Fairing compounds and repair putties

[jeffwagnpete]

Thanks to my newly purchased Porter Cable Random orbiter sander! Today, I started the first phase of sanding the old paint using 80 grit sand paper. It went really well! However, I know there's a hundred or so topics on this subject on plasticclassic.com, but there are so many different opinions and I just want to be sure. There are also a lot of different products available for filling low spots and dents. My sailboat has alot of these small low spots and small dents above the waterline on the exterier hull. Before I spray the first coat of primer, I would need to fill in these small low spot areas and small dents. What is the best fairing compound to use? Would you use Interlux Epoxy Filler or something else? I just want to be sure. Thanks!!

Jeff

[Hirilondë]

I think you will find the consensus here is epoxy filler. Basically these fillers are epoxy resin and some or several solid fillers. You can buy premixed products where you simply add the catalyst or you can buy resin, catalyst and fillers separately and mix your own. The first is easier and the later is often cheaper and can be customized to the application.

[jeffwagnpete]

Ok, thanks Dave for your input, I really appreciate your time to reply to my post. This really helps me out when I get a direct answer like this.

[Rachel]

I've always used the "home mixed" versions that Dave mentions. Basically taking straight epoxy (mix that first) and then adding whatever was right for the project at hand (colloidial silica, fibers, microballoons, etc.).

However I have noted that Tim and others now use pre-mixed fairing compounds for some jobs. I bet they are really fine and a great texture for fairing, and I've been thinking that I might buy some for my next fairing project, whenever that may be.

I have not yet gone back to take notes, but some names that come to mind (if you want to Google) are Awlfair and Quikfair.

Basically, I don't think it's that they are anything you couldn't make yourself, but I bet it would be hard to get the ultrafine texture they have, and plus of course they are just ready to go.

By the way, do you have WEST System's "Epoxy book"? It's free (you can usually find a copy at stores that sell WEST), and it's a great "cookbook" for all kinds of epoxy stuff, no matter what brand of products you use. They explain all the different uses of epoxy (bonding, filleting, etc.) and give you "recipes" for the various fillers. They illustrate it with these simple-yet-effective line drawings that just make you feel like it's all so do-able! (Which it is.)

You can also read it chapter-by-chapter here on their website (each of the categories you click on are a chapter in the book, in order):

http://www.westsystem.com/ss/use-guides/

Rachel

[Tim]

FWIW, I have tried several times to like System Three's "Quik-Fair" to no avail. Despite these efforts, I simply despise it--texture, workability, sandability, mixability, and even smell (though that's unimportant, but when talking trash, go for it)--and recently threw out nearly unused containers of the stuff to avoid the temptation to use it ever again.

Just one man's opinion based on my own experience with the product.

[Rachel]

Thanks for adding that, Tim. I knew there had been one you disliked, and before buying any I had a mental note to go back and figure out which one that was. Now I can check that off my mental list!

R.

[Idon84]

I bought 3 1.5G kits of Quickfair for a screaming deal (here's my sign?). Never used anything else to know the difference. Used 2 of them for fairing the interior after removing the liner. I'm going to have to try something else. AND IT DOES STINK!

[Zach]

I buy glass microballons 10 pounds at a time. Around 70 bucks wholesale through Paxton here in NC...
A "50lb" bag of aerosil is around 52...

Mix it 2-3:1 balloons to cabosil depending on the application. 2:1 for doing fillets, 3:1 for fairing. Spreads like heavy whipped cream at 3:1, and sands like butter. I like slow hardener, or better yet tropical...

Pull it tight with a screed or flat piece of sheet metal.

Then follow it up with Awlgrips Awlfair, and longboard or airfile it out... A friend swears by cutting awlfair with awlquick, letting them sit for a few minutes and then thinning out with acetone and spraying it, I'm not quite that ballsy. Grin.

