Fiberglassing Over Foam - questions.

[cappisj1]

I have watched a couple videos that I found and read a couple stories but, I am still a bit intimidated to take the next step.  Any tips before I start?  What epoxy and fiberglass would you suggest?  Any other sites I should check out?

[lti_57]

I have done a bit of fiber-glassing I use the stuff you buy at Walmart or any auto store.
I have had great luck by pre cutting and numbering the pieces  and corresponding number on the foam.
  that's going to look good when you are done
 

 

[Wayne Orwig]

Did I hear that some resins eat foam?
Do you have to seal the foam or use epoxy?

[racasey]

West System epoxy is strongly recommended.  If you intend to apply multiple coats of glass, allowing the resin to cure between coats, then spend the few dollars more and get the calibrated dispensing pumps for the catalyst and the epoxy resin.  This makes getting the correct proportions quick and accurately.

Second recommendation:  buy a small plastic bubble roller.  Google Westmarine 388878 and view the tool.  These make applications bubble free and really help pack down the glass fibers.

Best wishes on your project,
Dick Casey

[racasey]

Capp, one additional thought.  If you intend to have the final fiberglass seat pan to look precisely like the foam plug you have made, then a slight alteration of your plug is encouraged.

If yes to the above, then you may want to extend the sides of the pan downward about an inch.  This will allow the sides to be of uniform thickness, flat and true at the "trim line".

Without some backing below the anticipated trim line, the glass fibers will go every which way, hard to control, and result is a sloppy lower edge to your pan.  The same applies to the front edge.

Ciao,
DC

[Huzo]

I have watched a couple videos that I found and read a couple stories but, I am still a bit intimidated to take the next step.  Any tips before I start?  What epoxy and fiberglass would you suggest?  Any other sites I should check out?

I did a very similar thing years ago with a Rob North BSA that I'd built a seat just like yours for. Once I got to where you are I covered the seat with plaster and made a female cast of the seat then made the seat inside the cast. Make sure you use a PVA release agent between the foam seat pattern and the plaster cast. Benefits are you'll still have the foam seat pattern if you bugger something up and if you put the time into smoothing the plaster cast and use PLENTY of release agent the seat will pop out with a good finish already. No matter how much release agent you use, it won't be too much. BTW, make sure the angles on your foam pattern will allow the plaster cast to come off and not "lock on", you can't go too far wrong really. PM if you want more info.

[charlie b]

+1 and on extending the plug to make a 'skirt' that you can trim off later.

Much better results to make a mold from the plug, then a part from the mold.

Finish on the plug is all important.  Any blemish will show up on the finished part.

The alternative is to just fiberglass over your plug but you end up with a lot of finishing to do.  To decrease that, use a vacuum bag over it.  Involves buying a bit of materials but makes for a much better part.  For parts like this you can just use a shop vac for the vacuum source.  Once cured you will have to do a lot of filling and sanding, but, it is a one shot deal.

The foam will have to be protected from the resin but just about anything will work, including masking tape.  If using something that doesn't release you'll have to 'dig out' the foam, but, it's not really a big deal. 

Last, you can also completely enclose the foam with fiberglass.  Shaped the underside the way you want, including reinforcing and brackets for mounting the seat.  The foam will make it very stiff.

[pitts12driver]

the other thing I'd recommend is cutting the fabric on the bias (45).  It will fight a lot less conforming to the compound curves.  I've built 4 airplanes with West Epoxy, but System 3 is also good stuff.  Squeegee out all of the excess - as you will have a lot of sanding in your future otherwise.

To get a good surface finish, I typically mix cabosil filler in with epoxy until it is a peanut-butter thick paste and smear it on.  It fills the weave quickly - and you sand 95% of it off.  Next is a coat of high-build primer to see what pinholes and contour issues remain.

Good Luck!

[boatdetective]

If the foam plug is Styrofoam, then the solvents in polyester resin will melt it (very rapidly).  Polyurethane foams will work fine.

