Cement Plaster Video

Here’s a brief summary of the cement plastering process we used on the exterior of our earthbag roundhouse:
Step 1: Put cement between the bags in the gaps.
Step 2: Add thin coat of cement over bags.
Step 3: Add more cement.
Step 4: Add more cement.
Step 5: Trowel the plaster smooth and use a sponge float to smooth out the finish.

As you can see, the process is quite simple, although labor intensive. It boils down to adding a little plaster at a time. Leave each coat rough so the next coat will better adhere. No plaster mesh is needed — the plaster sticks to the earthbags, no problem. Resist the temptation to overwork the plaster. The total process took about five days of work for two workers spread out over a little more than week (some days there was no work). A third worker helped the last day.

Caution: Research the techniques used by plaster professionals in your area and follow their lead. The techniques in this video show what works in a rainy/humid climate, but they can cause problems in dry climates.

More videos at my Earthbag Video Channel.

7 thoughts on “Cement Plaster Video”

  1. Wow that ended up looking great. I was concerned about how the plastering would be on what looked like an unsteady base but you have done great!

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  2. We average ~50 mm of rain annually, and about 70 cm of snow. It’s a pretty arid region, save for this year which has had record rain. So we would probably be safe using cement then, so long as we use multiple coats? Or maybe we could use cement as our base and top it with lime?

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    • I think you’ll be okay with cement plaster if you use multiple coats and maintain it against cracks. But like I said, it’s not a sure thing. There’s currently a lack of testing, and also a lot of variables. For instance, you want to ventilate excess moisture from the home. You don’t want moisture to migrate through the wall and build up behind the cement plaster, where it could weaken the earthbags. So put some thought into eliminating interior moisture: use good quality bath and range hood fans that vent to the exterior, etc. Use a wood stove to dry the air.

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  3. Is cement a good plaster for the earthbag domes (i.e. no protective roof)? Everything we’ve read has been leaning towards lime, for breathability and long term durability, but it sure would speed things up if we could go with cement… We’re going to be quite tight for time this year due to disastrous spring/summer weather and if we do go with lime the schedule is even tighter because of the longer curing time required (before first frost, which hits early in our area). I’m just curious if cement is a viable option for us, or whether we should stick with our original lime plaster plan?

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