Ashes stuck on my cubic charcoal briquette?

Hi, am making charcoal briquette using 6% starch as binder and 4% clay, I got a good briquette with no crack, and good density. But the problem is, the ashes stuck on my charcoal briquette, and I need to shake it hard to remove ashes, even I reduce clay to 1% and same problem. Anyone can advise me how to solve the ash problem?

The ash often depends on the wood use to make the charcoal.
Down here in AU we have some woods that produce next to no ash at all when burning with enough oxygen but also those that fill your fire pit with more ash than what had wood in.
And same as you noticed, in a lot of cases this ash is quite resistent and stable.
Maybe changing to a different brand of charcoal might be worth a try if you don't make your own.

Many years ago I made my own charcoal sticks for a very old but loved pocket warmer.
Unlike briquette I used charcoal dust as the base but the pricipal would be the same.
But thinking about it: Maybe your particle size for the charcoal is too fine?
I needed a stick that produced quite solid ash so the cleaning is easier.
Going really fine for the charcoal and using a lot of pressure helped a lot here.
Also improved the burning time quite nicely.
But the main difference to mormal mixtures was that I only used one binder apart from high pressure: wall paper glue, which is Methyl Cellulose.
I can't remember the ratio I used but I do know I started with the standard ratio as on the pack and then dilluted it down several times.
At least to the point where is was more runny than a gel.
Starch should work in a similar way but AFAIK won't fully burn off unlike the methyl cellulose.

If you don't mind the hard work I would suggest to proceed like this:
Use bentonite clay (cat litter should state it on the bag) instead of normal clay and grind it up as fine as possible (ball mill?).
Don't use any starch or methyl cellulose at this stage.
As a binder you only need a max of 10% by volume.
The mixing should start dry and you add water by spraying until you can form stable lumps by pressing in your hand that won't fall apart and produce a clean break.
Press these as hard as you can then let dry in open air or by forced drying with heat until all moisture is gone - I prefer to use a digital scale that has at least two digits, e.g 0.01g resolution.
If these briquettes still give you a hard ash try a bigger particle size for the ground up charcoal.
Here you can still use all the dust but the ration dust to big particles should not be higher than 40/60.
This will help the ash to break.
In case that still fails replace the bentonite with methyl cellulose and try again.
That should work fine but you need to find the right amount of cellulose to wate plus the max amount of this watered down mix within your charcoal mix.
A too much is clearly incidcated by a glaced look of the briquetted when dry not enough binder results in a briquette that crubles easy, especially when dropped on a hard surface like concrete.

Good luck!