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Bondo on nail heads on new exterior siding?

19172 Views 17 Replies 15 Participants Last post by  TBFGhost
Hi all! Been a while. I have a prep question. I am going to be painting a house that will be having some siding replaced with new pre-primed horizontal wood siding. The contractor doing the siding work says he can patch all the nail heads. I asked the HO’s what type of patch he will be using and apparently he wants to just spackle all the nail heads. I suggested light weight bondo instead and feel it will hold up longer. The contractor, not wanting to deal with the bondo, then came back with the idea of him priming the nail heads instead and leaving the bondo to me. I told the HO’s I don’t think that it is a good idea since they will of course want to use galvanized nails, which would rust if painted or primed. The contractor then told the HO’s he does it all the time and does not see the problem and says if he primes first, then the bondo will adhere better.

So, my question is; who is correct? If the siding is already pre-primed, why would it need to be primed again to use the bondo? I have used bondo on new pre-primed fascia (nail heads), sanded the bondo, primed with oil primer and then painted two coats paint. That is the way that I know to do it. If you have another way, please let me know. Also, please let me know what your opinion is regarding bondo vs spackle. Thanks so much.
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with 2 coats of paint wont the exterior spackle hold up fine?
Why are you covering the heads with anything besides paint?
I think you're making a mountain out of a molehill using bondo. Why would the lightweight out perform the regular? And priming before applying it? The rougher the surface the better for that stuff.
As I had mentioned before, the goal is to avoid the nails from rusting, but also it looks better to hide them. I know that bondo cracks with time, but spackle seems to fail sooner. One painter suggested caulk (ie. dap 230); flexable and long wearing. I would really like to hear opinions from more painting contractors if that is possible. Thanks.
Not a painter, but bondo will pop out, if they don't want to see the nail heads caulking them seems to give the best results that I have seen

Is this smooth siding or rough? If rough, spackle, etc... is out as you will have lots of smooth areas that will be bigger than the nail heads
Pre-prime = RE-prime.

Ideally, any new boards should be backprimed as well.

Pre-primed material usually has low-end primer, AND is too dried-out/dirty to hold paint decent.
Most primers are too brittle/dirty after a month.

Nail heads:
* Bondo's overkill...
* Top nails off with OIL primer.
* When these spots are well-dried, THEN do the filling with a good Exterior wood-filler.
* When this is dry, feather-sand flush.
* Remove dust, brush a hazy prime-coat on the filler. THIS can be Latex primer.
* Now, re-prime everything. Saturate any end-cuts with primer too.
* Make sure siding is vented in some manner!!
* Your little "Nail-head sandwich" is complete:
Nail >>> Oil primer >>> Wood-filler >>> Hazy primecoat >>> FULL primecoat >>> 2 Paint topcoats.

Maybe a little more time-consuming, but it's the right way.
Nailsheads rarely rust through a hardened coat of OIL primer.

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wood bondo won't if you prep the surface right, use 80 grit sand paper or rougher to profile the surface. It gives the wood bondo something to bite into. I have wood bondo on a couple places on my house and it is fine *going on 2 yrs now*. Caulk the nailholes with elastomeric caulking.. done. Seriously. Bondo would take freaking for ever to do... just not the right application.
All good info. Thank you. Anymore painting contractors want to take a shot at this one? :2guns:
Still not sure why you wouldn't just caulk them.

Bondo and spackle are just silly talk.
What about good old painters putty? Cualk is going to shrink and show the nail hole.
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I got a tip from an experienced builder. Uses automotive rattle can primer, oil based,much easier than a brush, best rust protection, drys fast, no cleanup. I use elastomeric caulking cpd. or caulk. I have done some tests and exterior latex Spackle does not hold as well as the flexible alternatives. You need some elastic ability if you have temp. extremes. Caulk can also work. Wood filler like DAP[acetone/MEK base] can work if you want a harder covering. Bondo is good for interior fills such as in door jam repairs around locks, hinges. The woods absorption of water causes the Bondo to lift on ext. repairs. Bondo works best on metal or fiberglass.
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Whats the siding???

If rust is such a concern, he should be using stainless nails. I pretty much use stainless on all exterior work. Follow up with M+H readi Patch and oil primer.
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The HO's said it is some sort of Pine, but I can't remember the exact name. They said it is primed on both sides and on the ends, which is really good.
Red power house 550
Powerhouse Siliconized Elastomeric Sealant for joints with dynamic movement.
What we use for this humidity down here an it works out great they have blue tube an red. killer stuff
Ditch the bondo. Use an oil primer to cover the nails. Any water based primer will influence rusting with the nails.
Whats the siding???

If rust is such a concern, he should be using stainless nails. I pretty much use stainless on all exterior work. Follow up with M+H readi Patch and oil primer.
This is exactly what I was going to say. Nail, fill, prime. Done.
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