I walk down it with 80 grit on a soft 7 inch pad, then switch over to an air file or long board with 120. 220 at the most before going to Interlux Precote, which fills in pretty much anything and goes on like milk.

Awlfair is awesome, as it doesn't take on air. At all. Period. You pull it, and have no pin holes. None. A really really tiny amount goes a long long way.
I balloon the glass before it has cured, so it fills the weave before you have to sand anything. Pretty much means that after I'm done putting the glass down, the ballons are mixed and I smear it out. Saves having to grind away the top of the weave of the glass to get a good tooth for the compound to grap.

[Hirilondë]

A friend swears by cutting awlfair with awlquick, letting them sit for a few minutes and then thinning out with acetone and spraying it, I'm not quite that ballsy.
.

I would never ever thin out epoxy. You are changing the chemical make up now and who knows what you end up with? I leave the chemistry to those who make the stuff and I stick with experimenting with the fillers to end up with the consistency I want to work with and the hardness, sandability and other characteristics I want to end up with. If you want a thin epoxy then I recommend you buy one, not try to change one that does not meet your needs to begin with.

[Rachel]

I balloon the glass before it has cured, so it fills the weave before you have to sand anything. Pretty much means that after I'm done putting the glass down, the ballons are mixed and I smear it out. Saves having to grind away the top of the weave of the glass to get a good tooth for the compound to grap.

Aha, so you apply the microballon-mixed fairing compound before the glass has cured past the green stage? Now why didn't I ever think of that? It seems so obvious now.

Rachel

[Zach]

Yup... Right after the glass is on, the compound comes out.

If its getting painted white, I add white pigment to the balloons to cover any darker patches of glass... then Precote comes in an eyeball melting white... Makes for quick progress.

Dave, as a rule I don't thin epoxy unless I'm rolling something like the underside of a cabin sole where deeper penetration and speed is important. Or wetting something out with resin that is super cold mollasses, way outside of its temperature window on something that has no need of being structural.

Zach

[Commander-147]

Thanks Zach and Tim for some imformative responses on this topic. I have been struggling with the same question and was happy to see your enlightening posts.

Thanks

[Hirilondë]

Yeah Zack, I still don't like the idea of thinning epoxy for any application. I don't think it improves the penetration much if any and I don't like that I may have reduced it to a really poor material. It isn't like a one part paint where you have just added more vehicle which will evaporate out. Epoxy doesn't dry, it goes through a chemical cure, and you are changing the chemistry with a material that is not supposed to be there. Most if not all manufacturers recommend against thinning.

This article gives one such professional opinion on the subject of thinning. You will note comment #3 in the article

"3) Water resistance of a piece of wood is not enhanced by deep penetration. Wrapping wood in plastic makes a pretty good waterproof seal without any penetration at all. Likewise, an epoxy coating on the surface is more water-resistant than a thinned epoxy coating that has penetrated deeply into the wood because, in most instances, the epoxy thinned with solvent is porous."

The hot recoat method Zack mentions works superbly. In stitch and glue dinghy building filets, tabbing and fairing of joints can all be done in one day with out any sanding until the end. Not only does it save an absolutely incredible amount of sanding, but you get a primary chemical bond between all layers. It does require being completely prepared and having a good amount of working time in one day if any significant area is being worked on. The planning and long day will be more than compensated for in the end.

[Quetzalsailor]

Applying filler to 'green' layup? Brilliant! I hope to remember that.

I use West 105 + either their fairing filler or their microballoons. My grump re: these fillers is that subsequent patches and filling do not have the same sandability, that is, there seems to be a less filled, more resin-y layer right at the interface and that does not sand out as well. It's also hard to get the same resin-filler ratio by eye, which gives a similar result.

[Rachel]

The hot recoat method Zack mentions works superbly. In stitch and glue dinghy building filets, tabbing and fairing of joints can all be done in one day with out any sanding until the end. Not only does it save an absolutely incredible amount of sanding, but you get a primary chemical bond between all layers.

