My in-laws have a deck out the back of the house. They're old and the deck hasn't been maintained in 10 years or more.
Many of the boards have blackened and are lethally slippery if the weather is even mildly damp. Also, several of the boards feel "spongy" when stepped on.
Is there anything I can do to restore this, firstly so that it's safe to walk on, and secondly so that it's good to look at.
Also, if "sanding" is part of the solution, the boards are ridged, do you need a special sander for ridged boards? (The boards are ridged like these . . .)
Will the spongy boards need to be replaced, or can they be treated somehow?
P.S. Forgive me but I know next to nothing about wood/gardening/DIY etc, but these jobs are falling to me now.
UPDATE To answer some queries . . .
The picture is from a catalog, to show the boards are ridged.
I don't know for sure, but would bet the farm that the decking is wood.
It'll be the weekend before I'm out there again, I'll determine the material and take pictures of the deck.
I'll also try to get in under it and see where the sponginess is coming from .
. . . and guys thanks for the responses so far, this really is all rocket science to me.