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View Full Version : microballoons and no tape for a stitch and glue tender- strong enough?



peterchech
04-17-2013, 11:16 AM
I DON'T WANT TO TAPE THE JOINTS. I don't want to sand them. Wizbang makes his joints thicker on his dinghies so as not to need tape, but he uses some heavy duty filler. If I make the joints pretty thick on the inside, is there any reason microballoons would be too weak for such a light duty application? How thick should the joints be really?

I am building a bare-bones, CHEAP, super quick build, as light as possible little tender. Based on the Apple Pie dinghy, stretched by maybe 9 inches to 7'9 more or less.

http://www.masepoxies.com/sp/125876/images/finishedDinghy.jpg

I bought the BCX 1/4" ply, $22 per sheet, and don't want to spend much more than that. I have a few mostly clear "whitewood" (lighter than df) 2x4's to cut up for the gunwhales. I have some epoxy and microballoons just sitting in my basement so I think I'll go S&G.

I don't want to do much sanding, because I want to cut out the panesl after work friday, slap it together saturday, and paint it with left over house paint on sunday morning. That's why I don't want to tape it up, because in my experience sanding its edges adds significantly to the time of build. It's sailing season after all!

This is a CHEAP, slapped together beater dinghy. No sailing. Just towing behind my boat, rowing and mostly motoring with a 2.5 hp 4 stroke ob from boat to shore with two adults and a dog. Don't talk to me about protecting the wood with xynole, sheathing in glass, or anything like that. I want it to be as light as possible without spending money on marine ply or more glass/epoxy. I may even make the transoms out of 1/4" ply too, reinforced by 3/4"x1.5" solid wood at the sheer and at the motor mount.

Ian McColgin
04-17-2013, 11:21 AM
Microballoons are air. If you like air holding your joints together, fine. Personally I'd use something a bit more structural than air.

OK, serious answer - not on your life.

It's fine to not use glass. Light is good. But epoxy seal atleast all ply edges. If you can spread a thin coat of epoxy on the whole boat as a primer, better.

Where you can save some money is your paint. Use Sears Best Exterior Latex or something similar. Easy on. Tough enough.

G'luck

Peerie Maa
04-17-2013, 11:56 AM
I believe that Wiz fills his epoxy with something structural like ground cotton fibres, so that he is creating a fillet of cellulose reinforced epoxy.

JimConlin
04-17-2013, 12:07 PM
There's no free lunch. Use glass tape or a structural filler. A 50 yd. roll of 4" 8 oz. glass tape is about $30.

wizbang 13
04-17-2013, 12:13 PM
yes, west 403. cotton. inexpensive, not hi tech. A one inch putty knife ground round should be plenty for an 8 ' pram.
quarter inch is fine for the transom . I put a 40hp on a three eights transom. ( with bracing).

sanding filets is easy if you have the right tool . Cut sandpaper discs a bit oversize and glue them on a softpad. pre made store bought discs do not overlap. It is the overlapping part that sands the filet. That said , saving on sanding is not the reason I avoid tape.
You may be trying to build too quickly . SnG boats are easy to go caddy whompass crooked. I like to do the bottom and transoms, then let everything harden up , and test and re brace the boat before going to the sides, then putting the rubbers on later again.
make an X of strings fore n aft and have them touch in the middle.
but please don't use balloons for structure just because you have them on hand, that is def going too fast .
bruce

paul oman
04-17-2013, 12:27 PM
It really comes down to surface area. How far will your fillets overlap the ply and how thick will they be?

I generally just tape the inside on my stitch and glue projects and then hide the tape with thickened epoxy (which is sort of a fillet application)

micro-balloons are like tiny marbles. They roll past each other making the epoxy easy to slump. poly fibers or fumed silica look like tree branches and tend to resist slumping.
note too that the micro spheres come in different densities - most vendors offer 0.7 g/cc while we offer 0.6 g/cc and 0.28 g/cc for folks that want super fine and super light spheres.

capefox
04-17-2013, 12:40 PM
All the joints on those panels appear to be nice acute angles that will take a nice thick fillet that will hold a small pram together. Make sure you use a filling material that adds strength: milled fiberglass and cotton fibers are good choices. The micro balloons are more suited to fairing and cosmetic filling purposes, which you say isn't important to you.

Have you considered installing log chines? You could measure the panel joint angles, cut the lumber to match, caulk the joints with an epoxy/filler bog, and then nail or screw the whole thing together with silicon bronze (or at least well-sealed brass) fasteners.

