Is 2k Primer moisture and waterproof?

MJM

MJM

Promoted Users
I'm still trying to understand what products can and can't do, so I can use them under the conditions I have to work with. As an example, I recently learn that polyester primer is not moisture or waterproof with the exception of Clausen Rust Defender Polyester Primer.

With that said, is 2k primer moisture and waterproof?
 
2K urethane primer which is what I'm assuming you mean, is not waterproof. If you have epoxy as your undercoat it's not an issue. Where it becomes an issue is when applied over bare metal or filler over bare metal. Then sitting for any length of time. It can and will absorb moisture from the atmosphere.
 
the only truly waterproof paint or primer i am aware of, at least in autobody, is epoxy. polyester for water absorption is along the lines of 2k urethane. its not quite the sponge that body filler is but not 100% waterproof either.
 
Chris_Hamilton said:
2K urethane primer which is what I'm assuming you mean, is not waterproof. If you have epoxy as your undercoat it's not an issue. Where it becomes an issue is when applied over bare metal or filler over bare metal. Then sitting for any length of time. It can and will absorb moisture from the atmosphere.
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Since I didn't know 2k is urethane primer, let me ask a couple more questions about 2k urethane primer.

1. Is SPI 2k regular build and SPI 2k high build, urethane primer? The Tech Manual doesn't specify. It only says those two 2k primers can be reduced with SPI urethane reducer.

2. Why can 2k urethane primer be wet sanded when it is not waterproof?

3. Since the 2k urethane primer will absorb moisture from the atmosphere over time, shouldn't it absorb water from wet sanding?

These are serious questions to me. The reason I decided to use Clausen Rust Defender was its moisture and waterproof abilities. This allows me to sand the product this winter, and let it sit until next spring before final paint and not worry about moisture intrusion.

I haven't decided yet whether to spray two coats of epoxy over the Clausen polyester, then finish sand to 400, then epoxy seal before bc/cc, or..........finish sand the Clausen polyester to 400, then seal with epoxy before bc/cc
 
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not to answer for chris but he did mention if u have epoxy as your undercoat, then the moisture wont get passed the the epoxy to the metal and create an issue.

as far as wet sanding 2k urethane, ive wondered this myself. but it seems common practice.

also , consider that collision work and restoration work are 2 different things.
 
MJM said:
Since I didn't know 2k is urethane primer, let me ask a couple more questions about 2k urethane primer.

1. Is SPI 2k regular build and SPI 2k high build, urethane primer? The Tech Manual doesn't specify. It only says those two 2k primers can be reduced with SPI urethane reducer.

2. Why can 2k urethane primer be wet sanded when it is not waterproof?

3. Since the 2k urethane primer will absorb moisture from the atmosphere over time, shouldn't it absorb water from wet sanding?

These are serious questions to me. The reason I decided to use Clausen Rust Defender was its moisture and waterproof abilities. This allows me to sand the product this winter, and let it sit until next spring before final paint and not worry about moisture intrusion.

I haven't decided yet whether to spray two coats of epoxy over the Clausen polyester, then finish sand to 400, then epoxy seal before bc/cc, or..........finish sand the Clausen polyester to 400, then seal with epoxy before bc/cc
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1. Yes
2. Because the two aren't necessarily related. Not being a smart ass but that's the only way I know to answer it.
3. Yes it probably does. To what extent? IDK.

I would take the moisture waterproof claims of Clausen with a grain of salt as in general poly primers are as porous or more so than urethanes.

If you have epoxy as your groundcoat then there is no real need to worry about 2K or poly over it absorbing moisture. Any that creeps in from wet sanding will be gone when it dries. Any moisture /humidity from sitting is not an issue either as long as you have epoxy as your undercoat/groundcoat.
 
Think of 2K urethanes as somewhat resistant to water short term, but over time can absorb moisture from the atmosphere if left sitting without topcoating. If epoxy was used first it's not a problem.
 
Chris_Hamilton said:
Think of 2K urethanes as somewhat resistant to water short term, but over time can absorb moisture from the atmosphere if left sitting without topcoating. If epoxy was used first it's not a problem.
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That is why you often see primered panels left outside (for some time) blistering with rust spots. Was the same with the old lacquer primer also.
Lot of folks still use 2K or lacquer directly on raw steel, and are not aware of the benefits of epoxy.
 
2. Why can 2k urethane primer be wet sanded when it is not waterproof?
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Think of it like (sort-of) wood, porous and will absorb water but will also give it up.
When you wet sand urethane primer you give it plenty of time to evaporate after washing, wipe drying and cleaning with W&GR.
All that said, personally I haven't used much 2K lately on the few jobs I do and used only epoxy for primer and surfacing.
 
i learned the hard way that 2k primer was not what i thought it was.
question, other than filling/leveling, is there any other reason to use any thing other than epoxy? you see where im going here, if its not going to be a restoration or it doesn't matter if its not that smooth.....
im thinking i can get away with just epoxy.........i may change my mind though once i see it?
 
Chris_Hamilton said:
1. Yes
2. Because the two aren't necessarily related. Not being a smart ass but that's the only way I know to answer it.
3. Yes it probably does. To what extent? IDK.

I would take the moisture waterproof claims of Clausen with a grain of salt as in general poly primers are as porous or more so than urethanes.

