View Full Version : TR2/3/3A Pixel primmer size

05-22-2018, 12:38 PM
Pixel primmer size, well I put another coat of primmer on the hood because the epoxy was starting to come through and there some scratches. I must have had the pattern set too high or the temp was too low or no reducerů.. Anyways I sanded it off and still had problems with scratches and I cut deep again. So this time I am going to use some reducer and wet sand.

The guy at the paint store suggested wet sanding with 400. My question is should I use only 400 or start with 220 and work down to 400 when wet sanding.

05-22-2018, 02:04 PM
Are you sanding high build primer?

Have you done all your blocking work?

Normally, what I will do after I get all my blocking done (I like using a guide coat for this) down to 180/220 grit I will reprime and then wet sand to either 400 or 600 grit wet. 400 would be the minimum for me.

After this process, the car should be ready for paint.


05-22-2018, 02:42 PM
Yes Tush this is the fourth time on the hood. I have sanded down with blocks and glazed the dings a couple times. This last time the epoxy started shadowing through. Yes this is high build primmer.

Are you suggesting because it has been block to spray some high build and start sanding with 400 and go 600? What size tip? I used a 1.4 with no reducer and now I am thinking 2 coats with reducer and 1.2 tip. I would take a picture, but the area is too fine to see.

05-22-2018, 02:43 PM
In general...

I use dry paper between 30 and 100 grit before the first coat of primer goes down. (Exception to this would be if you prime under your body filler...as then I would still use dry, coarse to cut the filler).

Once the first coat of primer is down, and no more filler is required, then all sanding should be wet with 220 grit. This includes all coats of primer, up until you are happy that it’s time to spray the top paint.

When you have sprayed a coat of primer, and it looks like it is good enough that you may be able to spray the top coat over it, then switch to wet 400grit.

If you are re-spraying over a top coat, with minor runs or flaws...use 400-600 grit wet.

Of course you may always use a higher grit at any stage...but using a lower grit than I recommend will scratch too deeply. Lower grit damages what you have done...higher grit just takes longer to sand.

Oh...last comment and I’ll let you get back to sanding?!?...the reason for the wet is it prevents the paper from fouling and causing deep gouges in your work. 220 paper used dry can leave gouges like 60 grit! Also, the water helps the paper to last a bit longer by keeping it clean.

05-22-2018, 03:52 PM
Hey John thanks for chiming in; yes that is what happened I used some 220 or maybe 120 to start over a ruff second primmer job and it cut too deep in just a few spots, so there are a few scratches after I sanded the whole thing with 400. I thought they would come out, but no. What about reducer? I am outside and it might be 70 degrees and the tip? My guts tell me go to 1.2 from a 1.4 and reduce it because the last time the primmer was too bumpy.

05-22-2018, 05:20 PM
A dash of dishwashing liquid in the sanding water will help keep the grit clear and speed sanding a bit. Follow the package instructions on sanding grit and mixing the paint. They built it and know what it needs.

05-22-2018, 06:43 PM
Are you using a quality 2 pack high build primer.

05-22-2018, 08:57 PM
Not exactly sure what you mean Malbaby. The stuff they sell local is called 4 to1 primmer and you use hardener. I painted the pieces with the 1.2 tip mixed up 6 ounces of paint 1.5 oz reducer 1.5 oz hardener with an outside temp of 74 degrees. I am very happy with the results. The pixels are smaller; the gun sprayed much better and it looks like it should knock down nice by wet sanding. Before, the pixels were large and the sanding was miserable. I might re-due the apron.

05-22-2018, 09:59 PM
I use a 4-1 Matrix branded primer ( 4 parts primer to 1 part primer activator). Matrix doesn't suggest that you should reduce the primer at all. For a high build (or even a medium build primer) a 1.2 tip is very small IMO. I would use between a 1.5-1.8 tip depending on weather I was shooting a medium build or high build primer.

Regardless of the product I am using, what does your Tech sheet say for the primer you are using? It should tell you if you can mix a reducer, what temperature ranges you can spray at, fluid tip size,gun air pressure settings, flash times, number of coats etc etc. It's very important to follow these guidelines especially as a novice like me.

