Many coats of gelcoat to hide primer issue

[aaronhl]

I repaired some areas on a red fiberglass hull, then sprayed gray duratec sanding primer over the repairs…I noticed when I sprayed red gelcoat over the gray primer it took several coats to hide the primer. It’s almost like the red gelcoat is translucent and every layer I put on just makes the gray primer look more wet/darker…finally able to get good coverage after spraying a lot…what would you guys suggest I do for the remaining repairs I need to spray red gelcoat over the primer or is that just how it’s gonna be?

 

[aaronhl]

Looking for advice- maybe it’s my technique or equipment I’m using, currently thinning with acetone using a 2.5mm hvlp- thinking of upgrading to a gelcoat dump gun, maybe waiting a little longer between coats too

 

[ondarvr]

A dump gun is not an upgrade.

Reds have a terrible hide to begin with, then thinning it with acetone, or thinning with anything, only makes it worse.

Depending on the amount of acetone added you can't build up enough gel coat thickness at one time for it to hide, so it will require multiple coats.

Adding a small amount of acetone doesn't tend to cause problems, adding enough for it to spray like paint may.

 

[aaronhl]

So a dump gun isnt really an upgrade in terms of being able to put a better coat down?

It has a bigger capacity and I feel it will make it easier to clean going through a couple gallons of gel at a time...So I can put down a lot more gelcoat without having having to disassemble the hvlp guns (those are a pain to clean out)...Feel like I can't put the several coats down fast enough without having to disassemble and clean it. I saw the dump gun tip is double size of the hvlps I've used and you spray it at like 60psi so seems like it would put a lot of gel down fast??

How long should I wait in between layers of gel on the outside of a boat (not in the mold process)? Maybe I am rushing things and would get better coverage if I waited, to not disturb the previous coating...

I guess I will use white Duratec next time but I like how I can see the shade of gray duratec change colors when I sand it, maybe the red would cover better over the white

A dump gun is not an upgrade.

Reds have a terrible hide to begin with, then thinning it with acetone, or thinning with anything, only makes it worse.

Depending on the amount of acetone added you can't build up enough gel coat thickness at one time for it to hide, so it will require multiple coats.

Adding a small amount of acetone doesn't tend to cause problems, adding enough for it to spray like paint may.

 

[Blueknarr]

Mix white and grey primers to get a lighter grey that is easier to cover.

 

[aaronhl]

Here's the project I am working on, I sprayed red and black gel on the bottom half of the boat+transom, I am now working my way into to cabin and upper half, you can see how much gray duratec I used on the top areas that will need covering with red P.s. I have to wet sand

 

[aaronhl]

If only duratec sanding primer came in a red color lol

 

[aaronhl]

Mix white and grey primers to get a lighter grey that is easier to cover.

Good idea I guess that would be ideal because it is light but still may be able to see the color change as I sand it, where were you several months ago HAHA

 

[Blueknarr]

You could also ask your primer supplier add red colorant to the primer.

 

[ondarvr]

Duratec does come in red, but it would be a bit tricky to get that color.

Dump guns are the lowest level of tech you can get. If you need to put a lot of gel coat down quickly they do work though.

A 2.5 mm tip is too small for doing a large job, you need at least a 3mm.

 

[kapnD]

Ideally, the primer would be white, and the entire boat sprayed with that before applying the red, or a coat of white gelcoat prior to red.
Red gelcoat doesn’t hold up well in sunlight, so a good PU paint like Awlgrip would likely render a more satisfactory finish.

 

[Tague]

Gelcoat is going to be tricky but not impossible at all. Anytime you spray red either in paint or in gelcoat the underneath needs to be a uniform color. I'm not a fan of dura-tech, I wont go into why but there are better polyester primers that are fare less expensive. I would spray the whole thing in evercoat featherfill primer. Sand to 80 or 120 being careful not to burn through the primer. Then shoot your red gelcoat. However it is much easier and you will have much better results with using paint instead of gelcoat.

 

[aaronhl]

Thank everyone for the input, all of it makes sense to me...Do you think I could spray one layer of white gelcoat over the gray primer as a way to hide the gray? I am wondering if just one layer of white would have better coverage than the red, and then red over white may take less coats to cover...I may seem like I am trying to cut corners rather than make the whole boat one solid color, still learning about gelcoat process here

 

[aaronhl]

Gelcoat is going to be tricky but not impossible at all. Anytime you spray red either in paint or in gelcoat the underneath needs to be a uniform color. I'm not a fan of dura-tech, I wont go into why but there are better polyester primers that are fare less expensive. I would spray the whole thing in evercoat featherfill primer. Sand to 80 or 120 being careful not to burn through the primer. Then shoot your red gelcoat. However it is much easier and you will have much better results with using paint instead of gelcoat.

No tell me why you don't like Duratec - and the Evercoat seems more like a car paint products than a boat...I've had bad luck with some paints under gel before

 

[ondarvr]

The differences between Duratec products and something like Evercoat may be significant, or irrelevant depending on the desired results for the specific application.

The first difference is viscosity, Evercoat and similar automotive primers tend to have a lower viscosity due to how they are used and the typical auto body shop equipment. Most of the time a high build isn't required on cars, yes they have high build primers, but high build in the automotive world is different than in the composites world. High build in automotive is 5-10 mils, Duratec standard primers easly build to 30+ mils thick, the Duratec High Build primers can be built up to 125+ mils if needed. If someone desires a lower viscosity with a Duratec primer they can add a reducer to get it where they want it. Adding the reducer will allow it spray, level and flow better, but can reduce the amount of build you can achieve at one time.



The base resins are different too, Duratec is targeted more to the marine, aerospace and mold building markets, these market segments tend to require higher heat distortion temperatures and better physical properties.

The other market where Duratec products are used is in high end automotive restoration and modifications. The Corvette restoration world uses them a great deal, others do too.

Most people don't realize how many different primers there are in the Duratec line up. You can have an easy sand primer, or ones that are formulated for more demanding situations.

There are two lines, the polyester based products and the VE based products, each having many different nuanced options and colors. Polyesters have a heat distortion temperature around 200F, the VE versions close to 300F. The VEs are frequently used in the high end car restoration market due the high HDT, they can paint the car with a very dark color and the surface doesn't distort from the heat in the direct sun. The VEs are also used below the waterline, they make for a very good primer and/or barrier coat base for long term immersion.