The Paint Quality Institute receives numerous questions on the subject of paint from professional contractors. Some of those questions are basic, some advanced, and some especially interesting. Here’s a representative sampling of those questions, along with their answers. The questions are received via the PQI Web site – www.paintquality.com

Priming Painted Surfaces                                   back to top

Q I know that it is important to prime bare exterior surfaces like wood and metal, but is there any reason to use a primer on a surface that has already been painted and is basically in good shape?

A It’s often helpful to use an appropriate primer, even on a surface
that was previously painted. That’s because primers promote uniformity of appearance of the finish coat, including both hiding and sheen or gloss uniformity. In addition, quality primers improve mildew resistance and promote good adhesion.

So, by using a primer on a previously painted surface, you’ll not only get a good-looking paint job – you’ll also gain some added performance benefits.

Dry Crocking                                                  back to top

Q I’ve heard of a problem called “dry crocking.” What is it?

A When the color of a surface comes off when rubbed with a dry cloth, it is called dry crocking. If the color comes off when wiped with a wet cloth, it is called wet crocking. These problems can occur if a very highly pigmented flat paint has been tinted, or an incompatible colorant or pigment has been added to a paint.

Opaque Stain vs Paint                                       back to top

Q What are the similarities and differences between an exterior opaque acrylic latex stain and an acrylic latex paint?

A Exterior opaque acrylic latex stains and paints both contain pigments, a latex binder and certain key additives; both are water-based; and both dry to form a film on the surface to which they are applied.

As for their differences, exterior stains often are formulated at slightly lower viscosity than paints, which means that stains tend to apply in a thinner coat. Also, stains are generally formulated with a pigment-to-binder ratio that allows them to dry to a flat or satin finish, whereas paints are available in all gloss ranges, from flat to high gloss.

Calcimine                                                      back to top

Q Could you please provide some information on calcimine?

A Calcimine (also “kalsomine”) is a white or tinted wash applied to interior plaster surfaces that was popular about 50 years ago. It was supplied as a dry powder mix of calcium carbonate (chalk) and glue (usually casein). contractorsmen mixed it with water to prepare it for application.

If you believe it is present, remove it by scrubbing. Then, rinse the scrubbed area thoroughly. Once dry, apply a high-adhesion, oil-based interior primer, followed by a latex paint as a finish coat.

Pressure-treated Wood                                     back to top

Q I need to paint a pressure-treated wood fence, but the wood has not dried after treatment and is dense and obviously wet. Should I let the wood weather before painting it?

A Tests show that oil and latex paints do not adhere as well to weathered wood as to fresh, unweathered wood. So, generally speaking, all new exterior wood – treated or untreated – should be painted or stained promptly after construction.

However, when treated wood still contains moisture from the treatment process, it is best to allow it to dry for two to four weeks before coating. This is especially important when using oil-based paint, which can lock moisture in and lead to rotting.

When painting treated wood, apply one or two coats of a quality exterior wood primer. For the best durability on treated wood, apply two coats of a top quality exterior latex paint over two coats of a quality primer. While either a latex or alkyd primer can be used, a quality latex primer will provide the best long-term crack resistance.

Wax Bleed                                                     back to top

Q We need information on wax bleed. Can you explain what it is, and how to address it if it occurs?

A Wax bleed is a phenomenon that can occur with exterior hardboard siding as it weathers. Hardboard siding is made by pressing wood fibers under heat. A small amount of paraffin wax is included in the process to enhance water resistance and minimize water absorption, which could otherwise lead to swelling and warping of the siding.

This wax may migrate to the surface and accumulate there. It may come through a factory primer if left unpainted, or through some paints. It then tends to pick up dirt, and can foster the growth of mildew. Fortunately, manufacturers of hardboard siding became aware of this problem and have improved production techniques as well as the quality of factory primers. As a result, this problem is less common than before.

We have conducted exposure tests on repaint of wax bleed and found that quality acrylic house paints tend to have adequate adhesion to the surfaces we tested, despite the hydrophobic nature of the wax.
We also found that a paint’s resistance to wax bleed is related, to an extent, to the level of pigmentation. Flat paints resist wax bleed less than satin paints, for example. In general, we have not seen wax
bleed when an acrylic latex primer is applied first.

