Sanding gel coat fast? How?

[LakeFever]

Sanding the old factory gel off is proving to be painfully slow. This took 3-4 hours of 40 grit Diablo paper with a 5” Da. I don’t really want to grind because most of the hull is ready for refinishing aside from removing the old gel I don’t want to add a bunch of body work. I sure hope some of you have some tips on what process to use to remove this old gel faster

[Instigator]

Why?

[LakeFever]

The factory gel is extremely cooked and damaged. The finish is half exposed metal flake and by the time we sand the metal flake smooth? The rest of the gel Sands off in seconds so we are starting fresh. The underside of the hull has a lot of crazing so we want to expose all glass to run a lay of vinyester csm over it all before priming and spraying new gel. Here’s a pic to show some of it

[averep]

LakeFever, no matter how you sand the flake down, once you put that csm on it your in for a full fairing job to smooth/shape it back , not alot of flat surfaces to make it easy on a HydroStream, why not fix the crazing/stress cracks, cover/ prime the hull with Duratec high build primer, block sand that and then start the regel process, your looking at alot of work to fair/reshape a HydroStream, John

[LakeFever]

We are planning to prime the hull with duratec. There is so much damage under the hull I can’t see saving any time by trying to spot repair. We are not afraid of work, but don’t want to waste time if there is a better way is why I started this thread. The gel on the front of the deck could probably be left and filled over but for long term sink/print through I can’t see that working out well which is why I’m stripping it off. Start fresh, no lipstick. That said I’m not set on running csm over the whole bottom until I get the gel sanded off and then commit to a plan. Regardless getting the gel off is my focus here. Not really wanting to grind it because that adds more fairing

[XstreamVking]

A grinder with a 50 grit disc is the next step up on the aggression scale. A variable speed grinder set to a lower speed helps to control the amount of damage you do.

[Instigator]

Looks to me like a project that will never get finished.

Id guess 100’s of hrs of labor to get it close to faired well enough to finish.
Aint a single straight line on those decks.
Theyre continuous compound curves.

And probably add weight to it.

At best, a HUGE project.

I hope you prove me wrong.

[LakeFever]

We estimate a week of sanding for two men full days at the rate we are at. Sucks, but it needs to be done we didn’t come this far to start cutting corners. I might try the high speed grinder with flexi backing disks at 36 grit and see if I can remove it a bit more gently yet faster. I used this method on the transom exterior gel before glassing but wasn’t too worried about refinishing level smooth. Thanks for the input, looks like I’m stuck with what I feared it would be

[XstreamVking]

If you take some x-tra time while glassing the deck cover on, a lot of fairing can be done at the same time. Applying filler (resin and cabosil) and glassing over before it hardens will quickly flatten out the bumps when fin rolled. Only one way to get rid of cracks IMO, and that's to glass over them with at least .75 OZ matt.

[LakeFever]

A guy I know recored a vector ten years back or so and did paint over gel on the hull spot repair where needed etc. I did not see the build I only saw the after math a few years ago the whole factory skin peeled off his hull at high speed. He was ok but it looked horrific. My thinking was to use csm over the entire underside with derakane to really strengthen up any fractures in the factory glass that is certainly there plus I have five holes I patched from above and I want them to be protected well. Fortunately I do have considerable experience refinishing autos so I’m not lost on what’s involved with fairing so that will help.

I like the tip on the wet lay xstream thanks. I know we are in for a ton of work and as of now I’m still leaning towards paint on the deck and gel for the hull. Fortunately the deck is in pretty decent condition and won’t need a ton of body work

[averep]

LakeFever, I like to use a 3m soft 8" soft pad with 36gt, very flexable and spin at buffer speed as to not gouge the bottom up, when you hit the mid/rear area maybe a jitterbug sander, air type, 60gt wet sand , you don't have the space in between the strakes to really swing a disc grinder, either way you"ll need to do some serious prep after your done, filling lows, gouges, etc. You will have to skim a coat of resin over the thousand tiny air bubbles your gonna open up by removing the gelcoat, ofcourse there's more prep to do before glassing but that can wait till you finish the sanding job, remember that faster is not always better, here it's more important to keep the bottom as true as possible, it will reduce work later, John

[MattGreen]

Lots of good advice here, got a couple other ideas for you to mull over. More than one way to re-skin this cat.

Big-yacht yards use industrial sandblasters for anti-fouling paint removal. This sometimes goes through the gel if too aggressive. Maybe you could use this approach to intentionally remove all your gel ? You'd still need to sand afterwards obviously but probably way less filling and fairing needed than the surface you'd have after grinding.

The next idea is really outside the box but read on. There's a technique called laser ablation that uses a hand-held laser with a beam about 2" wide to remove surface coatings from sensitive surfaces. The laser vaporizes the surface coating, which is sucked away by a mini ventilation system built into the laser nozzle. I have witnessed it first-hand at one of the refineries I used to work at. The demonstration was removing a combination of lead-based primer and asbestos-containing insulation mastic from a Monel reaction vessel. This technique apparently can be applied to composites successfully:
https://www.sciencedirect.com/scienc...75389213000928
The companies that do this kind of work specialize in surface prep on sensitive, expensive surfaces/objects/equipment. Not sure where you are located but if there is a petrochemical industry around, you might find one of these. It was amazing how cool the underlying surface was - I bet this would not cook the underlying glass.

On adding a layer of CSM to the whole outer skin - I understand why you want to do an overall surface reinforcement, but have you considered a different type of reinforcement ? CSM soaks up a ton of resin while not really adding much strength. How about like 6-oz woven E-glass cloth ? Although this material is not used a ton in regular fiberglass boating building, it is readily available and used a lot in epoxy-saturation wooden boat building. Inexpensive, drapes really nice over major curves, uses very little resin to wet out, and leaves a smooth, easily-sanded surface. It would be great for suppressing print-through. I've used lots of 4-8oz cloth over the years a quite like it actually.

Hope you don't itch too bad after all this,
Matt

[LakeFever]

I spent a lot of time last night reading up on the duratec vinylester primer and one of the features claimed was its good for priming over old rough gel coat before refinishing. As I said I’m not keen on lipstick but maybe this is worth a try, certainly on the deck at least which would save a day of sanding.

I really appreciate all the input gents, I still have some glass work to do and I’m going to gel the interior so I can get a feel for how gel behaves. I think I’m going to spray it too just to get some practice with that process.

[WaterZebra]

Sanding the old factory gel off is proving to be painfully slow. This took 3-4 hours of 40 grit Diablo paper with a 5” Da. I don’t really want to grind because most of the hull is ready for refinishing aside from removing the old gel I don’t want to add a bunch of body work. I sure hope some of you have some tips on what process to use to remove this old gel faster

How about blasting with walnut shell media? If you get down to the flake layer you can never get that effect back. Flake distribution is totally random and relies on gel coat gun technique. Almost an artform. Very popular thru the 90's but rarely done today.

[LakeFever]

I’m flaking this hull again. I would have tried to work with the factory flake but the guy I bought it from had ground and sanded quite a bit if it plus the damage done to the deck lip during separation. I was super excited when I bought this thing because it was already stripped. This is my first fiberglass restoration and I have learned a ton and still learning. If I knew then what I know now I would have never sold my Valero it’s gel and interior were mint