Scratches on swim platform

SteveK said:

STB. Care to share why you need to thin the gelcoat and even the video is unclear as to what thinness compared to the as is can of gelcoat. Use a syringe, then pour styrene (amount of each).

Can you compare to a liquid consistency we can relate to? Why is it not thinned to start with?

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Hey Steve,

Out of the can, the viscosity is appropriate for application by brush or roller. It doesn't really flow out ridges to flat. And, it won't spray well, if at all. It mostly splatters.

Out of the can is fine, even beneficial, for a roller or brush because the goal is to over apply and then sand down and polish. With it more viscous, it stays put better.

To get a visual, see how the unthinned product, while very much a flowing liquid, stands up in a small puddle in this video, which is a companion to the other one I posted:


The thickness is thicker than whole milk but thinner than honey. Maybe as thick as a table syrup? It may depend a little on brand and temperature.

Even for paints like Perfection or Awlgrip, they get thinned differently (different thinner) for spraying than for brushing. The film thickness per coat and amout of flow expected is very different between the two methods of application.

It is hard to say how much I thin the gelcoat. 10% would be a good guess. I usually thin it until the viscosity seems to me to be a hair more than spray paint, then try it, then adjust in tiny increments until I like the flow.

I wish I could give you a good scientific answer, but I don't do this super super frequently and each time seems to be a little different w.r.t. how much gelcoat, how much pigment, how much thinner, the air temperature, the humidity, horizontal vs vertical, etc.

I mix it for color first, and place some directly on the boat to check, immediately wiping it off with acetone. Then, when I like the color, I thin and test spray onto cardboard. If I need to thin more, I do. One can make.more than needed and, if over thinned, just go back to the less thinned portion.

I always start by mixing more gelcoat than I'll put into the sprayer bottle. That way I can add some back if I over pigment. I have also added some back to thicken the coat for more coverage. But I then needed to deal with small amounts of pigment.

The thing I learned is that too much light is as bad as too little light for color matching. I really like indirect sunlight. Darkness poses an obvious problem. But on super bright days when the sun is right on the repair, I can't tell the difference between the shades very well. They all looks bright white. I end up seeing the repair later in different light and realizing give got to sand a bit and try again for the perfect color match. Obviously something can be used to variously shade the repair to check color originally. But I haven't been so good at that.

paulga said:

If not using the smaller patch, I would need to buy a can of "one step finish" and some tubes of tint to use the sprayer. I wonder if a smaller can is available.

What tint are needed for different "grey scales" of white?

View attachment 154315View attachment 154316

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Hey Paulga,

They have kits that have a bunch of pigments. I've always used one of those. Total Boat or others may have more options w.r.t. size, possibly even in premixed colors that will get you close.

STB said:

Hey Steve,

Out of the can, the viscosity is appropriate for application by brush or roller. It doesn't really flow out ridges to flat. And, it won't spray well, if at all. It mostly splatters.

Out of the can is fine, even beneficial, for a roller or brush because the goal is to over apply and then sand down and polish. With it more viscous, it stays put better.

To get a visual, see how the unthinned product, while very much a flowing liquid, stands up in a small puddle in this video, which is a companion to the other one I posted:

The thickness is thicker than whole milk but thinner than honey. Maybe as thick as a table syrup? It may depend a little on brand and temperature.

Even for paints like Perfection or Awlgrip, they get thinned differently (different thinner) for spraying than for brushing. The film thickness per coat and amout of flow expected is very different between the two methods of application.

It is hard to say how much I thin the gelcoat. 10% would be a good guess. I usually thin it until the viscosity seems to me to be a hair more than spray paint, then try it, then adjust in tiny increments until I like the flow.

I wish I could give you a good scientific answer, but I don't do this super super frequently and each time seems to be a little different w.r.t. how much gelcoat, how much pigment, how much thinner, the air temperature, the humidity, horizontal vs vertical, etc.

I mix it for color first, and place some directly on the boat to check, immediately wiping it off with acetone. Then, when I like the color, I thin and test spray onto cardboard. If I need to thin more, I do. One can make.more than needed and, if over thinned, just go back to the less thinned portion.