What Type Paint Is It?                                       back to top

Q How do you tell what type of paint is on a surface? If the paint is peeling, how do I find out if it’s oil or latex paint?

A If the paint is at least several years old and peeling, take a piece
of it and bend it. If it cracks, it is most likely oil-based or alkyd paint. If it seems flexible, it is probably latex. However, highly pigmented economy latex paints also tend to crack when flexed this way. If it is a combination of one type applied over the other, the oil-based portion is more likely to crack, while the latex part will be more flexible.

Another test is to soak the piece of peeling paint in some acetone or fingernail polish remover. If it dissolves or significantly softens, the peeled paint is likely to be latex. Be sure to use safe practices when working with acetone or fingernail polish remover.

Aluminum Storm Windows                                  back to top

Q What is the best approach for painting aluminum storm windows without a previous finish?

A Take the following steps:

• Clean off any dirt by scrubbing with detergent and water,
  then rinse.
  
• Look for a white powdery oxide, especially likely to be on the exterior surfaces, and scrub off as much as possible with a non-metallic scouring pad. Rinse.
  
• Apply a water-based, corrosion-inhibiting primer. Apply a full
  coat; don’t spread it too thinly. Allow it to dry overnight.
  
• Apply a top quality acrylic latex exterior house paint in a flat,
  satin or semigloss finish, depending on the appearance desired. Avoid painting surfaces that will come in contact and rub
  against each other.
  
• Use painter’s tape on glass. Carefully remove the tape as soon
  as the paint has dried to the touch.
  
• Don’t paint if the outside temperature has been below 50ÞF (10ÞC) the past 24 hours, or is predicted to drop to such in
  the next 36 hours. Don’t apply the paint in direct sunshine.

Textured Ceiling                                             back to top

Q I have a customer with a blown-in, textured ceiling. What type of paint roller and paint should I use?

A If the ceiling has any discoloration at all in any areas, vacuum the ceiling with a brush nozzle, then apply a stain-blocking interior latex primer. Use a half-inch nap quality synthetic roller cover. Keep at least two windows open wide while applying the primer and while it dries. Allow it to dry at least overnight. Then apply a dead flat latex wall paint using the same type roller cover.

Solvent vs Paint Thinner                                    back to top

Q What is the difference between a solvent and a paint thinner?

A Solvent is a general term used for different organic liquids.
Examples of some used with paints and coatings are lacquer thinner, paint thinner, naphtha, denatured alcohol and turpentine.

Paint thinner is a specific solvent used with oil-based paints, stains and varnishes. Paint thinner is made primarily from a solvent called mineral spirits. Paint thinner is similar to “lighter fluid” and “charcoal starter.” It is less flammable than lacquer thinner and gasoline.

Another solvent used by painting contractors is VM&P naphtha (Varnish Makers and Painters’ naphtha), which evaporates faster
than mineral spirits.

Boiled Linseed Oil                                            back to top

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 faster.

Masonry Sealer vs Primer                                  back to top

Q What is the difference between a masonry sealer and a masonry primer? I have to paint a new cinder-block horse barn. Since masonry sealers are lower in price than masonry primers, I would prefer to use the masonry sealer if it will be sufficient to seal the surface so that I can then paint over it.

A A masonry sealer generally has very little or no pigmentation, whereas a primer is pigmented. Sealers also usually have much lower solids content than do primers, which accounts for most of the difference in price. Typically, you would need two or three coats of
a sealer to get the same dry film thickness as obtained with a primer. In your case, an unpigmented masonry sealer should do the job.

Some additional points: masonry sealers are available in both water-based and solvent-based formulations. Make sure the product you choose is recommended for new masonry, which can be quite alkaline (at the mortar joints, in your case), and is also recommended for painting.

Once the sealer has dried at least a day, apply a quality 100%
acrylic house paint, either flat, satin or semigloss, depending on the appearance desired. This type of paint will resist problems with alkalinity and efflorescence that are sometimes associated with new block walls.

Or you can use an exterior latex primer recommended for this type of application. With a primer, you will get better hiding and uniformity of appearance than with a sealer.

