Decision time - Resin

[Locke N Load]

I have posted the same on THT so to dual readers my apologies, but I wanted the opinions of those sole CSC users as well.

I believe I have reached the point of analysis paralysis. I am ready to order materials to skin the Coosa transom from the inside, raise the stringers a couple of inches, replace the deck with Carbon Core, build a bracket with Coosa as the core, make new bulkheads/console, repair cut-outs in the hull and fill in the cap in places for my Seafari. The glass will be 1708. The question then is what resin?

As I understand it from plenty of online research and no actual experience, polyester resin is the standard boat builders use because it is strong and stiff and cheap. It, however, lacks bonding strength for new parts to old parts compared to epoxy resin. Epoxy resin, on the other hand, is very strong, more flexible/less brittle, bonds well to existing parts and is most expensive. Vinylester resin is a sort of compromise between poly and epoxy, but more similar to poly and priced between the two.

For its bonding strength, I am strongly leaning towards using epoxy for the transom, stringer, deck, etc. work I need to do. The bracket could be done with poly since it will be a separate part, but any reason not to just use epoxy since I will be using epoxy for everything else? Same for the deck since bonding to the hull isn't as critical strength-wise compared to the transom and stringers?

Or am I overthinking bonding strength? Will poly provide plenty of strength for the inside skin of the transom to the hull, raised stringer section to existing stringers, bulkheads to hull and deck to hull? If epoxy will be a noticeably superior product for these applications I will use it, but if it makes little to no difference I will use poly.

Then the follow up question, if epoxy really should be used is, what brand? Some are way more expensive than others and I figure I am going to need 30 gallons. It makes a difference if I use Raka at $47 per gallon or U.S. Composites house brand at $40 compared to Total Boat at $100 or West Systems that I won't even comment on. Any recommendations or alternatives I am not aware of?

Hopefully, temperatures will be improving soon and I want to be ready with the materials now that I have my boat shed in place. Thanks all.

[smilinmatt]

I've used all the epoxies that you've mentioned, except TotalBoat. The only one that stands out is West Systems. It blushes horribly and costs more than twice anything else. I built two boats from Bateau (2002 G12 and 2009 OB19) both with System 3 epoxy. I'm in the process of rebuilding a 23' Sceptre from the stringers up, and I'm using RAKA epoxy.

I'd say the only drawback with the RAKA is that the resin and hardener are almost the same color, so you just need to make sure you don't mix them up.

I also built a casting deck on the front of a 13' Whaler using polyester resin and glass to tie it in. After I was done, I was able to peel the deck off the boat by hand. Last time I used polyester.

Since you'll be buying the epoxy in "bulk", there isn't much cost difference between epoxy and polyester. Polyester also has a short shelf life, so if your project takes longer than expected, you could end up spending more on polyester than epoxy.

Also make sure the glass you use is compatible with epoxy. That won't be a problem if you're sourcing them together, but there is glass with binders that are only dissolved by polyester.

[FLexpat]

Yeah - I definitely would not use polyester; it does not stick to old work well, shrinks, and blisters. Depending on what I am doing, I use either Raka epoxy or vinyl ester. Vinyl ester has about a 3-6 month shelf life but the MEKP catalyst is more like 2 months. Epoxy is very long - I have been told a few years (thats good for me ). Both VE and Epoxy have very low water permeability and shrink lots less than polyester. Gelcoat will stick to VE but not as well to epoxy. If it is going to be painted with an epoxy or remain bare, I mostly use epoxy. In higher humidity epoxy will blush but VE does not have that problem. I usually use peel ply on epoxy to eliminate that problem. For me epoxy is a little easier to use since you just pick the right hardener and go with it rather than trying to figure out how much catalyst to use for the expected temps. I used epoxy for my transom recore and other 'hidden' work, but used VE for my new decks since I am using a VE based gelcoat on those. Short version - they all have pros/cons; kinda depends on exactly what you are doing. And avoid poly for anything except mold making.

