Strengthening plywood with fiberglass and resin/epoxy

Hi, I'm trying to make a board similar to a skateboard. I'd like to use 1/4" plywood but 1/2" would work too. The problem is that it's not strong enough to support a person. I've heard of using fiberglass with an epoxy/resin that will drastically increase the strength of whatever you put it on. I was wondering if anyone could give me some advice on how and what to use to strengthen wood.
A couple of things to consider: -Keeping the weight down.....a couple of pounds is not a big deal, just not 15 or more.
-How to apply graphics or even keep the natural look of the wood- do you apply graphics under the fiberglass?
-Can I paint the wood? Before and/or after the application of the fiberglass? The use of stains?
-How much stronger will fiberglass make the wood?
-Application?
-Prices?
-Where to buy?
-Other options?
Thanks, Jay.
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On Sun, 10 Jun 2007 13:39:41 -0700, snipped-for-privacy@uga.edu wrote:

Check out the fiberglass cloth they apply to wooden boats and airplanes. You end up with an amazingly strong, lightweight structure. Check this out:
http://www.roarockit.com/d_builder.php http://www.lushlongboards.com/index.php?cPath 9_252 http://users.pandora.be/Toothless/Toothless/pages/instructions/instructions_index.html
There are a few experienced boat builders here. I'm sure they'll chime in with some really good information.
--------------------------------------------- ** http://www.bburke.com/woodworking.html ** ---------------------------------------------
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snipped-for-privacy@uga.edu wrote: > Hi, > I'm trying to make a board similar to a skateboard. I'd like to > use 1/4" plywood but 1/2" would work too. The problem is that it's not > strong enough to support a person. I've heard of using fiberglass with > an epoxy/resin that will drastically increase the strength of whatever > you put it on. I was wondering if anyone could give me some advice on > how and what to use to strengthen wood. > > A couple of things to consider: > -Keeping the weight down.....a couple of pounds is not a big deal, > just not 15 or more. > > -How to apply graphics or even keep the natural look of the wood- do > you apply graphics under the fiberglass? > > -Can I paint the wood? Before and/or after the application of the > fiberglass? The use of stains?
If you build a fiberglass/plywood sandwich, the plywood becomes a filler and it's strength is of little value.
What you want to do is done every day; however, foam is the normal core material, not plywood, to keep the weight down.
What are you trying to build?
Lew
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milky.
The fg will stick to wood better than it will to paint. Probably best to dye it, though a thin stain shouldn't hurt much.

It will make it much stronger, but not all that much more rigid unless you make it quite thick. One of the nice things about fiberglass is how flexible it is.

that explain it.

Glass is cheap; epoxy is not. I buy it by the gallon for about $100, but I am sure smaller containers are available.

Aluminum? I just saw a TV show on making skateboards; quite interesting.

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snipped-for-privacy@uga.edu wrote:

Check out http://www.epoxyworks.com /, specifically the article titled, 'Fortifying a spare-parts "Scootboard"'.
All of the strength is in the fiberglass (or, in this case, carbon fiber) skins. A common boatbuilding technique is to laminate fiberglass top and bottom skins over balsa. The balsa provides no strength by itself; it just holds the two skins apart. Think torsion box.
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You might try TAP Plastics if there is one in your area, they carry the cloth and the resin. I think if I was going to fabricate a skate board, I would make the core out of Balsa wood, and in the area where the trucks are to be fastened reinforce this area with either hardwood or even a plate of steel that you can drill and tap to secure with machine screws..
The process is one where you mix the resin and then "paint" the goo onto your core. While wet, you then lay the cloth over the sticky stuff and smooth it into the goo.
When the resin cures, you then paint on a another layer of goo, and completely saturate the underlying cloth. Another layer of cloth is then applied and smoothed over and then recoated. You keep this up until you get to the desired thickness, and then you change to a finish coat that tends to dry a little less sticky than the undercoats. The finish coats can be clear or it can be pigmented. For a skate board you might also get some additives that you sprinkle on the top to give you some traction.
Alternatively you could finish the whole thing smooth and apply traction tape.
If your goal was to make a thin board you might forgo the core and make yourself a female mold to form the board into. Here you have to be careful to maintain the appropriate draft angles, and the process would be to make the mold smooth and then you wax it or spray a mold release agent. Now you paint on the finish coat or gel coat, and then work your way backwards by then applying the resin, glass and resin, and any blocking for attaching the wheels, and finishing with a finish coat for the bottom when you have built up the board to the desired thickness.
It stinks to high heaven, and mucking about with the fiberglass cloth will give you little micro-cuts that will leave you itching for a while, but by doing it yourself, you can get anything you want.
--
Roger Shoaf

