Regulation

Reminder
The decree N° 69-558 dated 6 june 1969 concerning the particular measures of workers protection applying to the stripping, tarnishing or desanding works with an abrasive jet stipulates:
"the abrasive used must not contain more than 5% (regarding its weight) of free silica", knowing that it concerned only the pure silica and not the silica mixed under the form of silicate.
Since then, the abrasives composition is checked on the occasion of frequent samples on the sites by the work safety in order to avoid the silicosis risks for the users.
This decree really disrupted the entire profession since it was about eliminating quickly the most natural and the less expensive natural abrasive agent at the very origin of the impact treatment, "the sand".
The sand use was so universal that the term "sandblasting" now inappropriate, remains only like a synonym since it is still used to designate the process whatever the product used is. Nevertheless, the decree that make the "no siliceous" products in accordance with the law brings a considerable progress regarding the user's protection. It is reinforced by the order dated 14 january 1987 relative to any packaging or container holding some abrasives which have to include obligatorily a mention:
"indicating the presence of free silica as soon as the weight rate exceeds 5%".
From then on, new products appeared on the market and their qualities were undeniably superior to those of the sand. These products quickly supplanted the sand. To date the siliceous products use is thus forbidden, but allowed in some applications where the projection is made by a wet way process, or a dry but humidified process for the cleaning without dust of the façades.

The wasted abrasives

General points
The abrasives called "wasted" abrasives are generally used in recycling cabinets, or in outside sites. They replaced the sands of siliceous origin which use is now forbidden (see below). In this category of "no siliceous", abrasives, we find generally short lasting abrasives from different origin and manufacture and in particular:

The cement laitance abrasives
The crushed blast furnace cement laitance abrasives are made of complex silicate with a varnished aspect. They are the noble manufacturing wastes which are dependent on the raw material and the elaboration process. The blast furnace cement laitance abrasive has a performance comparable to silica sand. Nevertheless, its major drawback comes from its high dust emission whose effect is a bad appreciation of the product by the users.
- It is presented under the form of dark colour acute angle crystals.
- It has an apparent density of 1.3 and a real density of 2.6.

The scoria
The various metallurgic scorias are also some residue used as wasted abrasives.
The most used are the copper scoria whose aspect is black varnished and the grains are angular.
The copper scoria have the advantage of creating less dust, but the drawback of increasing the stripping time which results from the difficulty of appreciating the quality of the stripped surface. They have also an average lasting superior to the cement laitance abrasives but like the latest, they often leave blackish marks on the surface and non metallic inclusions, visible or not.
- the hardness's vary between 6 and 7 Mohs.

The synthetic abrasives
Unlike the previous ones, the synthetic abrasives are not manufacturing waste, but the outcome of a specific process. They are produced from a molten mass of aluminium silicate glass, elaborated through a high temperature controlled fusion, cooled down and crushed. The rigour and the consistency of the manufacturing process bring to these abrasives obvious qualities which are the following:
- a stability of the raw material,
- a colour which does not leave blackish marks,
- a clear and perfectly dry dust,
- a rough and bright surface aspect,
- a reduced consumption.
They are presented in hard and sharp crystals whose colour ranges from topaz to brown with:
- an apparent density of 1,3,
- a hardness ranging from 6 to 7 Mohs.
- a granulometry from 0,3 to 1,7 mm
(3 grades, 50-80, 20-30, 12-14)
- a using cycle variable from 1 to 3 (depending on the calibres and uses).

The quartz sand
Made of natural silica, it is at natural state in numerous rocks under the form of sand. It is generally of white colour according to the purity of the extractions veins.
It was the first abrasive used in projection by compressed air in cabin or in wasted abrasive.
This choice was made because of its hardness (7 on the Mohs scale) and its great abrasivity. The grains, very fragile, quickly fragment while giving off a great number of fine particles. Its use was forbidden and abandoned because of the substantial risk of silicosis generated by the dusts which can be inhaled (from 5 to 6 microns). (See reminder above). Nevertheless, its use still remains, essentially for the wet way projection, in sleeves stations or automated machines, or for the humidified dry way projection for the cleaning of the buildings façades.