I've often done the multiple layers, and even tabbing, all in one go; but just never thought to do the fairing. That may be because my glasswork is not always pristine, and so I need to go back and do some sanding before it's easy to fair (i.e. there are lumps and such that will throw the fairing off, and even sometimes air pockets I have to deal with). That said, I now realize there's no reason I still couldn't do some fairing right away (and sometimes my glass work is pretty decent right off the bat).

It's weird, but I just had it in my head that glasswork (multiple layers, granted, and even filleting) and fairing were two separate things, separated by curing, removing blush, sanding, and solvent washing.

But as they say, it's never too late to learn something new :)

Rachel

[Hirilondë]

......but just never thought to do the fairing. That may be because my glasswork is not always pristine, and so I need to go back and do some sanding before it's easy to fair (i.e. there are lumps and such that will throw the fairing off, and even sometimes air pockets I have to deal with).

You can always remove some lumps and drools with a cabinet scraper while the epoxy is still green and continue to use the hot recoat method. Have your cake and eat it too. I often use the cabinet scraper even if I am done coating so that later the sanding is less work. In case anyone hasn't noticed, I hate sanding. I refuse to cut corners that sacrifice the results, but working more than necessary doesn't improve the result.

[Zach]

Yeah using proprietary fillers can be nice, but it sure is expensive. You get easy to sand stuff that has some structural integrity... But really if you have to do much grinding, its because what was under the glass was lumpy, or you are using to much resin and it is floating the cloth. Take a straight edge or batten to her and fill the low spots with glass. before you start. Other times its the edge the glass the bites you... A lot of times I kill a layer of glass in the corners, and come back to lap the next piece to the same place if dealing with a large piece... then I'll add a smaller piece on top to tie everything together, then pull a coat of filler across it and blend everything. Think cockpit sole to cabin sides, or to the inside of a toe rail, transitioning from the hull to a molded rub rail... You can do it all in one piece, but it sure is a pain in the rear.

On real complex shapes I'll take a piece of brown paper, or rosen paper from lowes, and cut it to see what shape works. Add enough radiuses, fillets and curves... and you end up cutting darts and working it till it sets up. Contrary thought, its easier to do something complex with fast hardener as about the time its almost right, you can hold it in place as it gels. If you get a blister or goofy dart whip out the scissors and cut it out... then lay your next piece down cut so it works nicely going the other way. Lastly, when you build something, keep the sides square and straight and put as big a roundover as you can on it.

If you are dealing with pieces smaller than a foot in width, lay it out so you cut the cloth with the longest possible run of stitching. If you are doing something big enough that you have to stagger in other pieces, butt the seams a little loose rather than putting them edge to edge and run a little cabosil between them so there is no void. A 1/4 inch to 3/16ths as best as you can. Otherwise you have to grind through the top layer of glass to get rid of the lump, or float a lot of filler to raise everything.

Top and bottom edges of the cloth as it comes off the roll separate if you don't have a real sharp pair of scissors or just can't get them rolled out You can get the edge that wants to fuzz up to lay flat by vigorously rubbing your hand from side to side across it working from a 2-3 inches in out to the edge loosening up the bundle.


I use a 4 quart mixing bucket to stir in the microballoons on big surfaces. A mixing stick that is 2-3 inches wide is the quickest, helps to radius the bottom edges to the same as the bucket scraping around the outside, say one swoop a second nice and steady till it falls in. Once its thick enough to start dragging on the stick, i add cabosil til the it quits drizzling off the stick when you pull it out... then just a little more. If you are using fast hardener or using a lot... the viscocity of the mix cuts towards the tail end of the pot life so it needs to be a little thicker than perfect so when you are doing the final detail touchups, it drags perfect. Tropical hardener is really nice for this. Grin. West System is interchangeable hot, so you can roll the hull in fast, wet out the glass in slow, and microballoon it with tropical and everything will play nice together. This also means that if you run out of fast while mixing a pot, you can top up with slow... Good reason to mix by volume!

