Epoxy Frustration

[SWA]

Been working like the devil to get the epoxy done on my little sailboat. Want to paint and get in the water this year. Viscious cycle, put the epoxy on, sand it smooth, see the fiberglass weave, repeat cycle. Using 220 grit sandpaper, rolling on two applications of epoxy before sanding. My title for this job should be maker of extremely expensive white dust. Not sure what the problem is, but at this rate the boat will never leave the garage!!!!!

Steve

[kc8pql]

Either use thicker coats of epoxy so you won't sand thru or, since you're going to paint, use micro-baloon fairing compound. This assumes that the fiberglass was properly wetted out when you put it on.

[ 02-22-2005, 05:23 PM: Message edited by: kc8pql ]

[landlocked sailor]

And consider scraping, rather than sanding. Rick

[Bill Bliss]

Scraping is excellent advice. See WB#165 about using cabnet scrapers on epoxy.

Scraping takes of the high spots while leaving the lows. I did not discover this until I had already completed the outside of my hull -- and I was sanding as much off as I was putting on. I was erroneously focused on getting a smooth surface too early. Do not be obsessed with getting a uniform frosty finish over 100% of the surface -- let the low spots stay and just touch them up with a scotch-brite pad to rough them up a bit. It's too easy to overdo it with sandpaper.

When I worked on the inside of the hull, I had read Robb White's article in WB165 and put it to use. It made for much more plesant work (less dust). Granted, the scrapers dull pretty fast with epoxy, but overall it was a time-saver.

By the way, although I am not a brand loyalist as a rule, I did notice that the actual Scotch-Brite pads (3M) cut better than the brand X.

I usually applied 3 coats in one day to take advantage of the green-cure window. But I would never do more than 3 coats without scraping or sanding. If I scraped within a day or so, I found that the scapers dulled a lot less quickly than if I waited a week.

-wcb

[Todd Bradshaw]

As long as you're not sanding deeply into the fiberglass and cutting a lot of it's fibers you may not really have a problem. It's possible to "see the weave" by just sanding down slightly into the tops of the fibers. Woven fabric is a 3-dimensional thing where yarns go up and over other yarns as the cloth is woven. Once laminated, there are small "peaks" in these spots. Sanding down only slightly into them tends to show as a whitish grid. Between the peaks of the yarns, you're only sanding resin, so it tends to show up as a different color, making the grid stand out visually. In general, it's a good rule to stop sanding as soon as you see any spots where the grid is starting to show, but when feathering out reinforcement patches, repair patches or overlaps between different chunks of fabric it's routine to sand deeply into the cloth. These spots aren't weaker or more vulnerable than the cloth around them and usually finish-up just fine - both under paint and for the most part, varnish as well in the case of clear finishes.

It is important to avoid cutting halfway through the cloth that's supposed to be reinforcing your boat and things tend to go smoother if you apply the proper number of filler coats to give you some sanding cushion, but if you're just starting to see a bit of weave showing, I doubt you really have a problem. Fussing over the job again and again may not be getting you a better or stronger boat.

[RodB]

The most likely explanation for your problem is not applying epoxy thick enough...or sanding way too much.

When glassing my 18 foot skiff I squeeged on the first two coats of epoxy and then rolled and tipped the last two coats. I have sanded to a nice satin finish with 80 grit paper (and my right angle aggressive ROS).... no problems that I can remember...BUT I do think applying the epoxy evenly and uniformly is the key.

Its quite easy to apply the first two coats evenly with a squeege but the last two coats require more technique and patience. If you use a 7" roller cut in half (3 1/2") and cover approx 10 sq inches at a time...then tip very lightly with a foam brush... you end up with a very even coating of epoxy that covers the weave of the cloth very nicely at the end of four coats. I also think temperature ranges in the 70-85 degrees allow for the easiest conditions to get nice leveling and uniform thickness of coats. Cooler temps make for greater viscosity and make for more difficult conditions for producing nice even thickness coats...but good technique can still get nice even coats with epoxy at its thicker end of the spectrum in the cooler temperatures.

Good luck,

RB

[ 02-23-2005, 05:27 AM: Message edited by: RodB ]

[WayGray]

Great discussion. I am just getting ready for this step and appreciate the review and advice on the subject. Thank for bringing it up.

[Cullen T.M. McGough]

Here's a trick used by time-honored hacks:

When applying new fiberglass

1. wet out surface
2. lay down glass
3. wet out fiberglass
4. immediately mix up epoxy + micro balloons into a nice yogurty thickness and apply on top of the still-wet fiberglass
5. spread this around with a wide spatula so you get a roughly even thickness
6. let it harden

You'll now have a nice 1/16 to 1/8 layer of epoxy-balloons to grind down fair, before applying another fairing coat.