Polyester resin shrinks- Epoxy does not. If you make the foam into a plug, then splash it to make a female mold, then laminate the part in the female mold- then the shrinking of the polyester will help it release from the mold. Pulling epoxy parts out of a mold will not be quite as easy.

If you are using epoxy- then you really should do all the laminating of the finished part in one shot. Once the epoxy cures- you would have to grind the surface to get decent adhesion with successive layers.  If you are using no wax (often termed "laminating resin") polyester resin, then the cured surface will remain sticky enough to add subsequent layers without sanding - but don't be ridiculous about it (you open window should be no more than, say, 8 hours to be safe).

Although epoxy is a superior resin, I probably would go with polyester. On reason is the ability to use fiberglass mat. Mat will conform easier to  tight corners after the binder dissolves. The binder in mat will not dissolve with epoxy.  I would still use directional fibers- but there is more tailoring involved.  Speaking of that- all your layers of glass should be tailored and cut out beforehand.  Do NOT try to do it with single sheets. Manipulating wet glass is a learned skill. Best to start off with manageable pieces. Make sure you have decent overlaps at each seam.

If everything is cut out beforehand- once you catalyze the rein the process should go smoothly. You don't want to be screwing around with shears cutting wet cloth.  Tight corners could require darts in the cloth. Plan for that beforehand.

Vacuum bagging is very cool- but many steps ahead of where you are at. Don't bite off more than you can chew.

"Cabosil"- colloidal silica- is a filler that mixes in easily. However, as you might guess by the name (silica), it is a hard compound that does not sand easily. The West System kiosk has other resin fillers (410 & 407) that will make much better fairing compounds. If you are making a polyester part, then there are off the shelf fillers that will work fine. As mentioned- if you take the time to make a plug then a female mold, then you finishing will be minimized. However- this means the plug must be perfect. 

Your part has a very pronounced undercut and very sharp corners. This will never translate to a female mold unless the mold is designed to be disassembled. Multiple piece molding is way beyond your level. Even if you make it a male plug and pill the part directly off it, the edges of your seat are very, very sharp. Round them over so the glass fibers can wrap around it.   

Plaster over foam sounds like a fairly brittle surface. Unless you are very delicate, it sounds like that layer could crack fairly easily with aggressive sanding. I would recommend putting down a single layer of mat fiberglass, then fairing the fiberglass with some filler. The finished plug should be waxed with a minimum of 4-5 coats of carnuba wax (butchers wax). You nned to buff between coats with a machine- not by hand. Spraying PVA release is the final release coat.

Your finished plug is the "male mold". The part taken from it will not be as nice as a part from a female mold. However, you avoid all the agita of making a female mold that has the proper "draft" and radiuses to pull a part. If you are careful in how you tailor the glass, then the surface should not be that much of a nightmare to fair.

Good luck
 

[Rusnak_322]

I have done a lot of fiberglassing and made a similar seat for a cafe bike.

I covered the foam with foil and packing tape, then waxed it to make it easier to remove. I used some special mold wax that I got from work, but hard car wax will work.

A tip is to take a board and cover it with foil, tape it to the bottom, use that to wet the glass. Pour some resin on the glass and spread it out. Cheap disposable paint brushed work well.

Cut a lot of glass matt or cloth, but only make small amounts of resin as it will go off faster than you expect.

I have used high end resins and stuff bought at auto parts stores and really didn't notice any difference when working or in the finished product.

I also don't care about adding a few extra oz to the weight of the part. Thicker can equal stronger. I did glass in some wood to add strength, 1/4" x 1/2" to make some beams on the bottom of the flat surface that held the seat after I pulled it from the plug.

[boatdetective]

 :1: on foil for release. However- that is only true with polyester. Epoxy will bond to the aluminum. On the"board" section and flats- you might consider MDF. It cuts and machines easily and remains flat when cut.  You can take a router to the edges with a round over it to make a nice clean radius.