The best one to keep in mind... is G-flex is water proof. That means if you have a drip from somewhere, you can mix it up with a lot of cabosil, fill the drip... then glass over it. It really sucks having water wash the resin out of glass...

Back to fairing:

For intricate stuff I use a 2 inch chip brush to apply it. Fluff up the brush and pull out any of the loose hair. On things i care about being perfect the first time, I put a blob on a piece of plywood or cardboard and use a wide plastic squeedgee (the green ones taste better. Grin) and work the air bubbles out so I don't have any pin holes after it is ready. As far as squeedgees go, pay attention to the edge. One side has a mold seam and flash. This will drag the cloth and not give as smooth a coat as if you use the other side.

You can omit working the air out if you are switching to awlfair... it doesn't take on enough air to be worth mentioning. Keep the saw dust out of the microballoons and use a new bucket/clean mixing stick and gloves. It sucks to have to pick out stuff off of the boat to get the filler to pull tight... sucks worse when you find a little mountain mound of fiberglass wadded up. Focus on that one spot, and grind it till it is a touch low... then add fairing back. Otherwise when you are getting things flat, you'll likely hit it again later in the process.

Overkill the microballoons so you can burn back the high spots with 40 or 60 grit, then switch over to 80 and work it flat without getting in to the glass. I use the wide squeedgee and follow the grain of the biax... I mean, the stitching... so it has less lumps. When you get close to the edges of the glass, make sure you have a real sharp scissors when you cut the glass so it hasn't started unravelling. You can get around that a little by coating the surface with fast hardener and letting it tack up, wetting out the glass on a wet out bench. (Plywood table with polyethylene sheet stapled to it...) roll up the wet out glass and take it to the boat. A little cross-mojination happens and it sticks a bit better. If I am wetting out on the bench, i go a little wetter than it needs to be and focus on air rolling out most of the resin and squeedgeeing off the excess. I find when it is wetter, its easier to place the glass cloth where it needs to be, drier it hangs up and starts being a pain. On the outside corners, I put a light coat of cabosil on them with slow hardener, so the glass has something to goop down to when it wraps around. Keeps it from unrolling when you turn your back, it really doesn't take much at all.

For pulling huge fillets, glass the corner with one layer... pull the fillet and kick it with slow or tropical hardener so it doesn't turn into a sizzling hotdog weenie. When it starts setting up, add the next layers of glass. This traps the fillet so it can't crack out, and lets the glass stick in the corner easier... it just smushes into the goo.

I make filleting sticks out of sheets of polyethylene, then cut a sanding block out of pine or juniper on the band saw to the same radius, taking the line on the top and bottom so if the walls aren't square it doesn't cut in. I take a piece of adhesive paper and stick it in a section of fillet that I really like... and then sand the block to fit. Hit it with a pencil or something so you know you have contact everywhere. You might guess, this means it takes two fillet sticks... One that is a little bigger radius for pulling the fillet goo. One that is a little smaller, for pulling the fairing goo on top. The hard way is to take a sheet metal screed and pull it through the corner as tight as you can.

Hope this stuff helps speed up the process and improve your finish. There are probably some bad habits hidden in there, but that's how I do it.

Zach

[Zach]

Oh... on mixing stuff by eye... Go get a scoop of the proper size for your bucket or bag of ballons and cabosil.

Mix the resin by volume in a big pot, add scoops of balloons until it turns into whipped cream. Add cabosil till its starts to stand up.

After awhile its not by eye, but by feel...

West system is 5:1 so 6 parts total. 1 and 1/4 units plus a 1/4 for 1 1/2 = 6 parts. 2 1/2 to a 1/2 is 6 parts... 5 lines of resin plus a 6th of hardener.
A stick with measurements works when the bucket is nasty... Mark one side with 1/4 inch measures, the other with half... You can make different batch sizes. Mark them big and small. Derrrr!

