Fibreglassing 101?

I need to make a couple of horns ( for audio use ) and have a couple of questions as I never worked with this stuff before...

The local Home Depot clone ( in scandinavia ) sells the glass fibres, polyester resin, hardener and gelcoat wich should be everything I need ?

The mold is made from a big chunk of MDF ( Medium Density Fibreboard ) that I laminated from several smaller sheets, then cut the horn flare contour in it on a lathe..

To give you an idea of what I am trying to do I put a picture of an existing horn here:

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The mold I made fits inside the horn.. Note that the actual horn I am trying to make is round, not rectangular like this..

Can anyone give me some idiot proof instructions on where to go from here, before I waste 100$ worth of fibreglassing ingredients?

If not, heres a few questions:

How do I get the surface thats touching the mold as smooth as possible? ( The mold was turned on a lathe, so it is smooth, but I'd prefer the fancy shiny surface :-)

How do I keep the fibreglass from sticking to the mold?

Any tips that may come in handy?

I know that this process involves nasty chemicals and nasty dust, so I will be doing this outside wearing some sort of dust filtering mask..

Thanks in advance

/peter

Reply to
Q
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That surface needs to be as non-porous as possible. Seal it with whatever your fiberglass supplier has on hand and recommends. Furane is one product, sprays easily, dries fast, sands readily, polishes shiny, smells terrible. It's not very durable though.

After sealing the surface, use a specialty type paste wax. Apply wax, let dry as recommended (perhaps overnight), and buff. Do about 6 coats. Do not try to speed the process. You might also bake the mold in a warm oven between coats to help get the wax to penetrate the surface. For at least the first part, apply a couple of coats of PVA (from the fiberglass supplier). Spray it on if you can, it won't brush very well on a waxed surface.

I can't tell you how many times I've heard that folks making their first piece don't get the mold sealed and waxed properly, and end up with the mold and the part permanently bonded together. So you might try sealing and waxing some samples first to test that your technique is adequate. The first release on a new mold can be troublesome. Try getting a little compressed air into one corner. If that doesn't work, try getting some water into the released areas to dissolve the PVA. After the first release, add another coat of wax. If the first part was tough to release, you might use PVA on the second one as well. But if the mold is properly prepped, all releases after the first one should be easy. The tail on your horn doesn't appear to have much taper, and the part is going to shrink around the mold. So expect the part to have a good grip on your mold in that area. You might make the first part a single layer thick. That will give you some layup practice, and enable you to peel the part off the mold if it's stuck in some areas.

Wayne

Reply to
wmbjk

1.Mold release to prevent the part sticking to the mold, one brand name is Freekote, choose one that cures at room temp.
  1. The gel coat goes on first, that's what makes the smooth surface.
3.Follow the directions for the resin system you have picked out, i.e. cure times for the gel coat before bond coats and fabric, shouldn't have any problems.
  1. Do wear protective gear, you can build a reaction to the stuff over time, so no bare hands.
  2. Good luck!
Reply to
Franklin Newton

Any local boat repair guys? Marinas? They'll show you just what you need.

Reply to
Eide

"wmbjk" skrev i en meddelelse news: snipped-for-privacy@4ax.com...

The supplier is a local Home Depot clone w. highschool student employees, so I doubt they have any recommandations :-)... They do have a boating supply dept, wich is where I found the fibreglass stuff..

I found some silicon based mold release designed for Polyester resins at an electronics supply place.. I just ordered a couple of cans..

Any clue if boatwax will work?

PVA is regular (white) wood glue ?... I could add a little destilled water and spray it on

Someone mentioned using babypowder on the mold as a release.. Will that work?

I could integrate a quickrelease fitting for the airhose in the mold, so I can blow air between the mold and the piece..

I could do just a few layers on the mold, let it harden and add more layers after I remove it from the mold... This would help the shrinking problem to some degree, or am I way off track ?

Thanks for the input so far!

/peter

Reply to
Q

"Franklin Newton" skrev i en meddelelse news:AWgCe.5966$ snipped-for-privacy@newsread3.news.pas.earthlink.net...