If I were you, I'd use thick structural fillets backed up by one layer of two-inch glass tape on the inside and outside. (A 50-yd roll only costs about $15.)

JimD
04-17-2013, 12:54 PM
Micro balloons are not strong enough for filleting. Don't do it. Seriously. If you want cheap then take a belt sander to a piece of wood and make your own wood flour. Cheaper than balloons and suitable for the application.

htom
04-17-2013, 02:29 PM
Micro ballons are intended to break easily, leaving tiny holes to be filled at the next pass of filling. They are almost anti-structural. This would be a bad use of them.

James McMullen
04-17-2013, 02:35 PM
I wouldn't do it. Tenders see hard life. Bruce gets by while doing the wrong thing purely because of his charm and his mojo--things that the rest of us ain't got. You just need to learn how to tape seams correctly, and you're never going to get there if you don't practice.

Dusty Yevsky
04-17-2013, 04:24 PM
I DON'T WANT TO TAPE THE JOINTS. I don't want to sand them. . Peter clearly states his reason for not wanting to tape because he doesn't like sanding down the edges. However, there is a very easy way to deal with tape edges. Get a really sharp chisel plane and pare down the edge to a taper after the epoxy has set but before it has hardened. This is a lot easier than it sounds and saves heaps of sanding. Then just fill the weave, sand (just a little) and voila! an invisible but strong joint. I think this is as least as easy as fairing a fillet made with balloons. If you're still anti-tape I'd advise using chine logs before I'd trust a fillet made only with microballoons. Chine logs on this design make a lot of sense and are also really quick, cheap, easy and fun to make. If you're still not convinced take a lump of cured epoxy/microballoon mix and whack it with a hammer. Then decide if you'd trust your or your loved ones lives to this construction. I'll guess no.

capefox
04-17-2013, 06:23 PM
Do you have Aero and Herschey's chocolate bars in your area? Try this experiment -- snap an Aero in half and then crush it. Eat it. Then try the same thing with the solid Herschey's bar. Which one was stronger? The Aero is like the fillet with the micro balloons. Oh, and share the chocolate with your significant other. You need to canvas all the political support you can muster when you build a boat :-)

johnw
04-17-2013, 07:46 PM
If you want to avoid tape, use milled fiberglass, not microballoons.

Cuyahoga Chuck
04-17-2013, 08:14 PM
Glass tape has mucho tensile strength. That's why it is used when gluing ply panels togerther. Fillets have unknown tensile strength. Filleting was only introduced to supply a curved bed so the fiberglass's memory would not cause it to lift. There is no pervayer of boat plans I know of that promotes leaving the glass tape out. Like a glue and screw needs screws, S&G needs tape.
Here is my 8' dinghy.
http://gallery.bateau2.com/displayimage.php?album=343&pid=36798#top_display_media
Every seam is glassed. It's as stiff as a cob. It don't leak, it don't squeak and I know it will get me home even if I go way out there. A few times I dwelt upon the fact that I was in a boat the size of a bathtub and was more than I mile from shore. I was fairly confident that if anything spoiled this trip it would be because of me and not the boat.
I use the wet on wet technique. Fillet over the ties, glass right over the wet fillets. It goes fairly fast. And the weight came out at 65 lb.

Woxbox
04-17-2013, 08:21 PM
If you want to avoid tape, use milled fiberglass, not microballoons.

I've found goop thickened with milled glass harder to sand out smooth than goop over glass tape. I wonder, Peter, if sawdust isn't what you're looking for. It will put some fibrous material in the mix and won't inhibit sanding.

johnw
04-17-2013, 08:55 PM
I've found goop thickened with milled glass harder to sand out smooth than goop over glass tape. I wonder, Peter, if sawdust isn't what you're looking for. It will put some fibrous material in the mix and won't inhibit sanding.

I use it because it's much stronger than cotton or wood fiber. I put waxed paper up against it to make it cure smooth, and what lumps remain, I fair with fairing compound. You really don't want to put a lot of tiny glass daggers in the air, so sanding the milled glass doesn't appeal to me.

The usual method is not to put goop over glass tape, but to put down the goop, and put the glass tape over it, so that you don't have too sharp and angle on the tape. My feeling is, if I'm going to put glass on it, and I'm going to put fillets on it, why not put the glass in the fillets, so there's only the one step?

