What can I use for epoxy fairing/filling that can be sanded in <1 hour?

Hi,

I am rushing a plywood/fiberglass/epoxy boat build that I need to finish as fast as possible. I am at the stage where the boat has been glassed, and now it's time for fairing, filling in small defects, pinholes, sanding down bad fiberglass spots, priming, more sanding, etc.



The issue is that in my temperatures (24-30°C right now) regular epoxy with fast hardener still takes 12-24 hours before it can be sanded, otherwise it gums up the paper. This leads to a lot of wasted time. Say I fill in bad/low spots, wait for epoxy to cure, sand it down, and then realize I missed a spot. And now I have to fill it and wait another 12 hours at least before I can proceed to the next step. We've all been there.

In contrast, polyester-based body filler can be applied and sanded in less than half an hour. Which would be amazing to use here, except that polyester on epoxy is a big no-no, especially on larger areas.

So my question is, what can I use for fairing/filling on top of epoxy that cures in less than an hour at least? Even 5-min epoxy takes at least 3-4 hours to reach the stage where it doesn't gum up the paper. Are there any epoxies that are specifically formulated for fast repairs? Or any other materials that can be mixed with epoxy (above or under) without incompatibility issues?

Something is wrong if you are waiting 24 hours for fast epoxy with filers to kick off.

Systems 3 Quikfair claims to allow 5 application periods in 24 hours. But that is a little much in my experience. From application to sanding for me has typically been about 5-6 hours.

But I would just take the work out in the sun. It’ll go really fast with sun on it. Fast epoxy with filler in sun is about 3 hours.

Another thing you can do is water bath your epoxy. If you measure the resin and hardener separately; put the containers in 120F water bath before mixing. It will cool a bit when you add the fillers, but will kick very fast; so start with very small batches like under 100 grams total.

fallguy said:

Something is wrong if you are waiting 24 hours for fast epoxy with filers to kick off.

Systems 3 Quikfair claims to allow 5 application periods in 24 hours. But that is a little much in my experience. From application to sanding for me has typically been about 5-6 hours.

But I would just take the work out in the sun. It’ll go really fast with sun on it. Fast epoxy with filler in sun is about 3 hours.

Another thing you can do is water bath your epoxy. If you measure the resin and hardener separately; put the containers in 120F water bath before mixing. It will cool a bit when you add the fillers, but will kick very fast; so start with very small batches like under 100 grams total.

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Hey, thanks for the advice. We do get hot days but cold nights this time of the year, so that probably contributes to 24 hours of wait time. I'll look into Quickfair and if I can get it here in EU. But even 5-6 hours is a lot compared to 30 mins of polyester fillers...

And yeah, I do try to work in the sun, unfortunately it has been raining a lot lately. Sometimes I put the boat under a tarp with an oil heater. But that still takes many hours to cure. Heating the resin and hardener before mixing is something I do too sometimes, but that only seems to affect pot life, not the total cure time.

Well, it's clearly a trailer sailer - I don't see a problem. In the automotive world, applying good quality body filler over epoxy primers is totally normal. I would scuff sand the whole boat, shoot a couple good coats of epoxy or hybrid epoxy primer on it. It is sandable in about 20 minutes. Then use a good body filler with minimal talc content - say 20% or less. There are some fillers without talc, but are hard to find in my experience. After blocking all the filler out, shoot some more primer on and paint. Not sure about being fast though, It's a lot of work to finish a boat, but I guess it beats waiting around for epoxy to kick. It'd take me at least a couple weekends to get that boat ready for topcoat. I happen to be blocking out an old '95 Chevy diesel dually at the moment.

philSweet said:

Well, it's clearly a trailer sailer - I don't see a problem. In the automotive world, applying good quality body filler over epoxy primers is totally normal. I would scuff sand the whole boat, shoot a couple good coats of epoxy or hybrid epoxy primer on it. It is sandable in about 20 minutes. Then use a good body filler with minimal talc content - say 20% or less. There are some fillers without talc, but are hard to find in my experience. After blocking all the filler out, shoot some more primer on and paint. Not sure about being fast though, It's a lot of work to finish a boat, but I guess it beats waiting around for epoxy to kick. It'd take me at least a couple weekends to get that boat ready for topcoat. I happen to be blocking out an old '95 Chevy diesel dually at the moment.

