section,  we’ll  cover  some  of  the  most  commonly encountered  types. OIL-BASED   PAINTS.—   Oil-based  paints consist mainly of a drying oil (usually linseed) mixed with  one  or  more  pigments.  The  pigments  and quantities of oil in oil paints are usually selected on the basis of cost and their ability to impart to the paint the desired properties, such as durability, economy, and  color.  An  oil-based  paint  is  characterized  by  easy application and slow drying. It normally chalks in such a manner as to permit recoating without costly surface preparation. Adding small amounts of varnish tends to decrease the time it takes an oil-based paint to dry and to increase the paint’s resistance to water. Oil-based paints are not recommended for surfaces submerged in water. ENAMEL.—   Enamels   are   generally   harder, tougher,  and  more  resistant  to  abrasion  and  moisture penetration   than   oil-based   paints.   Enamels   are obtainable in flat, semigloss, and gloss. The extent of pigmentation in the paint or enamel determines its gloss. Generally, gloss is reduced by adding lower cost pigments  called  extenders.  Typical  extenders  are calcium   carbonate   (whiting),   magnesium   silicate (talc), aluminum silicate (clay), and silica. The level of  gloss  depends  on  the  ratio  of  pigment  to  binder. EPOXY.— Epoxy paints area combined resin and a  polyamide  hardener  that  are  mixed  before  use.  When mixed,  the  two  ingredients  react  to  form  the  end product.  Epoxy  paints  have  a  limited  working,  or  pot, life, usually 1 working day. They are outstanding in hardness, adhesion, and flexibility-plus, they resist corrosion, abrasion, alkali, and solvents. The major uses  of  epoxy  paints  are  as  tile-like  glaze  coatings  for concrete  or  masonry,  and  for  structural  steel  in corrosive environments. Epoxy paints tend to chalk on exterior exposure; low-gloss levels and fading can be anticipated.  Otherwise,  their  durability  is  excellent. LATEX.—   Latex   paints   contain   a   synthetic chemical, called latex, dispersed in water. The kinds of latex usually found in paints are styrene-butadiene (so-called synthetic rubber), polyvinyl acetate (PVA or vinyl), and acrylic. Latex paints differ from other paints in that the vehicle is an emulsion of binder and water.  Being  water-based,  latex  paints  have  the advantage of being easy to apply. They dry through evaporation  of  the  water.  Many  latex  paints  have excellent  durability.  This  makes  them  particularly useful  for  coating  plaster  and  masonry  surfaces. Careful surface preparation is required for their use. RUBBER-BASED.—  Rubber-based  paints  are solvent thinned and should not be confused with latex binders   (often   called   rubber-based   emulsions). Rubber-based paints are lacquer-type products and dry  rapidly  to  form  finishes  highly  resistant  to  water and mild chemicals. They are used for coating exterior masonry and areas that are wet, humid, or subject to frequent washing, such as laundry rooms, showers, washrooms,  and  kitchens. PORTLAND   CEMENT.—   Portland  cement mixed  with  several  ingredients  acts  as  a  paint  binder when it reacts with water. The paints are supplied as a powder to which the water is added before being used. Cement paints are used on rough surfaces, such as concrete, masonry, and stucco. They dry to form hard, flat,  porous  films  that  permit  water  vapor  to  pass through  readily.  When  properly  cured,  cement  paints of good quality are quite durable. When improperly cured, they chalk excessively on exposure and may present  problems  in  repainting. ALUMINUM.— Aluminum paints are available in  two  forms:  ready  mixed  and  ready  to  mix. Ready-mixed  aluminum  paints  are  supplied  in  one package and are ready for use after normal mixing. They  are  made  with  vehicles  that  will  retain  metallic brilliance  after  moderate  periods  of  storage.  They  are more  convenient  to  use  and  allow  for  less  error  in mixing  than  the  ready-to-mix  form. Ready-to-mix  aluminum  paints  are  supplied  in two packages: one containing clear varnish and the other,  the  required  amount  of  aluminum  paste  (usually two-thirds  aluminum  flake  and  one-third  solvent). You  mix  just  before  using  by  slowly  adding  the varnish to the aluminum paste and stirring. Ready- to-mix  aluminum  paints  allow  a  wider  choice  of vehicles and present less of a problem with storage stability. A potential problem with aluminum paints is moisture  in  the  closed  container.  When  present, moisture may react with the aluminum flake to form hydrogen gas that pressurizes the container. Pressure can cause the container to bulge or even pop the cover off the container. Check the containers of ready-mixed paints for bulging. If they do, puncture the  covers  carefully  before  opening  to  relieve  the pressure. Be sure to use dry containers when mixing aluminum paints. VARNISHES In contrast to paints, varnishes contain little or no pigment  and  do  not  obscure  the  surface  to  which applied.  Usually  a  liquid,  varnish  dries  to  a  hard, 8-3