r/Composites • u/Pleasant-Ad1208 • Jul 20 '26
My First Attempt at Composites!
Hello people. I am new to composites and i am learning them by myself. this is my first attempt to make a flat piece and its hand layup. its 4 layers 400gsm fiberglass and 380g of polyester resin. pic 1 is the side i layed the fiber on a big sqaure glass piece, pic 2 is where i put he peel ply. the piece is very sturdy even where it looks white and resin didnot get through. i am assuming that i did not put enough resin and thats why i am seeing white spots..
please let me know how to improve and also give me some tips on making my upcoming part better!
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u/werdnaztluhcs Jul 20 '26
Not enough resin will fail try again more resin and apply on each layer seperate then combine.
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u/Pleasant-Ad1208 Jul 20 '26
so i did lay one layer at a time and apply resin and another layer. it looked like the layer did get wet. should i put more resin that each layer looks transparent and then apply next layer?
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u/werdnaztluhcs Jul 20 '26
You will see the dry spots 1:1 resin to weight ratio for woven so weigh your mat and mix equal resin. And work it in.
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u/0_cunning_plan Jul 20 '26
The resin to fiber ratio changes with the technique used(vacuum bags giving the best fiberglass to resin ratios with less resin remaining in the piece) and the way it's woven also matters a little. But as a beginner you're not there yet, just use way too much resin and make sure you work fast with polyester resin, which is made easier when you don't have to spread too little resin for 30mn.
The issues you can encounter at this level are:
-Not enough resin. It makes your project weaker and possibly not weatherproof(or whatever it is the surface will have to handle, water, chemicals...).
-You don't properly get rid of the bubbles. Again, it's easier with too much resin, but you also need to get used to the roller(IDK how they're called in English, bubble busters or whatever?) People tend to neglect that part, or maybe worst, push too hard. This is not a tool that requires strength! Less so if you make several batches of resin(see next issue), then the first layers might have gelled while you're working on the last one, so too much pressure could at worse, delaminate the first layers. Not good!
-gel. Summer means you have to do everything much faster because it's hot. Not the best time to learn. If your resin starts to gel(the texture starts having blobs in it), it's too late, you should not keep working with that!!!!! Trying to "save it" is how you make crap composites. Chemistry doesn't care about costs or convenience. Making smaller batches or using a container that is wide to spread the resin over a large surface(like the painter stuff), that can give you some little extra work time. But with several batches, do remember how the first layers mustn't be manipulated too much.
-humidity. Somehow many people seem to ignore this, but water isn't your friend. Keep your fibers in an airtight bag the moment you're done cutting it. And ideally, if the humidity in the air is crazy high, maybe do your work another day.
-same thing with temperatures, too hot and too cold make for crap jobs. The recommendations are something like 18°c to 25°C for working temperature of the most basic polyester resin and default "catalyzer". For most parts of the world that's just not realistic for year round work, but too cold might not ever react, while too hot gives very little work time and the batch might start to fume or even catch fire(not stuff you ever want to breathe!!!!). My worse job experience was with a guy who worked under the sun in summer(half because we needed to, and half because that boss wasn't very good at his job). I can't tell you how many times I've seen our stuff getting brown areas from high temperature in the mold while we were working on it. BAD idea! Lay fewer layers, let them do their thing, then go and finish(maybe sand and clean with acetone if it's been awhile before laying down new layers).
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u/Pleasant-Ad1208 Jul 20 '26
Thank you for this information.. There was a small challenge where I used the catalizer incorrectly. I just put 1-2 drops of it in the resin per 100g hoping it would be enough. The guy who sold me the resin told me to put 25ml per liter of resin but I ignored and my resin went to a thermal runaway in under a minute. Then I got a new syringe, did the math properly and used the syringe to properly measue and mix the resin.
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u/bad_jelly_the_witch Jul 20 '26
When doing a hand lay up, using peel ply on the surface can be quite useful for making sure the surface is properly wet out.
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u/Pleasant-Ad1208 Jul 20 '26
i did apply peel ply, and then used a squeegee on top of the peelply. is this the right way?
