Mp 170 as a sealer

South Tipp

New User
Another question. Does anyone seal MP 282 primer with thinned down MP 170 before urethane top coat? Am I over thinking or does it have merit? Would it help the top coat cover, or a wasted step? Also, congrats to Rod and others on this site. The information provided here is extremely useful. I just read another useful page about the equivalent grits on 3M pads. Very helpful indeed.
 
Thanks for the mention. You shouldn't need to seal the surfacer if you're using compatible products. I've never needed to and always finish off surfacer sanding with 400 grit prior to applying the topcoat directly. As I recall, B-maniac likes to add a coat of epoxy after the surfacer and before the topcoat for the best possible adhesion (i.e. chemical vs. mechanical) of the topcoat, provided the topcoat is applied within the epoxy time window. That's probably true but I've never had an adhesion problem not doing it, so for me it's just an extra step that may be desirable but not really necessary.
 
While I don't use MP170, I do use a sealer coat of my epoxy primer. It gives me that one extra coat in case I missed a spot (like on the engine block behind a fuel line or something). It is also helpful if it has been a few days between the time that I epoxied and the time I want to paint. The sealer will extend your window and promote adhesion. Since it's thinned down, you can throw on a coat of sealer and be topcoating it in 30 minutes or so. You can't do that with a normal coat of epoxy. What I normally do is put on one good coat of epoxy, wait a day or so and apply another. After a day or so, I hit it with a sealer coat and I'm ready to paint it either that day or the next. I say next day because some of my projects are rather large, so one coat start to finish can wipe me out. Something small, you could easily do a sealer coat and paint/clear all in the same day. Below is my 6030 under 1 coat of epoxy. If you can imagine, each coat it is quite a job start to finish. Also if you are wonding what the bits of tape are, it is masking tape. I do this after the 1st coat of epoxy is applied. I do a walk around and look for any places I might have missed and mark them with tape. That way I am sure to get them covered on the 2nd coat. As stated in another post, I use a 2-part epoxy from a company called southernpolyurethanes. I highly recommend it over any ppg or omni products.


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"You can't do that with a normal coat of epoxy." The MP 170 sheet says you can topcoat in 30 minutes. I have done that many times. True that is difficult for me to both prime and topcoat a large tractor in the same day. I usually topcoat the next day. Then I do all the parts I have removed and topcoat the parts I have removed and topcoat them the same day, over a period of days. There is no reason to use a thin coat of epoxy on the chassis, If you have a 3 day window as MP 170 does, and you are not ready to topcoat, you can apply another coat and have another 3 day window, as for as I know, but why? Unless you are very short on time, I would topcoat the chassis (3 coats) instead of applying more epoxy.
 
The P sheets for the old high end DP40 epoxy primer listed a mix ratio for using it as a sealer coat, as I remember 10% maximum and was same reducer we used with Delstar top coats. The newer lead free version DP40LP does not, or did not list same usage. I have not looked recently since I switched over to MP170. While it is not listed on the P-sheet I have reduced MP 170 in a similar manner using MR180 series reducers with great results. You must be careful to not get carried away with the reducer, I never go over 1 part in 10.

The worries with recoating epoxy primers are not in doing it too quick but in waiting too long. In reality there is no idle wait time between priming with 170 and top coat. By the time you get your primer gun rinsed and a batch of top coat mixed and in a gun you can right at applying it. For best adhesion on sheet metal and in hot weather you need to pay very close attention to the P-sheet recoat window however there is no need for panic if the job goes a bit long, meaning a day. For castings you can stretch it out a few days and will have zero problems. Cool weather also allows for stretching it some. In any case if it has set for weeks you dont recoat it without prep work.
 
Read about halfway down the better column and you will see MP170 listed as a sealer.

http://us.ppgrefinish.com/getdoc/d83573a6-f62e-4731-b3f6-cba5f38bb688/Omni-System-Selection-Guide
 

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