my reply: The answer is nothing….we spray and mix, advising the owner/builders of their options.

Many are happy to have the trowelling done as a work party to save money, promote community, spread the SB song, etc. The results are not professional, which is why I encourage clients to do a sponge-rubbed “sand” finish on both exterior and interior walls to remove the less than perfect trowel marks and bring out the soft sand texture. If the clients want something more controlled, then I encourage them to hire a professional plasterer to lead the volunteers; otherwise, we cannot help them and ask them to hire a professional crew.

The work party developed as a way to help the owner/builder around here get the plastering done quickly, to protect their building and make it livable sooner. Some larger homes were taking two years to plaster; one commercial building, built with soft shaggy bales burned (according to the fire chief, the fuzz carried the fire up into the rafters and through the 3,000 sf./278.71m2 roof in 23 minutes). The owner delayed plastering a long time while deciding whether or not to use stucco wire.

One compromise is for us to spray the scratch coat only as a work party; the work is less exacting than the final coats and we leave the site knowing the bale wall surfaces are safe. Several friends have done two work party spray coats with us and followed them with simple gyprock mud, sometimes tinted with latex paint. This interior finish is either satiny smooth or textured to taste.

Another interior finishing variation is to dilute the drywall mud to the consistency of heavy cream, add sand, and brush it on the walls (bale or drywall) to continue the pattern used on the exterior walls. This worked well for matching the texture of the drywall with the bale walls and required no sanding.

In the summer of 2001, a client decided to use colored finishing stucco as the brown coat. We sprayed it on 1/2 in. thick instead of the usual 1/8 in. depth. The results were astonishingly fine. Imasco brand in Canada works well and their Technical Services Department remained silent when we inquired about using their material in this manner. La Habra in the U.S. discourages the practice but clients have opted to use it anyway and with good results. One job cracked a lot on the south wall but I believe it was the result of too few workers rushing and thereby overworking the material.

In the spring of 2003, a client, who works for LeFarge Cement in southern British Columbia, used two cups of Bayer brand ferrous oxide colourant per 90-lb. bag of stucco to colour the brown coat we sprayed on his house. We used a half bag of colour additive for 2,000 sf./185.81m2 of wall area, the walls were given a sponge finish and the result is a soft, earthy red tone.

Resources

For more information on the Bayer Ferrox Pigments, contact Bayer representative Kieren O’Conner at 1.412.777.3180 in Pittsburg, PA.

Another source is Jennifer Cohill in Phoenix, Arizona, at 602.266.0462 or check with your local stucco supplier.

Concretech in Delta, B.C., supplies a full line of concrete colouring products from www.concretech.com or toll free at 877.952.0157.

Habib John Gonzales is director of Sustainable Works, a consultation service, teaching the fundamentals of straw-bale construction in British Columbia, Alberta and the Yukon Territory, Canada. Habib is a pioneer of load-bearing strawbale in western in Canada, and developed a low-cost, homemade moisture meter (see TLS# 22 for plans as well as the article on p. 10 of this issue.) This article, under the title “Stucco Pumping Iron,” appeared in TLS#33 (Plaster issue) – copies are still available as a back issue order or on the TLS #1-40 CD. The original of this article in TLS#33 has additional info on the stucco pumping iron not present in this updated and condensed version.

Habib’s contact info is <habibg@netidea.com> Sustainable Works, 615 Cedar Street Nelson, British Columbia, Canada V1L-2C4 Tel/fax: 250.352.3731