If you overfill, underfill, run out of resin... prop up the bucket on something till the lines align. Thats the glory of going by volume, its adjustable on the fly.
If you overfill by a lot, you can dump the resin out into another bucket even if the bucket is used... so long as there isn't a whole lot of hardener still floating around it won't gel up in a normal pot life.
You have to be careful though, if you over do the hardener you'll get a wicked amine blush... West Systems fast can be just nasty, orange oily leftovers. High humidity after dark does it to me from time to time.

If you read the fine print about West Systems you have wiggle room:


105, 205, and 206 can go 6 pumps resin to 5 of hardener on the lean side... Which is good to know.

Basically, if you are close over doing the hardener is worse than having almost enough... Remember though, you can top up with any of the same system. 5:1 or 3:1, but not inbetween. (That I know of, need to call and ask.

Zach

[Tim]

Everyone's got to figure out their own way forward. Mixing shop-made putties can only be learned by doing it and by knowing enough basic information to determine which materials to use for which job or desired characteristic. Both West System and System Three offer excellent epoxy manuals that will cover all this information, should one be interested.

But it's really dangerous to even begin to suggest that one can be even remotely sloppy with the mixing ratio of epoxy resins and hardeners. Even striving for the best accuracy under real-world conditions will result in slight inaccuracies--and that's why there's that little bit of mix ratio wiggle room built in to the formulations. The product would never succeed in the real world if it had to be 100% accurate, obviously, since that minute level of accuracy isn't possible in shop or field. But never, ever count on this "wiggle room", because it really doesn't exist, and to suggest this as a means of making do is simply unacceptable.

I do not condone sloppy or "too cool for school" epoxy mixing. It doesn't take any more time to do it correctly every time...and ultimately takes far less time, since you avoid the possibility of wasted and miserable time when sloppy batches go bad (which they will).

People read this forum to get good advice on how to do the job right. Anyone posting suggestions on work ethic and technique must bear the responsibility of this mantra.

Folks, mix your epoxy with care. Period.

[jeffwagnpete]

Wow! This is great stuff from everyone who replied. It is why I have the upmost respect for this website and those who have been doing this for many years or by trial and error and are willing to pass this along to the beginner. Thanks so much fella's!!

Jeff

[Zach]

Tim, anything you'd like to add one getting a fair surface from the layup technique? I'm curious how you do yours.

That being said, don't take me that I'm condoning or endorsing mixing by eye out of a waxed paper cup, which I've seen done with no illeffects by more than a few highly paid professionals. (I am but a lowly paid one, I guess the difference is I measure? giggle.)

Show of hands who knew that was a window available. If, you have more time than money and run out of hardener in mid pump on the last of 6... It WILL kick. How many batches that get thrown away are the last one, right before you are about to head out from the boat because of some unforeseen circumstance? You can either set it aside and see, or use it and risk having to grind it off later... I prefer to know the outcome is within the boundaries allowed by the manufacturer.

I know I set aside more than my fair share, before calling up the tech line and asking point blank where the flexibility is, and if Slow and Fast play nice together. I got tired of having a pot that wasn't right, setting it aside and having it kick off perfect, melting out the bottom of the bucket.

It is good information to keep stashed in the back of your brain, I seriously doubt anyone would stray from the 5:1 ratio every time for cost cutting or what have you...

I have had more glue failures from contaminated cans of hardener, with the pumps left in them than I have anything else. .. makes bubble gum. I have a spare laminated mast beam that is glued together with bubble gum, which is still quite strong, I parked my truck on top of it. If you mix the hardener and it turns milky, don't use it for anything important. Unscrew the pump or lid of the hardener and set it under a heat lamp or near a heater in winter. Do test batches until it is clear and the moisture is cooked out. (Thanks Tech line...)

