skim coating is using diluted with water joing compound. You can apply it with a heavy knap roller then trowel it out.
There are three or four setting time compounds. With the water, it will off set that a bit, but 45 minute mud is good to work with when new at it.
I would put on one coat, let it completely dry then sand it down a bit and apply one more. Sand and prime then its ready.
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