9
Cementitious Coatings
Cementitious coatings provide corrosion resistance to substratess uch as
steel by maintaining the pH at the metal/coating interface above 4, ap H
rangew here steel corrodes at al ow rate. The proper selection of materials
and their applicationisnecessary if the coating is to be effective. To select the
proper material, it is necessary to definet he problem:
1. Identify all chemicals that will be present and their concentrations.
Knowing pH aloneisnot sufficient. All pH indicates is whether or
not the environment is acid,neutral, or alkaline. It does not identify
if the environment is oxidizing, organic or inorganic, alternately
acido ralkaline.
2. Is the applicationfumes,splash,o ri mmersion?
3. What are the minimum and maximum temperatures that the
coating will be subjected to?
4. Is thei nstallation indoors or outdoors?T hermal shocka nd
ultraviolet exposure can be deleterious to many resins.
5. How longisthe coating expected to last?This can have an effect on
the cost.
Surface preparation prior to applicationo ft he coating is essential. The
surface mustb ef reeo fm ills cale,o il,g rease, ando therc hemical
contaminants.T he surfacem ustb er oughened by sandblasting andt he
coating applied immediately after surfacep reparation. An intermediate
bonding coating is used when adhesion betweenthe substrate and coating is
poor or where thermal expansion characteristics are incompatible. Coatings
are installed in thicknesses of 1/16 to 1/2 in. (1.5 to 13 mm). They may be
appliedbycasting, troweling, or spraying. The spraying process, known as
Gunite or Shotcrete, is particularly useful on systems with unusualgeometry
or with manysharp bends or corners. It has the advantage that there are no
seams that are often weak pointsasfar as corrosion resistance is concerned.
CAT8247—CHAPTER 9—6/10/2006—12:50—SRIDHAR—XML MODEL B–pp. 509–513
509
Cementitious Coatings
Cementitious coatings provide corrosion resistance to substratess uch as
steel by maintaining the pH at the metal/coating interface above 4, ap H
rangew here steel corrodes at al ow rate. The proper selection of materials
and their applicationisnecessary if the coating is to be effective. To select the
proper material, it is necessary to definet he problem:
1. Identify all chemicals that will be present and their concentrations.
Knowing pH aloneisnot sufficient. All pH indicates is whether or
not the environment is acid,neutral, or alkaline. It does not identify
if the environment is oxidizing, organic or inorganic, alternately
acido ralkaline.
2. Is the applicationfumes,splash,o ri mmersion?
3. What are the minimum and maximum temperatures that the
coating will be subjected to?
4. Is thei nstallation indoors or outdoors?T hermal shocka nd
ultraviolet exposure can be deleterious to many resins.
5. How longisthe coating expected to last?This can have an effect on
the cost.
Surface preparation prior to applicationo ft he coating is essential. The
surface mustb ef reeo fm ills cale,o il,g rease, ando therc hemical
contaminants.T he surfacem ustb er oughened by sandblasting andt he
coating applied immediately after surfacep reparation. An intermediate
bonding coating is used when adhesion betweenthe substrate and coating is
poor or where thermal expansion characteristics are incompatible. Coatings
are installed in thicknesses of 1/16 to 1/2 in. (1.5 to 13 mm). They may be
appliedbycasting, troweling, or spraying. The spraying process, known as
Gunite or Shotcrete, is particularly useful on systems with unusualgeometry
or with manysharp bends or corners. It has the advantage that there are no
seams that are often weak pointsasfar as corrosion resistance is concerned.
CAT8247—CHAPTER 9—6/10/2006—12:50—SRIDHAR—XML MODEL B–pp. 509–513
509