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Exterior Wood Lap Siding & Paint Peeling Demons

My home was built in 1920 and has wood lap siding as its exterior surface. Although this siding is 88+ years old, it still bleeds a considerable amount of sap in certain areas... This is only part of the dilemma. This old siding just doesn't seem to hold onto the paint. It was painted 3 years ago: one coat oil-based primer then 2 coats of latex. It needs repainting already, and, this time, I hope to get it done correctly and have it last just a little longer.

- Is there a sealer I should use before priming?
- Any way to prevent the sap from bleeding through?
- What primer is best suited to tackle this difficult task? & is it oil-based or latex?
- Which exterior paint is best prepared to bond and hold?

I really know very little about painting, so any suggestions/advice would be greatly appreciated!


J Roper
Re: Exterior Wood Lap Siding & Paint Peeling Demons

In referrance to your concerns on s sealer to use before painting, there are sealers that can be applied on new wood before painting but not for repainting. On the sap bleeding on a house that old, I am suprised. The old timers used shellac to seal the sap in. Today there are synthetic versions of shellac that will do the same thing. Zinnser is a good one made for exterior . Some of them dry so fast that they don't have enough time to penetrate into the wood. Sherwin williams makes an oil based stain blocking primer (101 exterior wood primer) that will block stains and dry slow enough to penetrate. After that use a premium quality of acrylic latex paint.
Paints sold before 1978 can contain lead! If that is of concern to you, the prefered method to make it safe is to encapsulate it. That requires an adhesive coat and a top coat with a mil thickness of anywhere from 7-8 mils to 16-18 mils depending on the product. Some of the thinner encapsulants don't have the flexability needed to keep them from cracking due to thermal shock. (expansion and contraction)
The best one out the is Rhino Shield Ceramic Coating. You can Google Rhino Shield to find a dealer and more info. They will do all of the prep work and apply the product and it has a 25 year warranty. It's a credible warranty based on independant testing by BASF. Absolutly worth checking it out with having to repaint so frequently.

Re: Exterior Wood Lap Siding & Paint Peeling Demons


I too am surprised that a house of 88 years is still weeping sap.

As to the paint peeling problem, there are possibly two things going on: First, your house is 88 years old and undoubtedly has many coats of paint on them, most being oil paint. Oil paints block vapor transfer much more than latex (acrylic) paints. In effect, you now have an almost impermeable vapor barrier on the exterior of your house. Moisture generated inside the house wants to migrate to the exterior atmosphere, but becomes trapped in the wall cavities and the wood of your siding. When the heat of the sun warms the siding, vapor pressure forms, breaking the bond of the paint to the siding and the paint pops.An 88 year old house would have little or no vapor barrier or insulation on the inside. You should try to limit moisture accumulation in the house through good fan ventilation in baths, kitchen and laundry. Also limit use of humidifiers in winter.

The second thing which might be happening is the application of latex paint and primers over years of oil paint. Oil paint is brittle and becomes more so with age. Latex paints are more elastic, stretching with changes in climate. Latex paint and their primers also have tenacious bonding. Brittle and elastic is a bad combination. The latex paint can actually break the bond of the old oil paint to the wood or previous layers of paint. Peeling is the result.

Unfortuantely, the ultimate solution is to remove the years of paint accumultation and start over. Sorry, not a pleasant thought! This Old House has tried a couple new products in past episodes with good results. One is a new type of stripper which works by breaking the bond of the paint rather than dissoving it like older type strippers.It is non-toxic, requiring no protective clothing. It is painted on and left overnight. The paint then rapidly zips off with a scraper.

The other new product is an electric hand-held infra-red device which rapidly heats up the paint breaking its bond. It has no open flame and will not cause a fire. http://www.thisoldhouse.com/toh/article/0,,386353-3,00.html

As to painting the newly stripped house: I am from the old school and still prefer an oil based primer, followed by at least one coat of acrylic house paint. The primer may be tinted toward the finish color.

I think the stripping and oil primer should go a long way toward correcting the weeping sap problem too.

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