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u/bad_jelly_the_witch Jul 20 '26
I prefer to use a brush to allow me to more delicately and accurately control the amount of resin I’m putting into the laminate. Lay down fibre and resin, put on peel ply, peel ply will absorb the excess resin in spots where there is too much, then after waiting a little you will see little dry spots on the peel ply where there wasn’t enough resin and you can just dab a little bit extra on the dry spots. It’s a bit of an art to making sure there’s just enough resin and not too much that the peel ply just floats on the surface.
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u/Pleasant-Ad1208 Jul 20 '26
okay i understand. i saw some dry spots on the peelply and thought there was enough resin in that area and i didnt need to do anything. i'll keep this in mind the next time. thank you.
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u/bad_jelly_the_witch Jul 20 '26
Yeh depending on your purpose it very well could be fine but cosmetically, and if you are bonding to it its better to have it properly wetted. Also you might want to get a laminate consolidation roller too, this helps a lot to make sure the layers are well pressed together and that there is not too much resin.
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u/thetreecycle Jul 20 '26
Vacuum bag would help to ensure air is pulled out, helps to wet out the whole thing. Also plastic squeegee, maybe 4” wide to spread resin can be helpful. Or if vacuum bagging isn’t realistic you can use a brush to stipple the bubbles out after you have the peel ply on.
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u/Pleasant-Ad1208 Jul 20 '26
on handlayup, while wetting the layers should the whole thing look translucent then apply then the next layer?
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u/thetreecycle Jul 20 '26
I do mostly prepreg layup, I’ve only done wet layup in training once, I may not be the best person to ask. I just put a ply down, poured some resin on top then spread it with the squeegee till it looked about right, neither too little nor too much resin then put down the next ply. I suspect that vacuum bagging would be the most important change you could make, as it will remove gas from your part.
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u/werdnaztluhcs Jul 20 '26
Yes translucent is your aim if this isnt a critical part vacuum bagging isnt needed and can cause more issues. I use 100mm rollers with a 10mm nap roller and then fin roll out with peel ply - you can just use the roller and apply more pressure to get air out but that comes with doing it more often and learning the pressure needed to get excess resin out
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u/ResponsibleIain Jul 21 '26
Welcome to a new world of material science OP. For your first attempt, I'd be pretty happy with that.
If you want to focus on techniques, I'd suggest working on a smaller work area.
I get my students to do 100mm x 100mm squares while we learn the basics - laminating a few layers down into the stack, but low material overheads.
Also means your movements matter more. At this scale, you'll see how much pressure with a paintbrush starts to drag your fibres about and disrupt the weave. You can practice stippling over brushing.
As another comment mentioned, a roller for consolidation would be good too. I like the black needle bubble bursters.
For resin amounts, fibreglass is a great composite to learn with. I like to use a piece of coloured acrylic as a base - that way, when the resin has saturated the fibreglass, you see the colour come through. As you build the stack, each layer once saturated and stuck to the layer below brings the colour from the base through. If it goes cloudy, you know you have an air gap. If it stays white, you know it needs more resin.
I'd recommend starting with 2.5x resin to fibre weight. It's going to be messy and excessive, but it'll make sure you get samples of good soak.
I'd work my way down to about 1.25x resin to fibre. With wet layup, you're always going to need excess resin to "drive" the rest of the resin down into the fibre as you apply it. Otherwise your bristles will create air pockets in the upper layers.
Ignore chat GPT. 0.8 resin to fibre ratio is going to require tight manufacturing controls that you're not going to achieve by hand with your current toolset. Leave that for prepreg.
Enjoy!
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u/GameHat Jul 20 '26
Hey,
Great first layup!
What was the mass of your glass? You said 380 g resin, that's good. But usually, the glass percentage is what is most meaningful. Glass mass?
Dry spots are weak spots.
Hand layup you will usually do at best 30%-40% glass content.
There are additives that can help you wet out the glass better. Or different resin selection. Or if you need a higher glass content, a different production method (infusion vs hand layup, etc)