I had someone ask me about the lifetime of exterior primer. I didn’t have an answer for them, so here it is, maybe someone here will know.
They are slowly painting the exterior of their house and have a time table of getting it sanded/primed this year and painted next year. He wanted to know if the primer would hold up for 8-16 months without the final coat of paint on top of it? (below freezing in the winter and up to 100 in summer)
I’ve never really had a situation where I didn’t cover up the primer within a short time, so this is an unknown to me. I think they’re using exterior Kilz. I briefly glanced at their website, but didn’t see an answer.
Personally, I realize I’m gonna go to restoration-Hell for suggesting this, but I tend to think it would be better to put vinyl or some other lower maintenance siding on rather than messing around with painting it every 5-15 years. But they think wooden clapboard is “charming” (I think its a PITA). We will see how charming it remains by the time they’re done with it.
Replies
I'm not an industrial chemist, but I used to paint for a living.
The purpose of primer is to provide a surface for the finish coat to bond to. Theoretically, the primer coat can last a year or more. The problem is, the longer they leave the clapboards without a finish coat, the longer dirt and possibly algae can form. So it's in their best interest to paint that top layer,with its UV protection and higher solids content, as soon as possible.
If they keep painting at their current rate, they might as well paint the Golden Gate Bridge.
priming is a good thing to do
they should just understand that they should reprime as they go
most primers harden as they cure ( maybe 3 or 4 wks max ) and should at least be mechanically etched before covering
I don't know about Kilz, but most primers say on the can they need to be covered within a fairly quick period of time, say, 30 days. The reason is that primers are formulated for maximum adhesion. In order to accomplish this, they give up on the competing properties of weatherability and UV protection.
If the can doesn't say, telephone the manufacturer.
First - can your friend read?
I hate to sound so - whatever - but there are directions on the label of every can of paint I have ever used.
Every can of primer that I have read says to cover it with topcoat within thirty days. There is a reason for that.
the primer will still be there and look sound in a year, but it has no UV resistance. So it will be shedding it's top surface - chaulking. This is true with any exterior paint, but more so with primer.
That means that they wil be applying new paint to a surface that is disintegrating as they work. They would need to lightly buff or sand it to remove the loose microscopic scaling and dirt that would prevent a good bond. There is also a good chance that they would want to apply a fresh coat of primer. I would.
I rebuilt a house five years ago or maybe six, hwere the painrter they had hired for the exterior was a one man show. He was doing great and thorough work at scraping and sanding down to the wood, and immediately priming after , before it could get wet or begin to shed lignan fibre.
But he was going all they way around the house and it was winter before he got back to the front so he painted finish copats the next year. I asked him if he trusted the year old primer. "Sure, it's still there ain't it?"
Bottom line - most work he does and other painters of same quality here is with same paint and process except for the delay. it lasts at least ten years. This house is staarting to peel and flake, and a lot of the sepaaration is between finish and primer - the point of the bad bond from the old surface.
So if your friend ignores what is on the lable, they are condemming themselves to a disappointing result.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Thanks for the replies, I've passed them along.
I had been wondering why they didn't just prime and final coat the parts they could get to and then to the rest next summer. But I'm no paint expert.
Personally, I'd just try to get it all done in one season, but I'm funny that way.jt8
Speaking of UV, sanding and priming...for clapboards in direct sunlight, hopefully they're sanding only what they can prime within an hour.
Regards,
Tim Ruttan
Instead of Kilz have them get a tinted primer by the same manufacturer of the top coat paint.
I had an opportunity to ask a Behr "factory" rep this same question. I was prompted by the fact that there was no mention of maximum times on the can for either the interior or exterior primers. Here's what he told me:
1) It's better if it doesn't get wet. Must keep dry for a least 16 hours (e.g. even no dew) and no rain before top-coating.
2) Top-coat on the 3rd day (16-24 hours give maximum "hide").
3) Your enemies (on top of rain) are smog, dirt, and sun.
4) The paints are so good that they'll work way beyond these times; but, you'll end up with less quality than you paid for.
Phill Giles
The Unionville Woodwright
Unionville, Ontario
<Top-coat on the 3rd day (16-24 hours give maximum "hide").>
Phil, I must be missing something here.
If maximum 'hide' is in 16-24 hours, why did he say topcoat on the 3rd day?
Well, my interpretation was that if you finish priming at 6:00PM, you either work afternoon shift tomorrow, or skip a day. As drying times are not cast-in-concrete, a little extra time to ensure the primer is dry sounds prudent..
Phill Giles
The Unionville Woodwright
Unionville, Ontario
Well, that'll work. Thanks.