Boat Builder Central - Builder Forums

I can define a mil, but what does it really amount to.

Obviously, it’s not “fairing”. But what should you expect it to ‘fill’?

Maybe like “2.5 mils dry coat will fill scratches from ‘X’ grit sandpaper.” (Will it or should it be used to fill any weave at all?)

Or is that the wrong way to think about it?

Maybe another way to ask is: How do you know when to switch from fairing compound to primer?

I’ve never really tried to get anything other than a passable surface on anything.

Jbo

caveat -- I'm an idiot.

I refused to sand more than 80g. One coat of primer seemed to hide 80, but 60 was noticeable. some 80 was noticeable in areas that I got lazy in though. 2 coats all 80 was hidden. 4 coats all 60. Nothing bigger than 60 ever really "vanished" after 4 coats. That was with system 3.

I think the EMC covered a lot of the other sins (small pinholes, lines from runs, etc) via its self-leveling. Weave never really hidden. basically if you can feel it with your fingertip (vs fingernail) I'd keep fairing. That or enjoy not caring about what hits the ugly parts of the workboat.

jbo_c wrote: ↑Fri Jul 29, 2022 11:46 am I can define a mil, but what does it really amount to.

Obviously, it’s not “fairing”. But what should you expect it to ‘fill’?

Maybe like “2.5 mils dry coat will fill scratches from ‘X’ grit sandpaper.” (Will it or should it be used to fill any weave at all?)

Or is that the wrong way to think about it?

Maybe another way to ask is: How do you know when to switch from fairing compound to primer?

I’ve never really tried to get anything other than a passable surface on anything.

Jbo

Each paint should specify how to prepare the surface on its TDS(Technical Data Sheet). The primer will tell you to sand with something like 80 grit or 120 grit. The topcoat will tell you to sand the primer with 240, 320, or 400 grit. Whatever grit the paint specifies just work your way up to that, your work with each grit should eliminate the deeper scratches from the grit before.

As an example here are the directions for painting epoxy coated surfaces with system 3 yacht primer:
https://cdn.shopify.com/s/files/1/1000/ ... 985314394

Epoxy resin‐coated surfaces: Some epoxy resin systems
leave an amine blush on the surface. Amine blush can
interfere with the adhesion of the SilverTip Yacht Primer.
Remove surface blush by using a Scotch‐Brite pad with
detergent and warm water. Then flush the surface with
fresh water.
1. Sand the epoxy surface with 100‐120 grit
paper.
2. Fill surface imperfections with SilverTip
Quikfair. Sand repair areas until smooth
using 100‐120 grit paper.
3. After sanding, vacuum or with clean, dry
shop air remove sanding dust.
4. Wipe the surface with denatured alcohol
and clean rags.
5. Apply SilverTip Yacht Primer with roller and
brush, or by spray application. At 70 degrees
SilverTip Yacht Primer can be recoated
without sanding in as little as 2‐3 hours.
After 72 hours, the SilverTip Yacht Primer
must be sanded, use 220‐320 grit paper.
Repeat steps 4‐5.
6. 2‐3 coats of SilverTip Yacht Primer are
necessary to achieve a smooth, uniform
surface.
7. After 24 hours @ 70 degrees, the SilverTip
Yacht Primer can be top coated. First sand
with 220‐320 grit paper. Repeat steps 3‐4.

Thanks for the feedback. Good “real world” example Jaysen. That’s pretty much what I was looking for.

Funny enough, the System three is the primer I was looking at when the question ovcurred to me.

Jbo

The question that is really important that you need to ask… how much do you want to worry about smashing into things?

If you are like me, it’s better to worry about “hard enough to break things” than “hard enough to mess the paint”. With my very work boat finish knock a dock piling, rock wall, beach, or even dropping the hull onto concrete doesn’t really bother me. She’s not winning a beauty contest no matter how fancy the paint job is because I will damage something every. damn. time.

If you are going to boat rough, the finish doesn’t need to be showroom.

jbo System 3 Primer will not fill any weave. You need to fair any fiberglass on your barge. It will also not fill any bubbles/holes in the fairing so get them out before priming. Good fairing. Tom

I used Pettit 2-part epoxy primer and states 1 coat is enough for a fresh hull but 2 coats for best water barrier. After I finished the first coat, sanded a few places back down to the surface. 2nd coat I sanded everything very smooth and exposed the surface again in a few places.

Question 1: Can I topcoat even with a few places sanded through? It is 320 grit smooth right now and we are talking bottom and sides of the hull.

Question 2: If question 1 is NO, can a go back and use Pettit high build primer over the two-part epoxy primer?

If I sand anymore, I hope it is the topcoat and not that two-part epoxy primer.

OQ yes to your question 2. you do not want to leave any part of the boat unprimed. Tom

TomW1 wrote: ↑Wed Aug 24, 2022 10:31 pm OQ yes to your question 2. you do not want to leave any part of the boat unprimed. Tom

I started stirring the high build primer this morning before I checked the web. It has been setting a few years and wanted to check if it would still mix up. So will be ready to prime this morning.

Thanks TomW1 for the reply.