WARNING: you'll have to take some care in the temperature and thickness of the epoxy involved. Too hot or too thick will cause bubbling.

If you don't want microballoons, or some other thickener, don't forget you can remove the amine blush with a scotchbrite pad and good 'ol hot water. Scrub hard!

[fair&fair]

It seems like the above method is going to introduce a rather heavy workload for someone who is simply trying to get rid of fiberglass weave. Making sure everything is completely wet out to begin with helps. Using peel ply is a great way to get rid of weave and achieve a surface that can be primed. Peel Ply is not cheap, but niether is time...in this cas well worth the price. As a boatbuilder who has done a fair amount of fairing, just slapping on putty willy nilly is something I try to avoid at all costs.

[FG]

are you seeing the weave when you wipe it with a damp cloth?

If not, you may be done.

[SWA]

Yes I do see small sections of weave when I wet the surface with a cloth. I am assuming that I am sanding to much, and will try to use a scraper (will be a first for me!). After you use a scraper, do you still stand? Does the scraper take well to the curves of the boat? I guess that I will know shortly after I start this process ;) Thanks to everyone for their help. I am also trying to apply the epoxy in thicker layers.

Steve

[Bruce Hooke]

After scraping epoxy I like to sand VERY lightly with 220 paper just to give the surface a bit of tooth for the paint to grab onto. I don't really know if this is necessary. A scraper can be bent somewhat to conform to bends (especially if it is a thin scraper to start with), but for really tight curves (especially concave surfaces) a regular scraper will not do the job and you may have to go back to sandpaper. Curved scarpers are available but I think they are going to be more trouble than they are worth except maybe for situations where you are trying to remove a lump, such as might be left by filling a hole or dent.

If you are just seeing a little of the weave then as Todd noted I don't think you have a problem.

[Todd Bradshaw]

Steve, are you planning on painting the hull or using a clear varnish finish? If you're going to paint it, seeing a bit of the weave isn't a problem as long as the surface is smooth. It will paint just fine and isn't a liability. Continuing to add and sand or scrape off additional resin on top of it isn't going to make any kind of practical difference in the quality or strength of the finished boat. If it will be a clear, varnished finish the best way to hide (as much as possible) exposed weave is probably to wet-sand those areas down to somewhere in the 320 grit range to polish the exposed fiberglass strands as much as you can before varnishing.

This is a picture of the lower stem area of a very large strip canoe. It's a feathered build-up from one layer of heavy (9 oz. if I remember correctly) fiberglass cloth to about six layers. On this boat, durability in that area had to be a higher priority than cosmetics. The feathering was done with a combination of filler coats and sanding and you can clearly see the weave where the layers feather-out. Even so, it's smooth and very strong. Had it been a painted hull, nobody would ever know that the weave showed from the process of sanding it to a feathered reinforcement patch. In this case, it's in a place that's hard to see and which is underwater when the boat is in use, so it worked out fine even under varnish. It was sanded to about 100 grit with a feathering disk on a big grinder. Had I decided to wet sand it to a finer grit, the weave would have been less visible.
http://www.imagestation.com/picture/sraid115/p0884c39cc2f38081484679d12953b6f3/f8cbc5a5.jpg

[L.W. Baxter]

Originally posted by Cullen T.M. McGough:
Here's a trick used by time-honored hacks:

When applying new fiberglass

1. wet out surface
2. lay down glass
3. wet out fiberglass
4. immediately mix up epoxy + micro balloons into a nice yogurty thickness and apply on top of the still-wet fiberglass
5. spread this around with a wide spatula so you get a roughly even thickness
6. let it harden

You'll now have a nice 1/16 to 1/8 layer of epoxy-balloons to grind down fair, before applying another fairing coat.

WARNING: you'll have to take some care in the temperature and thickness of the epoxy involved. Too hot or too thick will cause bubbling.

If you don't want microballoons, or some other thickener, don't forget you can remove the amine blush with a scotchbrite pad and good 'ol hot water. Scrub hard!This is an interesting suggestion, in that it contradicts what (little) I know of using epoxy and fiberglass.

I thought that FRP stood for Fiber Reinforced Plastic. The idea of slathering on a thick layer for fairing on top of the glass would seem to be backwards.

I will be fairing and glassing a plywood hull soon. My plan is to fair with epoxy and microballoons first, then apply the glass over the top as reinforcement, and then apply only enough epoxy to fill the weave of the glass.

If one can apply a thick layer of epoxy without reinforcement, why use glass at all?

Just curious.

--L.W.

