Laravel UNION ALL not working with where statement

I want to get two queues to one.

$buildings_queue=IngameBuildingQueue::where(DB::raw('UNIX_TIMESTAMP(`start_time` + `duration`)'),'<=',time());
$recruit_queue=IngameRecruitQueue::where(DB::raw('UNIX_TIMESTAMP(`start_time` + `duration`)'),'<=',time());
$queue=$buildings_queue->unionAll($recruit_queue);
dd($queue->toSql());

Laravel throw [ErrorException] Undefined property: Illuminate\Database\Eloquent\Builder::$bindings but when I delete where() methods everything works fine.

How can I fix it?

via Chebli Mohamed