04 Lexus GS300 paint job - strip to bare metal or stop sandi

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PostPosted: Tue May 10, 2022 7:13 pm
Hi everyone,

First of all excited to be here as I've already learnt so much by searching through existing posts. Seems like an awesome community and glad to be a part of it!

I have been doing a lot of research over the last two months, and am getting ready to do a base coat/clear coat DIY paintjob on my 2004 Lexus GS300. I live in AZ and it has 215000 mi on it so no surprise but the paint is pretty worn on the roof/hood area with significant clear coat peel.

Here is my current situation - I have found a local paint shop which rents out their booth to the tune of 150 bucks a day. They have a huge 80 gal Campbell Hausfeld compressor so air delivery is sorted. I plan to finish trim removal and sanding the car before I drive it to the shop, and at the shop, clean the surface and apply masking tape. The kind of paint I will be using is:

1. Kirker Low VOC 2k Urethane primer
2. Kirker Low VOC Urethane Basecoat (Dark Jade metallic)
3. Kirker Low VOC Urethane Clear coat

with a TCP global HVLP paint gun (https://www.amazon.com/TCP-Global-Brand ... B001N1E9Y8).

So basically I am going to spread the sanding over two weeks or so. Here is my quandary:

How deep do I sand when prepping the car??

If I sand down to bare metal, I cannot protect the car as there is a significant time difference between me finishing sanding and driving it to the paint booth to paint it. Would this be enough time to rust the metal and make primer application difficult?

If I don't sand down to bare metal, where do I stop sanding? At the primer? Of course this begs the question as to how good the existing paint is. AFAIK the paint on the car is oem and it hasn't been resprayed anywhere. From my research I have read that generally factory finishes are good and can be painted over.

Thank you in advance!



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PostPosted: Wed May 11, 2022 12:36 am
I'll probably get flamed for saying this... But the factory primer is excellent. It would be a shame to take it down to the metal.

I'd sand it down to the primer then a sealer coat (and a bit of high build primer for the rough bits) and then what you have planned.

Good score re the rented paint booth!

I'm sure what ever you decide will work out well.



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PostPosted: Wed May 11, 2022 1:24 am
Makes sense! That’s what I thought too, as it’s not a super old paint job. Thank you for the pointer!

A few rookie questions but from my research and watching a lot of videos, I compiled the following steps that I plan to take while prepping the car:

1. Start block sanding with 180 grit.

2. Then move to 240 grit.

3. Then move to 320 grit.

4. Then move to 400 grit wet sand.

5. wash the car, remove all oils, solvents etc. After this apply primer.
6. now apply basecoat.

Do you think following this procedure will ensure that I get the best available surface for the new primer, base and clear to stick to? If you think there are any steps I need to insert/delete please let me know!

And my second question is: can I also use the same procedure above for plastic parts (front/rear bumper, side skirts) considering plastic is way more flexible?

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PostPosted: Wed May 11, 2022 4:48 am
It's the same old question of how far do you sand, but the answer is always the same: all the way.

While it's true that the factory primers are excellent these days, nobody can sand evenly enough to leave an even coating on the metal. You'll have dips and gouges, no matter how careful you are, and they will show up in your final coats. Not to mention that exposed edges where feathered, are prime spots for reactions with the coats you are going to apply.

The other thing is that once the clear has degraded, the paint underneath, which needed the clear to protect it, has been compromised and could lead to later failure.

Take the paint off down to the metal. then apply a coat, or three, of epoxy primer. This will protect the metal and you can block sand it if necessary, to flatten. If the surface is good enough then you won't need a high build primer at all and you can just do top coats in the booth, meaning that you should be able to complete that process in a single day. That will save you at least $150 of booth hire.

The epoxy you should be able to do at home, even outside if you have to, since it does not contain isocyanates and doesn't present the same health risks as a 2K paint. Still need a mask, though. You can block it down to level, fix any problems and finish with P800 before you take the car to the booth, leaving just a final wash and dry before painting.

Get yourself a 5" angle grinder and some poly paint stripping discs. I wouldn't give an apprentice the job of block sanding clear off with P180, even as a joke. Seriously. Today I bought a new 125mm Makita grinder to replace one that finally died after about 10 years of stripping paint. Cost me $339 but my next job is to take 55 years of paint and who knows what else off a 1965 VW Beetle and I want to finish the restoration within about 3 months. Get a corded grinder and make sure it has variable speed. You don't want, or need, those discs spinning at 12,000rpm and building up heat to warp the metal.

I finish to P240 on a DA before primer. Even P180 is ok if it's going to be a build primer. P400 is way too fine. P80 on the metal, under epoxy is good.

For plastics, strip with P180 on a DA, with an interface pad. Never use anything coarser or you'll tear the surface of the plastic instead of sanding it. Then prime and block to P800 wet or P600 dry. Again, not coarser or you'll see he scratches through the metallic.
Chris



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PostPosted: Wed May 11, 2022 4:07 pm
Chris,

Thank you so so much for your explanation. You have convinced me to go bare metal all the way!! I will add epoxy primer to my list of supplies.

