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Here’s a question I had about using American Clay over a brown coat of Natural Hydraulic Lime Plaster (NHL):

The plasterers did not get two interior walls brown coated this last time and we were wondering about the curing time of the NHL and the American Clay finish coat. Have you ever done a clay (or other material) as a finish coat over the NHL? Would 7 days be long enough to let the brown coat cure before putting on the final coat?


I was just wondering with the good breathability of the American Clay if it would be ok to do that. I don’t want to rush and be stupid about it. Just thinking of different possibilities.

Here’s my answer:
You can do the finish coat over the NHL as long as the coat has had adequate time to dry and shift. If, however, the coat is still not done curing, you run the risk of getting cracks in your finish coat. American Clay is a very thin coat, so those cracks would be all but impossible to cover up. That said, it is best to put on a couple coats of standard clay before the American clay to get the finish they show in the books. Those coats might be enough to provide some flexibility for the finish. I guess what I am trying to say is that it is a risk completing the finish coat before the NHL brown has fully cured. You may be fine, but I cannot guarantee that you won’t end up with cracks. I would wait as long as you can and do a proper job of curing the brown coat if I were you. That could happen in a week depending on the climate, but it could take longer too. I hope that gives you some direction.

For more information on Natural Hydraulic Lime please visit St. Astier’s Natural Hydraulic Lime Plaster at www.Limes.us. Please click this link for a Complete How-To Guide to Plastering with NHL. Happy Baling.

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About the Author

Andrew Morison is a licensed contractor specializing in straw bale and green construction. He has shown thousands of people how to build their own straw bale projects through his comprehensive series of instructional straw bale, concrete foundation, and plastering DVDs. You can check these out at http://www.LearnStrawBale.com.

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Categories: Plastering