question about fabric covering

On Thu, 07 Sep 2006 19:36:19 -0500, Robbie and Laura Reynolds wrote in :

I'd try an epoxy resin.

Epoxies come in a multitiude of varieties.

There is a pretty thin kind with long pot life that's good for gluing fiberglass to balsa wood.

Problems:

-- Would epoxy stain the cotton a different color? I see a slight yellowish tinge to all the epoxies I use.

-- Getting a nice, even coat. Use an epoxy spreader or old credit cards or some other kind of scraper to distribute the epoxy evenly. This works moderately well with fiberglass on a properly prepared substrate. If I leave dings in the balsa or lite ply, they tend to fill with epoxy, of course. I don't know whether the scraper method would work with cotton.

A friend told me he had success with water based polyurethane and fiberglass. Once the first coat dries, it should be pretty impervious to the next coat (pure speculation).

I never can remember the rule for which of those comes first. I always have to look it up when I fantasize about using dope. Perhaps some day I will actually try dope again and get the rule straight.

One thing with dope: I think it dries from the outside in and takes a long time to dry completely. You might have better success just by giving the parts more time to dry.

I don't know nothin' 'bout gettin' the fabric to fit nicely around corners. :o(

Marty

Nitrate was the first dope, used on World War I aircraft. It has great adhesive strength and is generally good stuff, but it is also highly flammable. Then butyrate came along and solved the fire problem, but it doesn't adhere quite as well. On a large surface such as an amp this isn't a problem, but you want nitrate adhesive quality on wing ribs, etc. The next generation of airplanes used nitrate first, then butyrate on top. The other reason why is because the solvent in butyrate will soften nitrate to make a good bond, but you can't put nitrate over butyrate, not that you would want to.

It does. It's not a chemical cure, it's a solvent evaporation cure. More drying time is probably a good suggestion. I can't smell the amp any more, but it stunk for a couple of weeks after I started using it to play at nightclubs. It really stunk up the garage while I was finishing it. (detached garage, fortunately) You're right that I should have waited longer between coats. Maybe that's my answer right there, although I recall that I had edge lifting problems on the first coat.

Thanks for your other tips. The guy who is building my cabinets for me told me to try acrylic base that artists use on canvas. It's a water-based, thick, milky compound that forms polymer chains when the water evaporates.

Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

To get the fabric to stick to corners, you might want to try SIG "StixIt". This is lightly brushed on the area(s) you want adhered and let it dry. Then position the covering where you want it and apply heat to activate the adhesive. An iron set to about 225 - 250 degrees will activate it. The adhesive is quite strong. On models I have had the wood fibers separate when trying to remove the covering. If you do need to remove the covering, just apply heat again while keeping a tension on the covering. If the covering material overlaps itself, you will need to apply it to the overlap area.

I have also had excellent results (again on models ) using 1/2 oz (0.5 oz) - 3/4 oz (0.75 oz) fiberglass cloth and Minwax "Polycrylic". I normally adhere the fiberglass with a thin coat of poly, working from the center of the piece out toward the edges. When dry (about 30 - 45 minutes), I then apply a second coat of poly. If you will be painting the item, the weave can be easily filled with a mixture of 1 part microballoons to 4 or 5 parts of poly. Sand when dry and then apply a final coat of poly. Be careful when sanding as it is easy to sand right through the fiberglass. Water base polyurethane does not yellow with age and is compatible with almost every type of paint. It will provide protection against the occasional beer spill, but not against cigarette burns. This type of finish has about 60% of the strength/hardness of a fiberglass resin type finish, but it is easier to apply, has no fumes and is a soap and water clean up.

Assuming that I use StixIt or Balsarite to stick the edges down, which is an excellent suggestion, can I apply dope right over it? How about water based polyurethane or acrylic? Has anybody tried this? I'll try it myself, but if somebody else has already done it that saves me a lot of trouble.

The major idea here is to choose a cloth that has the correct look, and glaze it on so I can see the cloth. It is a classic look, like the old saxophone cases I mentioned, so I'm assuming that the blues community will embrace it. I think fiberglass is out, in favor of black cotton cloth. The problem with this is the bubbling tendency that you run into with cotton. I wonder if the problem I had with white glue was because although wet cotton would shrink tight, maybe the glue wanted to shrink more. The butyrate didn't have this problem, and if the water based products that you are referring to don't shrink, maybe they wouldn't bubble either.

Hi Robbie . . . long time no yak.

You might consider BalsaRite brushed directly on the wood. Works quit nicely for bonding fabric to just about anything.

The BalsaRite will not fill the weave, and you can iron it on all edge and corners and then use a heat gun to shrink it everywhere else (o just iron it all over).

Most fabric stores have polyester in every color under the sun, plus few dozen truly awful prints. The only 'down side' is that fabric stor polyester is not shrink controlled the way aircraft coverings are, s you could have as much as 35 - 40% shrink, depending on the fabric d jour.

Sometimes the BalsaRite looks lumpy in the can and goes on lumpy. No to worry, under heat the stuff flows out and the lumps disappear.

Sig Stix-It works the same way

-- the-plumbe

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On Thu, 07 Sep 2006 21:19:31 -0500, Robbie and Laura Reynolds wrote in :

Ah--that may be a clue. I think I read that if you can still smell the solvent, the dope is not yet fully dry.

I love the smell of dope, at least in small quantitities.

Sounds like good stuff.

If you want to stick with the dope, you might try putting a base coat on first, then come back with the doped cotton.

