Fibreglass work

[Benonymous]

Good tips

There's some good tips in this thread. My Dad and I built a 37' yacht from scratch (and I mean scratch, a bare patch of lawn in the back yard) We used polyester resin and a combination of chopped stand mat and woven rovings (mat). During the process, we learned much about the process of construction with composites. Since then I've used GRP to make motorcycle bodywork and recently made a desk out of carbon fibre/epoxy using a vac bagging process.

Here's my tips.

When handling resin or mat, always wear gloves.

When handling resin or mat, always wear a respirator.

When handling resin or mat, always wear eye protection. Polyester hardener (MEKP) will blind you, permanently, if splashed into the eyes.

There are two types of polyester resin that are common, waxed and unwaxed. Waxed resin cures leaving a film of wax (or something waxlike) on the surface and is not suitable for doing multiple laminations without being thoroughly sanded between layers. Unwaxed resin leaves no film and can take another lamination directly. Mostly, unwaxed resin is refered to as laminating resin.

Epoxy resin is easier to use than polyester in my opinion. When you're buying it, look out for the hardener you're getting. You can get fast and slow curing hardeners. Fast curing will solidify in about 5 hours where slow can be 8 to 12 depending on temperature. As a previous post mentioned, if you're vacuum bagging, you'll appreciate the long "open" time of epoxy. Open time refers to the period between mixing and gelling, when the resin can't be worked any more. Epoxy cures without giving off any powerful smell but that's a trap because the chemical released has been known to cause multiple chemical senstivity and other unpleasant health effects though most of these have been observed in people using 2K (two pack) epoxy paints without proper protective equipment. The hardeners can affect the colour of the resin too. Fast hardener is a darker yellow than slow hardener (in West System resins) and if you want a nice glassy look on a CF part you might choose slow hardener for its greater clarity.

Chopped strand mat (CSM) is exactly what it sounds like. Lots of similar length loose strands in a random mat. The strands are loosely held together with a binder which dissolves in resin. When you wet out CSM, it will cooperate nicely for a few passes with a roller or brush but after that, look out, it will start to disintegrate and clump and turn into a big fucking disaster. As a previous poster mentioned, generally, you don't cut CSM, you tear it. My Dad used to make newspaper templates of the sections of CSM we needed on the boat, then we'd tape them onto the CSM and tear around them. You tear CSM to avoid a raised edge on your lamination. Ripping will feather the edge. If you want precision, you can cut, then rip out some fibre on the edges to feather them.

Woven rovings or mat are exactly that too. A cloth made of glassfibre but each weave thread is made up of many continuous lengths of glass fibre in a bunch which is a roving. You can buy roving on a reel, John Britten used carbon fibre roving a lot on his motorcycles. The big difference in woven mat is that there are loads of different types, uniaxial, plain, biaxial, triaxial, twill, satin, quadraxial. All of these have different properties and strengths and it would take me ages to go through all of them. Plain weave is good for most applications but twill is better at conforming to compound curves. My desk project used carbon fibre in a twill weave and a biaxial, stitched fibreglass.

Reinforcements can be a lot of different fibres but the ones that would be useful in automotive applications are glassfibre, kevlar and carbon fibre. The benefits of glassfibre are cost, and availability but on the downside, it's not particularly strong. There is a product called "S glass" which has better strength. Kevlar is an immensely strong fibre but an absolute cunt to cut. This goes for kevlar in a laminate or fresh off the roll. The only way to cut any amount of it raw is to use ceramic bladed scissors or shears. After it is in a laminate, any attempt to cut it will result in drama and leave a fuzzy edge which will not sand easily. It will have to be trimmed with the ceramic blades or some other method to get a decent cut edge. Carbon fibre does not come in a CSM format so you'll have to deal with all the many variations of woven mat to find the weave that best suits the job. Compared to fibreglass, carbon is amazingly stiff and strong but on the downside when it does fail, it snaps like a carrot. The cost compared to fibreglass is pretty staggering too.

For doing a basic lamination with any of the above materials you should use the proper tools. You will need some cheap paintbrushes or a squeegee to distribute the resin on your cloth. After wetting the cloth out thoroughly, you should use a metal paddle roller, or grooved metal roller to squeeze the air bubbles out of the cloth or CSM. Doing this will ensure that you get the best fibre to resin ratio in your layup. Excess resin will end up on the outside surface of the layup where it can be sanded off. If using polyester resin you should have some way of measuring or weighing it so that you can add the appropriate amount of MEKP. Don't use any more than you have to, it won't improve the result and could, if you're extremely silly, catch on fire. If you're using epoxy, get the pump dispensers that fit the bottles, getting the correct ratio is piss easy then, provided you can count.

