Unfortunately in our experience the quality of the final product is proportional to the amount of money spent on it in consumable material. I'd do this with a piece of dacron peel ply the shape of the fin plus an inch or so in every direction, and a layer of airex breather cloth or a nice non-textured paper towel (several, actually) on top of that, then the wax paper or a real nylon release film. The bag of sand is, however, an excellent compression method we have used many times before.
Also, it looks like that is red paint-it's doubtful that the epoxy will adhere to paint well, I'd sand all the paint off, then scuff the G10 with 60grit sandpaper as roughly as I could.
In addition to what is stated above, I would recommend parchment paper. I've used it for pressing fiberglass plates and it creates a near perfect finish. It also doesn't seep through. I have used wax paper and it does seep through, but not parchment paper. Quite cheap for a large amount.
You want water like consistency. Actually you want a laminating resin, which will be quite a bit thinner than what you used. You also want more working time so you do not have to rush.
Epoxy does not stick very well to plastic. It stick rather poorly to waxed plastic. Mylar sheets are a good choice, waxed.
You cannot pile enough sand on to get the result that you likely want, which is a compressed laminate. Let's say your surface is 6" x 4". This is 24 square inches. If your sand bags weighed 24 pounds, then the resulting pressure is one pound per square inch. That is, not much. This is why people use vacuum bagging methods. Even a poor vacuum system will get many times the pressure you can achieve with sand.
Alternative methods:
Vacuum bagging. Probably the best method. If you have a food saver around, you can use that to do the job. Search for food saver vacuum bagging wings.
More pressure. Get some thick slabs of plywood or metal. Get some sheets of the spongy foam that used to be used to wrap receivers in RC planes. Make a sandwich of your fin, surrounded by your fabric and epoxy, layered between waxed plastic sheets, layered between sheets of spongy foam, layered between solid plates. Use a big vice and/or several big c-clamps, and squish it. Hard. You can get adequate pressure this way.
Stick then laminate. Get a can of 3M77 spray contact adhesive. Lay a piece of fabric larger than your fin on top of some newspaper, preferrably outside. Spray a rather light coat of 3M77 on one side of your fabric. This should be a mist coating, not a layer. You are not painting it. You are making it tacky, like a weak tape. Lay your fin on top of this, squish it down, then pick it up. Flip it over, and smooth the fabric down to full solid contact. Now do the same for the other side. Trim the excess. Now that the fabric is where you want it, you can brush on laminating resin with an acid brush. Wet out the fabric but be gentle with it. Epoxy softens 3M77. Once wet out, blot up all excess epoxy with paper towels. Leave to dry. You will have filling to do with this method, unfortunately. Note that ideally you want fabric to wrap around the leading edge of your fin. You can do that with this method, using one larger piece of fabric.
Gerald
Adhering to the paint is unfortunately not a measure of success, unless you are only looking for cosmetics. Failing to adhere would be utter failure!
The test is to bend your part until it breaks. What is the failure mode? If the failure mode is delamination at a force lower than what the core can take, then you have achieved negative progress. You've added weight without an increase in strength. That is, the fabric separates from the core but the core doesn't break at that load. So the added fabric was useless.
If the failure mode is breaking of the fabric and the core pretty much simultaneously, then you've probably added strength or at least stiffness.
If the failure mode is breaking of the outer fabric but not the core, then you've done an adequate job of laminating. Unfortunately, the material added to the core was of inappropriate structural properties for the job.
I hope this is of some help. I'm not intending to be critical. I'm presuming the reason you are working this out is that you plan to make a rocket that will require such reinforcing.
When working with composites, one of the goals should be to have the part, when it comes out of the mold or bag or whatever laminating tool is used, be as close to a finished part as possible. Already painted. Glassy surface. Etc. Pop it out and it is done.
There is a very good reason for this (other than just saving time). Epoxy sticks to cured epoxy by mechanical bond. Epoxy sticks to uncured epoxy (of a compatible system) by both mechanical and chemical bonds. This is stronger. Use of peel-ply to leave a surface suitable for the next laminating step, is a tool used when one cannot for some reason perform the whole lamination at one time. The result is inferior, but probably better than not using peel ply in such situations. If this is the outer layer, then one has to sand the surface or at least fill the surface. It is easy to sand the fibers and damage their structure. I would say that peel-ply on the outside of the final layup should be considered a no-no. Besides, with proper prep work, one can achieve a painted finished result with near perfect glass like surfaces, all as part of the layup process.
