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greendane

Paint Removal and High Build Primer

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greendane    8

Hi All,

 

I've got a related thread going on my keel maintenance project (link below) but this is a little more specific. I've combed the forums some but haven't found what I'm looking for. Feel free to point me the right direction if you know of something. 

 

Anyway...the keel-replacement project is growing the more I look at the bottom and on one of the seams on my Core Sound 17, there is enough unevenness to want to fair it out. However, I've trying to avoid using fairing compound because I don't like the idea of sanding down to get to the epoxy because I've found that so far I end up hitting the weave of the fiberglass and I don't want to go all the way to wood, re-epoxy, reglass, and then prime/fair/etc. If there is an easy way to strip it (latex paint) without doing that, I'm all ears. 

 

In lieu of fairing compound, I've been thinking that I could scrub enough of the paint to get down to the primer only and then put high build primer on and go from there. I'm not looking for a perfect finish--or even close. I want to get this boat ready to get back on the water. But the seam is bad enough that I prefer to tackle this much while I have it flipped over. So specifically (though I am open to a whole different approach too)...

 

1) What high-build primer is good for this application? Looking for specific product recommendations. Only want to buy a quart. 

 

2) Are there better ways to remove the paint without harming the weave? (I'd be ok with fairing compound if I could get a good starting point that the compound would stick too.) 

 

I will be repainting the whole bottom with the same paint I already have since it's (a) the same color and (b) the same as what was put on originally. All of course once I am done with fairing this bit out, attaching the keel+skeg and reinforcing the bow for abrasion with Xynole. 

 

Thanks in advance. 

 

-Bryan

 

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PAR    194

Removing paint from inside the weave is best done with a flap wheel, used fairly lightly. Yeah, you'll ding some fibers, but you'll remove most of the primer. Fillers (any type) are best over the sealed substrate, as you know, but if the coats are thin, you can have some primer contamination under the filler (fairing compound) and still have it stick pretty good. You'll make a career out of using high build primers to fair up proud seam tape lines. It's just too much material to apply and smooth out. Additionally, you don't want primer laid down this thick anyway. Use a flap wheel of modest grit, say 60 and get most of the primer off the surface, next hand scruff with a rough Scotch Brite pad to scratch up the remaining primer, the wheel missed, then apply a thin coat of fairing compound (System Three Quikfair) with a plastic applicator. You'll sand 80%- 90% of this off once it's dry, but you'll be fair, which is the point. Now you're ready for paint prep.

   You can also consider chemical strippers, which will remove the primer, without harming the weave. You have to be very careful with these, as you can remove paint in places you'd have prefered not to. Tape off and protect any areas where the slightest hint of some splatter can happen, and rinse the area very well after the deed is done. Then you can scuff up the now primer free areas, in prep for fairing compound.

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greendane    8

Well...I almost deleted this post as I, as I often do, grew pretty impatient with my project. I had a stripping disk (like a heavy duty Scotch Brite pad) for my drill motor, so I went to work as light as I could. I was going to only strip about a 10 inch wide section around the seam. The first section went well but when I put a straight edge down, I could see that the dip I am trying to fill is almost a quarter inch deep and a decent fairing angle will mean filling in about 10-14 inches wide to make it gradual anyway. (A career out of using high build primer is right!). So, I stripped a lot more off but as I got going, I noticed that the epoxy was really thin in places toward the front and I went into wood without even trying. So I stripped from the seam all the way forward to the bow. I'm going to put a two coats of epoxy, followed by Xynole over a much larger section (I have two yards anyway and was originally only going to do about 10 inches either side of the centerline). Now that I'm down to epoxy, I can use the fairing compound and get at least this part faired properly. 

 

Thanks Par. I'm sure I haven't seen the end of stripping. I'll get a flap wheel and hopefully do a less aggressive job of it next time. By the time I got toward the end, the pad was "dull" enough that it actually worked pretty well. 

