Can't remove "shadow" from unelevated transparent FloatingActionButton

Question

After spending multiple hours researching this problem, I decided to ask instead of wasting more time on such a (seemingly) easy task.

I'm trying to implement a FloatingActionButton with transparent background and no broder, to show just a custom icon. I know that the material design discourages it, but I need to do it this way.

The problem I face is that there is a shadow showing, which I don't want. Since I set elevation to 0dp I don't know how it got there and thus how I can remove it.

Here is the code for the fragment containing the FAB:

<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/fragment_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/bg_sample"
android:elevation="0dp"
android:fitsSystemWindows="true">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/fragment_grid"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:fitsSystemWindows="true"
        android:gravity="center"
        android:padding="10dp"
        android:stretchMode="columnWidth"
        android:verticalSpacing="25dp"/>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        style="@style/AppTheme"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|center"
        android:layout_marginBottom="@dimen/activity_vertical_margin"
        android:adjustViewBounds="true"
        android:elevation="0dp"
        android:fitsSystemWindows="true"
        android:scaleType="fitCenter"
        app:borderWidth="0dp"
        app:fabSize="normal"
        app:layout_anchorGravity="bottom|center"
        app:layout_behavior="ScrollAwareFABBehavior"
        />

</android.support.design.widget.CoordinatorLayout>

Here is my AppTheme:

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
    <item name="android:fitsSystemWindows">true</item>
    <item name="android:spotShadowAlpha">0</item>
    <item name="android:shadowRadius">0</item>
    <item name="android:ambientShadowAlpha">0</item>
    <item name="selectableItemBackgroundBorderless">@null</item>
</style>

The onCreateView of the Fragment in which I set the transperancy:

@Override
public final View onCreateView(final LayoutInflater inflater, final ViewGroup container,
                               final Bundle savedInstanceState) {
    // initialize variables
    View view = inflater.inflate(R.layout.fragment_desk, container, false);

    coordinatorLayout = (CoordinatorLayout) view.findViewById(R.id.fragment_layout);
    fab = (FloatingActionButton) coordinatorLayout.findViewById(R.id.fab);
    fab.getBackground().setColorFilter(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);

    return view;
}

TL;DR: How can I remove the shadow shown in the second picture?

EDIT: It seems, that this problem is linked to the fab size. I set design_fab_size_normal to 200 just to see, what it does. Turns out it doesn't affect my icon size but the size of the shadow.

Here is the dimens.xml:

<resources xmlns:tools="http://schemas.android.com/tools">
    <dimen name="design_fab_image_size" tools:override="true">64dp</dimen>
    <dimen name="design_fab_size_normal" tools:override="true">200dp</dimen>
</resources>

Answer 1

It should be:

app:elevation="0dp"

instead of:

android:elevation="0dp"

You can also do it from your java code by using:

float zeroElevation=0.0f;
View.setElevation(zeroElevation);