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Discussion Starter · #1 ·
Hi yall,

I haven't been on in years, but today turn for some needed expertise :)

I have an old asbestos sided house and did some major repairs on two walls from water damage. I don't necessarily love the asbestos stuff, but it holds paint like crazy - I haven't had any peeling in 25 years. So, I was careful to not break the old pieces when demoing and will reuse the same stuff again.

Now the question I have is has anyone ever back-primed this old stuff? Or the new non-asbestos replacement from GAF (Weatherside) fiber cement siding. I would guess that hardie may also behave in the same way. It was never back-primed and lasted all these years, but now that I have it all down, my over-engineer-everything brain is wondering whether to back prime before putting it back up. My concern is that if anything needs to leach out, it may mess with the new paint coat.

TL;DR

Does anyone have experience or knowledge about back-priming old asbestos siding (or the current day fiber cement look-alike replacement from GAF

Thanks!
 

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I stopped handling asbestos (literally) several years ago. Won’t touch it at all.

We handle a lot of cement board siding, and what I have observed is that cement board siding that has not been back-primed, there is notable paint failure on the fronts.

Cement transmits moisture, so peeling paint on the front is a predictable result if not back-priming.
 

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View attachment 112846
Wish I had a better picture, but this is one we handled this summer, where we confirmed it was not back-primed.

The paint was randomly blistering all over the house. We had to scrape it like an old wood house before painting, and a lot of paint came off.
I looked at a place a few years ago with siding just like that. Hardie board? The entire house was completely surrounded by trees that basically blocked almost all sunlight. Green algae was everywhere. The paint was coming off the siding in sheets everywhere, and the place was huge. I looked at it in the fall and they were going to get back to me to start in the spring. Then Covid hit and I never heard from them again. At the end of the day I was pretty happy not to have got that job. It would have been a scrapeathon from hell.

I have no idea how you scrape that surface without destroying the profile, but it's gotta be done.
 

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Not sure what the data sheets spec for GAF, but Hardi I believe makes no mention of back-priming their siding. Since they do however stress the importance of priming end cuts to prevent moisture intrusion, it stands to reason that back-priming might be beneficial, if for no other reason as to aid in dimensional stability.

As for asbestos, I really don't know. I've painted plenty of it, but I have no idea if back-priming would help. I've seen old homes where the asbestos siding was in near immaculate condition, despite never having been back-primed.
 

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Discussion Starter · #6 ·
Not sure what the data sheets spec for GAF, but Hardi I believe makes no mention of back-priming their siding. Since they do however stress the importance of priming end cuts to prevent moisture intrusion, it stands to reason that back-priming might be beneficial, if for no other reason as to aid in dimensional stability.

As for asbestos, I really don't know. I've painted plenty of it, but I have no idea if back-priming would help. I've seen old homes where the asbestos siding was in near immaculate condition, despite never having been back-primed.
I was thinking the same thing - that asbestos has been on the house since 1960s without any backpriming, so maybe it's a good idea to just leave it. I've also painted tons of this stuff, but never off of a house. I've got kind of a unique case here with the asbestos off and looking to put it back on again, lol.

Re Hardi - I did find something online where a Hardi rep recommends against back-priming to allow for easier drying if any water does enter. Especially is a rain-screen is installed behind the siding. Nothing mentioned about it in any official Hardi literature as far as I could see.
 
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