Mudcracking                                                  back to top

Q Recently, I came across five new houses where the paint had cracked. Some of the cracks were hairline and some spread open about 1 1/8". The cracks were concentrated in the corners, but
could also be found on some flat sections of the wall. Does this
sound familiar to you?

A Yes, this sounds like classic “mudcracking.” Some of the causes
of cracking like this are:

• Applying the paint too heavily, especially in corners. This
  is more common with inexperienced airless spray operators.
  
• Applying paint when the temperature is below the
  recommended minimum.
  
• Applying a latex wall paint to new drywall without the
  benefit of either a general purpose or PVA primer.
  
• Applying the paint under very fast-dry conditions.

Garage Floors                                                 back to top

Q How do I prepare a concrete garage floor for paint?

A If it has been previously painted, clean the surface with a caustic garage floor cleaner and rinse thoroughly. This will tend to lift poorly adhering paint.

If the surface is bare, smooth concrete, etch it first with a muriatic acid solution. Follow the manufacturer’s directions for application and safety. Then rinse thoroughly with plenty of water to dilute any residual acid, and to flush off residual salts.

Rejuvenating Latex Enamel                                back to top

Q Can latex enamel be rejuvenated? I have 20 gallons that were stored in an unheated building. I think the paint froze and has now separated. Should I drain off the liquid, and what can I put in it when
I re-mix it?

A You may be able to reclaim the paint. Open each container and do the following:

• Do not pour off the liquid. This should be kept as part of
  the paint.
  
• Look for any signs of rusting or deterioration of the containers.
  Wherever you see contamination of the paint, discard the entire container.
  
• Remove any obvious skins or hard pieces. Leave soft lumps
  in place.
  
• Now stir the paint in the containers thoroughly. The best bet would be to have the containers shaken at a paint store. If this
  is not possible, use a paint stir-stick and stir each container thoroughly for 5-10 minutes.
  
• If, after stirring, the paint seems smooth, uniform, and free of specks, and is not thin or runny, it should be fine to use. However, check each container first by applying some of the
  paint to a scrap surface and look for uniformity of gloss and color. To play it safe, don’t use it in a critical place like a living room.

Frozen Paint                                                  back to top

Q Can a quality latex paint be harmed if it is has been frozen
and thawed?

A Yes, latex paint can be harmed if it is frozen. Problems that can occur are reduced gloss, separation of ingredients and/or formation
of “grit” or lumps. Often, however, a paint may survive one, or even
a few, freeze-thaw cycles.

If a paint is frozen, thaw it slowly. Then thoroughly stir the paint. If
it appears to be smooth, normal consistency and of the proper color,
it is probably fine to use.

Metal Doors                                                   back to top

Q Can you please tell me what kind of roller to use for metal doors?
I keep getting roller marks and I have been using a 10 mm roller.

A For water-based paint, use the best quality roller cover available with a synthetic nap. For oil-based paint, try a mohair roller nap. 10 mm is a good nap length. Before starting, pre-wet the cover with water if applying latex paint, with paint thinner if applying oil-based paint. Then remove as much of the water or thinner as you can by squeezing the cover and rolling it on newspaper.

You may need to thin the paint slightly before painting. Make sure there is plenty of paint on the roller. Don’t apply any excess pressure to the roller while painting. Roll an area only two or three times; don’t keep working it.

Application Temperature                                    back to top

Q I read on your site that exterior painting should be done when it's over 60°F (16°C). How long after application does this guideline apply? For example, if the forecast calls for daytime temperatures in the mid-60s but overnight temperatures in the low-40s, is that a “go” or a
“no go”?

A The 60°F (16°C) guideline is ideal. The minimum application temperature on the label should be followed. This is typically 50°F (10°C) for latex paints. We suggest these points:

• Do not apply the paint if the air temperature is below the recommended minimum, or is predicted to drop below the
  minimum for the next 36 hours.
  
• Do not apply the paint if the surface temperature is below the recommended minimum. For example, if the temperature during
  the night was 35°F (2°C), and the temperature is up to the recommended minimum of 50°F (10°C) at 9:00 am, and you are painting aluminum siding, the siding itself is probably too cold.
  
