Transom and floor repairs - Page 3

bacchus60 · #21 02-28-2010, 01:14 PM

Nymack, I cant find your post re polyester resin. Are you saying put some polyester resin (maybe with fairing fillets) on top of the Arjay and then gel coat?

I have posted a fwe pics, more to come.

bacchus60 · #22 02-28-2010, 01:19 PM

Couldn't load all at the same time

nymack66 · #23 03-01-2010, 10:39 AM

Please read this carefully, once done you then understand why you will use a epoxy or polyester base filler or jelly to flare it out ..For example if you are going to use Gel Coat to finish it then is MUST be a polyester filler and so on...Below is cut and paste from a Pro not me !!

Polyester Resin
People hear and read things online about polyester resin, epoxy and types of glass, much of it has a grain of truth, but many times it gets blown out of proportion.

Yes, once the resin has cured you get less of a chemical bond and more of a mechanical bond, but there are still reactive sites in the old layup (resin) to bond with. The mechanical bond, while not quite as strong, is not weak and will take a great deal of abuse. You test the bond in the lab by pulling it apart, if it's been prepped well and the bond is good, glass fibers will be torn from each surface, which is common. Sometimes it doesn't separate along the new bond, it may be deeper into the old section or new one, it may also be a combination of the two. If you did a poor job of prep, or if the surface was contaminated for some reason, then the bond may (will) be poor and it may pull apart easily with little or no fiber sticking to each surface.

The most common cause for the line of thought that polyester doesn't bond to anything, is people doing a repair with little or no prep work, sometimes not even cleaning off the old dirt and gunk, then using cloth as the first layer. This type of repair will fail almost immediately and then the resin is blamed. For the best results use a grinder with 36 grit or coarser paper and keep the surface clean.

Epoxy does bond better, the problem is, you still have polyester under it, so if you exceed the stress level the polyester substrate can handle, the epoxy layup will still pull right off, only with some of the polyester still stuck to it. It's almost like the polyester to polyester test, except all of the failure is in the polyester substrate this time.

Mat is used to build bulk and sort of help with the bond. If you use cloth or roving as the first layer, there is a resin rich layer between the glass and substrate, this resin rich layer is weak, Add glass fiber to it and it becomes strong, this is the roll of the mat, the fibers in the mat are random and will fill the area that cloth and roving won't. Now when stressed there is glass near the surface of the substrate, not just resin, so it will not fail like a cloth only layup will. The bond is actually the same, it's just that the resin isn't failing near the bond line now.

Epoxy is much stronger, so this resin rich area at the bond line is not as likely to fail when only cloth is used.

Mat has the lowest strength of the typical types of glass on the market, it's not weak and may add strength and stiffness (don't confuse stiffness with strength), but other types of glass do a better job at adding strength for the same weight. Cloth works well for some things, but I rarely use it and most boat builders don't use it either, as the cost is high for the strength it adds. Roving is strong and is less costly than most other types of fabric, plus it's very easy to work with, so it gets used a great deal. Biaxial type products are very strong and add the least amount of weight and cost more, much of the time they come with a thin layer of mat stitched to them for better bonding and to help hold the resin in place.

There are also two types of glass E and S, E is the most common and is what you will find most of the time. S is stronger and costs more, to buy it you normally need to special order it. When it comes to other high end types of fibers like carbon or Kevlar, use epoxy, they don't work well with polyesters.

Not all polyester resins are of the same quality and neither are epoxies and it can be very difficult to know what you are buying. I'm not an epoxy guy, so I won't give information on it because it may not be accurate.

Polyester boats normally have a skin layer on the hull of a better grade of resin, it may be a straight VE, a VE-DCPD blend, or a straight ISO. This is a thin layer near the gel coat for better water resistance, this layer is commonly chopped, but it may be hand layed with mat. The rest of the hull and deck are normally made with an ORTHO-DCPD blend, it's not as strong or water restant, but costs much less.

What you buy in the store is normally a straight ORTHO, because DCPD's and the blends with it added, have a shorter shelf life and they need a long shelf life for the retail market. You can get ISO and VE resin, but you normally need to go to a fiberglass supply store and ask for them, they will cost more. The VE will be stronger, more water resistant and bond better than ISO, which in turn is better than ORTHO, that leaves DCPD's at the bottom, but they do offer very good surface profile because they shrink less than the other types. Straight DCPD's aren't used that often, they're typically blended with one of the other resins, to lower the cost and help reduce the shrink.

For a typical repair anything but a straight DCPD works well, and you won't be able to buy it, so don't worry about it. Boat builders assemble the entire boat with these standard polyester products, some are chemical bonds and some are mechanical bonds, rarely do they fail. The larger the boat, the more mechanical bonds there are because of the length of time it takes to build them.

Always check to see how the resin and /or gel coat is supposed to be used, does it have wax added, if it has wax in it you need to apply the next layer before the first one gets hard, if it gets hard you need sand and clean the surface very well before applying the next layer. What catalyst % is recommended, what do they say about about adding other things to it. Don't over or under catalyze and always measure it, don't add large amounts of anything to thin them, when you add more than about 5% it can start to have negative affects. Stir well after adding anything, not just a couple swipes with a stick or brush.

While it is important to use good products when doing a repair, it's more important that you use good methods and do it correctly.

bacchus60 · #24 03-01-2010, 12:49 PM

Nymack - AWESOME, thank you. I love this site!!!!!!

scook · #25 08-07-2010, 07:53 PM

I found a little crack inside at the bottom of my transom and probed it - there's some soft material. Found this thread and started researching Git-Rot and ended up on WoodBoatForum: http://forum.woodenboat.com/showthread.php?7967-Git-Rot

For penetrating and KILLING the rot, look at the post(s) by Dave Carnell. He's a retired chemical engineer and describes the use of antifreeze for this purpose - it's definitely worth reading. I'd be interested if anyone has comments.

Lumberslinger and I will probably use this info. on jobs - I've got one in mind right now, in addition to my transom.

I'm thinking of hogging out the soft stuff, treating with antifreeze and when it's dry, filling it with a product (to be determined - probably mixed with sawdust0 then glassing over.