Before attempting any composite work you should spend a lot of time in preparation.

A container, with a lid, big enough to dunk your rollers, squeegee, brushes etc should be on hand. Leave the lid on while you're working and whip it off when you're finished to do your cleanup.

Put your gloves on.

If you're using polyester resin measure your resin and hardener out and have them standing by.

Make sure you've got a mixing stick or paddle.

Cut or rip all the cloth you're going to be using. Trying to handle scissors or a knife and cloth when your hands are covered in resin, is the short road to a fucked up job and loads of regret. So it's very important that you have all this sorted before you mix any resin. Cut the cloth before you mix. If you're using woven cloth, try to spot the edges that are falling to bits and remove the loose stuff. You always cut the cloth oversize so this won't affect the layup itself.

Polyester has a very short open time so you've got about twenty minutes tops before it begins to gel. Epoxy is more forgiving in this respect. Get your cloth wet through. Glass will turn from silvery white to a dark transparent look, depending on what you're laing up over. Carbon gives you less of an idea about how wet it is but it does darken where its wet and it reflects less light.

Get to work with your roller. It's easier to spot air bubbles in glass than kevlar or carbon, just give the whoe thing a good going over, gently.

If i've got another lamination to put on (5 is the practical limit for one layup) I might change gloves to make handling the cloth easier. Woven cloth will just fall apart on the edges so check again for any loose,fraying bits and piss them off before they tangle around your roller.

Once you're done, clean up your tools, make sure the lids are on everything and go have a beer or nine.

I bought all my carbon cloth from ironbark composites in Vic and I get my West System resin from whoever's selling it the cheapest at the time. Dick, at Ironbark, often has specials on carbon so tit's worth checking his web site.

ironbarkcomposites.com.au/

[Benonymous]

echo

[Horse]

great post! lots of good info there, could you throw up some regarding vacuum bagging?

[BigMuz]

Good post mate. Cheers

[Benonymous]

Vac bagging can be one of the most frustrating excersises in the world. Chasing leaks in your bag, having cloth fold, and running out of open time are just some of the hair extracting fuckups you'll encounter. Having said that, there's no way to make a hand layup as good as a bagged one. I've seen a website from a bloke who did some excellent vac bagged motorcycle parts and other auto bits using the most basic materials you could think of. He sourced a vacuum pump from a hospital auction and used garbage bags as vacuum bags. When I started, I thought I'd get some decent materials as I was doing a paying job so to that end, here's a list of materials.

Bagging film: Cheap as shit and comes in a 4M wide format off a roll so you can go 4M x LOTS. I tried using cheap shit like polyester drop sheets and stuff when I was experimenting but its full of holes and won't hold a vacuum. When you are cutting film for your bag, give yourself a good 20-30% over the size you'll need for the part. You need room in the bag to take up curves and irregular shapes. As previously stated, bagging film is cheap so do yourself a favour....

Tacky tape/mastic: Mastic is like super strength BluTack and comes on a roll. The stuff I had was yellow and is extremely effective. The method is to lay out your bag, pull the mastic off the roll and stick it down leaving the wax paper on the upper side. Leave it this way until you're ready to seal the bag. Once its on, it's a done deal, any attempt to peel it off or move it will stress and ultimately rip the bagging film which may result in you tossing the film and the mastic.

Peel Ply: This is a woven material that sits between the layup and the bagging film. The idea with peel ply is that it allows the excess resin to pass through it as the vacuum compresses the laminate. The resin will not stick to the peel ply and equally, the peel ply will not stick to the laminate. By letting the excess resin out of the layup, the optimal resin to fibre ratio can be achieved. This will mean maximum strenth and minimum weight. Part of this process is getting the vacuum pressure right but the range is reasonably big so it's not super critical unless you're making a structural part that your life will depend on. I didn't use actual bespoke peel ply, I bought ripstop nylon fabric from Spotlight but any fine weave nylon will do. I found out subsequently that real peel ply is cheaper

Perforated Release Sheet: I've never used this but it's meant to stop the peel ply from going stiff and loading up with resin. If this happens, the peel ply might not want to part from the item you're making. I've never used it but seen it work and the excess resin ends up between the release sheet and the bleeder.

