When I glue teak I clean both surfaces to be glued with acetone or alcohol. I do this to remove the natural oils teak has from these surfaces to improve the bond. I let the cleaner dry (only takes a couple minutes with tone or alcohol) so as not to contaminate the epoxy. I have never heard anything good about adding thinners to epoxy.
If I am gluing very porous materials with epoxy I sometimes wet out the 2 surfaces with epoxy with no cabosil or 406 for absorbtion. Then I add the filler and apply a second coat before bonding and clamping.
The heating idea Charlie mentions works well, but keep in mind it speeds up the cure as well, especially the stuff still in the pot.