[Rusnak_322]

I did a very similar thing years ago with a Rob North BSA that I'd built a seat just like yours for. Once I got to where you are I covered the seat with plaster and made a female cast of the seat then made the seat inside the cast. Make sure you use a PVA release agent between the foam seat pattern and the plaster cast. Benefits are you'll still have the foam seat pattern if you bugger something up and if you put the time into smoothing the plaster cast and use PLENTY of release agent the seat will pop out with a good finish already. No matter how much release agent you use, it won't be too much. BTW, make sure the angles on your foam pattern will allow the plaster cast to come off and not "lock on", you can't go too far wrong really. PM if you want more info.

Looking at the shape of his foam, the only way to save it would be to make a 2 piece mold split left and right. That complicates things for someone just starting out.

[boatdetective]

Rusnak- you're right- there's no way you could pull this. In fact, the reverse in the bum stop looks a bit severe- to the point that I think you could get impaled in even a mild accident. I'd recommend rethinking the shape for safety reasons alone.

[cappisj1]

Thank you for all the tips!!  I wound up extending the foam to get a good final bottom edge. Not wanting to make a copy of the seat I just used resin and mat over the mold.

I think it looks ok for now but is one layer of mat strong enough? 

[racasey]

Without knowing how you intend to attach the seat pan to the frame, one layer of mat is probably far too thin.  In very general terms, I'd expect a thickness approaching 3/16 of an inch as a minimum. 

Because chopped glass mat is made up of randomly applied short fibers, it lacks the structural strength of woven glass with long straight fibers.  Consequently with mat, more layers may be required to achieve regidity and load bearing required in a seat pan.

Ciao,
DIck Casey

[Tom]

Some good advice on working with the glass and resin. 

[cappisj1]

So I took in what I read and ended up at this point. I used fiberglass mat and resin from auto parts store, the patch/repair "kit".  I found the mixing instructions not very detailed. They said use 1/4 of can and 1/4 of catalyst tube. Well it was hard to see in the can and the catalyst was in a tapered tube. I must have guessed correct as I had good working time and it set up just fine. So here is the seat after sanding. (I really would like to cover this with heavy fiberglass cloth for some reason)

So what's my recommended next move here for the direction I went.  Cloth, another mat bondo???

Thanks again!

[racasey]

If this pan is only a single layer thick, it will require several more layers.  I'd phone a local supplier of fiberglass as used in boat building and see what they stock in woven materials.  Woven glass cloth is generally 38 or 50 inches wide.  You will need 3 or 4 more layers.  Cloth in the weight of 6 - 8 ounces will work fine.  You will need about 2 or 3 yards of cloth, and may need more resin and the correct catalyst.  Ensure you get the correct resin.  Ideally this will be your final layering and you do not want the part sticky. 

Pre cut the cloth and carefully arrange your layers on your work table, before mixing the resin.  It may not be obvious, but as you apply layers, the "Joints" need to be over lapped.  Think of bricks in a brick wall.

Looking at the seat, I see the flat seating surface (includes the sides) and the hump as two distinct areas.  I see the hump having two surfaces; the vertical flat (facing your butt) and the curved "bump".  So first layer on the hump would be cloth cut only for the vertical flat and another sheet cut for the bump.  With the cloth parting line at the "razor sharp" edge you created.  The next layer, a 3 inch wide strip centered along the "razor"' ties the two separate sheets of cloth together.  Layer 3 looks much like layer 1.  Layer 4, like layer 2.  Earlier a writer suggested you cut the cloth on a bias, this is good advice, and on the bump, may well be necessary with cloth to get it to lay down on the spherical surfaces.

Meanwhile you are layering the flat seating area, and tying this area into the hump with alternating joint lines to ensure all your joints are layered, not butted.

In the end, you want all of the layers to be of appropriate uniform thickness, with all joints overlapped to prevent weak areas when stressed under the weight of your body, or when some clown presses too hard trying to push start your bike. 

Additionally, you want minimum resin, and no air bubbles.  What in the beginning may have looked like pouring honey on a waffle, now begins to look like framing a house.  You are building a structural part, and careful design and fabrication are required.

I think areas along the razor and its outer corners may need additional layers to ensure adequate thickness when you begin sanding to get the contours correct.

Best wishes,
Dick Casey

[Rusnak_322]

You can buy the cloth at any auto parts store or Wal Mart.

