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914World.com _ 914World Garage _ Fiberglass and epoxy questions, Paul or anybody w/experience?

Posted by: neo914-6 Sep 3 2006, 02:14 PM

I'm working with TAP marine epoxy resin and various weights of mostly fiberglass cloth material. TAP is great but you have to find the experienced guy (like Home Depot or OSH) for good information.

I chose epoxy because it's odorless (CA neighbor friendly) and has good bonding strength. It requires more precise mixing ratios as I've found out the hard way.

The questions
Is the 914 top covered with a gelcoat? Does epoxy bond well to gelcoat?

How long should you wait between laying the next layer of cloth?

If more than 24 hours do you need to sand the surface for the next layer?

Is there a water soluable layer you need to wash off or you may have delamination later?

Posted by: swl Sep 3 2006, 02:38 PM

Dunno anything about TAP. I used East system when I built my kayak. Most epoxy resins are similar but ymmv amongst brands. You seem to have the right info:

1. Next coat is a timed affair. In order to get a chemical bond between coats (instead of just a mechanical one) you want the undercoat to be set but not hard. The boat building guys talk about the thumbnail test. If you can press moderately with your thumbnail and not see a dent then you are ready for the next coat. The set time is sensitive to temp so it varies. With East system it was about 6 hours iirc. Makes 4 coats a marathon.

2. If you can't get the next coat on before it is hard then you have to sand it to get a good mechanical bond. I

3. Most (but not all) epoxy systems have something called an amine (sp?) blush. It is a (slightly) greasy residue from the reaction. It is normally washed off with water and vinegar I think. East doesn't blush so I didn't have to worry about it.

Bonding is an interesting question - don't have a clue what the best surface would be. This is going to be a mechanical bond so you are just sticking it on.

Here's a link to a good boatbuilding board - there are a lot fiberglass guru's hanging out there. http://bearmountainboats.com/phpbb2/index.php

Posted by: JPB Sep 3 2006, 03:55 PM

Well bro, epoxy MUST be laminated in timely intervals so as not to sand between layers. If you apply your layups/layers within the manufacturers maximum time, usually 6 hours max, you don't need to prep between layups.

Epoxy is great for penetrating in something before bonding and usually dries/cures slower. It is also sensitive to UV rays like sun light so you need to paint it once applied/finished.

Not all epoxies are water proof and usually need an over coat for water proofing or else it will disolve in the rain.

Some folks will use the epoxy for the first few layups and then switch to a 100% waterproof fiberglass after the epoxy has been cured and preped. Elmer makes a great waterproof resine which is available at Lowes.

If you are applying your resin and cloth to a gel coat surface, its best to try a small area and see how well it adheres before ya go and do it all.

Gluck!

Posted by: neo914-6 Sep 3 2006, 04:35 PM

thanks guys!

I'm thinking of using Carbon Fiber now in less layers with comparable strength to save layup time. My friends Ducati had one or two thin layers for the fenders.

One more question, what have you used for primer or paint base besides gel coat? I'll have a thin coat of filler but there may be areas where the resin is bare...

Posted by: swl Sep 3 2006, 08:18 PM

As long as the resin is sanded you should get a good bond. The only thing to be wary of is the effect of different chemistry. Make some test pieces and hit it with the primer reccommended for your finish coat.

Posted by: swl Sep 3 2006, 08:27 PM

oh - btw. Lots of people are alergic to green epoxy. Cover up and use a respirator when sanding. Doesnt hurt to do so when doing the layup either.

Posted by: alpha434 Sep 3 2006, 08:46 PM

Make sure you have a really good look at the whole spectrum of materials before getting in deep with C/F. It's EXPENSIVE. You may be able to get it down to just 2 layers, and then use foam board or something else to reifore it in just a few key areas.