"Painting" machine shed roof with primer only?

[KYErik]

My dad has just pressure washed all the loose old paint off the roof his 50x90 foot 1970's era Morton machine shed and is getting ready to spray it with Zinnser Bullseye 123 primer (rated exterior/interior, water based) with an airless sprayer. The primer is white and he wants the roof to be white (it was originally white as well).

The primer label states that it SEALS wood, concrete etc. and that it sticks to galvanized metal- so- does he really need to add a coat of true paint on top of it? In other words, will the primer hold up/last as long by itself as it would with a top coat of true paint?

He doesn't care if it has a dull finish (like all primered surfaces do).

Thanks in advance for advice.

 

[Stimw]

The best thing for the roof is "Elastomeric Coating". The box stores sell it in 1 and 5 gallon cans/buckets and comes in white.
You can roll it on or spray it and it is water clean up.
I used it on an old metal mobile home roof and used to use it on semi trailer roofs when I worked in that field 15 years ago.

 

[KYErik]

How long would the elastomeric coating last Vs. Paint or primer?

 

[EddieWalker]

Zinsser 123 is my favorite primer. It's very good at a lot of things, but I have my doubts about using it for an exterior finish. My understanding of how a primer works is that it requires a finish paint over it because it's not designed to protect the surface from the elements. I would think that moisture would get through the primer and allow problems like rust or mold to form.

There are quite a few products out there that are designed exterior metal roofs. Henry makes some very good stuff and it's sold at Home Depot. Rustoleum has some stuff for rusted metal that is pretty good too.

Eddie

 

[3930dave]

I'm thinking the primer won't stand up well on it's own, but that's only a guess. I'd also expect the dull finish to hold/trap more fine dirt than a smooth topcoat paint.

My favourite outdoor paint at the moment is an oil based porch paint, that contains urethane. What I'm using is an in-house brand from Home Hardware in Canada, but I'd expect most of the major quality paint brands in your area should have something equivalent. Designed to be walked on, it's a pretty tough finish.

I think the coatings that Stimw referenced will be pretty good, but wanted to mention this porch paint - at the volume you need it may give you a better price point (?).

Rgds, D.

 

[Stimw]

How long would the elastomeric coating last Vs. Paint or primer?

I had it on the MH roof for 10 years with only minor touch up.
I think it has a "years" rating on the can.
I need to coat an old 20' X 20' section of my 48' X 50' shop. I will pressure wash, let dry and then apply.
The stuff is like a good grade of latex paint to apply.

 

[Midniteoyl]

Primer is not UV resistant..

 

[KYErik]

Thanks guys. He got 85% of the roof covered with primer today. I'll let him know that he will have to use a topcoat of either true paint or the elastomeric coating to make it last.

He had a "drive by" barn painter paint this roof about 3 years ago for $1800. Within one year, 3 inch by 3 inch sheets of paint were flaking of- of course by that time, that guy was long gone never to be seen again...

 

[/pine]

FWIW...When Zinnser's first came out with 1-2-3 Primer I used it on an old asbestos tile house...I had originally intended to overcoat it but it looked very good with just the 1-2-3...I called the number on the can and they told me that it did not need to be over coated...that was in the late 80's and the paint is still holding up with no chalking, flaking or peeling...

Have used 1-2-3 hundreds of times since and have never been disappointed...it's a little hard on brush buildup but worth the effort to deal with it...It can also be tinted to many colors but it is limited on how much pigment they can add...