space between under my deck and my house.

[JKW]

Hello.

I have a 3 inch gap between my house and yard, which runs along the width of the house, under my deck. Under my deck is a lot of gravel and dirt.   I noticed there was previous water damage from the previous owners time and it seems to be the location in the basement of efflorescence.   Is there something i can pour in the gap to stop the rain and water from snow melting continuously getting down there.

Many Thanks.

JW

[Jim Katen]

How about bentonite cat litter? 

When dry, it'll flow like sand all the way to the bottom of the void. Once it gets wet, it'll swell up and serve as a decent water barrier. 

[JKW]

Thank you for your reply. I will look into that.