[Todd Bradshaw]

I've done it both ways, but on boats which get different kinds of use. Using microballoon fillers on top of the glass has characteristics which in some cases keep it from being a good method. First of all, it's not very tough. If the boat is one which will get beached, the stuff is pretty soft and won't handle abrasion well. If you're looking to add impact or tensile strength, it adds very little, if any, and can be pretty brittle. Sanded microballoon-based filler mixes are also a pretty poor base to paint over. Sanding cuts a lot of the balloons on the surface open, leaving tiny, air-filled craters which don't hold paint very well. The techs a Gougeon say to always sand and then top-coat microballoon fills with plain epoxy, sand that smooth and then paint if you want a high quality paint job that lasts. There are other fillers which make a harder, tougher surface and paint OK, but they tend to be pretty hard to sand smooth if you have a whole hull to do. Fiberglass on top, filled with plain resin is much harder and more abrasion resistant than a balloon fill on top. It also adds strength and generally will flex farther before failing or shearing away.

My favorite method of fairing with balloon fillers is to use a notched squeegee to spread the balloon mix. The stiff blade has square notches about 1/8" to 3/16" deep cut into it, 3/8"-1/2" apart all along the blade part. You mix test batches of resin/balloon mix until you get one which is thick enough that it will stand up without sagging and flowing until it cures. This takes a lot of filler but it's critical that the stuff hold it's shape. Once you find the ratio of resin to filler, you stick with it. The hull is squeegeed with the mixture as neatly as possible. It's almost like you're using a comb with the notches leaving small square ridges of filler in neat rows, all over the hull. Once cured, you longboard the hull by hand to a fair shape. It's fairly easy though, because you're only sanding down the tops of the ridges, which is actually a fairly small percentage of the hull's real surface area. You can sand the ridges down to almost nothing or leave them pretty tall, depending on how much of a hump or hollow a particular area has which needs to be faired-out.

Once the longboarding is done more filler is mixed and slathered over the hull using a spreader with no notches. You drag it along the ridge-tops, filling the spaces between the ridges. When that cures, a light sanding cleans everything up and you have a fair surface. This can then be resin top-coated and painted for things that won't be dragged up on a beach or bounced off of rocks. That's how I faired the cast iron keel on my Starboat. I've also done the same thing to a lumpy canoe hull prior to fiberglassing, filler coats, etc. I guess I'd make a pretty poor ceiling plasterer, because just slapping a wad of filler on and trying to trowel it out uniformly has never worked for me. At one point, I thought about trying to become a speed doctor (a guy who tweaks and fine-tunes racing sailboats for rich guys). That's when I first tried the notch method for fairing and the results were quite impressive. O a plywood hull, it might be overkill unless you use really shallow notches, but keep it in mind if you ever run into a heavy-duty fairing job.

[Bob Smalser]

Originally posted by SWA:
Been working like the devil to get the epoxy done on my little sailboat. Want to paint and get in the water this year. Vicious cycle, put the epoxy on, sand it smooth, see the fiberglass weave, repeat cycle. Using 220 grit sandpaper, rolling on two applications of epoxy before sanding. My title for this job should be maker of extremely expensive white dust. Not sure what the problem is, but at this rate the boat will never leave the garage!!!!!

SteveThen simply stop building that way once this project is done. I don't...and I likely won't ever.

Sound, tight, easy-to-maintain and easy-to-repair boats were made for centuries before "manufactured wood" and the Goo Brothers came along.

With the advent of inexpensive portable sawmills, there is a rapidly-increasing number of all sorts of folks milling and selling excellent air-dried stock in almost all parts of the country, so absence of wood that's up to the task isn't an excuse any more. Find them on Woodweb.

Gooed and glassed boats are often designed and built with no view ahead to future repairs or restoration, and simple structural repairs that would take hours on a traditional boat can take several unpleasant days on a Goo Boat. No more fun or interesting than repairing a fiberglass boat, either.

I'll show you exactly what I mean in another week or so.

[ 02-26-2005, 03:50 PM: Message edited by: Bob Smalser ]

[paul oman]

apply epoxy to the fiberglass cloth - cover the wet epoxy with wax paper or poly plastic. Let the epoxy get hard - peel away the plastic or wax paper. Surface tension will keep the epoxy from draining out of the weave - result - less epoxy, less weight, smooth surfaces

paul oman
progressive epoxy polymers
www.epoxyproducts.com/marine.html (http://www.epoxyproducts.com/marine.html)

[L.W. Baxter]

Interesting tricks, gentlemen!

Todd, your comb-over method sure sounds slick. I don't think I'll need it for my current project, as I'll only be doing some spot touch-ups. (It's already pretty fair, you see. ;) ) Your points about the fragility of unreinforced epoxy gibe with my own limited experience.

Paul, if I understand you correctly, using wax paper one can avoid adding coats to fill the weave, achieving a smooth surface in one go? Save money, time and weight... Brilliant!

--Lee