Cannot read property 'materials' of undefined

Timber3D.ts

/// <amd-dependency path="lib/babylon" />
declare var require:(moduleId:string) => any;

var BABYLON = require('lib/babylon');
import Timber = require('app/object/Timber');

class Timber3D extends BABYLON.Mesh {

    /**
     * 3D object instance
     */
    object: BABYLON.Mesh;

    /**
     * Object instance from project
     */
    objectData: Timber;

    constructor(timber: Timber, scene: BABYLON.Scene) {
        super(timber.id, scene);

        this.objectData = timber;

        var object = BABYLON.VertexData.CreateBox(
            {
                width: timber.width,
                height: timber.height,
                depth: timber.depth,
            }
        );
        object.applyToMesh(this, false);

        this.material = new BABYLON.StandardMaterial("texture1", this.scene);
        this.material.diffuseTexture = new BABYLON.Texture("images/textures/lamelle.jpg", this.scene);
        this.material.specularColor = BABYLON.Color3.Black();
        this.material.emissiveColor = BABYLON.Color3.White();

        this.position = new BABYLON.Vector3(timber.position.x, timber.position.y, timber.position.z);
    }
}

export = Timber3D;