If knowledge is power, and power corrupts, what does this say about the
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it is one structure instead of multiple structures glued stuck together. I have never heard of this finish coat you refer to. Since hardened epoxy isn't the least bit sticky, how could the finish coat be less sticky?
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Have you ever installed a fiberglass shower stall?
The gel coat is hard and smooth, but the back side has sort of a sticky feel to me.
You could be correct about the best technique for laying up the glass, my experience was only onetime helping my brother fiberglass a plywood boat and that was done in several stages.
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
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cures where it is exposed to air. You can either cover it with poly or use a top coat that will cure with air exposure. Epoxy isn't like that.

stick to the one before. It is much better to do it in one pour, if possible.
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Sun, Jun 10, 2007, 1:39pm (EDT-3) snipped-for-privacy@uga.edu stumbles in and mumbles: Hi, I'm trying to make a board similar to a skateboard. <snip> -Other options?
"Similar" to a skateboard, eh? And, "other" options? We don't even know what you want to do, so how can we offer options? So many questions; so few details. Makes one wonder. How about some details?
JOAT If a man does his best, what else is there? - General George S. Patton
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On Sun, 10 Jun 2007 13:39:41 -0700, snipped-for-privacy@uga.edu wrote:

Use balsa instead of plywood, slice it to your thickness on endgrain, use more than one piece, edge glue the pieces together just to hold to make a rough panel (flat board with wax paper helps here), then cut your final shape . Glass it all around, be sure to wet in the glass to the balsa endgrain, it will soak up a lot of the epoxy and because it is on end, will give you very good compressive strength. Tensile and torsion strength comes from the glass/epoxy, balsa does nothing there.
That is the way many fiberglass boat decks are constructed and they are very strong. Other method is a foam or honeycomb core, but more expensive, don't know if you can get a small quantity of honeycomb.
Internet for prices and sources of glass and epoxy resin. Most recently I bought from U. S. Plastics, they had the best price. Hobby shops for balsa. I managed to get a 4 X 4 piece of balsa to slice into my tiles for some boat deck repair.
Don't paint the wood. will seal off the endgrain and it's not pretty, so you don't want to see it. Paint the component afterwards or put a coloring agent in the final coat of epoxy. Final coat will probably need a thickening agent to get the build up you need to not be sanding into the glass cloth.
my $.02 worth
Frank
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On 10 Jun, 21:39, snipped-for-privacy@uga.edu wrote:

Fibreglass is generally used with polyester resins, not epoxy. Epoxy is used for the really high-end stuff, but it's expensive and a pain to work with. Unless you've tried GRP already and found it wanting, then you're best sticking with the cheap stuff.
Although this stuff is easily available, the prices for small quantities in car spares places are ridiculous too. Any reasonable- sized city will have a fibreglass specialist selling it far cheaper.
As to the "adding strength" issue, then you have to think carefully about what "strong" means in your case. Simply adding a bit of resin and maybe mat to plywood will make the surface harder and may make attachment points less likely to pull out. However for real strength in bending, and especially stiffness and resistance to bending, then you're more likely to make a double-layered fibreglass beam with two strong surface skins and a weak filler material between them that's there as a former, not for strength. You can make surfboards and airplane wings with just a foam core, so you don't need to be using heavy plywood any more. You might well find yourself going from "GRP as an addition" into a full-blown GRP structure design, using a core that's just the lightest wood (or foam) you've got.
There's an awful lot already published about this stuff. Search for boat or surfboard building advice.
Plan to make several. Most people find it quicker to get it right second time around, after some pratice. 8-)
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Andy Dingley wrote:
> Fibreglass is generally used with polyester resins, not epoxy.
Not true.
There are a lot of epoxy/glass laminations out there, including my boat.
> Epoxy > is used for the really high-end stuff, but it's expensive and a pain > to work with.
Again, I take exception.
Slightly different methods of layup, but it ain't rocket science.
Glass/Epoxy ratios of 50-50 are quite common. Higher with vacuum bagging.
Glass/Polyester ratios of 35-65 are about as good as you can get.
Bottom line....................
Glass/epoxy is much less weight for the same strength.
> Simply adding a bit of resin > and maybe mat to plywood will make the surface harder and may make > attachment points less likely to pull out.
Mat is strictly for polyester, not epoxy.
It adds weight, but not strength.
> However for real strength > in bending, and especially stiffness and resistance to bending, then > you're more likely to make a double-layered fibreglass beam with two > strong surface skins and a weak filler material between them that's > there as a former, not for strength. You can make surfboards and > airplane wings with just a foam core, so you don't need to be using > heavy plywood any more. You might well find yourself going from "GRP > as an addition" into a full-blown GRP structure design, using a core > that's just the lightest wood (or foam) you've got.
Yep, which is why I asked the question, "What are you building?"
Lew
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wrote:

I'd suggest that you're unusual in this, being significantly more experienced than most. Maybe boatbuilders are fussier.
Certainly here in the UK, for "hobby" levels of work or even small dinghy makers, polyester is _far_ more common than epoxy. Just the price of resins is enough to swing it.

I've never used epoxy that didn't need vacuum and controlled moderate heat. This has been with either prepreg carbon, or Kevlar. I've never used a grade of epoxy that wasn't fussy enough to require this -- when I've been working at that level, with glass, or 20-30 years ago it was always just polyester. There are certainly such epoxies around that aren't so fussy (I use West System for general gluing), although I've never used it seriously for fibreglass.

If you have the skill to achieve that sort of wetting out. "Typical" UK amateur skill levels (I'm coming to this from the kitcar world) are often distinctly heavyweight, certainly on the first projects.