I always start by mixing more gelcoat than I'll put into the sprayer bottle. That way I can add some back if I over pigment. I have also added some back to thicken the coat for more coverage. But I then needed to deal with small amounts of pigment.

The thing I learned is that too much light is as bad as too little light for color matching. I really like indirect sunlight. Darkness poses an obvious problem. But on super bright days when the sun is right on the repair, I can't tell the difference between the shades very well. They all looks bright white. I end up seeing the repair later in different light and realizing give got to sand a bit and try again for the perfect color match. Obviously something can be used to variously shade the repair to check color originally. But I haven't been so good at that.

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Looking at Total Boat's product, their instructions read, "Thin TotalBoat Gelcoat with styrene, only as needed (up to 15%, adding more can affect the color of the cured gelcoat)."

Thanks @STB

STB said:

Hey Paulga,

They have kits that have a bunch of pigments. I've always used one of those. Total Boat or others may have more options w.r.t. size, possibly even in premixed colors that will get you close.

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Hi Paulga,

I guess I can add that I've always made the most use of white, black, red, and yellow.

STB said:

Hey Paulga,

They have kits that have a bunch of pigments. I've always used one of those. Total Boat or others may have more options w.r.t. size, possibly even in premixed colors that will get you close.

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I saw this repair kit yesterday. is this kit what you mentioned? is it also applied using the same Preval sprayer?

For what it is, that's as good a kit as any for doing it without a sprayer -- which is a perfectly viable option. I suspect you'd want more than the 1oz and also want reducer if you were to spray. They do sell a 4oz version.

The thing that I dont like about that kit -- and I'm sure is the source of most of the negative reviews it has (among many good reviews) is that it is an unwaxed gelcoat and doesnt include any PVA.

Unwaxed gelcoat is said to cure only in the absence of air (I think it actually has to do with off gasing certain important chemical(s) that exist in minute quantities, e.g. the catalyst(s), vs exposing to air, but same thing in practice). So it has to be sealed off completely or won't cure. This can be accomplished by covering the repair with a film (the included release film or wax paper, etc), ensuring that the are absolutely no bubbles and the repair is totally sealed. Or it can be accomplished by spraying on a sealant, most commonly PVA, which is available in tiny pump spray bottles.

I like PVA much better. It doesn't mess up my repair. When I used release sheets, I always feel like I need to make the repair thicker and wider to be able to squish it down while getting the air out.

In general, I use unwaxed gelcoat and PVA for deep fills and then waxed gelcoat and a sprayer for the top coat.

I don't know if I've ever been in that day, but if I didn't have any waxed gelcoat for the finish coats, I'd probably just spray unwaxed gelcoat and then use PVA.

I'd have to have a very large repair before I'd want to use sheets instead of PVA. Sheets have the advantage of being faster to remove from a large surface when done. PVA has to be cleaned off with (warm is better) water and a rag.

There are also wax additives and other release agent additives that can be added to vanilla gelcoat, but they can be harder to dose in small quantities, which is why I'd like to buy it that way or use PVA over the top.

With PVA, you want to apply it fairly promptly before the reducer evaporates out to any significant extent. If that happens the cross linking doesn't happen fully and it will never cure, remaining soft to sticky forever. People seem to do repairs then try to seal them with film or PVA or whatever hours later -- and then get shocked that it didn't work.

Why not try this...buy that kit and some PVA (poly vinyl alcohol, not wood glue). Do the repair by hand without a sprayer. You'll be fine, even if it takes a couple of tweaks to make it right.

Next time, add a sprayer and some more reducer to your toolbox. You'll already have the coloring agents. Try your hand at spraying. You'll have already practiced the fill and finish.

Doing it this way you can do your whole repair with that kit, a cheap thing of PVA, and the sanding and polishing supplies.

Don't make this a bigger deal than it is. I know it can all be intimidating with so many options and so much chemistry.

But once you get started, you'll practically be done! Really!