Bleeder Cloth: The bleeder is the last layer in the bag (fuckin' lot's of layers eh?) Bleeder is a loose mat of springy nylon fibre and I used a material from Spotlight that's intended for stufing quilts and so forth, they call it "batting" I think. The bleeder does two jobs, it allows all the air to be drawn from the bag by staying porous even when it's crushed by the outside air pressure. Bleeder also soaks up excess resin. I have found that you can reuse bleeder that isnt soaked with resin and at a pinch, you might be able to reuse some of your peel ply too if you're really stingy

All of the layers have to be bigger than the part you're making and the bleeder has to extend all the way out to where the vacuum line hooks up or the bag will choke off the vaccum and you wont get the compression and consolidation you are trying to achieve with this wildly complicated setup.

Vacuum Pump: My pump was sourced from the venerable Bay of e and is designed as a pump to evacuat refrigeration systems. I used some research to find out the CFM I would need for the job and then bought a pump with double that capacity. Now, you're going to hate me for this but you absolutely have to have a vacuum pressure cutoff on the pump. Even a large capacity version of these chinese bastards will overheat drastically if it's left to run. They are short duty cycle devices and will start to fume oil mist out of the breather if they get too hot. This is a real fuckoff when you want all your molds and gear to be grease/oil free and the stupid fucking pump is filling up the shed with oil mist! My cutoff switch came via a mate who works for a large gummint department and is a real nice bit of old Brit engineering. The cutoff operates an electronic timer to set the top up cycle and the timer drives a 240v relay to control the pump. Without the timer, the pump will fire up every time the switch senses a poofteenth loss of vacuum. All designed and wired up by myself. I do a lot of this type of electrical/electronic work. You'll also need a vacuum gauge and a bunch of air hose. On the business end, I have a vaccum lift suction cup of the type you'll find in process machinery. To hook up the line to the bag I first put a "stage" in the bag, this is a piece of perspex with a hole drilled in it. The stage is there to give the suction cup something hard to seal against. I make an X cut in the bag over the stage and then attach the cup with a bit of detergent wiped on it to help it seal. You can get bespoke fittings for vacuum bagging that have an interior and exterior component that you can clip a line onto. Some people use a trap for any stray resin but I haven't so far.

Doing your layup: As in my previous tips post you must have all of your cloth, your peel ply, bleeder and bag pre-cut before you mix any resin. This bagging process has so many fucking traps you'll be kicking youself if you forget something and end up trying to cut peel ply or bleeder while your part is slowly curing and the whole job is turning to shit. Be fucking patient and methodical!!! Doing your layup is very similar to a normal hand layup and I would strongly reccommend slow hardener for any bagging job. I spent three hours straight doing the layup on the desk I made and had the resin cure on me because of the heat, only just saved it and $400 woth of carbon fibre! You will still need to wet your cloth out thoroughly and use a roller on it to release trapped air.

Layers layers layers: Once you've finished your laminating, lay your peel ply over the wet layup and try to eliminate all the folds and creases that you can. Those you cant, make the neatest fold you can. Alternatively, if you have a blade to hand, slit the peel ply and cut the fold out. You're trying to get the peel ply as flat as possible, if you dont, resin will accumulate in folds and wrinkles. This is where you'll appreciate the long open time on your resin. There's no need to rush when you've got 5 hours of open time. Next, lay your perforated release or bleeder if youre not using a release layer. The bleeder has to come right up to where the vacuum line will be going on. Pop your stage onto the bleeder in the position you desire.

Sealing the bag: To set up your job, you'll need a nice big flat surface. Most workbenches aren't wide enough so I'd advocate getting a sturdy trestle table or whatever so that you've got lots of room to lay out your bag. The easiest way to bag up is to make a full envelope. This means, sometimes, that you'll lay your bag out first and then put your mold in the middle, secure the loose bag (with the mastic already on it) so it stays out of the way and do your layup. Once you've got your part laminated and all the layers on it bring the bagging film over the top and lay it loosely in position. Effectively, you only have to seal up three sides using this method as the film is folded.

