I'm looking at some datasheets for interior plaster by Saint-Gobin (which unfortunately are not available in English as far as I can tell) and I'm miffed why some interior (white) cement-based plasters are advised to be sanded as the final smoothing step and for others the advice is to wet float them. As far as I can tell the maximum aggregate (sand) size is the determining factor, those that they advise to float have max particle size of 1mm, the other ones are in the hundreds of micrometers range. Is this the determining factor, or are there other considerations?
To add some details, these are all skim coats. The one with 1mm max particles allows for maximum 5mm layer, while the other ones (hundreds of micrometers particles) only 2mm layers.
Best Answer
Yeah, after trying this in practice, this floating 101: you can't bring out aggregate that's much finer than your float's sponge. The max 200um stuff turned out to be some lawyerly spec (as in them not getting sued if someone finds a spec of sand in it); in practice it's as fine a flour or even finer (perhaps close to toner dust). There isn't any float in the typical hardware store that has a sponge that fine. You can "float" it of sorts, but you're not really bringing out the aggregate, just leaving impressions that match the sponge's pattern. You can surely do interesting decoration this way, but it ain't floating.