Good luck--and let us know how it turns out. The blue amp certainly is eye-catching.

Marty

That's a good idea. We had a day devoted to Stitts Polyfabric in my aircraft classes when I got my A&P license. It's a polyester fabric with polymer dope to match. Can you use butyrate on it? I happen to have a gallon can of butyrate.

I have used common Baking Soda mixed with the water base polyurethane to fill the weave it sands easily and leaves a smooth surface. I was surprised the first time I did this and after applying the Monokote covering the fiberglassed section is barely visiable, mainly due to the slight color difference between the bare wood and the fiberglassed section.

Roy

Well I used to design amplification equipment and teh cabninets for a small company some years back - we used leatherette of course - and the way we ended up doing it was this. I can;t say it will work as well with an open ave type finish

First of all the cheap way to finish large surfaces was with PVA white glue in presses. Cheaper stuff was done this way and then cut later and we edged the stuff with alumnium angle to cover the joins

For actual amp cabinets, we would wrap a striop around the case with PVA, and leave it. Once dry the girls then had the job of finishing the edges. Only one glue really worked - a rubber latex adhesive that smelt of ammonia. Copydex comes closest in 'brands' and I have seen similar glues in builders merchants. Its more or less a water based contact glue. Solvent based contact also worked, but was too expensive for production.

I have to say that something like Balsaloc, or even ironing fabric onto drieed PVA may work for you.

My worry is that the glues will contaminate the weave and you won;t be able to show it off..

If possible, just stretch it over and dope it down?

I have used an acrylic clear wood varnish to hold silkk and glass cloth to foam. Worked well. Comes up hard as glass...starts milky dries clear.

Use denim for them. :-)

I think that if you can glue the edges down with something and then shrink the cloth, an acrylic over the top will stick it and fill the weave.

Vacuum bagging is potentially useful too..put it in a plastic bag and remove the air..until it all sets. That works better on epoxy that sets rather than dries tho.

I build speakers as a hobby. You might try Parts Express. They sell anything and everything for speaker building.

They have some material that is used for speakers that you iron on like model covering. I got my first ideas for cross-overs and cabinet building from...

Awesome designs ! My first pair were the Dayton DIII's. I love them and have not heard any speaker below $1K to match them. For $300, I think they are great !

I use a utilitarian approach to performance grade speaker enclosures. I have decided to use the same material that is sprayed onto pickup truck beds to protect them.

Performance grade speakers are moved constantly from one venue to another and suffer the slings and arrows of constant moving and handling. Appearance is not as important as function in this type of enclosure. Besides, in the long haul, I feel that this material will look better than any kind of pretty finish in a short period of use.

Ed Cregger

Ed,

Parts Express has the iron on stuff that has a "rough" finish to it. I am told this is for toughness and to give those types of speakers something for you to grip with. It's the same stuff that is used on speakers for concerts and has to handle the "roadies" rough treatment. You are right, I wouldn't put a pretty finish (veneer/stain/etc.) on a speaker that was going to be handled and moved allot.

Well, that was the original idea, and it looks very good on the one that I already did this way. The only thing keeping me from being completely enthusiastic about it was the edge lifting problem, and if I can solve that with Balsarite I think I may have the problem licked. But I have a question about Balsarite. On the blue amp I moistened the cotton to make it stretch out, and I applied the dope right through the wet cloth. It tightened itself just like it's supposed to, which I thought was very exciting because I never actually did this on an airplane before. If I'm going to stick the edges down with Balsarite, I'm wondering if I can have the cloth wet, or if it needs to be dry. If it's going to be dry, I'd probably have to Balsarite the whole cabinet to prevent lifting. Come to think of it, maybe I could iron one edge down, spritz the whole thing, and the iron would dry the other edges as I stick them down. I'm getting excited again. I can't wait to try this.

As one with experience in aircraft fabric covering, I would use the aircraft-grade polyester fabric. It's unshrunken, and you would glue down the edges first (use Stits Poly-tak or similar, which hardens quickly and is really strong) and then iron the fabric to shrink it tight. It's the same process we have to use on airplanes, which also have plenty of fairly sharp corners around the edges of end ribs, firewalls, trailing edges, and the like. Lumpiness caused by minor wrinkes or glue gobs are easily ironed flat. Use a calibrated iron, and no more than 350 degrees F. Better to do it in stages, with each pass a little hotter, to keep the weave relatively straight. With some practice you can straighten it out with intelligent application of the heat here and there. After shrinking, a clear finish can be applied to bond the whole thing to the surface, another technique used on fabric-covered wooden airplanes. Wet-sand with 220 grit silicon carbide waterproof paper, and give it a final spray coat. Comes up like glass.

Dan

Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

Yes. You can apply dope over it. The StixIt is a heat activated adhesive. I have used butyrate dope, acrylic enamel, acrylic lacquer, Rustoleum, Krylon and latex paints on fabric adhered with StixIt with no problems.

Remember, you want a thin coating of the StixIt on the wood. If you put a heavy coat on you will see some bubbles when it has dried (the bubbles can be sanded off ) and the bubbles MAY cause some small bumps in the fabric.

Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

A polyester fabric, stretched taut when initially fastening/gluing it down can be shrunk even tighter by using heat (a clothes iron will work fine for your applications ). You will need to play with the heat setting to find what temperature will shrink the cloth without burning/melting it, or over shrinking it. I suggest starting at about

Not sure about the butyrate, but the PolyTak would serve nicely.

-think- Stitts likes dope, but you'd want to check on it

-- the-plumbe

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