Etching with acid followed by a neutralizing rinse is, we all know, an accepted method of cleaning a concrete wall surface. But what if the surface is indoors? I am thinking in terms of an exposed-aggregate panel in a block wall over a parquet floor. I know this should have been done before the floor was laid, but it wasn't, and at the moment the risk looks considerable.
There is a fairly easy way around this. First cover the floor with a tarpaulin followed by a thick layer of newspaper. Prepare an acid paste with clean, medium-coarse sawdust. You must, of course, work with rubber gloves. Don't make too much at once, and don't make it so strong that it will eat up the sawdust immediately. A plastic bucket will be best. Then press the paste firmly over the surface. Experimentation will reveal how wet the paste needs to be to stick in place, how strong to have the desired effect, and how long it should stay in place. With the comparatively mild degree of acidity involved, and the fact that there is no outside durability danger, neutralization can be forgotten. When the surface is thoroughly dry it should be brushed with a stiff brush to remove any cement dust and traces of sawdust.