I have a LOT of questions but I will try and space them out. If they are dumb questions I do apologize in advance!!

1. I haven't used poly stripping disks before - is this a good example?

https://www.homedepot.com/p/Stark-4-5-i ... 73f2c66c00

2. My major issue is that I do not have an air compressor to shoot epoxy primer at home as I was planning to use the one at the shop. I am using HVLP guns so unfortunately buying a large air compressor to power the guns is not within my budget.

I did some research and it looks like epoxy takes two days to cure enough to sand. Is there any way to apply the epoxy without a sprayer at home? If not, I will have to bite the bullet and pay 500 for renting the paint booth Mon-Fri. Doable, but it would be nice to avoid that.

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PostPosted: Wed May 11, 2022 5:00 pm
Your link to the stripping discs doesn't work, and Home Depot insists I'm in Guam anyway. :knockout:

These are the ones I bought yesterday. Usually get the poly ones but if the ceramic ones last as long as they claim then they'll work out better value.
https://www.ebay.com.au/itm/124033385681?var=424865235919

Not having a compressor does make it a little more difficult to spray on the epoxy. Can you hire one? Might be cheaper than hiring the booth.

HVLP guns. :rolleyes: Why do people buy them? They need up to 50% more air volume and have up to 20% less transfer efficiency than an RP gun.
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PostPosted: Wed May 11, 2022 5:28 pm
Ah my bad! Thank you for the link, I will try to get something as close as possible to it.


Unfortunately I don't think so, my garage is too small and my apartment complex wouldn't be very happy if I tried painting outside.

So some good news (hopefully?) on the epoxy - I contacted the paint manufacturer and got the data sheets for the epoxy and primer I plan to use. Here is what the data sheet for the epoxy primer says:

"Allow a minimum of 30 minutes for ENDURO PRIME to flash before
topcoating. After applying two coats, wait a minimum of 45-60
minutes before topcoating.
After sufficient flash, ENDURO PRIME may be topcoated for
approximately five (5) days with no sanding required. After
approximately five days, epoxy should be scuff sanded before topcoat
application.
ENDURO PRIME may be wet sanded the day after application, or dry
after two to three days."

So from the first line, it looks like I can wait for perhaps an hour and apply the primer without sanding the epoxy.

Would you recommend this?

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PostPosted: Thu May 12, 2022 2:33 am
Sure. That's the beauty of epoxy, that it can be done wet on wet. Primer over flashed epoxy is fine.

But what you haven't allowed for is dust and dirt nibs that might need to be removed, runs that might need to be fixed and dents that need to be repaired and/or filled. If you use the fill primer then it will definitely need to be sanded flat and any peel taken out.
Chris



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PostPosted: Thu May 12, 2022 12:12 pm
Gotcha, makes sense. I have a question about the filler primer which I have described below.

Also just to clarify - all dented body panels on the car will be replaced with straight panels before the paint job. I have a dented fender, rear driver door and rear bumper which are very easy to replace and I'd rather do that than body work. So going into the paint job - absolutely no body work required.

So here is a hypothetical scenario:

I drive into the booth with my car stripped to bare metal, clean the car and apply 2 coats of the abovementioned epoxy. Owing to my time constraints, I cannot wait 2 days to dry sand the epoxy before applying the primer. So I wait for 60 minutes as per the technical data sheet and apply 2 coats of urethane primer surface that Kirker said I can apply over the epoxy primer.

Here is an excerpt from the technical data sheet for the 2k urethane primer surfacer (it is called 'PERFECT PRIME':

"Allow a minimum of 30 minutes for PERFECT PRIME to dry before
topcoating.
After sufficient flash, PERFECT PRIME may be topcoated for up to 18
hours with no sanding required. After 18 hours, scuff sand primer
surfacer before topcoat application to ensure sufficient adhesion.
PERFECT PRIME should dry dust free within 10 minutes and may be
wet sanded after approximately 2-4 hours. Wait 3-4 hours before
attempting to sand dry. ULTRA-GLO acrylic urethane and ACRYLGLO acrylic enamel single-stage topcoats may all be applied directly
over PERFECT-PRIME in a “wet on wet” application after sufficient
flash time has passed. "

So based on this data, I then proceed to wait 2 hours and then wet sand with a 400 grit block sander to get a nice surface for the basecoat to bite on. Then, apply basecoat.

So basically I am trying to bypass having to wait 2 days to sand the epoxy primer, by instead sanding the primer surfacer on top of that.

Do you think this is a good idea? Any drawbacks?

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PostPosted: Thu May 12, 2022 3:07 pm
Tuhrak wrote:So going into the paint job - absolutely no body work required.


I'd bet money that I could find damage that required at least minor body work on a car of that age.

Otherwise, your plan is sound, except for:

Tuhrak wrote:then wet sand with a 400 grit block sander to get a nice surface for the basecoat to bite on.


P400 wet is way too coarse to paint over with a metallic. As I said earlier, the scratches will show through. For metallic, P800 wet or P600 dry.
Chris
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