Urethane Waves?

O

OMC

Hello Everyone,

This is my first post on the site, and Barry and the team have been great with text questions, but I want to throw this out and see if:
1. It is bad enough to worry about?
2. How in the heck to fix it?

Here is he run down of what has happened so far. 63 Thunderbird stripped to bare metal.
Coated with SPI Epoxy Primer, 3 solid wet coats.
Small amounts of body filler (Evercoat Quantum one) block sanded.
Sealed again with Epoxy Primer
Countless numbers of coats of SPI 2K Regular Build Primer
Block sanded, block sanded, and block sanded countless numbers of times with 120, 220, 320, with soft sanders and 600 by machine (guide coat used in every grit), need to go to 800 before color. One gallon already on and mostly on the floor.

98 % of the body looks great when I wet sand and use 6 foot fluorescent lights. As with Newtons law, a spot always shows up that I am not happy with. The real issue is what is happening in the pictures below. The guide coat never shows a low spot and I have tried a 1 foot board and a 2 foot board. Any help is greatly appreciated, I just know that I have sprayed and sanded this spot 4 times in the last 2 days and it is not getting any better. The real problem area is in the # 2 pic, just below the body line.
 

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OMC said:
Block sanded, block sanded, and block sanded countless numbers of times with 120, 220, 320, with soft sanders and 600 by machine (guide coat used in every grit).
Click to expand...

What kind of soft sanders are you using specifically? When you block sand for the most part you want something that doesn't move much, is fairly rigid and cuts down the high spots to level them with the low, if a block is too soft it can just follow everything and you dont really accomplish flattening the panel. You think you do as all your guide coat is gone, but all you've done is sand off the guide coat giving you a false reading.
 
Sprint,
I am using the Style Line Soft Sanders brand, I cannot use a more rigid board because of where it lays on the body line, the spots are right at the curve. I just switched back to the 2 foot board again and used a super light touch and switching out paper like crazy and 2 hours later they are now out. I would sand till guide coat was gone, then reapply guide coat and tiny little spots would pop up. Thank you for the input.
 
Last edited by a moderator:
when your paper get loose it with ride the waves. keep it tight and plane the panel . do not go back and forth . tacky spray helps with this.
 
Given the contour of that area, I would be inclined to use something round and sand in crosshatch diagonally right up to the body line if that makes sense. I keep various size diameter and length pieces of PVC laying around for these type of areas. For pressure, as a rule if you hold the block in you fingers and not your hands, you'll be forced to sand very lightly...
 
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Lots of things I could say here's what comes to mind right now. First, and especially if you are a novice you should do all but a final sand dry. You said guide coat wasn't helping, that's because you are using too soft a block. Guide coat only helps if you are not using such a soft block that it takes it off. All your blocking should be done dry. When you get it straight dry, then a final wet with 400-600 is all you need to do. Secondly, use the right block for the situation. Using anything soft is not going to work. Flexible is good, soft is not. Use the most rigid thing you can get away with. Dura blocks work well, sometimes you gotta make your own. For that reverse like Gato said a round piece of pvc would be a good choice. Length of your block matters, especially if you are a novice. The longer the better. Learn to cross hatch when you sand. Meaning draw a imaginary horizontal line through the panel and sand at 45 degrees to that line. Go in one direction across the panel then back the other way opposite 45 degrees. Sand evenly across a panel, do one panel at a time. Don;t sand one area more than any other.
Most importantly learn to use your hand to find any waves. Your hand (not your fingers but your whole hand) is extremely sensistive and when you run it back and forth across a panel you can feel any highs and lows. Once you develop that you don't need to wet it to find high or lows. Closing your eyes while you do it helps, as does using a cloth or paper towel between your hand and the panel.
 
Chris_Hamilton said:
Lots of things I could say here's what comes to mind right now. First, and especially if you are a novice you should do all but a final sand dry. You said guide coat wasn't helping, that's because you are using too soft a block. Guide coat only helps if you are not using such a soft block that it takes it off. All your blocking should be done dry. When you get it straight dry, then a final wet with 400-600 is all you need to do. Secondly, use the right block for the situation. Using anything soft is not going to work. Flexible is good, soft is not. Use the most rigid thing you can get away with. Dura blocks work well, sometimes you gotta make your own. For that reverse like Gato said a round piece of pvc would be a good choice. Length of your block matters, especially if you are a novice. The longer the better. Learn to cross hatch when you sand. Meaning draw a imaginary horizontal line through the panel and sand at 45 degrees to that line. Go in one direction across the panel then back the other way opposite 45 degrees. Sand evenly across a panel, do one panel at a time. Don;t sand one area more than any other.
Most importantly learn to use your hand to find any waves. Your hand (not your fingers but your whole hand) is extremely sensistive and when you run it back and forth across a panel you can feel any highs and lows. Once you develop that you don't need to wet it to find high or lows. Closing your eyes while you do it helps, as does using a cloth or paper towel between your hand and the panel.
Click to expand...
 
Chris,
I am not a professional and not a novice, I always look to learn something. The block I have is flexible but I do not believe too soft (I could be wrong). Everything is dry sanded and the guide coat was working and I could not feel the waves but noticed it when I hit it with the final 600 then 800 for paint (using Acapulco Blue metallic in Axalta Chromapremier). The dura block worked great on the flats and the round was too small. I have blocks in all kind of lengths from 6 inches to 2 feet. Always cross hatching except where it is not possible for it to happen. All sections are done at one time and done with the same amount of strokes.Using fingers only and s very light touch has helped get most all out, I am doing a final spray right now and will sand again tomorrow.
 
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