Nice work! Very straightforward.

Worked very good after adding the loader.component to app.component

For who might get lost, few steps missing:

at app.component.html, add app-loader like:
<ion-app>
<app-loader></app-loader>
<ion-router-outlet></ion-router-outlet>
</ion-app>

at app.module.ts, declare the component:

declarations: [AppComponent, LoaderComponent],
entryComponents: [],
...

Btw, I’ve tested with Ionic 4.

Random question, how would you approach for disabling all buttons from the app meanwhile waiting for an http request?