M. J. Notigan
04-17-2013, 09:02 PM
Got kids or loved ones who would use this cheap and microballon filleted boat, too? Contemplate that for a moment. Sorry to be abrupt about it. Maybe you just ought to buy a fiberglass boat to avoid all hassle. Stitch and glue, tack and tape has building disciplines just like a plank on frame traditional build for a reason. And the last I checked no one in good standing has ever recommended what you want to accomplish. Darn North Jersey guys! And to think you want to take man's best friend out in this thing......:d
Regards,
Mike
South Jersey....

Lewisboater
04-17-2013, 09:12 PM
Talc (baby powder) makes a decent filleting material. If you don't want to sand, tape the edges of your fillets to get a nice border, lay in the material and smooth it out to a nice even cove then let it get tacky (so it holds it's shape if you touch it lightly), pull tape and then coat with a light coat of raw epoxy to finish. Make sure you cover all external exposed ply edges with a couple of coats of epoxy. Your Schedule might be a bit ambitious... by a day or so.

johnw
04-17-2013, 09:16 PM
Talc (baby powder) makes a decent filleting material. If you don't want to sand, tape the edges of your fillets to get a nice border, lay in the material and smooth it out to a nice even cove then let it get tacky (so it holds it's shape if you touch it lightly), pull tape and then coat with a light coat of raw epoxy to finish. Make sure you cover all external exposed ply edges with a couple of coats of epoxy. Your Schedule might be a bit ambitious... by a day or so.

But that's just the fillet that you then cover with fiberglass, right?

Lewisboater
04-17-2013, 09:30 PM
No... if done as large as Wiz's they should be quite strong enough. Remember... this boat isn't gonna take a pounding at 40 mph... more like 4 or 5. With the addition of the thwartship bracings from the seats and mast partner plus the knees in the corners... It should be just fine. This is just a quick and dirty boat to get onto the water with not much expectation of a long life.

johnw
04-18-2013, 12:46 AM
Wow. Bruce holds his boats together with lint, but at least that has fibers. I've never thought of talc as structural. All hail the great god Epoxy!

peterchech
04-18-2013, 06:22 AM
Ok looks like micro balloons are out...

I do have access to titanium dioxide, and talc, though the cotton filler sounds promising...

capefox
04-18-2013, 10:28 AM
Will the pram spend most of its life in the water? I've read a few articles that suggest talc is a less-than-ideal filler because it weakens a submerged joint over time. Talc won't produce an optimally strong joint like cotton fibers and milled fiberglass.

If cost is a factor: consider the amount of milled FG or cotton fibers you would need will cost you less than $10. Sometimes a fiberglass fabrication company will resell or give you some filler. A local shop that builds composites, including ornate spires for Mormon temples interestingly enough (http://www.ldschurchtemples.com/oquirrhmountain/), gifted me a gallon of milled fiberglass filler. I insisted on paying, but he declined. We have a lot of kind people in this state.

peterchech
04-21-2013, 11:42 PM
Ok... How about west 406, colloidal silica? It gets 4 stars on the can for "fillets", more than any other west filler, and is a "adhesive" type filler unlike micro balloons... Also very light... And I have some...

here is the build less than 2 hours from putting pencil to plywood, two people working: http://i961.photobucket.com/albums/ae96/peterchech/IMG_20130422_001651_zpsabfbdd6b.jpghttp://i961.photobucket.com/albums/ae96/peterchech/IMG_20130422_001651_zpsabfbdd6b.jpg

I stretched apple pie to make the side panels 8' long. Had to make the bow transom much narrower to fit on the foredeck of my 25 footer, it's now 2' at its widest. The widest beam is about 4 inches aft from center, and is 46" at the gun whales and 36" at the floor so 6 inches wider than apple pie.

johnw
04-22-2013, 12:32 AM
well, it's got to be better than microballoons.

Lewisboater
04-22-2013, 07:25 AM
Better known as Cabosil or Fumed Silica. Excellent Thixotropic properties. Wear a mask and don't breath the dust... which will float everywhere. Don't use it with ANY kind of breeze/wind anywhere near it. It will initially be hard to blend it with the epoxy but keep gently folding it into the middle and after a while suddenly it will all disappear into the mix.

