New to polyester resin

Just as long as you don't let some bozo tell you to add wax to laminating resin. Confine it to flowcoating when the boat is near complete.If nervous,practice on a small item first.

I have to suspect that a lot of money is being spent on epoxy resin by amateur builders because the believe it to be "better". It may form very strong bonds, but a properly designed polyester laminate ought to be adequate for it's intended purpose if good working practices are followed. Outside the realms of high performance boats, a slightly heavier laminate with polyester may be a good deal less expensive and still function very well. It may mean you can't compete for bragging rights by not having epoxy where it isn't really necessary. A commercial user, particularly one building for commercial use, will have to satisfy regulatory bodies that their boat is up to the task and they will have to build it at a price the market can accept. Not only do they have to meet these requirements, they need to make enough profit to stay in business. A slightly heavier laminate will probably be a more practical proposition that a more exotic and thinner laminate that wouldn't resist nudging a post quite as well.

 

wet feet, this is why I like vinyl ester.
Great performance with good economics.

 

Wet feet, well said.
Yes, I think we’ve all concluded that any talk of wax is not the direction I want to go. For me it’s not business, it’s personal for fun, so the economics are different. Also this is the biggest job I have ever done so I started with what I knew from prior repair work, epoxy. I also think, rightfully or not, that if epoxy is “stronger” it gives me a little fudge factor for inexperienced work. I’m probably “wasting” epoxy because I’m not trying to go with thinner laminates.

And with that said I am looking to learn to use polyester to save money but since I’ve done all the hull work with epoxy I need to still use epoxy to bond the polyester panels to the hull. Right now I’m just looking to use it for laminating bulkheads.
I think I’m on the right path. I was able to get an airless full cure with inexpensive vacuum bagging materials so I will continue that route.

 

A little vacuum works nicely. Masking tape and Home Depot plastic sheeting. (Plus real peel ply and breather)

 

So how long does it need to reach the full cure? Dependent on the amount of MEKP and the temperature? 64 degrees and 1.5%, I wanted to make sure I had enough time to work…

 

It will be more fully cured in six months than it is now!The topic of cure rates is quite interesting and a lot depends on one's definitions.The cure has started once it becomes too thick to laminate with and that isn't the same as having achieved full structural strength.For most practical purposes I regard it as sufficient for working with once it has reached a point where the component can be released and stored without distorting.Which is at a point when the maximum strength may still be some way off.The resin type makes a big difference and a number of suppliers vary the formulation to suit different climates as well as allowing for various manufacturing cycles.Some of the RTM formulations are geared to a cycle time of minutes rather than days or weeks and a manufacturer of truck fairings will be looking at producing several parts per day,per mould with a chopper gun.Most of us in the boat moulding sphere will be producing at a lower rate then that.Unless a post curing phase is introduced it can be several months before full strength is reached and you are fortunate to have such a benign climate,without major temperature swings and that being said,a good dose of sunshine is an effective way to push the process along a bit.

For practical purposes,your bag can come off as soon as you can't leave a mark with a fingernail in a resin sample left outside the bag.You did keep a small sample to check with,I hope?Its always useful to have a little over to monitor progress-only a little as the stink of a mass getting exothermic is never welcome in a workshop.If time isn't pressing for the part to be in place then overnight is probably sufficient and a Friday part released on a Monday should be fine.Leave the peelply until you really need to remove it as it will do a better job of protecting the surface than almost anything else and is already there and store the panel flat to prevent sagging.

 

be ready to work FAST with polyester - best comparison I have it's like mixing a quart of epoxy at one time on a hot day and trying to brush all of it into fiberglass in time LOL Your cup is gonna be smoking LOL But you can adjust your mekp ratio to give you extra time anyways
regular polyester resin doesnt need wax, only the iso or mold making resin does, but you wont be using that anyway
Best thing about polyester is that it soaks into fiberglass way easier than epoxy and it hardens within a couple hours to trim the fiberglass quickly if you need to move onto something else
depending on where you live in CA you will want to use polyester over 60F with a mask too
Mix fumed silica into the polyester resin just like you do with epoxy

 

Ignore the advice to add fumed silica and don't stray far from the recommended catalyst ratio.

 

Good question because this is probably the most important aspect to get familiar with when you are practicing, do not try to mix large amounts of polyester when first trying. There are so many charts out there, stick with millitres at first (even though we are in United States ) Because if say you mix 250ml resin with 1.5% mekp it's an easy conversion to ml 250ml resin x .015 = 3.75ml mekp - hopefully your mixing cups are both ml so you have one less conversion from quarts to cc to mls lol
1.5% is probably a good place to start at 65 degrees but do it in the shade, the sun can make things a lot hotter, i rarely even spray gelcoat in direct sunlight because the surface can get way too hot messing with your cure/layers
"Work" ing time and Full cure are two different things
At 65 and 1.5% you might have about 15-20 minutes before your fabric starts to harden a little bit or your paint brush gets really sticky, but your on the clock because it goes quickly
Full cure will be technically the next day, however within 2-3 hours you should be able to put you hand over it to feel its' solid, start trimming etc
You can actually feel the two differences with epoxy too but it's not as pronounced as polyester
anyways just my two cents

 

Ha why is that? I mean the polyester takes way less fumed silica to thicken it but can still be helpful to fill somethings, not talking strength

 

In part because increasing the viscosity will make it less able to penetrate the fibres and break down the binder and partly because the resin suppliers will have gone to some lengths to optimise the formulation of their prduct.Unless you have witnessed a problem,such as resin draining on a vertical surface,its best not to monkey with it.Even with a problem,its best to call the supplier in case that particular batch has been flagged up as not conforming to the correct specification.If a job requires a thixotropic resin,there is a good chance that one can be bought quite easily and it will stand a good chance of working.Its all about probabilities;who knows most about a product,the people who sell it by the truckload or the guy buying a can once in a while?Then there is the concept that the supplier will be keen to preserve their reputation and will be helpful with diagnosing problems in order to keep that reputation.If a problem develops and the call reveals that the product hasn't been used in "as supplied" condition,where is the fault diagnosis likely to point?

 

Ya I was more thinking to fill smaller areas or radius some inside corners all before adding cloth using straight poly resin

 

If you need impact resistance like on chines use gun roving to fill corners.

 

Um, what ? Please explain. why iso and mold making resin need wax ?

 

I am not exactly sure only giving the info based on a supplier's website that I order from here in USA, my guess is that you may want control over which layers remain sticky after they cool when making a mold?? I mentioned that type of resin in case the poster was looking at that type since he mentioned wax for the resin.