STB said:

You'll have to go touch it. It is hard from pictures. To me it looks like gel over fiberglass.

You can fix it by cleaning it out and then filling it with a resin-based repair putty from West Marine or similar, sanding to shape, and sanding past the damage, and then cleaning with acetone. From there you can apply your gelcoat.

They sell these very small sprayers that work with cartridge propellant. You can mix some gelcoat, tinting it a bit as needed, and spray it on. If the color isn't right, you can adjust a bit. Once ready, overspray past the edges of the repair. Get good coverage. Probably 4 or 5 thin coats.you can also brush it on.

Most gelcoat wont cure in the air, so the final coat needs a wax additive to make it self-sealing or to be covered tightly with a film. Once cured, finish sand and buff it.

Thickened epoxy can also be used, but is a bit more problematic. The bond is never quite as good as with resin and you need to clean it really well with water and a lightly abrasive cleaning pad before sanding and applying the gelcoat. This is to get off the amine blush, basically a water-soluable film that forms on the surface as it cures. Sanding before washing off the blush has a habit of pushing the amine carbamate into the texture from the sanding and making it harder to wash off. Since the amine blush is water soluble only water need be, or should be, used to clean it, but the cleaning step is important.

The process really isnt bad and can be done in a couple or few hours each day over a weekend. Total Boat and West Marine both have tutorials.

As with anything else, prep like masking and cleaning is as much of it as anything else. Ditto for the final sanding and buffing.

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@STB I think the "... 4 or 5 thin coats" are applied continuously. The boatus video tutorial at 6:08 shows 3 layers applied continuously. or do you mean to wait for each layer to cure, then clean and sand using 220grit to 320 grit before spraying the next coat?

I treat it like rattle can spray paint. I do immediate light overlapping passes, but I sort of consider than one coat.

But, light is the key. If you get it too thick, it'll run. That isn't terrible. You can just clean it, sand the runs, light sand, and overcoat if needed. Clean well to get the wax or PVA off or it won't lay or adhere well.

If you want additional coats, you can let it cure, clean it, light sand it, and apply more.

I actually consider it easier and more forgiving than spray paint. Once thinned, itnlays down about the same -- but itnis intended to get polished afterward to a high shine, so there is no harm in any minor contamination as it'll polish out.

Play with it on a piece if cardboard. You'll get the hang of it really quickly. Don't focus just on the boat. Have fun playing with it no-stakes first. Even a little practice will go a long way to having a confident technique.

That's my experience for whatever it is worth.

STB said:

I treat it like rattle can spray paint. I do immediate light overlapping passes, but I sort of consider than one coat.

But, light is the key. If you get it too thick, it'll run. That isn't terrible. You can just clean it, sand the runs, light sand, and overcoat if needed. Clean well to get the wax or PVA off or it won't lay or adhere well.

If you want additional coats, you can let it cure, clean it, light sand it, and apply more.

I actually consider it easier and more forgiving than spray paint. Once thinned, itnlays down about the same -- but itnis intended to get polished afterward to a high shine, so there is no harm in any minor contamination as it'll polish out.

Play with it on a piece if cardboard. You'll get the hang of it really quickly. Don't focus just on the boat. Have fun playing with it no-stakes first. Even a little practice will go a long way to having a confident technique.

That's my experience for whatever it is worth.

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I was searching if there is PVA in a small spray pump like you mentioned. The one I found from amazon has bad rating about pva is too thick and it only squirts a small stream rather than a mist. But one feedback confirmed a PreVal sprayer can be used to spray PVA. so I can get Preval spare bottle or some touchup jars to switch quickly.

I have a question on the buffing step. I know my repair only requires a rag but just curious. The compounding pad used in the boatus video tutorial (the sprayer version that you posted) at 8:07 looks like a 9" 3M 05711, do you know which pad is a smaller equivalent, say 6", up to 8"

Great questions!