Starting from the fold at one end, peel off the wax paper on the mastic slowly and get the top to lay down on the mastic without any wrinkles. If you fuck this up, all you can do is plug any leaks, you cannot get the mastic to let go once you've put some pressure on it. I'd have to say this part of the job will go much much better with two people as it allows you to stetch the film for a nice wrinkle free touchdown.

Once you have all the edges sealed, give the bag a once over to make sure it's nice and loose and the edges are free of folds/wrinkles. If you find any potential leaks in the mastic, you can generally give that area a bit of a massage to pull the wrinkle out and seal it. Check the corners that have the folds critically. Any leak here can be fixed with a wad of mastic.

Now the big moment. Find your stage and make your cut, crank up the pump and attach your sucker cup. This is the moment of truth, the air will draw out of the bag and slowly youll see wrinkles forming. Keep an eye on the wrinkles because you want to avoid a "bridge" where the bagging film streches across an area without touching it. Resin will accumulate here and make you say bad words when you look at your finished part. If you have your pump set up right, the little cunt should switch off when you've got 15 to 20 inches of mercury pressure.

Watch your bag...... is it re inflating? Look at the pressur gauge, is the needle climbing back to atmospheric pressure? If it is, say some bad words and then go looking or rather listening for the leak. Because it's negative pressure, you can't use soapy water to find it because it will get sucked into the bag and royally screw everything up. Epoxy + water = disaster. If the bag isn't leaking, you've done well my son. If the bag has a weeny leak, let the pump run every now and then to top up the vacuum.

I've only had a couple of bags that were leak free. What you should do now is check for bridging and severe wrinkling. Bad wrinkles could make an impression on your layup, don't forget, theres 55 pounds per square inch pushing down on your laminate. If you want to sort anything out, crack the vacuum, let the bag inflate and then pull the film around as needed, gently. At no stage should you panic. You've got 5 to 8 hours open time and many things can be dealt with. The only thing you can't really do is open up the bag but if you absolutely have to, cut as close to the mastic as possible and re-seal with more mastic. In my opinion you're halfway down the short road to a fuckup if you have to do this. If your bag is good and the pump is giving a burst every five to ten minutes, you've earned a fucken beer man, really!

Possible bodge methods. OK so you've got a pump but your fucked if you're going to spring for all the specialist stuff. You can make a bag by doing the following. Get some decently thick garbage bags (the orange ones for gardening waste are good) Make sure your part will fit in the bastard with room to spare. Get ripstop and batting from Spotlight. Do your layup and put in your layers. Put the part/mold into the bag. Put in your stage if you need one and tape it to the bag so you dont lose it (proper bagging film is transparent) Don't tape over the hole in the stage. Make sure the batting will be under the stage. Get some roofing silicone or liquid nails and run a big fat bead along the open end of the bag. Squoosh the bag shut and smooth it out. Connect the vacuum and start sucking. Watch bag/gauge as before. The silicone or construction adhesive will tend to wick into the bag and you don't want it on your part so make sure there's about 300mm btwen the bead of whatever and the part. Don't forget you're at a disadvantage with this method because you cant see what's going on inside the bag.

Now... just to prove I'm not full of shit, this is the desk I built for a local radio station.

[Horse]

Benonymous delivers!

that's a great looking desk mate, how many layers all up? and did you have a mold for the ends? I drew something up that has two curved ends like that with the actual width being 1200. The only solution i have come up with to make the curve is to create a plywood former which i then layup my shit around and vac bag the lot! I've put off doing it for the sheer head fuck that i think it is, and from what you've written I'm not wrong.

cheers

[10sec rx7]

if your going to vacuum bag it you may as well infuse it, its less tricky that trying to do it all wet etc and its only a little more on the expense side.. you will need a resin trap between the bag and the pump etc but nothing too hard to make

[Benonymous]

Thanks horse The base was an absolute prick to make. I used one lamination of CF which is a heavy twill weave (forget the GSM) rather than the more common plain weave. It was one of Dicks specials at Ironbark Composites. There's one layer of biaxial stitched fibreglass on the back then a bunch of stiffening boxes I made by wrapping CF around some 35 x 35 mm RHS steel then vac bagging it. The resultant product had to be cut off the RHS by slitting it the length of the pipe, another cunt of a job! The mold was constructed as a female using CNC cut MDF formers with a hard polystyrene sheet liner. The whole affiar looked like this..



