Oil-based primers better than paint/primer combination

 
Posted11/18/2018 6:00 AM

Q. For outdoor paint jobs, I have always used an oil-based exterior primer and then a separate acrylic latex exterior paint with good results. This summer for the first time I -- rather skeptically -- tried one of the new paint/primer combinations, which seem to be just about the only thing you can get these days. It was a dry day, with no rain for two days afterward. The wood was dry to start with and I scraped off the old paint, removed dust, etc., like I always do. The only difference was that I did not prime first but put on one coat of a well-rated paint/primer.

When I checked the woodwork a couple of days ago, I was shocked to see the paint is already peeling in places only months later. Do all these paint/primers peel off after only a few months? Are the results better when the old-fashioned oil-based exterior primer is used under the paint/primer coat? Is it possible to still get paint without built-in primer?

                                                                                                                                                                                                                       
 

A. Your earlier procedure was very good and the preferred way to paint most bare woods.

My expert contact in the industry told me the following: The paint/primer combination was started by one of the big box stores as a sales gimmick, but it is a myth. These paints are really self-priming paints; there is no actual primer in the products.

You should be able to find alkyd (oil-based) primers in professional paint stores unless your state has banned them because of the oil base. But you certainly should be able to get an acrylic primer, which does a pretty good job on most woods, cedar being an exception because of its oil content; alkyd is best on cedar. Zinsser's Smart Prime primer is an excellent choice under all conditions.

You seem to have prepared the surfaces well, but you haven't mentioned sanding, which is very important after scraping, etc. Sanding should be followed by wiping with a damp cloth to remove all residue (do not use a tack cloth as it can cause some of the resins in the old paint to stick to the bare wood).

If all old paint was completely removed, and you applied the paint on bare wood, I have no answer as to why it peeled so soon except that, perhaps, the lack of sanding and wiping off afterward may be responsible. Evidently it would have been best to prime the bare wood first followed by two coats of finish paint a couple of days apart, making sure the first coat was thoroughly dry.

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Q. A reader's questions about some recent column advise:

• Is it wise to install a ridge vent in cold climates? I am finding reports of individuals experiencing ice buildup on the fibers on these ridge vents in the winter. They claim the humid air exiting the attic causes frost to build up on the filter, restricting airflow. Then when it melts it causes water damage/mold. Is it better to stick with can venting and avoid ridge vents in this climate. I do not want to get myself in a situation that will be an expensive fix.

• (Our) house was built in 2004. The original vent is a soffit vent. Because we are replacing the roof, I was thinking of relocating the bath vent. I have the option to do soffit, roof or gable vents. I understand that gable venting is ideal but it would be a bit more complicated to have done in our situation. Would it be enough to go through the roof and use an R8 or R12 insulated flex pipe to exhaust it to avoid condensation buildup? My greatest fear is condensation, water damage and mold. Should the roof option be avoided? Is there a sufficient amount of pipe insulation that eliminates condensation?

• Is lead high boot flashing healthy/safe? Are there any other recommended products that avoid the use of lead you recommend?

A. I haven't heard of ice build up on the filter of Shinglevent II from exiting moisture, but that does not mean it has never happen. Its external baffle system reduces the chance of snow and rain being blown in inside the attic, a problem encountered by non-externally baffled ridge vents.

Falling snow does cover all ridge vents, but externally-baffled ridge vents usually free themselves over time because snow is porous and the attic air continues to move through it. Over nearly 50 years living in the mountains of cold Vermont, I have observed that the snow sublimated, little openings formed and widen as the days went by until the vent became clear.

                                                                                                                                                                                                                       
 

Venting by means of roof cans is not efficient and does not adequately vent the entire surface of the roof sheathing, which the combination of continuous ridge and soffit venting accomplishes.

As to your question about bath fan venting, I hope your newspaper printed my extensive description of the proper way to vent bathrooms last week, and the reasons why the only safe way is through a gable wall regardless of how difficult it may be.

Does your question about lead "high boot" flashing refers to plumbing stack vents? Why would it not be safe when it is outside on the roof? I am not sure I fully understand your question.

Q. Our roof is 16 years old, not leaking. When should we think about replacing it? Has there been any improvement in the reliability of asphalt shingles?

A. Organic felt asphalt and fiberglass shingles have a history of not living up to their stated life expectancy regardless of the brand. However, they have become somewhat better than they were some years ago when they were failing early at an alarming rate throughout the country, leaving roofing contractors stuck with much of the cost of teardown and replacement. There have been a number of class action suits against most manufacturers.

Your roof may still have many years. Just watch for deterioration manifesting itself by shingles severely curling on their exposed corners, showing vertical and slanted cracks or breaks, etc., as a start.

• Henri de Marne, a former remodeling contractor turned columnist and consultant, is the author of "About the House with Henri de Marne" (Upper Access Publishing). He continues to take questions from readers for this column and his website, www.henridemarne.com. Email questions to aboutthehouse@gmavt.net.

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