Spraying gelcoat over gelcoat

You say to use a hard back DA to start sanding at 400, what would use use on curved areas? I'm working on a boat now and not all parts are panels, in fact even the flatter areas as not truly flat...what advice could you give? flexible attachment? I would hate to have to sand by hand...Or would a 2-3" dia sander work better?

 

I guess it's hard to eliminate orange peel...So far I have only sprayed Duratec sanding primer and I do not find it to be a glossy finish right out of the hvlp even after sanding and polishing it is not a mirror finish...How easy is it to spray gelcoat with a glossy finish right out of the gun, or is that what the sanding and polishing is for? I have to respray a transom and I am afraid I would not be able to get a mirror reflection out of it, what advice could you give??, without adding anything else to the gelcoat like a 50/50 duratec option

 

A transom being flat presumably, should be easier to sand with progressively finer grit.

 

I've found the opposite to be true-a flat surface takes longer to flatten as the pressure applied is much lower due to the whole of the sanding pad being in contact.A curved surface normally has a much smaller area in contact with the paper and flattens faster.The flat surface is a lot easier for the inexperienced operator to deal with.The resurfacing of an entire hull isn't a particularly quick or easy job,but it can make the boat look like new-eventually.Once upon a time the buyers of new Hobie cats had a re-gel after one year included in the purchase price and it was a bonus for those sailing off a stony beach.

 

Depends what you use to sand it I guess.

 

There is nothing you can add to gel coat that will allow it to level, flow, spray, and cure tack free with a high gloss other than Duratec clear additive.

The gloss is only relevant if you don't want to sand the surface, if you're going to sand, then gloss is irrelevant.

What you want is a surface with as little orange peel as possible, but not use an additive like a solvent/monomer in high amounts to achieve it.

The primers are not designed to cure with a gloss, nor is the goal to be able to polish it to a high gloss.
The exception is the Duratec Surface primer version, it will polish to a bit higher gloss than the normal primers. This isn't a gloss comparable to the high gloss top coats though.

 

The smaller the surface of the sanding tool, the more likely it is to create an uneven surface while sanding. Since this is only cosmetic, it only needs to be acceptable to you, there is no right or wrong surface profile.

 

Good points so most curved areas need to be hand sanded? Any techniques you can share with power tools/attachments for not flat areas? When prep sanding at 80# grit to first spray the gelcoat and then finishing the gelcoat from 400#+ wet seems like a hard flat 6" disc was mark things up a bit, I will post a picture of a project im working on

 

So this has Duratec surfacing primer on it, I want to now sand it to spray red gelcoat (will be doing the boat in sections)
How would you sand the grey Duratec, seems like I could use the 6" flat disc on the flat transom and splash well but what about the outside areas?

 

I'd use a 5" or 6" DA and 80 or 120 grit, plus hand sanding with sanding blocks. And possibly a custom cut piece of wood in the shape of the radius. There are various rubber and foam hand sanding pads that will conform to a shape too.

Keep the DA pad flat on the surface, don't turn it up on edge, and stay away from any radius with it.

 

OK Thanks for the help as simple as this probably sounds to you guys, I am just now getting what it means to sand/polish as I've been working on several projects lately...if you only knew what that splashwell looked like a few years ago it sure feels good to see it with some Duratec over it...full transom replacement, flat spashwell and knees plus I had to repair the top sides and bow area that split from weight of snow in storage

 

Sorry to hijack the thread, I am just hoping to build off the info already to better understand the complete process of what gelcoat over gelcoat means from start to "finishing"
I got a quote an EXPENSIVE quote to paint this boat with Awlgrip and let me tell you this will be staying a back yard build for now and I'm glad I got that quote because it's motivating me to finish it myself and learn about the various material/process. I am pretty sure I can re-gelcoat this boat myself by spraying various areas to cut lines. If it doesnt come out perfect atleast I still have my 10k lol

He did give me some awesome free advice and say the original red gel coat and repairs may need about 4 layers of primer because it is various porous, without those multiple layers the finish coat wont come out well. So now after spraying several coats of Duratec primer around the repairs I see what he means...I am hoping spraying the gelcoat will be more forgiving that the thinner Awlgrip

 

OK technically this thread is about spraying gelcoat over gelcoat so what I have done is sprayed duratec over gelcoat and then gelcoat over the duratec, but I am thinking the process is similar (duratec doesnt need wax/pva)
So here is what I did today spraying a vivid red gelcoat over the sanded duratec primer. I ran out of red gelcoat because the duratec primer was too dark. Do you think I would have better luck with white primer next time?
Just wanted to paint part of the transom so I can get the outboard jackplate bolted on before winter and then worry about rigging the boat next year/ painting the rest of it. I'll try to use a red/black gradient maybe with metal flake in and around some of the curves so everything will blend.
I thinned the gelcoat 20% BY WEIGHT with lacquer thinner and that made it real easy to spray...When I was spraying 20% by VOLUME it was still clumpy
Oh Man the adrenaline is pumping when you are on the gelcoat shot clock LOL

 

Thinning the gel coat is part of the problem, it also degrades its physical properties.

Reds don't hide well, it's due to the limited types of pigments allowed for use. Thinning it also reduces its ability to hide the color under it, plus it limits how much you can apply without it sagging.

Mixing by weight and volume are very close, it shouldn't make much of a difference in sprayability. Although adding anything more than 3-5% starts to mess with the chemistry.

People frequently want to thin gel to spray it, the correct move is to increase the tip size to about 3mm. Most spray guns come with a 1.4 to 1.8mm tip. This is great for automotive paints, but far too small for gel coat and primers.

You can get a spray gun with a 2.5mm tip on Amazon for about $35, this size is great for the primers, and about the minimum for gel coat.

 

I have an ebay 2.5mm hvlp gun and a compressor to sustain the 40psi
I made some calculations by finding the weight of the gelcoat to be about 3x more than the thinner so by weight was the only way I could thin it enough so it wouldnt glob out of the gun, thinning it closer to 20% by weight was able to get the fine mist
I am not a professional, really appreciate your help on this board, I know thinning it like I have isnt ideal
Hopefully I get more gelcoat in time before the weather gets too cold I need to finish this transom next weekend
Not really looking forward to the wet sanding and polishing, I need to tool up before I can do that