• Not following these guidelines can cut years off the life of the paint job, and it may not be long before cracking and loss of adhesion set in.
  
• Oil-based paints are more forgiving than latex in this regard, but lower temperatures will still retard their dry, which can result in dirt collection, especially if it becomes windy.

Painting Vinyl Trim                                           back to top

Q Is it OK to paint the vinyl trim on vinyl windows? I've heard that it shouldn't be done because it might cause the trim to warp. Do you have any information on it? Perhaps there's a special paint or a technique that could prevent this problem? The trim is currently
beige. The owner wants it painted white.

A You should be able to paint the vinyl trim successfully. A general guideline with vinyl siding is not to paint it any darker than its original color, because painting it darker can result in warping. However, window trim is generally thicker and of a different construction, so it
is less likely to exhibit this problem. In your case, using white paint, there should be no problem. Some other points to consider:

• Wash the surface and rinse off. Lightly scuff-sand the
  surface with #180 or #220 grit sandpaper, and wipe off
  with a damp rag.
  
• Apply a top quality exterior acrylic latex paint. Choose flat,
  satin or semigloss, depending on the appearance desired.
  
• For best durability, apply a second coat after the first has
  dried thoroughly.

Peeling Wall Paint                                            back to top

Q While washing walls in preparation for painting, the old paint started to peel off. Does this mean someone used a latex paint over an oil-based paint? If so, how do we fix this to paint over the walls with a semigloss latex paint?

A It’s hard to say what caused the paint to peel off. It could be related to what was previously on the surface, the quality of the last paint, the strength of the cleaning agent, temperature when the last paint was applied, etc.

In any case, if you can remove the paint by soaking and rubbing, go ahead and remove as much as you can, because leaving it on may be unsatisfactory. Trisodium phosphate (TSP) is often used for cleaning painted surfaces in preparation for painting, but it is very strong and must be thoroughly rinsed off. A better approach might be to use a milder household cleaner.

After you have removed as much of the paint as possible, make sure the surface is clean, rinsed and dry. If the surface is glossy, scuff-sand it with #180 or #200 garnet sandpaper. Clean with a damp rag.

For best results, apply an interior, high-adhesion primer. It can be either solvent-based or water-based. Use ample ventilation, with at least two windows open in the area. If solvent-based, wear a respirator and eye protection while applying the primer.

Let the primer dry overnight. Choose a top quality interior semigloss latex paint, and apply using a 1/4" or 3/8" nap, high-quality, synthetic nap roller cover. Apply a second coat the following day if color and gloss uniformity are not as good as you like.

Removing Redwood Stain                                   back to top

Q What is the best method for removing a pigmented stain from redwood siding? The owner wants to restore the redwood to its
natural state so that we can preserve it with a clear preservative.

A There is no easy way to do this, as you might imagine. Consider these possibilities, but do not attempt to remove any of the stain if you suspect there might be lead in it:

Chemical remover – Paint remover can be effective, but tedious. Apply a stripper in a heavy coat by natural bristle brush. Protect skin, breathing and eyes with chemical resistant gloves, goggles, overalls and an appropriate respirator. Protect plants, and keep children and pets away. Do small areas at a time, about 10 sq. ft. maximum.

Allow the stripper to remain on the surface about 20-30 minutes,
then remove the softened stain with a 3" spackling blade, scraping
it onto a disposable drop cloth. Then move to another area. You’ll probably have to sand the wood after it dries to get the last of the pigmented stain off, and to obtain the look you want.

Sanding – Sand the wood with the grain, using #100 - #120 grit garnet or aluminum oxide paper. A 3" or 4" belt sander will work well
for bevel siding. Use care to sand the wood evenly and not dig into it. Wear goggles, gloves and dust mask.

Power washing – This is another possibility, but with redwood you need to be very experienced in this procedure to do it well and not damage the wood itself.

Note: Be aware that you will probably have to reapply the clear material every year or two to maintain appearance and to protect
the wood.

Painting Dark Paneling                                      back to top

Q I’ve been asked to paint dark wood paneling in a family room.
Please advise as to the best primer (preferably no sanding, and latex
if advisable). Also, what low-luster enamel would look the best?

