Fiberglass Experts

[Boatsb]

It's alway been my understanding that with polyester the amount of hardener can be changed within a range to suite temperature or working conditions. With epoxy you don't change the ratio just select fast or slow hardener.

Brian

The hardener for Polyester (MEK) has various strengths and can be mixed to speed up or slow down the reaction with the cobalt in the resin. Epoxy has a 2 part resin that can be mixed more or less base and catalyst to get faster cures and there are various catalyst mixtures available to cure faster or slower. both use an exothermic reaction to harden the resin. The difference is how the chemicals are added.

 

[CHECK 6]

follow this Linc these guys were very helpfull and have directions on their web site...Cory

http://www.masepoxies.com/public/

 

[Vincentc]

Changing the hardener/resin ratio will not affect the rate of cure but will affect strength. A too rich hardener ratio will make the cured resin SOFT. It's December, fast cure rate will not be a problem.

There is no need for any kind of cloth or mat (which is generally not compatible with epoxy) between the plywood and FG hatch. Cloth would add tenside strength, you are concerned with bond strength. Filled epoxy applied between clean and rough sanded surfaces will NOT come apart without destroying the surfaces. The filler of choice for this kind of bond is probably cabosil aka fumed silica. Microballons would be useful to fair the outer surface.

FG cloth on the outer surface of the plywood will add strength and stiffness to the composite structure created.

The advice to read some of the literature available from one of the epoxy vendors is appropriate here.

Regards,
Vincent

 

[Brian Degulis]

I took it apart ground everthing down to sound glass. Then 2 layers of mat wetted out with epoxy then I put on some resin thickened with a bonding filler. Pre coated the plywood with resin and layed it in with some weight. This was all done in one operation. I just have to put a layer of cloth on the plywood and drill and back fill for the hatch pulls paint it up and I'm done.


Brian

 

[Boatsb]

was the mat compatible with the epoxy? many are not.

 

[SKYCHENEY]

was the mat compatible with the epoxy? many are not.

This is true. What epoxy are you using? If West System and you bought the mat in their packaging, you should be fine.

 

[Brian Degulis]

MAS Epoxies I just started using it instead of West because it doesn't have the amine blush. The mat is supposed to be compatible with epoxy or polyester seemed to wet out just fine.

Brian

 

[bobk]

Brian, Sorry, I found this thread too late to inject a chemistry lesson. Lots of errors in the posts. But maybe not too late for an engineering lesson. A composite structure should be viewed like an 'I' beam. The upper and lower flanges need to have the same strength and rigidity if it will carry a load (like a real big guy stepping on it. The plywood is analogous to the web. It needs to separate the skins and be well adhered. Unless your wood is sufficinetly stiff to not flex on it's own, I'd suggest you build up the underside with enough glass to approximate the thickness of the top skin. You are prety much committed to epoxy now, but recognize, as one poster said, the binders in the typical fiberglass product are not intended for use with epoxy. They dissolve in polyester and make for a good glass/resin bond. A special glass is needed with epoxy.

Bob

I took it apart ground everthing down to sound glass. Then 2 layers of mat wetted out with epoxy then I put on some resin thickened with a bonding filler. Pre coated the plywood with resin and layed it in with some weight. This was all done in one operation. I just have to put a layer of cloth on the plywood and drill and back fill for the hatch pulls paint it up and I'm done.


Brian

 

[Brian Degulis]

I'm just fine with at a minimum duplicating what hat did when they built it. Which was a simple glass hatch with a piece of plywood laminated into the bottom. It doesn't look like they put much effort into getting the plywood to bond to the underside of the hatch. Looks more like they placed it on there and glassed it in. Since the hatch is already built and I'm just replacing the plywood which rotted out I really didn't want to try and bond it with polyester because Epoxy is a better choice for a secondary bond. As far as mat and epoxy go if the manufacturer of the mat and the resin both say it's fine that works for me.


Brian

 

[krush]

was the mat compatible with the epoxy? many are not.

This thread talks about the epoxy/mat concern....and some guys say it's bascially a non-issue because of how the matting is used (to add bulk and stiffness, not necessarily strength).

http://forums.iboats.com/showthread.php?t=260755


No need to make a science project out of a simple repair. The keyboard bandit internet engineers need to relax...it's a freakn' hatch!

