ᐅ Screw a wooden panel onto a concrete wall

I have a large window in the living room and want to install a wooden windowsill on the concrete base. The wood is solid spruce, about 4 cm (1.6 inches) thick and 2.8 meters (9.2 feet) long.

I am now looking for a way to fasten the wooden plank onto the base. I think 3-4 M8/M10 screws should be sufficient. However, I’m not sure which screws or anchors would be best for this purpose.

Important: the screws should be as inconspicuous as possible afterward. Maybe there are even caps for these screws in a spruce color.

Does anyone have tips on what I should look for to find a suitable solution?

Thanks and regards

Do not screw at all, as this will cause cracks. Use parquet adhesive to glue instead.

For example, Hilti screw anchors with countersunk heads. Drill the hole, then screw in the anchor using an impact driver. It doesn’t get any easier than that.

6 mm (1/4 inch) anchors are more than sufficient. I recommend using 5 to 6 anchors for a permanently strong hold.

Cover the countersunk heads either with a plastic cap or, even better, with sawdust mixed with wood glue. Then lightly sand the surface.

Of course, pre-drill the wood.

The tip from @Tolentino is also good: a quality construction adhesive.

Simply glue it.
There are also installation kits available. You can anchor (using anchors or plugs) into the concrete on one side, attach the other side to the wood, and then "slide" the bench in. However, in my opinion, this creates a gap underneath the board.

Adhesive would also work. There are plenty of products that can make it permanently secure.

Thank you, here is an important note.

Depth of the board = 25 cm (10 inches)
Depth of the base = approx. 15 cm (6 inches)

So, I have a 10 cm (4 inches) board overhanging. It’s possible that adults might sit on it occasionally.
It’s not an extremely large force acting on it, but do you think gluing could still work? That would actually be the most convenient solution!