Woxbox
04-22-2013, 07:53 AM
Much stronger but very hard to sand. Do everything you can to get a nice smooth finish before it hardens up.

wizbang 13
04-22-2013, 08:02 AM
moondust.
when west gives it 4 stars for fileting , they are assuming you will tape it . they are speaking to the ease of making a smooth job.
I would not /do not use it for no tape fileting

peterchech
04-22-2013, 10:17 AM
moondust :-)

I wonder if it's less work to cut up glass into little pieces and mix it into the epoxy or just save my scissors and tape the darned thing...

I have a question regarding design too but I'll post that in the design part of the forum I guess...

M. J. Notigan
04-22-2013, 10:45 AM
West 405 filleting blend is what I use. Often I will mix it with their 404 High Density to make a smoother, peanut butter type consistency. Then apply your tape and epoxy resin.

Cutting tape into little pieces is a nice idea. I tried it and it is a big FAIL. You cannot and will not make the desirable coved fillets with that stuff. Recommend you go the tried and true route with the proper materials and methods.

Either way you go, I wish you the best of luck.
Take Care,
Mike

Cuyahoga Chuck
04-22-2013, 10:49 AM
I am curious about all the talk of sanding fillets. Fillets only have to be big enough to form a cove to accomodate the glass. When I do the wet on wet procedure I use the proper size tongue depresser and strike off any exess with a putty knife and the fillets are clean enough to slap the glass right on.
Very strong. Very light. Excess use of epoxy is an important factor in increasing hull weight. Structural fillets require a lot more epoxy and deliver a lot less strength.

To keep hull weight down I used a good grade of underlayment which turned out to be as light as okoume, 20 lb/sheet. No matter what you do a hull made from exterior grade ply is going to be about 1/3rd heavier. Weigh a sheet before you cut it up.

wizbang 13
04-22-2013, 11:17 AM
"Excess use of epoxy is an important factor in increasing hull weight."
really ? I don't think so

capefox
04-22-2013, 11:25 AM
A gallon and a half of epoxy only weighs around 17 lbs right? The fillers a few pounds more. I guess it depends what one means by "significant weight."

johnw
04-22-2013, 01:53 PM
Better known as Cabosil or Fumed Silica. Excellent Thixotropic properties. Wear a mask and don't breath the dust... which will float everywhere. Don't use it with ANY kind of breeze/wind anywhere near it. It will initially be hard to blend it with the epoxy but keep gently folding it into the middle and after a while suddenly it will all disappear into the mix.

I don't use the stuff anymore because I don't want to breath it. I use cellulose filler (cotton fibers) instead for thickening.

capefox
04-22-2013, 02:16 PM
What sort of texture does the milled cotton give the bog? I think milled FG makes it a little sticky like bubble gum on a hot day.

wizbang 13
04-22-2013, 03:56 PM
a "pock marked " texture, not smooth.
yet , never "itchy" like milled fg

dinoa
04-22-2013, 04:24 PM
I don't use the stuff anymore because I don't want to breath it. I use cellulose filler (cotton fibers) instead for thickening.

You should keep FS in your bag of tricks. As mentioned when added it makes the mixture thixotropic so it won't run. A pure cotton flox epoxy bog will tend to run especially when placed on a vertical. Add a little FS and it sticks and holds like the proverbial snot.

Dino

wizbang 13
04-22-2013, 05:32 PM
You should keep FS in your bag of tricks. As mentioned when added it makes the mixture thixotropic so it won't run. A pure cotton flox epoxy bog will tend to run especially when placed on a vertical. Add a little FS and it sticks and holds like the proverbial snot.

Dino
na uh, I have not had that problem

dinoa
04-22-2013, 11:52 PM
Would you be interested in making your cotton flox smoother and almost creamy, so spreadable its incredible while not risking running? Adding a little FS will do it.

Dino

Tom Lathrop
04-23-2013, 08:04 AM
Wow, I guess this problem is all cleared up. We don't solve problems so much as trample them to death.

If you don't like sanding, then don't use any fibrous filler since it will leave a rough surface that is the dickens to sand smooth. If you don't want to use tape, then you need some fibrous filler. Choose your poison.

I revere the Gougeon brothers but if you are going for cheap, you need to stay away from their products. This pram sounds like the proverbial sows ear.

All filets that are expected to hold the formed shape should have cab-o-sil added.

The only way to get a free lunch is for someone else to buy it or to eat what you find in the field..

spirit
04-23-2013, 08:38 AM
Let's see now...
Two weeks more sailing vs a strong long-lasting boat.
You choose!