diff --git a/CHANGELOG.md b/CHANGELOG.md
index be5c362c2..a51cb9868 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@
 - Ability to bulk-import members from a CSV file
 - Ability to disable invoices generation and interfaces
 - Added a known issue to the README (#152)
+- Ability to fully rebuild the projets index in ElasticSearch with rake fablab:es:build_projects_index
 - Fix a bug: invoices with total = 0, are marked as paid on site even if paid by card
 - Fix a bug: after disabling a group, its associated plans are hidden from the interface
 - Fix a bug: in case of unexpected server error during stripe payment process, the confirm button is not unlocked
diff --git a/db/migrate/20150107103903_add_slug_to_trainings.rb b/db/migrate/20150107103903_add_slug_to_trainings.rb
index 69e0bec22..974b72af7 100644
--- a/db/migrate/20150107103903_add_slug_to_trainings.rb
+++ b/db/migrate/20150107103903_add_slug_to_trainings.rb
@@ -11,6 +11,6 @@ class AddSlugToTrainings < ActiveRecord::Migration
 
   def down
     remove_column :trainings, :slug, :string
-    remove_index :trainings, :slug, unique: true
+    remove_index :trainings, :slug
   end
 end
diff --git a/lib/tasks/fablab/es.rake b/lib/tasks/fablab/es.rake
index 16f3d4095..db66a5f1a 100644
--- a/lib/tasks/fablab/es.rake
+++ b/lib/tasks/fablab/es.rake
@@ -104,6 +104,19 @@ namespace :fablab do
     desc 'sync all/one project in ElasticSearch index'
     task :build_projects_index, [:id] => :environment do |_task, args|
       client = Project.__elasticsearch__.client
+
+      # ask if we delete the index
+      print 'Delete all projects in ElasticSearch index? (y/n) '
+      confirm = STDIN.gets.chomp
+      if confirm == 'y'
+        client.delete_by_query(
+          index: Project.index_name,
+          type: Project.document_type,
+          conflicts: 'proceed',
+          body: { query: { match_all: {} } }
+        )
+      end
+
       # create index if not exists
       Project.__elasticsearch__.create_index! force: true unless client.indices.exists? index: Project.index_name