I read on the James Hardie website that their pre-primed lap siding should be painted within 180 days of being hung. Is this really necessary? I covered a garage with it about 3 years ago, which I still have not painted, and I do not see any visible effect.
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Greetings wadsworth,
Don't know why your post took so long to get posted but maybe this'll be some assist.
This post, in response to your question, will bump the thread through the 'recent discussion' listing again.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
when in doubt add garlic
Oxidation interferes with paint's ability to bond. All paint oxidizes, but primer tends to oxidize faster than finish paint. My guess is that the 180 day time limit assumes you're planning to topcoat; if not, you probably don't have to worry.
Incidentally, I never trust factory primed surfaces to be ready to finish, since chances are oxidation has occurred before installation. If you ever DO paint, you should definitely sand, wash and re prime the surface first.
I concur with saulgood. Primers are made to bond tightly between the substrate and topcoats, but the compromise is that they give up on ability to resist weathering. So, before painting you should wash and re-prime. Be sure to use a 100% acrylic primer. Never use an oil based product on fibercement.
Be sure to use a 100% acrylic primer. Never use an oil based product on fibercement
Why not? The manufacturers recommend oil based primers - why do you feel they aren't good for fiber cement?
When I resided my garage with Hardiplank, I primed it with an oil based primer that was recommended by the manufacturer, even though the siding was "preprimed". I followed with two coats of good latex. Several years later, it still looks "like new".
The reason that oil based primers should not be used on materials with a cement base is that the oil in the paint will react with the alkali in the material and saponify (turn to soap). Then it will flake or peel.
James Hardie specifically recommends against oil based primers on their unprimed materials:
"Note - The use of oil based paints on unprimed fiber cement could result in increased surface roughness, loss of adhesion, cracking or excessive chalking. James Hardie does not recommend the use of oil based paints over unprimed fiber cement siding products. Stains containing linseed oil are specifically designed for wood and may not be suitable for fiber cement siding products, primed or unprimed."
Hardie doesn't forbid oil based topcoats over pre-primed surfaces, however if the primer has worn spots or has been exposed to the weather without a topcoat for a long period of time, I would not trust it to completely shield all of the cement from contact with a subsequent coat of paint.
They also say to
"Use primers and topcoats that are designed and recommended for cement based building materials (fiber-cement, masonry, brick or stucco)."
Oil based materials react with cementitious substrates, so I doubt there's an oil based paint recommended by the paint manufacturer for such use.
Other siding manufacturers may have other recommendations.
http://www.jameshardie.com/homeowner/technical/paintingtips.php
Interesting. Thanks for the info.
FWIW, the oil based primer I use is recommended by the paint manufacturer for Hardiplank. The product is Zinsser coverstain.
http://www.zinsser.com/primerapps.asp
I did look again on the James Hardie site, and they apparently no longer list approved primers, just paint. However, the Zinsser coverstain was previously listed as an approved primer.
I do see that they have added the note you cited about oil based paints, but don't see any comment on oil base primers specifically.
Maybe they have had problems more recently and changed their recommendation. Given the paint manufacturer's recommendation, though, it looks like I will be OK.
If the effects you cited were to occur, how long would it typically take to show up?
I've never heard of Cover-Stain. It is unusual that an oil based paint can dry in an hour. Must be something quite uncommon. They do recommend it for fibercement.
I don't know how long it might take to show up if there would be a problem, but since it is recommended by the paint manufacturer I would not expect there to be one.