Regardless, you should be commended for taking this on yourself. I'm sure that you will be very happy in the end and proud of your accomplishment.


05-23-2018, 09:20 AM
As I read your posts, I think the "pixels" you are talking about would actually be "stipple". It happens when the primer drys too fast and hits the panel as little chunks rather than a true liquid. It makes the surface look like a large piece of sandpaper. You can actually catch your fingernail on the little pieces of paint on the surface.

There are a couple fixes if you are getting stipple. First, use the largest tip you have. I think I have been using a 2.2mm tip when spraying primer. The larger tip will increase the paint to air ratio coming out of the gun and prevent the paint from drying at the tip. Second, keep the gun relatively close to the panel, with the idea of also reducing the chance the paint has to dry before reaching the panel.

Leaving a 2 part paint in the can too long before spraying (past the "pot life") can also cause stipple. Of course to fix that spray sooner after mixing the paint and hardener together. Remember that pot life is temperature dependent. Most pot life is listed in the directions for 70 degrees, so it will be slightly shorter at 74 degrees.

I would only use reducer if the instructions for your primer give that as an option. Then use the warmest temperature reducer you have (like 85-90 degrees) to slow the drying time of the primer. The idea is to get it to the panel wet enough that it flows into itself before getting tacky.

Because primer is thicker, you have to move the gun slower across the work than with the thinner top coats. This puts more paint down and gives it a better opportunity to flow into itself. The paint screw will also be opened very far for primer...until the paint lays down wet on your panel.

When you get the spraying combination right, the primer should go down almost perfectly smooth...no orange peal bumps (which is the moderate condition of the paint hitting too dry) or stipple (which is the severe condition of the paint hitting the panel very dry).

Well...lotta info. Hope some of it solves your pixels?!?

05-23-2018, 06:09 PM

Good point Tush, and it looks the build sheet says it can thinned and it talks about putting a tint in for different colors. That would be helpful because everything gets very gray.

05-23-2018, 07:24 PM
Reading the spec sheets, it looks like you should mix the 4:1:1. That being 4 parts primer (#21) with 1 part activator (preferably #31, but alternately #32 for slower drying), and 1 part reducer. If you are using #33 activator that will make the stipple problem worse. It looks like your tip size will work with the reduced mix. If they have different options for the reducer, choose the warmer temp. Note your pot life may be as short as 1 hour...so mix right before you spray.

05-24-2018, 02:14 PM
The actual wet sanding is not going to well with 400. There are some very small pits left after the top of the orange peel comes off. I cannot decide to go down deeper with 220 or 320 and to 400 or just stay with the 400 and just go through a lot sand paper. Any suggestions?

05-24-2018, 10:43 PM
Well it looks like working with the 400 will do it. It is going to take some time and a lot of sand paper, but the old Swedish carpenters’ would say, “The fast I go, the further I get behind.”

05-25-2018, 03:13 PM
I find that wrapping the paper around a small piece of foam camp sleeping pad speeds thing along by promoting uniform contact over a larger area.

06-04-2018, 10:34 AM
I like your idea for Wet sanding body panels Bob. I have been using a sponge, but I think it is too soft, maybe, and the flex pads they sell at the body shop store are a little stiff for all curves of a tr3. I looked on line at Eastwood, but nothing jumped out, or I felt the price was too much for a soft pad that I could not touch. I am going up to HD and see what they might have or perhaps purchase a sleeping pad at a store for camping.

06-04-2018, 12:22 PM
I am using 3/4" thick insulating board. The green type which I can form to conform to the concave curves and flat pieces for flat or convex areas.


06-04-2018, 07:31 PM
Where do you get that Dave? Like a building supply store?

06-04-2018, 09:43 PM
One of the big box stores. You may be able to find some in smaller than 4' x 8' sheets. Sometimes they have damaged sheets.

I had some left over from a project.

I am also using some flat melamine shelf boards with a handle attached to hold self adhesive sheets up to 220. Works better than the inline sander at times.