How to tell what resin was used on old repair and tips.

[boombots]

Background: New to the forum, and to boats... I picked up a project boat, and like many others before me ended up with a boat with rotted wood... I have a 1987 Fourwinns Horizon 190 with a 4.3 OMC. Runs great, motor and outdrive were kept in good order, boat is decent cosmetically, but upon digging in I found rot...a lot.

I have begun tearing it apart (drive off, floors torn up and 1/2 of the foam dug out) here is where I am now...

The transom was replaced about 5 years ago according to the previous owner who owned it for 14 years (mostly kept in the water in the summers). I could see this was true, it was replaced.

Upon pulling the seats I found the floors rotted, which led to stringers being bad too... That's ok, I paid 1200 bucks for it with titles for the boat and trailer, and it is a project anyway.

Upon stripping the floor boards and pulling foam I find that the motor mounts (also replaced with the transom it looks) are rotted as they were not glassed correctly against the stringer(what used to be a stringer, now just a hollow piece of glass). Add these to the list.

Now, I see rot in the lower port side of the transom. Turns out they had miss drilled a hole for the swim deck and left it uncovered and tried to plug it with silicone which did not work and it was under the water line too! Now it needs a transom again.

So I was originally going to just use the US Composites 435 Poly resin and 1708 Bi for the floors and stringers as the boat originally was done with poly and I was trying to stay on a budget... now my concern is that the transom and mounts, already having been replaced, used epoxy on the repair my poly repair would be useless over that. I could track down the prior owner and get the # of who fixed it and maybe they could answer...

So to make a long story short... any way to tell if a prior repair used poly or epoxy? Or any other tips for me along the way?

 

[alldodge]

Howdy

Have used both and from my vendor poly has a light brown tint when dry and epoxy dried clear. Different vendors use different variations which can change color. You can sand/scratch poly easy enough but it takes more effort to do the same to epoxy.

That said, when in doubt use epoxy. Only problem with epoxy other then dry time, blushing and temp, is you don't want gelcoat on epoxy. So with this being all inside work maybe just use epoxy, or at least on the transom,

Wish I had a proven way to find out

 

[ondarvr]

If you've worked around both you can usually tell the difference, but to describe the difference online to someone that has never used either one would more than difficult. There's a 99% chance it was repaired with polyester, like mentioned, epoxy tends to be a little clearer, with no amber look, plus no mat would be used with epoxy, epoxy would also be tougher to sand, but none of these are hard and fast rules, just tendancies.

 

[Ned L]

Take a heat gun to it. Epoxy will soften with heat, polyester resin will not.

 

[ondarvr]

The heat gun test isn't 100% either, depending on the exact epoxy and it's age, the TG could be from around 125*F for an easy to use surfboard type resin, to double that for a well cured more ridged epoxy. Heat can show a difference between the two though, so it's a good and easy test.

 

[fhhuber]

And... I use fiberglass cloth with epoxy all the time... So there's no guarantee that its poly if there is cloth in it.

Lightly sand an poly resin will have a plastic smell that usually is not present with epoxy.

 

[jbcurt00]

... I use fiberglass cloth with epoxy all the time... So there's no guarantee that its poly if there is cloth in it..

Ondarvr said mat, as in CSM (chopped strand mat) not cloth.

Mat and cloth are 2 different fiberglass products. 1708 has both 17 oz cloth w 1/2 oz mat on the back. If using poly, 1708 would be recommended. For epoxy, which doesn't need mat, straight 1700 would be recommended.
.

 

[fhhuber]

I've put the mat into epoxy too...

Its part of using epoxy when you aren't sure if the previous stuff was epoxy or poly.
Its a filler and a strengthening fiber Just epoxy is not going to hold in a lot of places where adding the fiberglass will make a very strong joint or fill a large hole with a lot less of the glue/resin

 

[jbcurt00]

I'll let ondarvr address the epoxy and using mat, if he chooses

Many that havent used resins and glass are unfamiliar w the terms and how different epoxy and polyester are, or the difference between 1708, 1700 or mat.

 

[ondarvr]

There is nothing that say's you can't use CSM with epoxy, and there are compatible types of CSM, the normal stuff isn't, but it can be and is used with lesser results.

Epoxy has no need for CSM in a laminate, even at the bond line, now if the surface is rough or irregular, CSM may conform better to the surface profile and let the cloth or other fabric lay down better on top of it, but normally you remove these irregularities in the surface during the prep work (sanding, filling)

In the epoxy world CSM is pretty much considered a waste of time and money, plus adds needless weight with no benefit, and since when people use epoxy they are typically looking for much higher performance, they avoid added weight and cost that provides no advantage. (added weight and cost is from the high resin content in a CSM layer, it can be double that of cloth or stitched fabics, and the CSM adds little to no strength.)

I'm not saying there is never a situation where CSM may not help in some epoxy application, but it's not that common.

 

[ondarvr]

Forgot to add, There is no benefit to using CSM with epoxy over polyester, it won't do anything to enhance the bond between the two, with or without CSM the epoxy is doing all the work. The idea of increased bond strength comes into play when using polyester with CSM in the first layer over anything, but the actuall bond is the same with or without the CSM. What is improved is the strength of the resin rich layer between the substrate and first layer of structural glass, polyester, being comparatively weak and brittle, needs the CSM to offer some strength in that region of the laminate. Without CSM the polyester resin fractures and fails, epoxy is much stronger and doesn't benefit in the same way when CSM is used.

 

[boombots]

Now that the motor is out I can get a better look at it, thanks for the tips!

I have been toying around going with composite boards like coosa for my own sanity (never worrying about rot again)