# alaphatic or dtm on ext. steel



## donnaepaint (Apr 1, 2010)

Does anyone have info on longevity using DTM compared to alaphatic acrylic urethane on steel structures. Project is exterior, pre-painted(latex) canopy with rusting steel supports and a T&G wood overhang. The environment is coastal w/ wind driven rain, salt air and fog at times.


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## SWGuy (Jun 26, 2009)

Are painting the overhang and canopy, or just the structural steel?


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## donnaepaint (Apr 1, 2010)

canopy also. It has dryrot issues due to some roof failure to be addressed by carpenter. Its already coated w/ s.g latex. Its a no-brainer. Longevity anyone?


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## SWGuy (Jun 26, 2009)

donnaepaint said:


> canopy also. It has dryrot issues due to some roof failure to be addressed by carpenter. Its already coated w/ s.g latex. Its a no-brainer. Longevity anyone?


Sorry for trying to make sure I understand your question. 


Salt Fog resistance
Method: ASTM B117

Aliphatic acrylic polyurethane- 7000 hours
DTM acrylic - 500 hours. 
So, I would say that the aliphatic would be about 14 times better. 

Does that answer your longevity question?


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## johnpaint (Sep 20, 2008)

SWGuy said:


> Sorry for trying to make sure I understand your question.
> 
> 
> Salt Fog resistance
> ...


What about uv resistance? I would think the dtm would be better.


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## SWGuy (Jun 26, 2009)

Polyurethanes will have better color and gloss retention than a dtm. 

I assume he is talking about an acrylic dtm.


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## donnaepaint (Apr 1, 2010)

No biggie SW, I appriciate the responses. I didnt mention that the steel is going white. Ive used dtm, latex and oil, and have used alaphatic on storage tanks. dtm holds its color better yet alaphatic is more durable and more chemical resistant but it seems to slightly discolor over time. Im interested in your guys opinion. What is "salt frog resistance"? Ive never heard of it. Thank you for the responses.


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## Wolverine (Apr 17, 2007)

Hi All,

The problem with the question is that it is comparing a 'chemistry' of paint to a 'charactaristic' of paint. DTM is not a paint chemistry but only descibes a paint that will work *D*irect *T*o *M*etal. Now, some DTMs are acrylic but there are plenty of other chemistries that are DTM. 

Now, if you are comparing an Aliphatic Acrylic Urethane to a DTM 100% Acrylic then about the only category the Acrylic would win should be cost. Now, if you want something that would be even better then you might look to an Aliphatic Polyester Urethane. 

Last, even then it's difficult to generalize. There are some Aliphatic Acrylic Urethanes that are very high performing for the money. They will rarely come close to a good quality Aliphatic Polyester Urethane (more $$$) in most cases. BUT... it is ALWAYS formulation dependent.


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