A As a minimum, you’ll have to wash down and rinse the paneling.
A light sanding is also advisable, although you can probably get by without it. There are interior water-based, stain-blocking primers that have excellent adhesion. You should use a stain-blocking primer to guard against the possibility of discoloration coming from the paneling and through the finish coat. Allow the primer to dry overnight.

For the finish coat, choose a top quality interior stain or semigloss paint of a brand with which you are familiar. We cannot give recommendations on particular brands of paints or other coatings.

Painting Pressboard                                         back to top

Q I will be painting a factory-painted pressboard product. Can you provide any tips on the “paintability” of this siding and what prep
work should be done?

A Assuming the siding is hardboard siding (panels that are made
from pressed wood fibers with a heavy paper overlay), we suggest
the following steps:

• Carefully remove dirt, chalk, etc. Do not gouge or dig into the original finish. Do not sand it and do not use a wire brush or scraper. Use a scrub brush and mild detergent. Rinse thoroughly.
  
• Once it is dry, apply an exterior latex primer recommended
  by the manufacturer for this type of material. Allow it to dry overnight. Do not apply the primer if rain is predicted over
  the next few days.
  
• Then apply a top quality exterior flat or satin house paint.
  Stop applying primer and paint about 3:00 pm.

Really Old Varnish                                            back to top

Q A tongue-in-groove porch ceiling looks as if it was previously
coated with varnish. The house is between 75 and 80 years old. The old finish is cracked and chipping everywhere. Do you recommend re-doing it with varnish? The owner likes the look of the wood, and would rather re-do it that way. Do you recommend sanding to bare wood?

A Yes, for best results, you will have to sand. Start by removing the old varnish by scraping. It sounds like it is brittle enough not to take too much effort with this approach. Set up platforms so you can conveniently reach the ceiling. Use a large, two-handed scraper and scrape the flat surfaces going down the boards, not across.

Use a shaped (e.g. triangular) scraper to get in the beading or grooves. Wear safety goggles and a quality dust mask (not a “comfort mask”). Once scraping is done, sand with medium-grit garnet paper, again going with the grain, not across. An electric belt sander will
work well.

Dust off thoroughly, and apply two coats of an exterior-grade poly-
urethane varnish, in a gloss, semigloss or matte finish, depending on the appearance desired. Use a quality 2 1/2" polyester brush. "Grain Raising"

Back Priming                                                  back to top

Q Is back priming new or replacement wood siding helpful?

A Yes. Applying an appropriate primer to the back can help minimize water intrusion into the siding. The source of such water can range from humidity in the building to water that wicks up from an under-lying roof. But take care not to create problems by entrapping water that is already in the siding material, or that could enter through an unprotected end grain.

According to the Forest Products Laboratory of the USDA, back
priming is best accomplished by applying one coat of a latex exterior primer. The Forest Products Laboratory reports that instead of a primer, applying one coat of a wood preservative is also effective.

Grain Raising                                                  back to top

Q As a contractor, I do a lot of interior bare wood staining and painting, ranging from doors and trim to fine furniture. Whenever I
use a water-based product like a primer or stain, I see fibers sticking up from the wood. These sometimes ruin the finished appearance, making it very rough. It is particularly bad with some cabinet woods like walnut and mahogany. What causes this and what can be done about it?

A This is called “grain raising.” The water in the coating swells the wood fibers and lifts them. The best thing to do is to preempt this by wetting the surface with a wet rag before applying the primer, stain or clear coating. The water will raise the grain. Come back in 30 minutes and sand off the raised “whiskers” using fine (#180 or #220) garnet sandpaper.

Be sure to sand only in the direction of the grain of the wood, never diagonally or across it at right angles. Then dust off the surface and proceed with the primer or stain, etc. Very little grain should now be raised by the application of the coating.

Have a Question?                                            back to top

If you have a question that is not answered anywhere in this manual, try visiting the PQI Web site at www.paintquality.com

Once there, click on the Quick FAQ’s icon. The FAQ area of the site lets you search by hundreds of key words through a library of paint questions and answers. Just choose an interior or exterior painting topic, and a list of common questions and answers will appear.