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PAR    194

If you tear up a good portion of the seam fabric, you shouldn't use Xynole to "tape" it up again. This stuff has no structural value, it just improves abrasion resistance. Replace the ground through tape with more cloth, fair the area, then apply the Xynole if you want the extra abrasion resistance.

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greendane    8

I was wondering about that. The seam is good. There was enough epoxy on it to not go through to the weave. The parts that sanded through were where the glass was on the hull. For these small parts, is it necessary to re-glass them (none bigger than a quarter)? Or will a couple of coats of epoxy together with the xynole be okay? 

 

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PAR    194

Xynole will take up a fair bit of vertical space, so you have to decide if it's worth the trouble or if it'll just add to your fairing chores. For small areas like you describe, I don't bother, just another wetout of neat goo, then prep for paint.

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greendane    8

Just re-inspected. There's more compromised than I thought. So I plan on laying a second layer of glass down and Xynole over it but smaller where I anticipate a bit more wear. How long do I need to wait to put that Xynole over the fill layer of epoxy?

 

And related--for painting epoxy--what primer should I use and prep should I do (including how long to wait. I assume a couple of weeks until it's all fully cured?)

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PAR    194

As soon as the goo is just barely tacky, toss on the Xynole. In fact I wouldn't bother, knowing the amount of goo the xynole needs to wetout, it'll serve to seal the filler well enough. 

   Primers can be about anything you want, though stick with acrylic or epoxy primers, so you don't have a compatibility issue, like you can with some alkyds. Let the last fabric coat cure for 3 days and go after "toothing" for the primer. Sand and smooth the primer once dry, blocking, fine tuning the fairing, smoothing, etc. as you go. Let the primer dry a week before top coating, so it can shrink up. If you're good, a couple of coats of primer will do, but if you're like most, you'll sand through at least one coat of primer as you find areas that need more attention, so plan on a final coat of primer to seal everything down, before the finish coat. I can never seem to get away with just two coats of primer. As soon as I start blocking it smooth, I always find low spots that need to be bulked up a touch, so I'll spot prime and try to fill these in with paint, rather than more filler. It all depends on how anal you are.

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PAR    194

Toothing is a good scratch, what sandpaper leaves behind. It provides a mechanical "keying" to the surfaces, literally something for the paint to get a grip on.

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Hirilonde    174

Coatings, be it paint, or a resin like epoxy bond to things one of two ways.  Mechanical, where they grip an already solid surface physically.  This works best when given some tooth as in the scratched surface Paul mentions.  Chemical, where the previous coat on the surface has not yet cured and the new coat can still bond chemically to it.  Chemical is best, but if well scratched and cleaned a good physical bond can be obtained.  This is why I like to try to get as many chemical bonds as my schedule allows.  It saves on sanding and other prep work.

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greendane    8

Question: since this is more of a repaint than a new job, and about 80% still has the old paint on it (see "bottom april 12" pic attached) what should I do to prep? (Keeping in mind, as I said earlier--I'm done with stripping except in spot areas as needed). I've gone over it a few times with a scotch brite pad (in a bucket of water, cleaning it out as I go), and planned to do so one more time. As I am going, there are a few issues I am not sure how to address exactly:

 

1) uneven paint layers. See "paint 1" and "paint 2" below. Can I (after a bit of scratching) go over this with primer to fill in some of the strokes, scratches, uneven spots? Is it ok to have the base primer, then the paint, then another layer of primer and then another layer of paint? 

 

2) On the transitions from epoxy (where I've stripped down) to this paint job, other than giving the epoxy and fairing material a good scratch, anything else I should be aware of? I'm assuming I'll need to do a little fairing with primer along the "coastline" (you have to admit it kind of looks like a map). 

