School Bus Stop Cob Bench

Last week we wrapped up the cob school bus stop bench in Arvada that we built in the spring. we gave it a quick coat of lime plaster to protect it this winter, and plan on coming back to do a finer finish next spring.

We are considering making the final coat a tadelakt – a traditional Moroccan water-resistant style of lime finishing. At the work party we tried out tadelakt samples on AAC – Aerated Autoclaved Concrete. They worked great and volunteers got a chance to learn about the process and science behind creating this shiny and smooth finish, plus a small tadelakt tile to take home.

For this coat, we hand mixed a small batch of lime plaster, using a combination of Type S lime and NHL (Natural Hydraulic Lime). The NHL helps to make the curing time faster, which is ideal when plastering late in the season when frosty overnight temperatures might arrive anytime.  Ideally, this coat will have at least a week of frost-free nights as it cures for the best durability.

This coat went on quickly. After wetting down the bench, we hand applied a layer then used sponge floats to roughen up the surface so water won’t erode it as easily. Extra lime plaster was recycled into the soil¬†around the base of the bench as a temporary weed barrier.

 

Thanks to everyone who made it out! We’re feeling great about this project and hope that it gets use by neighbors and children while waiting for their morning bus.

mixing lime plaster

Mixing the lime plaster with a mortar hoe in a wheelbarrow. For small batches this is very efficient.

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Before bench

Before: lime stabilized clay base coat plaster.

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bench after lime plaster

After: a light yellow sponge coated lime plaster finish.