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Popular Questions - Interior

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+Q. I have a question about rejuvenating paint (latex enamel)! My uncle was given 20 gallons of latex enamel paint, and he stored it in a barn, and I think the paint froze and is now separated. Should I drain off the liquid and what can I put in it when I remix it? Thank you!

A. You may be able to reclaim the paint; open each container and...

  1. Do not pour off any of the liquid. This should be kept as part of the paint.
  2. Look for any signs of rusting or deterioration of the containers, and where you see any contamination of the paint, discard that container of paint.
  3. Remove any obvious skins, or hard pieces; leave soft lumps in place.
  4. Now the containers have to be mixed thoroughly. The best bet would be to have the containers shaken at a paint store. You may have trouble getting this done, unless you are a friend of the owner! You may have the best chance of success asking at a store that sells the same brand as you paint. When using a shaker, be sure all paint is removed from the chime (groove where the lid fits), and be sure the lid is on tight. Or use a paint stir-stick and stir each container thoroughly for 5 to 10 minutes.
  5. If, after the mixing, the paint seems smooth, uniform, free of specs, is not thin and runny, not putrefied, etc., it should be OK to use; but check each container out first by applying to a scrap surface, and look for uniformity of gloss and color. Still, don't use it in a critical place like a living room.

Raw linseed oil

+Q. What is the difference between linseed oil and boiled linseed oil?

A. Linseed oil is the general term for the oil extracted from flax seed. Raw linseed oil has not been treated, and dries very slowly. "Boiled" linseed oil has additives called "driers" which make it dry quicker.

Polyurethane

+Q. What does the term "urethane" mean? How are polyurethane products different from other types?

A. The term urethane and polyurethane apply to certain types of binders used for paints and clear coatings. (The binder is the ingredient that holds the pigment together in a tough, continuous film, and provides film integrity and adhesion.) Urethane binders are made be reacting a compound with an isocyanate group with another group, often a hydroxyl group: R1-N=C=O + R2-OH --> R1-NH-COO-R2. The urethane polymer is also called a polyurethane. Aliphatic solvents and polymers are preferred over aromatic types in that they provide greater flexibility and exterior durability, although they are more costly.

There are different types of urethane systems:

TYPE I: one-component, alkyd reacted with a polyisocyanate; this is the usual "polyurethane" varnish used in residential and commercial applications on bare or stained wood (floors, furniture, doors, etc.); offers greater toughness and abrasion resistance than do unmodified alkyds;

TYPE II: one-component, has a polymer with unreacted isocyanate in the backbone; reacts and crosslinks upon application and exposure to moisture from the air; known as "moisture cure urethane";

TYPE III: one-component, heat-cured; the polymer contains isocyanate that is chemically blocked from reacting with hydrogen donors in the product, until the heating drives off the blocking agent; used in factory application;

TYPE IV: two-component, a polymer containing free isocyanate groups is mixed at time of use with a catalyst of monomeric polyol or polyamine; has short pot life;

TYPE V: two-component, a poly-isocyanate polymer is mixed at time of use with a resin containing active hydrogen groups; limited pot life;

TYPE VI: one-component, unreactive urethane polymer in solvent solution; forms the film upon solvent evaporation, but otherwise does not change (crosslink); PUD: "polyurethane dispersion"; dispersion of unreactive urethane polymer in water; used to modify latex coatings, particularly clear coatings, to boost mar resistance.

Bathroom staining

+Q. What is the dark stuff I get on the ceiling of my bathroom? It is in small areas about the size of a small coin, and is brownish in color. It is on parts of the ceiling, particularly over the shower area.

A. This is material extracted from a latex paint by the high humidity and moisture common in a bathroom, particularly after the shower has been used. Gradually, some of the thickener and surfactants commonly used in making latex paint are extracted and left in concentrated form on the surface of the paint. This generally does not hurt the durability of the paint, and rather is an issue of appearance. It can usually be removed by careful cleaning with a sponge and detergent with warm water. If you encounter this when you go to repaint the bathroom, be sure to remove as much of it as you can, before applying primer or paint. Be sure to rinse off all residual detergent before proceeding. Kitchen & Bath paints are in general formulated to minimize surfactant leaching. Allow the paint to dry at least overnight before using the shower; preferably allow several days' drying time.

Latex paints over oil based

+Q. Can you paint over an oil-based paint with latex paint or is it vice versa?

A. The rule of thumb is that, given proper surface preparation, for exterior use you can apply quality latex paints over oil-based, but not the reverse. However, if you have many layers of oil based paint, stick to using oil on oil. For interior use, generally you can use one over the other. Some manufacturers of latex products will recommend a primer when going over oil-based paint.

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