 

 

paint 2.jpg

paint 1.jpg

bottom april 12.jpg

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PAR    194

Primer the whole set of areas that will need new paint and hit it with a long board to see where you stand. From your pictures, you'll never fill the paint chip areas with primer, without many coats and blocking sessions. Essentially it's a decision about how fair and smooth you'll willing to accept. If it was me, I'd wholesale remove the obvious areas, trying to just get down to the epoxy, but not breaking through into raw wood. Next would be some light weight filler and continued longboard work. Eventually, getting smooth transitions between the old and new work, that can tolerate being filled with a high build product. A quick knock down of the primer in prep for finish coats.

   I know you're pretty much over this sanding thing. You wouldn't be the first, by a long shot to just lay down a  3 or 4 layers of primer, blocking it down as you go, just to avoid more grinding and fillers. This works and it doesn't appear the areas are too thick for this technique, it'll just take more sanding sessions, though sanding primer is a lot easier than sanding fillers. It's up to you. This is a not well seen location on the boat, so not everyone will know and it's not going to affect performance in any regard, so draw a line in the sand and we'll stick with whatever decision you make, unless asked by your better half, at which point we'll happily lie about not having a clue, to what they might be referring . . .

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greendane    8

Thanks PAR. The better half would have had me done with this already. Onward and upward...

 

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greendane    8

Okay--last (4th!) layer of filler is curing. I'll smooth it out next. Looking for confirmation/guidance on next steps order/timing:

 

1) I assume I don't have to wait to apply some epoxy over these faired areas (the datasheet doesn't say)

 

2) I plan on two coats of epoxy to seal it, seems like I read that somewhere

 

3) Wait three days for epoxy to cure before prepping for primer

 

4) Do the primer work, paint it on, sanding, repeat

 

5) Wait a week for the primer to set before top coat

 

6) Start on the top coat. 

 

7) Given this is latex, how long should I wait for good cure on the paint before putting on the trailer and sailing?

 

Thanks in advance!

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JPower210    4

Greendane-  in case it has not been mentioned, be sure to scrub any new epoxy, between coats if they cured, or the final coat if you put the coats on green, with a scotch brite pad and some warm water to get rid of any blush.

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greendane    8

Thanks @JPower210 . I'll definitely watch but the epoxy I have hasn't blushed at all in many coats. I have washed it a couple of times but I've been surprised how no blush has showed. Here is the stuff I used. 

 

http://www.duckworksbbs.com/supplies/epoxy/marinepoxy/index.htm

 

My main concern is getting these last coats on without sagging or runs. PAR recommended some silica for the vertical stuff. I'm thinking I'll maybe use a spreader instead of a roller and go thin but maybe three coats. Thoughts?

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PAR    194

Silica is very difficult to and is generally used to control viscosity. To fill a fabric weave, microballons, quartz pheres, etc. are common stuff to use,plus some silica to make a non-sagging mix.

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greendane    8

Soooo...chalk this one up to right tool for the job. I've been trying to keep the buying of tools to a minimum (though there is something inside that always wants more tools). I finally bought a random orbital sander. "What!?" you might say. "Why haven't you owned one from their invention?" I don't have a good answer. I bought the cheap $40 Ryobi. That thing has done a great job of knocking down the paint to the primer layer and I expanded the section on the bow where I'll be putting epoxy and I was able to sand down without hitting the weave of the glass, unlike with my previous methods. What would have taken me the better part of 8 hours I knocked out in 2. It's not perfect--I wasn't going for that. I wanted to get down to a good layer that didn't flake and still provided good tooth for the primer. This did that well and I felt like I had control of the machine. 

 

One "tool" that I should buy but managed to improvise is a good scraper. I'm not afraid to sharpen my block plane, so I took the blade out of it and began scraping paint off it it helped a lot. I used it both at a low angle and also almost perpendicular. The weaker layers flaked off easily and with the perpendicular approach, I was able to level out the thick layers (and eliminate some of the brush strokes. 

 

I know I'm going to find a million imperfections when I get the primer down, but I already feel better about the whole endeavor. 

 

Here's a question however. Any tips for masking? I still have to put a couple coats of epoxy down but want to mask the painted sections. 

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