Since you have your first layer set up, you will need to sand with 40 to 60 grit sand paper and use air to blow the dust off. You have something like 12 hours to put a second layer on and get a cemical bond. You are beyond that so you will need the sandi g to create teeth for the next layer to bond to.

You should also remove the foam and build up in there, especially around any curve.

The object it not to make a light weight part. The object is to make a part that is not going to flex when you put all your body weight on it. That way you won't get cracks in you new paint job.

With fiberglass, all their strength comes from the glass, not the resin. Adding extra resin only adds weight.

There is a whole engineering/art to design, using cloth in different directions. This is not available to you, so go error on thickness.

Post some pics from another angle, you seat looks cool. I want to see how it turns out, so be sure to post pics when complete.

[boatdetective]

All excellent advice.  Please take the time to read and digest what these folks are telling you. You have NOT designed the easiest part to make.

Even more thoughts:

As noted, a single layer of mat won't do. This material conforms easily, but is not very strong- so you will need to add more of it. Those sharp edges will be very hard to wrap around with any directional fibers. If you choose to ignore wrapping the edges- they'll just become hinges where the part will flex and crack.

Fiberglass boat cloth (as sold in autoparts stores) is not structural material. the fine strands will only give you a thin layer. Stiffness = thickness. This stuff is easy to work with- but it really is designed as the final layer because it will leave you a relatively smooth texture that will be easy to fair.


Remember that if you want a panel or edge to be reinforced, the fibers should cross the panel/joint at 90 degrees. You need to account for fiber orientation when you cut out the panels. In theory- fiberglass mat is "isotropic"- it has the same properties in every direction. Woven glass is "anisotropic"- so the strength varies considerably depending upon orientation.

Woven roving is like boat cloth, yet with much thicker strands. It will give you the strength you want plus stiffness. The draw back is that it can be tricky/delicate to work with for an amateur. The thicker strands will never wrap around the sharp reverse curves of your part. Getting the fiber orientation correct with this complex shape will be difficult. 


One other thing folks have not pointed out: you MUST use a layer of mat between every layer of woven cloth if you are using polyester resin.

"Stichmat" or biaxial cloth is a product that has taken over from woven roving. The directional layers are not woven, so there is no crimp to the fibers. The material is sold in a +- 45 degree orientation, so it tends to wrap corners more easily than woven roving. It also includes a layer of mat on the underside to help with adhesion.


If you just want to add additional strength in one spot or another, there is unidirectional cloth. It wets out easily and is a more surgical way to add strength.


As far as catalyst ratios: the rule with polyester is to shoot for 1-2% MEKP. No more, no less. That comes down to 10cc of catalyst per 32oz pot of resin. Do NOT wing it. The little squirt tube of kicker will be calibrated on the side.

Obviously, your weight will be on the flat seat. It would be prudent to incorporate a section of foam or wood as core material to thicken/stiffen this section.

On other thing that must be pointed out: if you just decided to lay wet mat over the foam plug, then there is no way you will be able to get rid of the foam once the laminate is finished. You didn't mention covering the foam with aluminum foil/tape/wax release.  In essence- you are now making a male "plug"- whether you intended to or not.

If it seems like this is all a lot of work- then you are correct. Making a custom part this complex as a first project demands some planning and patience.



 
 

[cappisj1]

I will get more of the same resin.  I have cloth in several weights already. On the first mat layer I made relief cuts going around corners and on the two mat pieces I used on the hump.  I layed the piece out on the mold and any place it buckled I made a cut (& marked the pieces placement - good tip). This allowed the piece to lay flat around the curve and overlap itself.

I did use blue painters tape over the white foam mold. Althow in my excitement I just now realized I didn't wax the tape

Before I start again, What about the low spots I still have. Do I need to fill them now before any more layers of glass or wait tell the end?  My first though is fill now with bondo so the next layers of cloth lay flat with less chance of air voids and better overall contact, but would this create a bonding/strength issue? 

