bite out of rudder

[sailingdog]

I'd point out that those tests were probably done with recently laid up panels for the test substrate. This means that the bonds for the vinylester and polyester may have been a combination of primary and secondary bonding, rather than solely secondary bonding. The primary bonding for polyester and vinylester resins depends on the number of active styrene bonding sites available. IIRC, the number of active styrene sites declines over time, so the amount of strength from primary bonding is much lower for older laminates than newer ones, as the styrene evaporates off as the laminate cures further.

I'd point out that vinylester and polyester resins are far more sensitive to proper mixing and ratios than epoxy and that getting a proper bond is easier with epoxy resin. Epoxy resins also shrink less than most polyester or vinylester resins and are more water impermeable.

Finding difinitive iformation concerning secondary bonds in frp systems is like hunting for gold, its out there but you have to search. I found this written for industry and it is the best I have seen so far.
http://www.dual-laminate.org/assets/images/Secondary_BD_strgth_of_FRP.pdf

It has nothing to do with boats but the chemical industry uses more frp than does the boating industry and their safety concerns are much more critical.

 

[Ross]

I post these links for their own value. Ester resins can use between 1 and 2.5 percent by weight mekp catalyst. I have always read that epoxy was intolerant of careless ratios.

 

[sailingdog]

Most epoxies are 2:1 or 3:1 or 5:1 mix ratios by volume, and it is pretty hard to screw these up by enough to make the epoxy not cure.

It is probably far easier to add the wrong amount of MEKP catalyst to polyester resin. If you add either too much or too little MEKP, the resulting resin will have relatively short molecule chains and be far weaker than it should be. Also adding too much MEKP to the mix can lead to bad things happening, especially if you're a novice and keep the resin in a tall narrow container rather than a shallow flat container....

I post these links for their own value. Ester resins can use between 1 and 2.5 percent by weight mekp catalyst. I have always read that epoxy was intolerant of careless ratios.

 

[Ross]

Most epoxies are 2:1 or 3:1 or 5:1 mix ratios by volume, and it is pretty hard to screw these up by enough to make the epoxy not cure.

It is probably far easier to add the wrong amount of MEKP catalyst to polyester resin. If you add either too much or too little MEKP, the resulting resin will have relatively short molecule chains and be far weaker than it should be. Also adding too much MEKP to the mix can lead to bad things happening, especially if you're a novice and keep the resin in a tall narrow container rather than a shallow flat container....

I guess I am the odd man here I weigh my resin and measure catalyst with a 12 cc syringe. That is enough for a quart of resin.
Epoxy can get very hot in a small container too.
But once again here is more information than you can use but it is free and has a good pedigree:
http://www.brertechnical.com/reichhold_manual.pdf

 

[Ross]

Chaeck out this ebay offer for glass cloth. http://cgi.ebay.com/10-lb-FIBERGLAS...emQQptZLH_DefaultDomain_0?hash=item563a634b44

 

[sailingdog]

Ross—

I generally recommend buying from a known retailer, since you can often get odd bits off of eBay. That may be 10 lbs. of material, but it could all be in 4"x4" squares or something equally weird.

 

[Ross]

If you read their product discription these are large heavy pieces and the supplier is Infinity FRP supply. Not a junk dealer. I have seen a few of those too, that pick up sweepings and package them as new small pieces. http://stores.ebay.com/Infinity-FRP-Supply

 

[sailingdog]

Good to know Ross... I've bookmarked their site.