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So you're saying that polyester filler on top of epoxy is fine, as long as that epoxy is scuffed and the fillet has minimum amount of talc? Does the talc inhibit adhesion with epoxy or something? I thought that adding polyester based anything on top of cured epoxy is a terrible idea, this advice keeps appearing over and over everywhere. Could you please explain in more detail why this isn't the case, as per your advice? Also, I assume that regular epoxy or epoxy primer doesn't make much difference for filler adhesion, as long as it's scuffed, correct? Or does it have to be a primer? The epoxy primers I've been using are definitely not sandable in 20 minutes, more like 2-3 hours at least. Maybe you are using some kind of fast epoxy primer?

As for the boat, she's actually designed to be car-topped rather than trailered. 40 kg (88 lbs) hull weight. I really hate trailers

Buy cheap diesel heater , no risk of poisoning and ability to work on cold days.

philSweet said:

I happen to be blocking out an old '95 Chevy diesel dually at the moment.

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Sorry for hijacking .'95 Chevy diesel is 6.2l or 6.5l Detroit ? I was shoocked when I saw Eldorado diesel for sale , the reason why GM should not make a diesel . Or some FWD regular sized cars.

montero said:

Sorry for hijacking .'95 Chevy diesel is 6.2l or 6.5l Detroit ? I was shoocked when I saw Eldorado diesel for sale , the reason why GM should not make a diesel . Or some FWD regular sized cars.

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So, please don't. There are forums for GMC trucks.

Before worrying about filler, maybe you should repair all the areas with bubbles and dry laminate. I think you could use a sprayable fairing compound like Awlgrip. It is not supposed to be used below the waterline, but that is for boats that are left floating all the time.

Congratulations on having a complete hull and deck.I have a feeling that some of our posters don't entirely understand life above 50 degrees north or the usage of dry sailed small boats.Perhaps also,the use of peelply isn't something they habitually do as it seems you had the useful idea to benefit from it's properties.A polyester filler of good quality would be perfectly fine,but it is important that you find a good one as the cheap brands tend to be bulked out with very porous powders.Here in the UK we have lots of the cheap stuff and a couple of higher quality brands,and it is those better brands which are suitable,but more expensive.The one hour cure is easily met but for the amount of surface area you are dealing with,it isn't that important as it will take two or three hours to carefully go over the entire deck or hull before sanding.The second application,to get the pinholes and minor blemishes will be much faster.You probably know that if you use a sprayable two part paint that you should be wearing an air fed mask to avoid the dangerous fumes,but when brushing,a good through draught of air may be enough,but at the risk of flies or debris landing on the surface.

montero said:

Buy cheap diesel heater , no risk of poisoning and ability to work on cold days.

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Thanks for the advice, but raising temps is only going to help so far. It won't make epoxy harden enough for sanding in 1 hour, at least none of the epoxies that I have. Suppose I have 2 hours to work on my boat in the evening. If my epoxy takes even 3 hours to harden, it means I can only do 1 filling/fairing per day. If it were harden in say 30 minutes, like polyester filler, then I could do it 3-4 times. That is why I'm so stuck up on finding a super fast hardening filler.

gonzo said:

Before worrying about filler, maybe you should repair all the areas with bubbles and dry laminate. I think you could use a sprayable fairing compound like Awlgrip. It is not supposed to be used below the waterline, but that is for boats that are left floating all the time.

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Like wet feet mentioned, that is peel ply in my pic. The fiberglass below is mostly fine, apart from the places where peel ply wrinkled and couldn't be pressed down, these areas will need to be filled in too. I'll check out Awlgrip, thanks!

wet feet said:

Congratulations on having a complete hull and deck.I have a feeling that some of our posters don't entirely understand life above 50 degrees north or the usage of dry sailed small boats.Perhaps also,the use of peelply isn't something they habitually do as it seems you had the useful idea to benefit from it's properties.A polyester filler of good quality would be perfectly fine,but it is important that you find a good one as the cheap brands tend to be bulked out with very porous powders.Here in the UK we have lots of the cheap stuff and a couple of higher quality brands,and it is those better brands which are suitable,but more expensive.The one hour cure is easily met but for the amount of surface area you are dealing with,it isn't that important as it will take two or three hours to carefully go over the entire deck or hull before sanding.The second application,to get the pinholes and minor blemishes will be much faster.You probably know that if you use a sprayable two part paint that you should be wearing an air fed mask to avoid the dangerous fumes,but when brushing,a good through draught of air may be enough,but at the risk of flies or debris landing on the surface.

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Thank you! Yes, I do try to use peel ply whenever I can, it saves a ton of washing amines and sanding. Could you recommend some specific high quality polyester fillers that have low powder content? I'm looking over the datasheets of the stuff I have locally available, but most don't provide datasheets, or don't even mention the powder content in them, so it's difficult to make the judgement. Maybe I will have something available from your list.