The styrene sheet bent around the inside of the curve. The top is missing in this assembly.

I laid this up on my own and because of the air temp, the fricken resin went off a lot quicker than I was anticipating. I had a massive bag as this part measures 1500 x 700 x 500mm. It took me three straight hours to do the layup and then when I got the bag on it I struggled to get a seal. In addition to that, the voids in the mold structure were really stretching the bagging film and in the end I had to settle for a really weak vacuum.

Not a good day.

The final washup of it was that I had voids in the part on the face surface (which was against the styrene sheet, nice and smooth). I had to fill the voids and do a shitload of sanding and refinishing to get the look you see in the above pic. 10sec rx7 is spot on, if I'd set up an infusion system, I could have just laid the cloth in the mold, bagged it, then let the resin soak through in the infusion process. Basically, infusion just introduces resin, via multiple small diameter tubes, into multiple areas of the mold. The vacuum draws it in. I'd also have to deal with the big open areas in the mold. Possibly some expanding foam or shaped polystyrene would have worked but I was on a deadline.

The desk top was a breeze. I had a female mold CNC'd out of a 12mm thick sheet of polyethelyne plastic, mounted it on a 20mm MDF board then laid it up with one CF and one biaxial glass, bagged it, pulled a perfect vacuum and left it overnight. Next I cut some stiffeners out of pvc water pipe that I shaved down on the router table to get a semicircular section, laid them out as stiffening ribs, CF over them, bagged, job done.

Of couse there was a shitload of sanding, filling and polishing in the mix too. Interestingly, as the parts came out of the mold, they weren't glassy smooth like I'd hoped so I just painted the top and base with resin. The resin flowed out all the brush marks (long open time) and then I just sanded it down from 120 to 1200 grit and buffed it. Champion!

[10sec rx7]

old beer kegs make great resin traps... ive got one lying around somewhere..

[BigMuz]

Welcome random dude who knows what he is talking about!

Good stuff.

[Benonymous]

Thanks bigmuz, glad to offer this stuff up. Composites look easy if you just look at the materials but to end up with a part that doesn't go straight in the bin, a bit of prep goes a long way.

[ChrisS]

So in the last couple of days I had a go at making up a Model A f/g cowl, which turned to shit but learned heaps from it (has beeen years since I have done any f/g of this size)

Few things I did wrong-
-I mixed the resign to hot which resulted in going off to soon
-I cut up the matting pieces to big, caused it to fall out of the mould as it was to heavy and hard to control
-Tried to rush it
-Didn't use enough gel coat...(I tried to spray it on with a gun)

Result.....

I prety much stopped when some of the air bubbles went hard so it only got one layer of matting (if that in some places)

Have started again with two coats of gel coat (brushed on this time), smaller strips of mat have been pre cut and labeled so I know what goes where and will go slower with each section when rolling it down.

Will do the f/glassing tomorrow and take some pics....

[F|sh]

most of the books i have read recommend one layer at a time to stop it "cooking" and sometimes two depending on size...

look for a book called how to repair fibreglass boats. has alot of good information in it and although its based for boats it will have info for you

[smee]

So, I want to make a sump Guard for the rally car.
From what I have discovered, I should use reinforcing. This could be done in just about any way.
I was thinking of strips of redwood I have, or buying in some grain end Balsa strips. I have considered Carbon nanotubes, but have yet to locate info or supplier.

Plan is to use an external mold using light weight gal.
Wax up and then apply PVA
Lay 3 sheets.
1 Kevlar, 1 carbon, and then , redwood and then Kevlar.
Place reinforcing brace of Balsa or Redwood to attach mount of guard across job, and then the ribs I have formed up along the job, then
lay 3 sheets, 1 Kevlar, 1 Carbon, 1 Kevlar.

I have seen some large fibre Carbon for sale at $150 a 5 metre roll, and Kevlar which is about $60 a metre.
I would use Vinyl esther resin as it would be better in regards heat and fuel/oil resistance. Or, should I use some other resin.

With this, I am thinking weight should be well reduced from the 30kg or so guard I have now.
Strength should also be there I am thinking.

I would then possibly screw some alloy strips along the ribs.

Ideas, thoughts.

[Ben Wilson]

Ideas, thoughts.

Flat surfaces are crap for composite strength, perhaps some roofing metal with the ridges could be usable?