[uncleboo]

Basing my decision on the information I learned here, I used epoxy for the transom and polyester for the deck. Everything is holding nicely, no cracks or delamination.

[dirtwheelsfl]

I echo Matt and Mitch's statements above. E-bond is another brand you can checkout. You can get it around 30/gallon these days i believe. Ive used hundreds of gallons of it but its been awhile. Its still the standard for alotta guys. RAKA is basically a thinned out e-bond. It wets out easier and doesnt blush as badly.

West system, forget it... The Gougeon (west system) guys also make one called "Pro-Set" that ive messed with but i dont know anything about price or availability on it.

You dont need to use a mat-backed cloth with epoxy so youre saving alot of resin without having to wet out all the thirsty mat, driving costs down. (although it sounds like youve got a roll of 1708 already?)

I think its much more forgiving than esters as far as working with it (extended working times, predictability of working times, much better bonding if your prepwork isnt 100%, no fumes really). When i DO work with esters i find alot more waste gets produced too because the gel time ramps up so quick. Its hard to accurately catalyze tiny batches of it too so you make more product than you need.

Secondary bonding, epoxy all the way.

Not that i havent seen great solid work done with esters but it was put to me simply a long time ago... "if ya want shit to stay stuck together, use epoxy"...

[Locke N Load]

Originally Posted by dirtwheelsfl

I echo Matt and Mitch's statements above. E-bond is another brand you can checkout. You can get it around 30/gallon these days i believe. Ive used hundreds of gallons of it but its been awhile. Its still the standard for alotta guys. RAKA is basically a thinned out e-bond. It wets out easier and doesnt blush as badly.

West system, forget it... The Gougeon (west system) guys also make one called "Pro-Set" that ive messed with but i dont know anything about price or availability on it.

You dont need to use a mat-backed cloth with epoxy so youre saving alot of resin without having to wet out all the thirsty mat, driving costs down. (although it sounds like youve got a roll of 1708 already?)

I think its much more forgiving than esters as far as working with it (extended working times, predictability of working times, much better bonding if your prepwork isnt 100%, no fumes really). When i DO work with esters i find alot more waste gets produced too because the gel time ramps up so quick. Its hard to accurately catalyze tiny batches of it too so you make more product than you need.

Secondary bonding, epoxy all the way.

Not that i havent seen great solid work done with esters but it was put to me simply a long time ago... "if ya want shit to stay stuck together, use epoxy"...

I do not have the cloth yet. I am planning on 1708 due to a couple of factors: able to build up bulk quickly and being a novice with fiberglass I am figuring using a stitched cloth will be easier to keep it in shape. I have read regular biaxial cloth like 1700 is great to work with epoxy since you do not have to worry about wetting out the CSM, but if you are not experienced with it it can pull out of shape easily. I know to get 1708 that has stitched CSM rather than the bonded type that needs a styrene based resin to melt the binder in the CSM to get it to shape.

[dirtwheelsfl]

Originally Posted by Locke N Load

I do not have the cloth yet. I am planning on 1708 due to a couple of factors: able to build up bulk quickly and being a novice with fiberglass I am figuring using a stitched cloth will be easier to keep it in shape. I have read regular biaxial cloth like 1700 is great to work with epoxy since you do not have to worry about wetting out the CSM, but if you are not experienced with it it can pull out of shape easily. I know to get 1708 that has stitched CSM rather than the bonded type that needs a styrene based resin to melt the binder in the CSM to get it to shape.

You typed out almost exactly what i was going to haha

1700 is stitched too but its like a snakeskin sometimes. You might consider using both. 1700 for all the big flat stuff you can do outside the boat and 1708 for the rest. Just have to get to doing it and see what you like and get comfortable with. Million ways to do it!

