I have a washed aggregate patio that was installed 35+ years ago. It is in remarkably good shape with very few cracks. The patio was poured in diamond shaped sections with what I believe was 1x4 lumber of some nature as the "seam". As you can imagine, this lumber has long since rotted away and I am left with channels where the lumber once lived. Over the years, some of the slabs have settled maybe 3/4 of an inch. I'd like to fill these channels to keep debris out but not really sure what to use. Getting new wood in there will be a problem as shifting over time has opened and closed these gaps slightly. Any ideas?