Recall that when I, personally, spray a thin finish coat of gelcoat I used waxed gelcoat so I don't need to use PVA or sheets or anything else over the finish. I like it to stay just as I applied it. The wax mixed in prevents the off gasing of the catalyst (or "exposure to air"), enabling it to cure.

I used unwaxed gelcoat and pva if I do build ups in thicker layer(s) leading up to the finish coat. I've also used pva when applying unthinned gelcoat by hand, in which case I overfill just a hair so I can sand it down to blend. In other words, I use pva when I am using gelcoat that isn't super thin and thinned and will be sanded, e.g. filling a chip in the gelcoat (but not deeper), before spraying a thin coat to blend.

If you spray pva over a thinned top coat you risk the droplets displacing the topcoat. So, you'll want a really good sprayer and to go thicker so you can sand down. I'd want to avoid that complication and risk. It is ticklish.

I'd recommend spraying a thinned, waxed gelcoat. Or appling the unthinned, unwaxed gelcoat by hand and over spraying with pva. It isn't that you cant spray pva over thinned, sprayed gelcoat. It just gets to be quite and unnecessarily ticklish.

Also remember that gelcoat isn't a filler. It is relatively brittle and, if too thick, it cracks when flexed. Thick and thin here is relative to a coatings film thickness, not the depth of a fill. When aintalk about filling with gelcoat, I mean filling defects in the gelcoat itself, e.g. scratches or minor crazing, nit deeper defects into epoxy, resin, or glass layers.

For damage deeper than the original gelcoat, fill with a filler and/or otherwise repair first, and then topcoat with gelcoat and blend it in and polish it up.

As for the wool pad, there are different ways they mount. What device are you polishing with?

I should also add that gelcoat does set up in a few minutes or so.

If you are spraying pva over thinned, sprayed gelcoat you need to be really careful to make sure the gelcoat has set first. If not, you'll have a muddy mess. Looking at reviews, it is pretty clear some people miss that step. Of course, if you wait an extended period of time before sealing off the uncredited gelcoat, it'll never cure.

You want to do the same when spraying pva over unthinned gelcoat, but it'll set faster and be a little more forgiving of being rushed.

Practice on cardboard. Try it waiting to long. Try spraying too soon. Try hitting it at afew times during the "right" window.

Have fun with it.

Let me also comment on one more thing, but from scuttlebutt, not personal knowledge.

I've never user an expensive gun to spray gelcoat -- just those cheap ones.

But, those who have used expensive sprayers have told me that waxed gelcoat isn't their friend because if they don't clean their gun right away, it gets really, really hard to clean the tips. They are the ones I've heard of spraying pva over sprayed gelcoat. They feel it makes their life easier.

I think most hacks like me just use waxed gelcoat each time and start fresh without worrying about cleaning sprayer tips.

In any case, if you are going to spray pva over thinned, sprayed gelcoat, be really sure the gelcoat kicks before spraying the pva. If you do that, anything the pva does to the surface should polish right out.

I was reading some of the complaints for various products and it really does seem like folks aren't waiting for the gelcoat to kick before spraying the pva and maybe are expecting splattered pump bottle pva won't impact a super fine finish at all, and I wouldn't bet on that.

In any case, as long as you let the gelcoat kick before spraying the pva, and get a good film of pva over the top, whatever it does to the finish should polish right off. Just let it kick so you get pva over gel, not the two mixed.

STB said:

Let me also comment on one more thing, but from scuttlebutt, not personal knowledge.

I've never user an expensive gun to spray gelcoat -- just those cheap ones.

But, those who have used expensive sprayers have told me that waxed gelcoat isn't their friend because if they don't clean their gun right away, it gets really, really hard to clean the tips. They are the ones I've heard of spraying pva over sprayed gelcoat. They feel it makes their life easier.

I think most hacks like me just use waxed gelcoat each time and start fresh without worrying about cleaning sprayer tips.

In any case, if you are going to spray pva over thinned, sprayed gelcoat, be really sure the gelcoat kicks before spraying the pva. If you do that, anything the pva does to the surface should polish right out.

