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So my partner and I are trying to resurface a concrete wall in an old house in Taiwan. Before I get into the nitty gritty of asking how, I just want to clarify my terminology first – I think I've got plaster and some other things confused.

This is what the room looked like after she and I finished scraping off all the loose material we could yesterday afternoon.

I used to think the top layer was plaster, but after watching some videos on YouTube, I'm beginning to think the plaster is the cracked, gray layer underneath, and the concrete is just below that. (I'm also hearing that ‘stucco’ is an alternative term for plaster, and that it's called ‘mud’ when wet?)

Is that right? If so, what is the (formerly white, powdery) layer on top?

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  • The terminology varies from place to place in the English-speaking world. For example the term "mud" is not really used in the UK, where the internal surface of walls is usually plastered using a gypsum-based plaster in two layers - a coarser ~1cm undercoat and a finer thin topcoat or skim-coat (the application/skill is called skim-plastering)
    – RedGrittyBrick
    Mar 22 '16 at 10:08
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Yep, you got the Plaster right, it's that coin-thick smooth white finish coating. But, that gray nook & cranny stuff looks to be a Cinder Cement, this stuff is quite weak compared to concrete.

If you were scraping off big bulges & partially loose exploded chunks of the gray stuff, then it's definitely Cinder Cement. That's exactly how that stuff reacts to moderate water exposure & freezing. It's not Stucco nor old plaster work's Brown or Scratch Coat.

Just fill in the big voids with most any kind of cement & then re-Plaster over minor cracks & holes while skim coating the whole room in Plaster. If this will be painted, then the Plaster can just be a Drywall Joint Compound. This is the cheapest & plenty durable enough.

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  • Exactly what i needed to hear. Thanks very much for the insight.
    – Ryan Lue
    Mar 22 '16 at 6:52
  • (any advice or resources on how to do a good, even skim coat, short of just plain having the experience?)
    – Ryan Lue
    Mar 22 '16 at 9:55
  • You'll want to add water to any ready-mix bucket & mix it up well. A thin almost runny plaster will go on quite easily & is the pro's biggest secret. But, just literally fling it on the wall if you want & then smooth & level it out. You can try roller painting it on too, this goes on very thin & it still needs trowel or wide knife (these can be easier) smoothing. Do a coat & let it dry, then (putty or wide knife) scrape off any ridges (trowel marks) & do another coat & repeat again. Lightly Pole Sand it all to mostly flat, this is cleaner & more easily gauged & controlled...good exercise :)
    – Iggy
    Mar 22 '16 at 13:41

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