As for painting, unfortunately my workshop is very drafty and dirty. I do try to clean it as much as I can, but there is a million places for dust to settle. I can spend the entire day with air compressor, vacuum and wet wipes, trying to clean everything, but then comes one good gust of wind from outside, bringing in new dust, and I'm back to square one. I don't have spraying equipment, so I'll be rolling and brushing, and I made my peace that there will be dust landing on the paint (even though I'll work with doors closed to avoid drafts, and a chemical respirator of course), which I'll have to polish out later.


EDIT: here is one of the polyester fillers that I have, Chameleon 505. Datasheet, safety sheet, hardener safety sheet. How do I determine the powder content in this filler?

I wouldn't get too concerned about the powder content,rather it is the type of powder that may cause concern as some may tend to absorb moisture if there is a scratch or other damage.Some filler has a harder consistency when cured and some has some flexibility.That Chameleon filler you referenced would tie you to a succeeding coat of the dedicated primer,which may or may not bother you but it costs both weight and time before arriving at a surface that is ready to receive the final paint finish.My preference is to use this filler P38 FILLER LARGE 600ML TIN - Motor Parts Direct https://www.mpdonline.co.uk/product/cm2-1-fillers/p38-filler-large-600ml-tin-p38-1/P38%2F1 .I have been suing it since the days when it could be catalysed with MEKP and that was quite a while ago.I wouldn't use it on a boat that wasn't dry sailed and I wouldn't sit a hull on wet grass for months at a time either but with those considerations out of the way,it can work well.

wet feet said:

I wouldn't get too concerned about the powder content,rather it is the type of powder that may cause concern as some may tend to absorb moisture if there is a scratch or other damage.Some filler has a harder consistency when cured and some has some flexibility.That Chameleon filler you referenced would tie you to a succeeding coat of the dedicated primer,which may or may not bother you but it costs both weight and time before arriving at a surface that is ready to receive the final paint finish.My preference is to use this filler P38 FILLER LARGE 600ML TIN - Motor Parts Direct https://www.mpdonline.co.uk/product/cm2-1-fillers/p38-filler-large-600ml-tin-p38-1/P38%2F1 .I have been suing it since the days when it could be catalysed with MEKP and that was quite a while ago.I wouldn't use it on a boat that wasn't dry sailed and I wouldn't sit a hull on wet grass for months at a time either but with those considerations out of the way,it can work well.

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Thanks! I'll see if I can get it shipped here fast enough. If not, how do I determine the type of powder used in a particular filler? I can't see it in my datasheet for that Chameleon filler, nor any others that I can source locally.

wet feet said:

That Chameleon filler you referenced would tie you to a succeeding coat of the dedicated primer

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You mean to say that regular epoxy primer wouldn't work? I need some kind of special primer? Again, did you determine this from the datasheet somehow? Maybe I'm missing something obvious in there :/ I assume you meant that in contrast P38 can be painted directly on, without primer?

EDIT: for small patches, can epoxy sticks be used? I've never used these before, but some, like this one, claim to be sandable in an hour. What bothers me is that they are single component, so I can't really grasp how it can be epoxy. Maybe these sticks are pre-mixed, with some hardening inhibitor that evaporates in air? Does it make any sense to use them as a filler, or will I get issues?

The epoxy stick that I'm familiar with is a two part thing with a core of one part and the second wrapped around it. You cut off a piece and then knead and and mix the stuff together. I'd really hesitate to use the stuff on anything I really cared about. For fairing it's hard to beat the ready made stuff like System 3's quick fair or Total boats similar stuff but sourcing it in your location may be a problem.

EDIT; I went back and looked at the whole post. Nice looking work. Were it mine I wouldn't hesitate to use a premium polyester fairing material, it's made for this kind of work. The stick type stuff would be horrible, a hard un spreadable lump that you couldn't feather in at all.

Skip Johnson said:

The epoxy stick that I'm familiar with is a two part thing with a core of one part and the second wrapped around it. You cut off a piece and then knead and and mix the stuff together. I'd really hesitate to use the stuff on anything I really cared about. For fairing it's hard to beat the ready made stuff like System 3's quick fair or Total boats similar stuff but sourcing it in your location may be a problem.

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Yeah, I'd really like to get quickfair/totalfair, but these seem to be pretty much impossible/astronomically expensive to get shipped here. But in any case, they harden in 4-6 hours to sandable stage, whereas I need <1 hour... Surely there must be something except polyester...