Fiberglass application question

billyp

billyp

Been Around the Block
I'm going to be doing a tail section out of fiberglass and I've never done any glass work so I have a question. My plan is to put a thin veil fabric as a base layer and 2 layers of woven fabric on top of the foam mold. My reasoning is I think it will be smoother, assuming my mold is nice and smooth of course, thus requiring less hours of filling and sanding. My question is this...will there be any foreseeable problems if I add a couple of layers of chopped mad to the UNDER side of the tail section for added strength? I wouldn't think there would be but like I said, I've never done any glass work so any advice would be great
 
Are you actually building a mold, or just popping a piece off the plug to use?

Making a mold, will cost you a bit more, but save you a shit load of time on finish work.
 
I was just going to do the traditional foam plug, shaped and taped then waxed and glassed. I had considered a mold but it would have to be two parts and I'm not sure I want to tackle that for my first time.
 
After pulling the plug adding the mat to the back would be good. For smoothness you can "hot coat" it like a surfboard, by adding styrene with wax dissolved in it to some resin and brushing it liberally. The styrene makes it runny and the wax aids in sanding as it comes to the top.
 
I've read different things about using epoxy resin with chopped strand mat, some say you can, some say you can't because it doesn't break down what holds the strands together like polyester resin does. I come to the Ton for answers....what say you???
 
Epoxy doesn't work so well with chopped strand. Polyester or vinyl ester. However, chopped strand gives you the most strength with the least amount of glass.
 
billyp said:
I've read different things about using epoxy resin with chopped strand mat, some say you can, some say you can't because it doesn't break down what holds the strands together like polyester resin does. I come to the Ton for answers....what say you???
Click to expand...

What he said^

You have to use a resin that has styrene in it to break down the bonds in the chopped matt. Any resin that uses MEKP as the catalyst will work, epoxy will not.
 
Though my preferred method of composite construction is with the use of a female mould, there are times when the male method is the only way to accomplish the task (I'm working on one now).
I've seen a bunch of projects where the builder has laid up layer after layer of mat on his buck, ending up with a surface finish that looked like a photo of the Himalayas from 60,000 feet, needed a ton of sanding and mucho filling with bondo to get a satisfactory product, but if you insist... there is (was?) mat available to use with epoxy. It has a different binder that holds the short range glass fibers together but when I went to buy some for a project, even the guy selling it said, "... it doesn't work very well...".
I think if you use a 6 ounce cloth like weave #3733 (sometimes called canoe cloth because a lot of guys cover their rip'n'strip canoes with it), a good quality resin and some patience, you should be able to lay down the part okay.
Things to do: first, make paper "ply" patterns to imitate the shape of the glass cloth pieces and see how they will fit - if you can get the paper to drape okay - and newspaper is cheap, right - transfer the shapes to your cloth, do a dry fit with the cloth and then have at it. You'll probably need to have a couple of pieces of cloth for each ply / layer you put down and one of the "rules of thumb" is to have at least a half inch overlap on the pieces, kinda like shingling - an inch is better. Try to stagger the overlaps a bit for each layer to minimize having a couple of really thick areas in your lay up. If you have an intricate or fussy area in your lay up that the glass cloth seems to have problems going around, try changing the angle that you cut the cloth out of your fabric roll, as cloth has directionality (warp along the roll, fill or weft across it) and it drapes around or into a shape differently depending on the warp direction - experiment with a scrap piece of cloth first. Some of my bike parts have a specific warp direction specified for the cloth and of course all of my aircraft work does - makes a real difference. You could get real jammy and start using different warp directions for each ply of cloth, but maybe a bit over the top for a first project?
If you know beforehand where you're going to drill the mounting holes, add additional localized pieces of glass cloth - use circular ones, small to large, a little larger diameter each time to spread the load out (think upside-down wedding cake tiers) to the lay up.
Six ounce cloth doesn't have a really coarse weave texture and it fills easily with most pinhole fillers and / or a couple of coats of primer-surfacer, sanding after each application.
As far as the number of plies (layers) of cloth you need, it depends on the part shape and use. I think that a lot of people go overboard on the thickness of the part, but better that way than the other way around I guess. You can also bond in stiffeners - you can use a lot of different materials - but again, maybe a little over the top for a first project?
Hope this helps.
Regards,
Pat
 
Wow, that does help! I'm planning on making my part with a layer of veil then layers of 3 or 4 oz cloth. Once it hardens and I scoop out the foam I'll be adding chopped mat to the inside for strength. I want to keep the outside as smooth as possible so I don't end up with trying to sand down the Himalayas. I asked about epoxy and mat besause that's what I have for a carbon fiber project, I've since ordered some polyester resin.
 
