I'm continuing with this thread since multiple searches both general (using Google), under Repair and Improvement, and in the thread Basic Painting Questions didn't turn up the information I am seeking ... at least in a way that I could take it in. I've also read West Marine's prep instructions on its DIY Bottom Painting site.
https://www.westmarine.com/WestAdvisor/DIY-Bottom-Painting Apologies in advance for duplication / incorrect thread / ignorance / length. The sailing is easy and I know how to paint, but the prep part is pretty much all new to me.
I have now got my boat upside-down: Collin Casey's 3/1/2004 step one.
My step two was cleaning algae with a plastic "steel-wool" scrubby, scraping barnacles, then washing with SimpleGreen, rinsing with water, and wiping blue paint residue.
The hull is now about 20% gelcoat and 80% old bottom paint (ablative antifouling applied with a brush). Some of it (brighter blue) is quite hard. Other parts are thin and came off when I scrubbed scum with my black scrubby. See photo.
- Hull after initial cleaning
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Neither the centerboard trunk nor the CB has ever been painted. My plan for both is to paint the areas where there was algal growth (thanks GL). This works out to about 6–8˝ in the trunk and 8–10˝ on the leading edge and sides of the centerboard.
I am now realizing that I haven't considered what additional prep work may be involved before painting. I am not racing this boat and don't really care about appearances, but am willing to invest time, effort, and dollars now — using my weekend time — for savings of all three down the road. Hoping, however, that I can be out on the water by the end, if not the middle, of July.
Condition of hull: Apart from the blotchy paint remains (and centerline issue described below), the bottom surface is in very good condition. No blisters, cracks, etc. And no leaks. She floated high and dry on her mooring for three months last summer.
Condition of centerboard: leading and bottom edges are worn through the gelcoat but firm and intact. Sides have lots of cracks . . . some radiating (spider cracks?).
Considerations, Issues, and Questions:- Keel/Centerline under the bow. A stretch of about three feet is pretty worn -- through the gelcoat. Close up, I see some dark green and black. See photo.
- Keel under bow
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Question 1: What preparation, if any, should I be looking at for this edge that probably gets the most wear, coming up on a beach, for example. (I had a roller added to my trailer last year so the boat no longer drops to the trailer frame when launching!) Is there a post that would fill me in (pun intended)?
- Centerboard - leading and bottom edges (also side cracks).
Question 2: What preparation, if any, do I need for the CB edges? Is is the same as for the keel/centerline?
Question 3: Can I ignore the side cracks (at least this, my second, year)?
- Centerboard trunk. WestMarine says after cleaning gelcoat:
You can then lightly sand the hull with 120-grit sandpaper or use a no sand primer instead, such as Interlux Fiberglass No-Sand Primer or Pettit Sandless Primer.
Collin Casey 3/1/2004 (above) recommended several layers of epoxy barrier paint. This sounds completely different from WestMarine's recommendation. Bob Lemaire explains when barrier coats are useful.
Bob Lemaire wrote: Let's Fix Anhinga! Part 3: The Hull and Painting » Tue Dec 02, 1997 1:00 am. Barrier coat bottom paint is neccessary if your gelcoatis damaged or is blistering and you are not drysailing. These paints are tricky to apply, and must be applied in several coats with strict time/temperature schedules.
Since the CB trunk gelcoat is undamaged and unblistered, I will skip the epoxy barrier paint and follow WM's option to sand with 120 grit. However, . . .
Question 4: I'm concerned about too many layers of paint impeding the CB's movement up and down. Will two layers of paint in the trunk and two more on the centerboard be too much? (I know GL advises shaping the CB foil but that is beyond me. )
- Hull - mix of bare spots and old ablative AF paint.
My understanding is that you sand to rough up the surface for better adhesion of the paint. And that you don't want to paint over paint that isn't well-adhered.
If old paint must be removed because it’s incompatible or too deteriorated to overcoat, be sure to have Aqua-Strip™, Ready-Strip® or other stripper system or other material on hand.
Question 5: How do I tell if the paint that remains on the boat is "too deteriorated to overcoat"?
Preparation of painted areas assuming I don't have to remove all of it. Some of it is really stuck on there. According to the compatibility chart, West Marine CPP Ablative Plus requires only "light sanding" before painting over existing ablative antifouling paint. Their general prep instructions advise 80 grit (which seems pretty coarse).
Question 6: Doesn't light sanding mean to use a fine grain paper like 220 as tomodda recommends below?
I discovered that rubbing hard (to remove hardened scum, etc.) with my black scrubby pretty easily removes the thinner areas of existing bottom paint.
Question 7: Is that an indication that the paint is too deteriorated or just that it is an ablative paint?
Preparation of white areas. Use 120 grit for "light sanding" of the gelcoat as recommended by WestMarine.
Question 8: Is this whole idea manageable ... applying some paint to sanded gelcoat and the rest to sanded bottom paint?
- Solvent cleaning. Collin recommended MEK. WestMarine talks about "solvent wash such as Interlux 202 or Pettit Dewaxer."
I like tomodda's economical suggestion in the thread Re: Basic Painting Questions Mon Oct 26, 2020 4:02 pm to use mineral spirits instead.
Question 9: Okay to use mineral spirits?
- Painting - number of coats. West Marine says:
2 or 3 minimum, with additional coat(s) on leading edges and waterline recommended.
I've read that if you put one layer down in a different color as a marker "signal" or "flag" coat, you can see what areas wear down first and apply a first coat of new paint just on the worn areas ... a way of using less paint overall from year to year.
Question 10: Sounds like a good idea. Thinking I'll pick up a quart of the same paint, different color. Any comments?
Plan1. Clean more and better. Use TSP per
tomodda's recommendation. Do solvent cleaning just before painting each section (CB trunk, CB, hull) ... allowing sufficient time to dry.
2. Prep worn edges (keel and centerboard). Put two coats of bottom paint on these two edges.
3. Prep everything else.
4. Paint the centerboard trunk and the part of CB that stays inside the trunk (2 coats).
5. Put the CB back in vertical position. Bed the plates. Retie the CB down line.
6. Paint the CB edges and leading sides below the waterline (2 coats) ... can do both sides while standing on the hull.
7. Mark waterline with grease pen and mask with tape. (Too late to have used the very cool hose-as-level technique now that it's flipped, so I will eyeball based on staining. Existing paint job comes up way high at the bow. I will just leave that.)
8. Paint the rest of the hull. Apply a flag color to the parts that are already white or thin. Then two coats of my CPP Ablative Plus blue.
Question 11: Does this order of things make sense? Comments welcome. : )
For painting I plan to follow Tomodda's plan except the roll and tip part. (New term for me!) I watched a couple of videos and think I'll stick with brush work. Less waste.
tomodda wrote: Paint prep: Clean with mineral spirits, wipe off with shop towel, second wipe with lint free cloth. (3rd wipe right before painting with tack cloth, below waterline only). Paint (roll and tip!), dry.
Next coat: Cut previous coat with 220grit, repeat paint prep/painting.