It looks like the was was cut incorrectly and not flush.
Filling gap between countertop and wall.
You ll need a drill with a no.
If it s not too wide i d line the back of the counter with crown molding or wall trim of some kind paint it with a high gloss paint so that it s washable.
Darciegage2 has the best solution.
I probably will be using the peel and stick kind because i have no experience with real tile.
Even if the gap is small and not particularly noticeable filling the gap with caulk prevents crumbs splattered oil and other small kitchen debris from collecting behind the countertop and gives the area a more streamlined appearance.
The problem is that the walls seem to have a serious bow to them and where the countertop pieces join in the corner there is about a 1 inch gap between the backsplash and the wall.
2 phillips bit a flat pry bar wood shims and a hammer.
A pencil tile trim would cover the gap.
Caulk normally used would not work because it s too large a gap.
Close the gap between counter and wall if the gap between the countertop and backsplash is more than 3 8 inch it s generally too wide to fill and is best handled with trim but you can try to close the gap to give yourself the caulk option.
Once the gap cover is the right size simply slide it into the gap between the stove and the counter.
I might add that replacing the wall is not an option right now.
You can also try filling the gap using plastic tubing.
If there is say an inch to inch and one half overhang across the front of your slab maybe the slab could be slid back say one half inch closer to the wall closing the gap enough that when you add a backsplash you could fill in the difference with foam backer stuffed into the space between back of countertop and wall and then use flexible caulk to close the gap would depend on how thick your backsplash is as to whether this might be a viable fix.
An obvious gap between a countertop and backsplash is unattractive and it can allow water to seep through.
Then use a pair of scissors to cut off the excess tubing.
As i ve evaluated my kitchen i noticed there is a large gap between my wall and countertop see photos.
The counters are flush up against the wall at the furthest ends from the corner.
First get pvc tubing that s inch thicker than the gap.
Slot it into the space until it s level.
If the gap is too wide to seal with silicone narrow trim molding can solve the problem.