I found some silicon based stuff.... If I start by applying a layer of polyester on the mold, let it harden and spray it with the silicon based stuff, will this be enough?

AHA!... I learned something new today :-)

The directions are on the cans, so that wont be a problem..

Yup... have heard about some poor aircraft maintenance person who sprayed his arm w. resin by accident.. The story says that the arm more or less rotted in a few weeks... Besides local OSHA codes on the fibreglass industry are mad here...I think you'd need less protective equipment to walk on the moon :-)

Thanks, and thanks for the input..

/peter

Reply to
Q

"Eide" skrev i en meddelelse news:yyhCe.64565$R21.12623@lakeread06...

I have been looking around the area to see if I could bribe someone to do these horns for me, but no luck so far.. Besides.. I might aswell play a little with nasty chemicals :-)

/peter

Reply to
Q

Silicone grease spread thinly, or petrolatum (Vaseline), or Rain-X.

This isn't that difficult. You don't fancy mold-release products.

You can also craft your mold out of that cheap pink polyester Bondo. Unlike the MDF, you can add it as well as take it away.

Reply to
Richard J Kinch

It's not that toxic, the Portuguese guys around here (RI) had been spreading it with their bare hands until a few years ago. Don't get me wrong, most of them aren't around anymore, and those that are have the shakes, but you won't be rotting your arms off.

Reply to
Eide

I have been making one off patterns molds and parts regularly for the boat and can tell you what works for me but I don't know what would be available where you are. Scandinavia is a big place. I think Denmark and Sweden have some good sources for composite materials.

Mold finish: I sand to about 120 and spray on a polyester based tooling primer called Duratec Surface primer. It is a soft high build polyester primer. Wet sand from 400 to 1200 then an automotive compound and finally a fine polish like McGuire's. Two coats of cake type carnauba based automotive wax as a base for the mold release.

Mold release: PVA is polyvinyl alcohol. A green liquid that dries to a thin water soluble film. Spray a very light coat as a binder coat. After about 10 minutes it will be dry enough to spray a wet coat.

Glassing: To do a proper job you need several different glass fabrics and the Home Despot is definitely not toe place to get them. Price is way to high and you will be lucky to find anything outer than 6 oz plain weave cloth.

Some terminology: "Gel Coat" is a thick surfacing polyester with lots of solids. It is the surface that you see when you look at most fiberglass boats. "Cloth" is a plain weave material. It comes in various weights from .5 oz/sq yard to 8 oz. and is used to reinforce the surface. "Roving" is a very heavy yarn woven into a loose fabric. It is used for strength and mass. "Mat" is a random oriented fiberglass felt like material used to fill the voids in the coarser roving and prevent the weave pattern from printing through the gel coat. "Sanding Aid" is a liquid wax additive that is mixed with the last coat of polyester resin. Polyester does not cure hard in the presence of air. The wax migrates to the surface and forms a shielding layer to keep air away from the curing resin.

Start with a sprayed on polyester gel coat as soon as the first coat has flashed off spray on another. You can roll it on but be careful not to damage the PVA release. Repeat until you have about 30 mills of thickness and let is cure for an hour or so. Then you can roll on some regular polyester resin and lay a scrim of 2oz cloth followed by a layer of 6 oz cloth and a layer of 8oz mat. You want the resin to fully wet out everything. Next come several layers alternating roving and mat to build the thickness you need. Cover the last layer of mat with some 6 oz cloth and seal it with resin with the wax additive..

Reply to
Glenn Ashmore

Yes, it is. But you should not take a water-resistant for obvious reasons. :-))

Nick

Reply to
Nick Müller

"Glenn Ashmore" skrev i en meddelelse news:xOlCe.171881$sy6.140027@lakeread04...

The main problem here seems to be limited availability simply because very few people do stuff like this at home.. From the sound of the replies I think I need to stop by one of the local yachtbuilders and see if they will sell me the materials I need.. The Home Depot clone only has one grade of cloth ( 300 grams per sq. meter ) and it aint cheap.... Altho: A common wallpaper type here is woven glass cloth is dirt cheap.. Could I use the Home Depot clone for the first layer ( the inner layer actually, but this is the layer that would be visible ) and just use the wallpapergrade stuff for a "filler" ? I dont need much strength, just need it to be relatively stiff...