 

[Boatsb]

This thread talks about the epoxy/mat concern....and some guys say it's bascially a non-issue because of how the matting is used (to add bulk and stiffness, not necessarily strength).

http://forums.iboats.com/showthread.php?t=260755


No need to make a science project out of a simple repair. The keyboard bandit internet engineers need to relax...it's a freakn' hatch!

Krush if you need to add bulk and thickness get yourself some enzite.

To refer to me as a internet engineer is to say Columbus took a boat ride. I do actually own a boat and do most all the work on it. Especially the fiberglass and I would probably be one of the people on the site with more than a weekend of experience at it. I may even have some steel rollers older than you.

My point has been the epoxy was my first choice of product for the job but it still would work out OK. The real strength comes from the 2 layers being sandwiched around the wood. Polyester and the mat are a better match to the existing materials and that was the first reason I had for their use. Cost, compatibility and ease of use are the rest. Dan (34hatt) will probably agree that the benefits of each material should chose it's use. He does a bit of glass work too by the way.

 

[Boatsb]

Damn Krush that reference is so relevant. I took the time to go to the iboats link you wrote and think that it may have been a joke. Please tell me they are not your source of information.
here is a good example of the high end modified bayliner on the site

 

[Brian Degulis]

Scott I agree polyester would work just fine. I had a friend up north that started doing glass repairs in the early 70s he used nothing but polyester and it worked fine. But It's always been my understanding that for secondary bonding epoxy is superior even if the base material is polyester. I'm not sure what the problem is or can be with the mat. I'm guessing that whatever the adhesive is that they use to hold the fibers together doesn't dissolve well in a resin without styrene? Yet when working with it it apears to work just fine it takes longer for it to wet out with epoxy but it does and the fibers apear to be free as they are in polyester.

All posts like this tend to get over complicated and some of it may not be relevent for a simple job like this. But that's fine you just might learn something that can be applied on some other project.

Everything's cured now and it feels very stiff and strong. My mother in law will be visting on Sunday so I can give the real strengh test then.

Brian

 

[Boatsb]

NO DON'T DO IT. The epoxy needs more time to cure before the mother in law test. Is she anything like Peg Bundy's mom from wanker county?

FWIW the mat adds to the adhesion of the polyester making it a non issue. I will be covering the seat of my fighting chair with epoxy and cloth and then repainting it. I am not against epoxy.

Did you like the hard top Krush had posted on the iboats site? I bet he worked hard on it. Nice lines too.

 

[krush]

Boatsb,

What is wrong with that hardtop. The lines may not be the best, but it looks like function is more important than form.

If you are laughing at his use of foam for a core, then the joke is on you. There is nothing wrong with what he is doing provided he uses enough material on both sides. Airplanes are built with the same methods.....

 

[Boatsb]

Krush the foam is not quite the same as used in airplanes. Nidacore, Coosa and others are a bit more appropriate for marine construction use. Then again it is a bayliner. How does it ride with the top on?

 

[krush]

The core (foam) doesn't have to be a structural member...

In that case it is merely acting as a mold.

 

[Boatsb]

I think he used polyisocyanurate foam and there may be an issue with out gassing and burning releasing toxins. It was probably cheaper and since it is for a bayliner there was not much thought to safety. Either way Krush that was one ugly top to put on that boat.

I still stand by my idea of using the right materials.

 

[Brian Degulis]

NO DON'T DO IT. The epoxy needs more time to cure before the mother in law test. Is she anything like Peg Bundy's mom from wanker county?

FWIW the mat adds to the adhesion of the polyester making it a non issue. I will be covering the seat of my fighting chair with epoxy and cloth and then repainting it. I am not against epoxy.

Did you like the hard top Krush had posted on the iboats site? I bet he worked hard on it. Nice lines too.

Now that's just terrible. I was referring to my mother in laws knowledge of structural engineering.

Brian

 

[34Hatt]

The core (foam) doesn't have to be a structural member...

In that case it is merely acting as a mold.

Not true the Idea of using foam is to keep the weight down if you use the wrong foam and just add more glass to make it strong well what did you achieve???
Also will that foam even hold up to a resin it may melt

That is just a cheap amateur move.

Now coosa would be a sweet way of doing it but the coosa may out price the boat