I'm remodeling a bedroom that was a attached garage. I have it gutted out to the studs,two of the walls are built on a 8" high concrete sill. I can see daylight between the top of the concrete and the bottom of the 2x6 sill plate. What would be best to inject in that area to seal it?

If you can lift the sections with a jack,high enough to allow the installation of new sill seal,that would be a great seal to use.

The walls are stripped to the studs?You attach a 2 X 6 to the studs(spanning at least 3)attaching with screws(2-3 per stud) and that becomes your lifting spot, this can be done at all parts,raising the walls just enough to allow for the 1/4 inch seal to sit properly.

Most sills are held down with some kind of nail/bolt/nut on threaded bar.. etc.You will have to decide if this is prudent for your needs or not.

Otherwise,you could just use a crowbar and lift the plate,inject a high grade caulking to the base and when you lower the plate back down,it'll smash the caulking making a nice seal too.

The origanal garage was 22'x20' it was made into two bedrooms. That would be a lot to lift, what's your thought on drilling 1/4' holes in the center of the plate every 6' or so and using a caulk gun injecting a construction adhesive or silicone caulk? The plate is a 2x6

You wouldn't get enough injected even at 6" openings.

Lifting the plate really isn't all that tough,attaching a 2 X to the walls at a height that the jack will get enough lift,then blocks to hold that section up,moving down the wall,lift/block,till you have the entire section up...

the 'pins' or whatever mechanical fastener will be in the way,a sawsall can remove them,placement of the sill seal then lowering the plate back down,drilling new fasteners and you have a proper seal, it'll last longer than the walls will...

The other method of slightly lifting the plate to allow for only a caulk tip to get in still requires the removal of the mechanical fasteners, either removal of the nuts(if threaded bolts were used or whatever the fastener might be.)Then you can add all the caulk with some even distribution making a proper seal.

New idea,

Perhaps a minimal expanding foam injected into the opening and then trimmed once it's cured,that way there would be no bump or ridge in front of the sill plate base.

Go to home depot or any hardware store or real lumber store and buy a can or two of expanding insullating foam in a can.it will be more than adequate

Sorry had'nt read the end of kbc's last post