Sounds reasonably simple... Although I'd need to replace the primer etc. for something local...

Seems I am going to the yachtbuilder again :-)

Seems I am going to the yachtbuilder again :-)

Excellent.. I needed some words here and there :-)

This was exactly what I was looking for, now I just need to source the materials and try not to end up spending thousands of dollars in the process :-)

/peter

Reply to
Q

But you should have model builder shops (planes, ships) that sell that stuff. At least per mail order. Or you get hints where to look for at modelbuilders forums (yes, the colorful forums are evil for NewsGroups users).

Nick

Reply to
Nick Müller

Know of any online shops in Germany that sell the fibreglass materials?... Am just north of you in Denmark, so it wouldnt be a huge problem getting the stuff from Germany?

/peter

Reply to
Q

Most of the model builders I know either buy their stuff at the place I mentioned or from Conrad in Germany.. Problem is the quantity... I need more than a model boat would need but on the other hand I dont need a 55 gallon drum of polyester :-)

I am going to Wacken near Hamburg in a few weeks (

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) and could stop in Hamburg if there are any good places to get the materials I need?

/peter

Reply to
Q

Yep! Here you go (even in English):

Don't know wether they ship to Denmark, but I guess. This company seems to be the best resource for that stuff. At least I've seen it referenced many times in model builders NGs. I'm not in the laminating.

HTH, Niick

Reply to
Nick Müller

Urgs! Not the best place. For anything. :-)

I'm from Munich, so I can't help you now. But I will post in de.rec.modelle.misc to find a shop for you in Hamburg.

Stay tuned ...

Nick

Reply to
Nick Müller

materials?...

This looks perfect.. I dont know about the prices, but compared to bribing a yachtbuilder to do the hoens for me this would most likely be cheaper...

It seems that they do ship to DK.. Now I am just confused about the quantities to order :-)..

/peter

Reply to
Q

I'd also check for any radio control model airplane clubs or experimental aircraft groups in your area as they might have several individuals that are conversent on the composite subject. How bout kit car manufacturers? They use glass bodies quite a bit. One thing I'm impressed with is the willingness of the r.c.m guys to offer knowlegable suggestions on subjects far from metal. Sometimes I think that rec.crafts...should be "materials" instead of metal.. Regards Pat

Reply to
patrick mitchel

All the materials I mentioned are regularly used by all sorts of composite workers. You should be able to find a distributor of FRP supplies somewhere around any major coastal city or you can search the web for mail order distributors Northern Europe. You might try Bang & Bonsomer in Finland or Armatech in Sweden. They are distributors but can tell you who sells their products retail. Or check with a local small boat designer for a source A quick Google came up with

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. FRP canoes use all the materials you will need.

In order from worst place to best places to buy composite supplies in the quantity and types you need are:

1) Model builder supply stores (Don't carry the heavier materials and they specialize in small quantities so the price will be WAY to high.) 2) Big Box building Supply stores ( very limited choice and high prices) 3) Commercial boat builders - ( have everything you need but no way to sell it to you. You have to rely on the sympathy factor) 4) Chandlers (boating supply store) (Usually can get anything you need but at a price) 5) Mail order boat building supply companies (Set up to sell cut length material and resins in liters)

As a wild guess I would think that an Electrovoice HPT42 horn would require about 250 ml of gel coat, 2 meters of 2 and 6 oz cloth, 3-4 meters of mat and roving and a little more than a liter of polyester. If your low end is limited to 1300 Hz you can build it a lot lighter than a low end horn. If you are working on a low end horn double or triple the roving and mat.

Either way be sure to roll out all the voids and consolidate the lay-up really well. Any voids are going to add unwanted color. Ideally I would vacuum bag the mat/roving lay-up. Keep the temperatures fairly low and cut back some on the MEK (catalyst) to extend your working time long enough to get the bag pulled before the resin kicks..

Reply to
Glenn Ashmore

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