I've switched over to plastic 5 gallon drums with gasketed lids, as my shop is onboard a boat... and the drums, a 200 yard walk away.

Second to that, is when a piece of trash gets stuck under the head of a metering pump... and makes bubble gum. I had to re-recore a section of my foredeck because of this. My work bench tacks up when I wipe off resin drips with acetone, and isn't sandable because of this.

The only time I have had a glue failure from mixing by volume, is using slow hardener with tjree 5 gallon buckets after dark... 2 of resin, and 1 of slow hardener, and ending up with 6 parts of resin. That gallon wet out a 50 inch wide, 6 foot long strip, and part of the next piece over half of it. That sucked to grind off to say the least. It looked like it was snowing, and I looked like a feather duster when done. Don't work while tired. I've had to mix 3 drums this year, stupidity happens.

I switched to mixing by volume, after finding that using a gram scale in a shop full of wood dust doesn't work very well.

Going by volume: The accuracy does not have to be there in the pour of the resin, which is nice in cold weather, or huge volumes. Accuracy is brought back into line by bringing the fluid level to the measuring lines on the bucket.. Set a corner of the bucket on something. Half way, or a quarter of the way between lines is evident. I gained confidence by testing your accuracy with a few different sized containers with water and see how close you they are when you are off an 1/8th to one side of the line or the other.

It just isn't rocket science. Knowing, that there is a window keeps one from being over anal about something that in the end either works, or doesn't. I'm not religiously against mixing pumps, so long as you mix a test batch the day before and make sure it isn't bubble gum the next day.

Everyone has a comfort level with the materials involved. Tim, whats your worst epoxy failure been?

Cheers,

Zach

[Tim]

I've never had an epoxy failure using West System epoxy. Coincidentally, I have never tried to make a batch work if I had the slightest doubt about its proper mixture. It's always better to set aside a suspect mixture.

I have had two suspect cases involving epoxy in my checkered past, both on my own boat: one with MAS epoxy, the other with System Three. In both cases, the product eventually cured, and I was able to proceed without redoing the work. I learned lessons. I made changes. Both suspect batches have been featured somewhere on the Glissando website; I don't even remember what the first one was, but the second was during a recore effort on my foredeck in 2003. I've not had a failed batch since. I have set aside away the occasional suspect batch over the years, but this is infrequent; typically, the batches I set aside cure adequately, but I'd rather be safe than sorry.

I completely agree that those silly spring-loaded pumps are very prone to failure and are frequently to blame for bad mixes. They don't last very long, and need to be replaced frequently if one chooses to use them; similarly, anytime these pumps have sat unused for any length of time, one should be careful to test their operation before using. They are imperfect, and I'm not about to defend their shortcomings. But one must be aware of those shortcomings if one uses those pumps, and it's dangerous to play with these ratios.

Disclaimer: I now use, and have used since 2004, a pre-metered West System gear pump, which admittedly is quite spoiling, and is also an expensive piece of equipment--but extraordinarily worth the cost for anyone using quantities of epoxy. It pays for itself in quality and consistency of batches, convenience, and time saved. Even with this pump, if it's not been used for some time, I am very careful with the first batch, and often dispense. mix, and then set aside a small batch just to be sure.

I haven't used a resin mini-pump since early in the original Glissando project (1999-2001). Back then, it didn't take me long to abandon the fussy things in favor of pouring from the container: resin in one measured pot, hardener in the other before mixing together. I don't miss doing that, but it was easy and led to consistent results. There is nothing wrong with measuring into cups, but one still must do one's best to ensure that the ratio is as close as it can be made under field conditions.

If unsure: get rid of the batch. It happens, but need not occur frequently (or even at all) with the slightest modicum of operator care. So I think the potential waste is minimal to negligible if one cares to be careful. And one should so choose. Haste makes waste.

This is all getting way off the original topic. I don't intend to respond further, as I've said what I need to say.