What do you mean by "mat" ? I'm referring to weaves, as well as choped strand. Maybe this is a local terminology issue?
Incidentally, there's an epoxy thread in rec.knives at the moment. How do you best attach scales to a metal frame ?
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Andy Dingley wrote:
> I'd suggest that you're unusual in this, being significantly more > experienced than most. Maybe boatbuilders are fussier.
Naw, just set in their ways and scared to death of $$ signs.
Just look at initial price of materials, not finished cost of laminate.
OTOH, you tend to get a little fussy when you are building for yourself, which is what I did.
> Certainly here in the UK, for "hobby" levels of work or even small > dinghy makers, polyester is _far_ more common than epoxy. Just the price > of resins is enough to swing it.
Again, got to look at finished laminate cost.
Yes, epoxy is more costly than polyester.
Yes, knitted glass used with epoxy is more expensive than 1/2 OZ mat and woven roving.
That said, you use less epoxy by weight and about the same amount of glass, thus the total laminate cost is about the same.
It is also far easier to wet out knitted glass with epoxy than it is to wet out mat and roving with polyester, thus there is some labor savings once you ramp up the learning curve.
> I've never used epoxy that didn't need vacuum and controlled moderate > heat. This has been with either prepreg carbon, or Kevlar.
Different world.
Never worked with either one, but understand they are a bear compared to knitted glass.
> I've never > used a grade of epoxy that wasn't fussy enough to require this -- when > I've been working at that level, with glass, or 20-30 years ago it was > always just polyester. There are certainly such epoxies around that > aren't so fussy (I use West System for general gluing), although I've > never used it seriously for fibreglass.
Standard WEST is laminating resin.
There are only 4-5 base resin (Part A) manufacturers world wide.
Shell, Dow, Ciba come to mind.
Lots of formulators for the hardener (Part B) like WEST.
> If you have the skill to achieve that sort of wetting out. "Typical" UK > amateur skill levels (I'm coming to this from the kitcar world) are > often distinctly heavyweight, certainly on the first projects.
It's a basic problem with polyester, mat and woven roving.
Roving doesn't wet out easily, thus the mat is used to hold the resin.
OTOH, epoxy readily wets out knitted glass so it is easy to squeegee out excess resin.
The trick is the knitted glass.
> What do you mean by "mat" ? I'm referring to weaves, as well as choped > strand. Maybe this is a local terminology issue?
"Mat and roving" describes a glass that consists typically of a layer of 24 OZ woven roving with a 1/2 OZ stranded mat stitched to it.
Been the backbone of the polyester boat building industry for years.
BTW, chopper guns in the USA are a thing of the past. Changes in the environmental laws have turned them into antiques.
It's only been the last 10-15 years that knitted glass has started to see some acceptance.
Old habits die hard.
> Incidentally, there's an epoxy thread in rec.knives at the moment. How > do you best attach scales to a metal frame ?
What does the term "scales" mean in the above?
Lew
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Flat bits of wood or antler. Typically a folding knife will have two thin metal "liners" between these and the blade itself.
If you're making a knife from scratch, then you rivet the scales to the liners (easy), then you rivet the liners together around the blade etc. (rather more work) If you're _repairing_ one though, you often need to re-attach or attach new scales to liners that are already in place around the blade, lock and folding mechanism. This is awkward, as it's impractical to use the scale rivets, owing to poor access.
The temptation is to glue the scales to the liners, which is dead easy but doesn't usually work too well. There's a lot of bending here and an inelastic adhesive will tend to break off. As many liners are brass, it can be a real problem. Personally (for repairs) I like to leave the stumps of old rivets behind as crude dowel pins.
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Andy Dingley wrote: <snip a tale of pocket knife reconstruction>
> The temptation is to glue the scales to the liners, which is dead easy > but doesn't usually work too well. There's a lot of bending here and > an inelastic adhesive will tend to break off. As many liners are > brass, it can be a real problem. Personally (for repairs) I like to > leave the stumps of old rivets behind as crude dowel pins.
Think I'll stick to boats<G>.
BTW, might try some epoxy thickened with microballoons as an adhesive for the scales/liners connection.
Yields a much better joint than plain epoxy.
Lew
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Others have given you a lot of good how-to information that should help you.
If you want some idea of how strong a piece of plywood becomes when covered with fiberglass, here is an example. I have a manufactured trench cover that is 4' wide and 8' long. It was made for placing over a ditch in a roadway so traffic can pass over it. My trench cover was made from a sheet of 3/4 void free 11 lamination birch plywood covered on both sides with about 1/4 inch of fiberglass cloth and resin. It is rated by the manufacturer to carry 3500 pounds per axle across a 4 foot span, and I'm sure that this is a conservative rating, as it has seen quite a bit more than that a few times without suffering any damage at all. When spanning a 7' gap I have had 6 people standing closely together in the middle of it and it has only bowed down about 1 inch. It's heavy though. It weighs about 90 pounds, which is over 2X the weight of a similar sized un-fiberglassed sheet of plywood.
A 1/4" piece of plywood covered on all sides with fiberglass cloth and resin should make an extremely tough scateboard, but it might not be thick enough to hold screws for attaching the wheel assemblies. You could go with thicker plywood or place metal inserts in the fiberglass/plywood assembly and then attach the wheels to these pieces of metal.
How are you planning to bend up the ends? Skateboards that I have seen were manufactured by gluing the plywood laminations in a form. In other words, they make the plywood to shape and then cover it.
Charley

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In adition to what has been said before: in order to obtain the lowest weight and the highest strenght, you must be carefull not to add too much resin. In commercial application, the parts are coverered with a plastic film and then vaccumed, to eliminate excess resin and/or air bubbles. Your option would be to press the layers into place using a roller. For finishing, auto body primer/filler would be good, sanded after each application, painted as desired, with a few coats of clear in the end. Try to get the sort of paint that won't crack easily when bent.
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