I was reading some of the complaints for various products and it really does seem like folks aren't waiting for the gelcoat to kick before spraying the pva and maybe are expecting splattered pump bottle pva won't impact a super fine finish at all, and I wouldn't bet on that.

In any case, as long as you let the gelcoat kick before spraying the pva, and get a good film of pva over the top, whatever it does to the finish should polish right off. Just let it kick so you get pva over gel, not the two mixed.

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does let the "gelcoat kick" = wait for ~5 minutes (for the gelcoat to set up) ?

"...just use waxed gelcoat each time and start fresh without worrying about cleaning sprayer tips" -- I didn't get it. should it be "unwaxed" here? if waxed gelcoat make the tip difficult to clean, then it is important to clean the sprayer tips after each use, right?

STB said:

Great questions!

Recall that when I, personally, spray a thin finish coat of gelcoat I used waxed gelcoat so I don't need to use PVA or sheets or anything else over the finish. I like it to stay just as I applied it. The wax mixed in prevents the off gasing of the catalyst (or "exposure to air"), enabling it to cure.

I used unwaxed gelcoat and pva if I do build ups in thicker layer(s) leading up to the finish coat. I've also used pva when applying unthinned gelcoat by hand, in which case I overfill just a hair so I can sand it down to blend. In other words, I use pva when I am using gelcoat that isn't super thin and thinned and will be sanded, e.g. filling a chip in the gelcoat (but not deeper), before spraying a thin coat to blend.

If you spray pva over a thinned top coat you risk the droplets displacing the topcoat. So, you'll want a really good sprayer and to go thicker so you can sand down. I'd want to avoid that complication and risk. It is ticklish.

I'd recommend spraying a thinned, waxed gelcoat. Or appling the unthinned, unwaxed gelcoat by hand and over spraying with pva. It isn't that you cant spray pva over thinned, sprayed gelcoat. It just gets to be quite and unnecessarily ticklish.

Also remember that gelcoat isn't a filler. It is relatively brittle and, if too thick, it cracks when flexed. Thick and thin here is relative to a coatings film thickness, not the depth of a fill. When aintalk about filling with gelcoat, I mean filling defects in the gelcoat itself, e.g. scratches or minor crazing, nit deeper defects into epoxy, resin, or glass layers.

For damage deeper than the original gelcoat, fill with a filler and/or otherwise repair first, and then topcoat with gelcoat and blend it in and polish it up.

As for the wool pad, there are different ways they mount. What device are you polishing with?

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I have a Bauer 5.7A short throw random orbit da polisher, it has a 6 in backing plate that supports up to 8" hook and loop polishing pad. I learnt some common pads from your video link and this post but those are 9" pads, so I was looking for smaller like 6" pads.

paulga said:

does let the "gelcoat kick" = wait for ~5 minutes (for the gelcoat to set up) ?

"...just use waxed gelcoat each time and start fresh without worrying about cleaning sprayer tips" -- I didn't get it. should it be "unwaxed" here? if waxed gelcoat make the tip difficult to clean, then it is important to clean the sprayer tips after each use, right?

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I am wasteful and just throw away the tips for the cheap sprayer. The folks with the good, real sprayguns obviously clean and reuse them. I've heard them complain that the waxed gelcoat gunks them up more. Like I said, those bits aren't first hand.

paulga said:

I have a Bauer 5.7A short throw random orbit da polisher, it has a 6 in backing plate that supports up to 8" hook and loop polishing pad. I learnt some common pads from your video link and this post but those are 9" pads, so I was looking for smaller like 6" pads.

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Can you post a picture of your polisher?

STB said:

Can you post a picture of your polisher?

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here is a video:

STB said:

I am wasteful and just throw away the tips for the cheap sprayer. The folks with the good, real sprayguns obviously clean and reuse them. I've heard them complain that the waxed gelcoat gunks them up more. Like I said, those bits aren't first hand.

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Also, yes, it means waiting fornitntonsort of gel and get tacky. You can sort of see the change in the way it looks. If you don't mind leaving a bit of a print to sand/polish later, you can also touch it with a finger or toothpick