X, +1 to you for correcting the oft-heard comment that mat is stronger than cloth - I even saw it in a car magazine awhile back. We could discuss fiber length, resin to fiber ratios and stuff like that, but probably no one really cares, right?
X, - 1 to you on your comment about woven roving. The fiber / resin ratio isn't that great, even though a lot of boat builders use it to build thickness / bulk / strength quickly during their layups but they're not that concerned about the weight as far as I can tell.
What we want to do is maximize the fiber to resin ratio of any composite part and with the "gaps" in roving weave, just not possible. Sure, a 20 ounce roving is a lot stronger (and heavier) than a ply of say, 6 ounce cloth, but compare apples to apples and do a lay up with an equivalent amount of cloth with different warp directions and then compare the characteristics again.
Woven rovings also have a tendency to do some serious telegraphing, to the point you can feel ripples in the surface of the finished part - though you can design the layup to minimize the problem.
Rovings are seldom seen in any (certified) aerospace composite part today; I remember the early Piper Cherokees used it in their 'glass wingtips and parts of their engine cowls around 1968 or so. The preference today is to use multiple plies of cloth with varying warp directions to maximize strength and minimize weight.
But all the poor guy wants to do is build a neat seat for his ride that won't look hideous or fall apart on him, so maybe us "armchair gurus" should give it a rest eh?
Pat
 
Thanks Pat, all input and opinions are apprecited, that's why i asked the question in the first place. But, you can only learn so much from the interweb, eventually you need to put your big boy pants on and do it. Experience is the greatest teacher. I'm making a fiberglass sheild for my son this weekend just to get my feet wet with foam, resin and glass, then onward and upward...

I'm only making a tail section and it won't be weight bearing in any way. If cloth is stronger than mat I'll just skip the mat and build with two layers of 3 oz, a layer of some 8.2 I already have and a layer or two of 3 oz on top to reduce the "telegraphing" of the 8.2 and require less bondo. I'll see how strong that is a go from there
 
no arguments, all great info
i see almost everybody trying to do a part with all mat in one shot and the outcome is horrible,and terribly messy it just so much more sense to layup multiple layers of cloth with laminating resin on a simple form like these cafe seats, it is much easier to work with and you can make a smoother part
 
billyp said:
Thanks Pat, all input and opinions are apprecited, that's why i asked the question in the first place. But, you can only learn so much from the interweb, eventually you need to put your big boy pants on and do it. Experience is the greatest teacher. I'm making a fiberglass sheild for my son this weekend just to get my feet wet with foam, resin and glass, then onward and upward...

I'm only making a tail section and it won't be weight bearing in any way. If cloth is stronger than mat I'll just skip the mat and build with two layers of 3 oz, a layer of some 8.2 I already have and a layer or two of 3 oz on top to reduce the "telegraphing" of the 8.2 and require less bondo. I'll see how strong that is a go from there
Click to expand...
using a layer of mat sandwiched twixt cloth is a good way to go to get the outer layers further apart hence a stiffer piece
 
xb33bsa said:
no arguments, all great info
i see almost everybody trying to do a part with all mat in one shot and the outcome is horrible,and terribly messy
Click to expand...

^^^ This is an excellent point that hasn't been mentioned yet. If you are not vacuum bagging, you don't have to do all the layers at once. In fact it is much easier to do 1-2 layers at a time, it helps to conserve resin, and limit bubbles. I usually will do one layer of 6oz weave with epoxy, let that cure for 12 hours, knock down any high spots with an orbital sander, then apply the next layers. I usually will do 3-6 layers of 6 oz. weave depending on what I'm making. Also if you have a fairly complex curve, twills drape very nicely.
 
xb33bsa said:
using a layer of mat sandwiched twixt cloth is a good way to go to get the outer layers further apart hence a stiffer piece
Click to expand...
They make some stuff, just called "Aircraft grade bulker" for that. Works wonderfully.
 
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