[Locke N Load]

Originally Posted by dirtwheelsfl

You typed out almost exactly what i was going to haha

1700 is stitched too but its like a snakeskin sometimes. You might consider using both. 1700 for all the big flat stuff you can do outside the boat and 1708 for the rest. Just have to get to doing it and see what you like and get comfortable with. Million ways to do it!

If I understand it correctly, strength will be the same between 1708 and 1700 layer to layer, but a buildup with 1708 will be stronger because you get a little bit of the corrugated box effect with the spacing from the CSM in multiple layers. Is this accurate? My process would be wet out the surface, lay the cloth down and add more resin to fully saturate. Like you said, a nice flat surface would make using 1700 manageable. Like the deck. Even laying up the transom vertically I could see it working. The problem I see would trying to get the extra overlap for tabbing to go in place. Also the rolling out air bubbles I could see being more difficult and why I am leaning towards the 1708.

[Bigshrimpin]

Be careful with the glue binder in 1708 when using epoxy. It can make a rubbery gummy laminate. I like 1808 stitch-mat with no glue binder when using epoxy. If you are laying up parts into a mold, Iso Polyester or Vinylester will save a lot of money and wet out fabric much more easily than epoxy. Any work below the waterline, I'd use epoxy.

[flyingfrizzle]

Originally Posted by Locke N Load

If I understand it correctly, strength will be the same between 1708 and 1700 layer to layer, but a buildup with 1708 will be stronger because you get a little bit of the corrugated box effect with the spacing from the CSM in multiple layers. Is this accurate?

Build up with 1700 of the same thickness will be much stronger than 1708 of the same thickness. This is due to the resin to cloth ratio. The long strands of 17oz biax is much stronger than the short cms strands. More layers of tightly spaced strands of cloth and less resin makes a stronger lighter lay up.
Now saying 3 layers of 1708 vs 3 layers of 1700 (layer vs layer) the 1708 would have more fibers with the extra cms and it would be thicker and build up faster. So the thicker 1708 with the extra resin and cloth would be stronger in that instance. But if you did 5 layers of 1700 vs 3 of 1708 it may use the same amount of resin and be the same thickness and the 1700 would be much stronger. Not sure if the 5=3 here but just for the general idea.
The box effect you mention would add strength from extra resin spacing with the csm but for me I want strength from the layers of long biax strands which are much stronger than short random cms strands. Cms just takes too much resin doing a hand lay up.
The only time I would use 1708 with epoxy is if it was all I had at the time or if the top layer needed fairing. Then I would place the CMS layer upwards so once sanded it would cut into the csm and not break the 17oz long strands. But like BigShrimpin mentioned trying to sand gummy epoxy is not ideal. In general sanding epoxy for any reason is not easily done.

I like the idea of using all types of resin Poly, VE and epoxy. The Epoxy is a must for strong secondary bonds to old glass. The VE is great for decks and parts that are wet on wet laid up. Poly is an economical choice for parts popped from molds with gel coat first layers. So each has its place. Doing a boat 100% epoxy is great if you can afford it but the other products work almost as well if used correctly in the right way. Look at the 60-70's vintage SeaCraft hulls that were all Poly. They have some signs of water absorption on the bottom maybe if left in the water a long time but they have held the test of time. Poly may not be as strong or you may not build up layers as light with it but it will do good if on a budget. If I had to chose only one it would be VE as it has the best of both worlds and a fair price but epoxy is hard to beat for gluing or bonding parts. I think if you can choose where to use what based on the parts needs you will save some funds plus to me VE and Poly are easier to use and the cure process goes much faster. It is easer sand and fair out over epoxy also so each has its benefits.

The main reasons I chose to use epoxy is:
1) super strong secondary bonds to old glass = no delamination
2) no water absorption like with poly = water proof almost
3) no csm needed so better glass to resin ratio = stronger & less weight
4) more elasticity so it flexes more before it cracks = flexibility
5) using high end fibers like S-glass, Carbon or Kevlar


If one of the above are not need I turn to VE. If I am doing a gel coated molded part I may use Poly.