If you have epoxy as your groundcoat then there is no real need to worry about 2K or poly over it absorbing moisture. Any that creeps in from wet sanding will be gone when it dries. Any moisture /humidity from sitting is not an issue either as long as you have epoxy as your undercoat/groundcoat.
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Thanks, I have a better understanding now of all primers, epoxy, 2k urethane and polyester with regards to moisture and water intrusion.
 
RenewAP said:
1K & 2K simply refer to 1 component (no activator) & 2 component (activated) There are a wide range of products and qualities of each product in those base categories.
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Colloquially when somebody says “2k primer” they are referring to a high build urethane primer and anybody who has any familiarity with automotive paint chemicals knows this too. Even the SPI urethane primers are called “2k” even though none of their other activated products are called “2k.”
 
MJM said:
Since I didn't know 2k is urethane primer, let me ask a couple more questions about 2k urethane primer.

1. Is SPI 2k regular build and SPI 2k high build, urethane primer? The Tech Manual doesn't specify. It only says those two 2k primers can be reduced with SPI urethane reducer.

2. Why can 2k urethane primer be wet sanded when it is not waterproof?

3. Since the 2k urethane primer will absorb moisture from the atmosphere over time, shouldn't it absorb water from wet sanding?

These are serious questions to me. The reason I decided to use Clausen Rust Defender was its moisture and waterproof abilities. This allows me to sand the product this winter, and let it sit until next spring before final paint and not worry about moisture intrusion.

I haven't decided yet whether to spray two coats of epoxy over the Clausen polyester, then finish sand to 400, then epoxy seal before bc/cc, or..........finish sand the Clausen polyester to 400, then seal with epoxy before bc/cc
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I have parts or entire cars sitting inside in sanded 2k for years. Poly primer is a pain in the ass. I only use it if you need excessive mil build to straighten. It kicks faster, sometimes requires extra large tip size, more difficult to clean up, more expensive, harder to sand than 2k, and I hate those stupid hardener tubes. If you're putting epoxy down first there's no issue using a 2k urethane, sanding, and waiting till spring. I can't imagine trying to sand poly with 400. It will load up the sandpaper so fast. That is why any time I'm finished with a blocking step, I spray a final coat of 2k to fill in scratches, and wet sand the 2k with 400.

Otherwise you're left with having to sand a lot more to cancel out the 220 scratches with 400. You think you're done and you still see 220 scratches. Once my 2k is wet sanded with 400, I shoot 25% reduced epoxy to seal and it's ready for paint.

Handy trick originally learned from Barry years ago.
 
Lizer said:
I have parts or entire cars sitting inside in sanded 2k for years. Poly primer is a pain in the ass. I only use it if you need excessive mil build to straighten. It kicks faster, sometimes requires extra large tip size, more difficult to clean up, more expensive, harder to sand than 2k, and I hate those stupid hardener tubes. If you're putting epoxy down first there's no issue using a 2k urethane, sanding, and waiting till spring. I can't imagine trying to sand poly with 400. It will load up the sandpaper so fast. That is why any time I'm finished with a blocking step, I spray a final coat of 2k to fill in scratches, and wet sand the 2k with 400.

Otherwise you're left with having to sand a lot more to cancel out the 220 scratches with 400. You think you're done and you still see 220 scratches. Once my 2k is wet sanded with 400, I shoot 25% reduced epoxy to seal and it's ready for paint.

Handy trick originally learned from Barry years ago.
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This is a great post but one I'd like just a little clarification on, please! The weather is cooling and I'd love to get my car ready for painting in the Spring. Right now, car has 2 coats of SPI epoxy put on it about four years ago. Thought is to DA the car with 180 and spray 1-2 coats of SPI epoxy on it followed by 2-3 coats of SPI regular high build within the 7 day window. Can I get agreement here?

Now for clarification...... you're not saying you block to 400, seal, then apply BC/CC months out are you? Likely, you block to 400 and seal when you're ready to apply BC/CC, correct?

Lastly, is 400 good enough for metallics when utilizing a sealer? I've read 400 for non metallics and 600 for metallics, however if using a sealer, 400 is fine???
 
Don't DA it, block it then hand sand and red pad all the hard to reach areas. Never let material build go to waste on something that's supposed to be straight.

Sealer can fill 400 for a metallic, but imo it's not a sure bet. It depends on the thickness of the sealer and the size of the metallic. Normally it's a yes, but for example a 1:1:1 epoxy put too thin, then followed by a small bright metallic might show something in the finish. You have to be careful.
 
Machspeed said:
This is a great post but one I'd like just a little clarification on, please! The weather is cooling and I'd love to get my car ready for painting in the Spring. Right now, car has 2 coats of SPI epoxy put on it about four years ago. Thought is to DA the car with 180 and spray 1-2 coats of SPI epoxy on it followed by 2-3 coats of SPI regular high build within the 7 day window. Can I get agreement here?

Now for clarification...... you're not saying you block to 400, seal, then apply BC/CC months out are you? Likely, you block to 400 and seal when you're ready to apply BC/CC, correct?

Lastly, is 400 good enough for metallics when utilizing a sealer? I've read 400 for non metallics and 600 for metallics, however if using a sealer, 400 is fine???
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You’re fine to sand your old epoxy 180 and then spray more. Only sand it to rough it up, so use a block.

I don’t block to 400, I block to 220. I wet sand the high build primer with 400. It can sit like this for awhile but should scuff with a gray scuff pad again before epoxy. Epoxy sealer reduced 25% has no problems filling in the 400.
 
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