Gerald
For small items like this, I'm surprised I haven't seen the ultimate in easy suggested yet -- a Food Saver.
Not only are the bags plastic, so the epoxy won't stick, but it also is an inexpensive vaccuum-bagging method. And it safely serves a dual purpose, with having kitchen uses, as well!
Cut your fiberglass exactly like you did, brush on the epoxy, then apply the cloth. When you're done with that, instead of placing it on waxed paper, slip it into a Food Saver bag, vaccuum out the air, seal, and let it cure.
All good tips. The fact of the matter is you don't know until you know. There is a difference between structural epoxy and laminating resin. Just Google it. Nice effort. It's more than I've been able to fit in the last couple months.
For small items like this, I'm surprised I haven't seen the ultimate in easy suggested yet -- a Food Saver.
Not only are the bags plastic, so the epoxy won't stick, but it also is an inexpensive vaccuum-bagging method. And it safely serves a dual purpose, with having kitchen uses, as well!
Cut your fiberglass exactly like you did, brush on the epoxy, then apply the cloth. When you're done with that, instead of placing it on waxed paper, slip it into a Food Saver bag, vaccuum out the air, seal, and let it cure.
-Kevin
You stated that the fin was a spare fin... so what you are doing here is teaching yourself how to laminate correct? Here is what I would add to your experience.
Wax paper aside, let's start with what you must have:
Applicator; Get some disposable horse-hair brushes or the $ .50 black bristle brushes from Wally-World. I prefer the black bristle, so I can pick out the bristles as they come loose.
Gloves: You do not want to build up an allergic reaction to epoxy, I hear it is bad. Get some of the purple gloves (also found at Wally-World) to use when working any epoxy.
I'm assuming the dishes and food ware removed from the table before you started...(?)
The fin was red... I assume that it had been painted. This surface would need to have been removed, otherwise you are laminating a structural system to the paint surface, which is a removable layer. Your glass laminate need to be adhered to a properly prepped structure (the fin) in order to gain the best benefit. Sanding a rough textured surface on the fin would be best. Gives the epoxy something to get a hold of.
Using thin epoxy; if you are planning more than one layer of glass, then add the layers you intend to lay up. Since the Mariah fin is G10, your epoxy can only soak in one direction, and that is towards the glass laminate you have applied. Multiple layers save much work and extra prep, but also adheres all layers into one structural system, not two or three seperate systems. You may also find that you use less epoxy over the course of the project.
You are learning, and that is good. Do not take what experienced members are saying as being negative towards you, it is constructive criticism...we can learn much from this to.
Lastly I will say that you should never work from a diningroom table, there are multiple reasons for this, the most important is it is not safe for anyone who may eat from there.
Good luck, and please post your progress.
I think you will find that a real release film is not that expensive and wont contaminate you part with wax https://www.airtechonline.com/econo/econo_a.html
Not sure what you 20 min epoxy you are using it should be a laminating resin such as west systems or aeropoxy. Not a bonding epoxy such as the hobby stuff.
The first prep would be to clean the fin with acetone or iso propyl alcohol and sand the fin with 120-240 Grit paper to expose the tops of the fibers without going through them. Grit blast works really well for this part.
Now wipe the fin with acetone and/or iso propyl with a clean lint free cloth. You should keep doing this until you get a clean wipe.
Wet the surface of you fin with a thin coat of epoxy
Wet out your fabric I use a bondo spreader but a popsicle stick works. It should be almost transparent if you are using glass.
Lay the fabric over you fin so that you dont trap any air work out the air bubbles if needed with a speard or stick.
Apply your release layer.
Apply your compaction this could be weight as you used. I have vacuum pumps so I use those this requires a vacuum bag. Make sure you have a resin trap so you don't suck resin into your pump.
Wait for the epoxy to cure.
Remove compaction.
Admire beautiful fin.
Celebrate!
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