1980s house, attaching to external wall

Our house was built in 1985. I am trying to attach a heavy shelf to a bedroom on an external wall. But the shelf keeps pulling the rawls out of the wall. It seems to just crumble. It's a couple of inches thick, then the cavity before, I am presuming, I am hitting the external block.

So any ideas what the internal wall is made of? I thought it should be brick behind plaster but its very crumbly. Also how can I attach to the external brick wall that's about five or six inches in beyond the cavity?

Would it not most likely be 18" cavity block plastered over? Are you sure that you're drilling into the block? I presume you meant "block" above when you said "brick"?

Oops, block I mean. I have no idea tbh. Just that it isn't holding a shelf. Anything can be done?

Sounds like cavity block all right, but 18"? It's more likely 9".

Measure the total thickness of the wall. A cavity wall with two full leaves should be 11 or 12" plus plaster: say 12-13". If it's a couple of inches less, it's almost certainly cavity block.

So now I've found another problem, a curtain rail has been pulled out of the wall by the weight of the curtains. It was in with a standard rawl. What can I do with these walls so that they will hold heavy weights?

Do you have a dry-lined cavity? Is there a gap behind the plasterboard?

[broken link removed] fixings will take a significant load in plasterboard. You can also get cavity and toggle fixings such as [broken link removed] and [broken link removed].

I have used the butterfly plugs (mentioned in the 2nd link on Leo's post above) for curtain rails, holding full length curtains, and these are inserted into plasterboard. No problems so far, and they've been hung a few years now. You can get them in B & Q, 2 different sizes as far as I can remember. The packet tells you the maximum weight they can support. Good luck.