I like how the seat looks now. I am afraid to put more layers on top and things get out of control. What about adding one more nice neat layer of cloth on the top then build strienght from the underside where I can be a little sloppy?  What about chopping the glass and mixing with resin to smear in the corners from the under side. Have done this on model planes and it gives great strength in corners.

All the information is great. I have adapted parts and pieces to match my comfort and perceived skill leaves.

[LowRyter]

All excellent advice.  Please take the time to read and digest what these folks are telling you. You have NOT designed the easiest part to make.

................... ................... ................... ........
Obviously, your weight will be on the flat seat. It would be prudent to incorporate a section of foam or wood as core material to thicken/stiffen this section.

On other thing that must be pointed out: if you just decided to lay wet mat over the foam plug, then there is no way you will be able to get rid of the foam once the laminate is finished. You didn't mention covering the foam with aluminum foil/tape/wax release.  In essence- you are now making a male "plug"- whether you intended to or not.

If it seems like this is all a lot of work- then you are correct. Making a custom part this complex as a first project demands some planning and patience.



 
 

I find his pretty interesting.  If I understand this right, you're saying that the foam piece cannot be removed?

If so, does that mean the bottom should be glassed over o completely encase the foam?

Could the foam be hollowed to make for storage space ?

If I misunderstood, please disregard. 

[Rusnak_322]

You can remove the foam, and you should. Use a chisel and take it out in chunks.

I would build up the undersides for strength, it won't have to look good.

Don't bondo now, the glass will not bond to it and will delaminate. Cosmetics comes at the end.

[Tom]

 :1: on one layer is not enough.  Consider how much flex there is to what you've made.  Remember that you're going to sit on this...your weight plus the vibrations and flexing of the frame are factors. 

Surfboards are foam core with glass mat and resin over it.  Some shapers will do some tricks to strengthen the board but usually the board is semi-disposable. 

[charlie b]

Foam removal.  Depends on what you are going to do for mounting.

Me?  I'd remove as much of the foam as possible.  Then cut a sheet of plywood thick enough to support the seat (1/2"?).  Then glass over that.  Put enough fiberglass matt/cloth between the wood and seat to fill all the gaps.  You could also make a compartment in the 'hump' at this point.

The top still needs a few more layers no matter which way you go.

[Tom]

 :1:

[boatdetective]

The resin will have bonded to the blue painter's tape pretty well- so nothing will release. Chopping out the foam will be a miserable job.  I would use a vibrating saw (like a fein multimaster). It will make clean plunge cuts. Try to round over the sharp edges of the foam with a rasp or sureform tool. Plan on covering the underside of the seat with fiberglass that wraps and bonds to the outer layer. In effect, this will make a "cored" part- much, much stronger.

The thin woven boatcloth is shite structurally. Trust me on this. You will need to use some directional glass where you can- but that will be hard due to the shape. More than likely, you will have to use all mat. In this case, the short fibers will mean you will need to use a LOT of material. One extra layer will not do it.

[charlie b]

If you want to get REALLY messy....use gasoline to dissolve the foam.  I have not tried it but have seen others do it.  REALLY messy.

PS also not sure of what residue it leaves behind.  Wasn't important for what it was used for.

[boatdetective]

If you want to get REALLY messy....use gasoline to dissolve the foam.  I have not tried it but have seen others do it.  REALLY messy.

PS also not sure of what residue it leaves behind.  Wasn't important for what it was used for.

I just looked it up- if you used blue board insulation, then it is XPS (expanded polystyrene, or "Styrofoam").  Solvents just may work for you!

If you can dissolve it away, that would be awesome. This would allow you to add coring and reinforcement on the inside of the part.

[cappisj1]

Got a chance to pull the foam out of the seat. Here is a pic of after pulling foam (top) and after pulling tap (bottom pic).  Even with no release wax the tape came off really easy.

Recap - White foam carved "mold" covered with blue painters tape but forgot to add a release wax over the tape. Used epoxy resin and fiberglass mat over the tape.

Again, thanks for all the ideas and advice.

Now that the foam is out I am going to build strength from the underside. I will add mounting points at same time. Once I feel it's strong enough I will start the bondo and finish work on the top.