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My duplex (I am tenant) is equipped with a helical staircase whose thirteen removable steps are raw wood (beech I guess). I vacuumed and then a well wrung mop to clean them. But the steps are never very clear. I would like to "clean up" and protect them in a fairly simple (non-slippery) way for easier maintenance. What do you recommend?

This is often the problem with wooden steps that are subject to a frequent passage likely to alter them. Sometimes tiny cuts are made in the wood, they then retain dust and dirt despite frequent cleaning. Since your steps are removable, the easiest way would be to drop them (one in two so that the staircase can continue to be used during their renovation) to work more comfortably in the workshop, or simply on a folding bench.
You can apply a scourer (at Libéron) that will eliminate any encaustic layers and encrusted dirt. You can also totally bare them by stripping and sanding. You will only have to reteint them, apply a wax or a new matte varnish.

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