Repairing Sub frames in a Polyester Boat

sand cured glass with 36 or 40 grit paper, then lay new glass to that. thats where the "chemical" bond comes in.
i havent heard of "softening cured poly before,,gotta look into that

 

Quickly the two polyesters resins have about 9,500 psi tensile strength. Ortho-polyester resin elongates about 2% before fracture, while isophthalic-polyester about 3%. What this means is the resin cracks before the fibers in the matrix have reached their full tensile strength. Vacuum bagged E 'glass is about as good as you'll get with iso and not cost much more then the plane Jane ortho. Iso has better resistance to chemicals and blistering too.

Next up the resin list is vinylester. This resin is preferred with modern high modulus fabrics, because it will elongate to around 5% and has a tensile strength of 11,500 psi. It's highly resistant to chemicals, blisters and more moisture resistant. It's high "peel strength" insures inner-laminate bonds are strong (a problem with weaker resins). It's the best of the polyesters.

Epoxy is a different animal chemically, being a fully cross linked polymer. It fills gaps, is higher in elongation, better at chemical attack, has a higher tensile strength, the highest peel strength and water proofness. The highest 'glass/resin ratios can be had with epoxy, which produce the strongest structures. A well bagged E glass laminate can have flexural strength in excess of stainless steel (try 90,000 psi) at one fifth the weight. Yep, it costs more but so do talented AND good looking hookers.

Chemical bonds are what you want, when strength is high up on the priority list. This is only available when a second layer of resin is applied over a yet fully cured previous layer. No "softening agents" or other tricks will do this. In repairs, it's not possible to provide this to a piece, so a mechanical bond must be used, which is little more then a clean, well toothed surface so the goo has something to grab on to. This is the primary reason we have to feather back the edges of a repair area, exposing lots of good, but well cured laminate, before applications of new material can be applied. It has to be tied in to the old surface and sufficiently revealed surface area is the only way.

The ortho and iso polyesters can stick to each other and to epoxy. They don't stick to epoxy very well, but they do stick if you don't need much peel strength.

Yes, there is a "window" in which a chemical bond can happen, though 16 hours would be my maximum for polyester and epoxy is more specific, usually just a few hours with a slow mixture or less with faster rates of cure.

 

You're making it awefully difficult to choose between the epoxy and the talented AND good looking hookers

How do you make a big layup with epoxy if you are only allowed a few hours ? A friend built an aeroplane using epoxy, and I must admit the panels were thin compared to polyester but very strong as well.

Could it be that if you build a boat from epoxy instead of polyester the cost could in the end be about the same ?

 

on a 4.5 million dollar boat thats made from poly,if you go to vinylester the cost goes to 5.2, epoxy i would imagine would go to 6 mill plus

 

I found out what the stuff is that you'd treat the cured polyester fibreglass with so you can get a decent bond with the new layups.

It's called stirene, available as a liquid and is an ingredient of the polyester resin - the smelly one.
Method is to clean and course and clean the cured fibreglass, then wipe the prepared area with a rag wetted with the stirene - caution not to use too much and it must defenately not be running. Allow 10 mins for the process to mature and fire away. Bonding is said to be nearly as strong as the original one.

Wrt the large area layups with epoxy, you get epoxies that cure from within minutes to even days. Depends how you want to use it.

 

Hi,

First of all thanks for the many replies to the original query.

Lets take a practical example. Snd say you need to repair a 24 in hole on the side of a polyester boat. The boat is prepared by tapering the glass to a fine edge starting from, say 3in outside the hole ( outside circle = 30in). The advice I got were 2:

1. Build the patch totally from epoxy resin for better strength and adhesion using the same amount of glass for strength. The problem mentioned with this method is that the epoxy patch is much stiffer than the surrounding polyester and since the skin in this area would want to flex differently, you would get crack at the polyester/epoxy edge.

2. The alternative suggested was to lay just 2 layers of cloth in epoxy and then, while the still at the green stage, apply the rest of the glass in isophtalic resin. This should give the bonding qualities of epoxy and retain the stiffness of the original hull.

the second option sounds reasonable to me except for the part were you lay the polyester on the green epoxy. I have never read about this method anywhere and I am not sure the still liquid polyester will mix well with the still uncured epoxy.

regards

 

Thats a fairly big hole. Someone parked his car there ?

Clean a large area around the hole 300mm+ inside and outside, laquer thinners works well, it will remove any grease and oil. Give some time for the thinners to evapurate.

Work the edges untill you hit gell coat. Taper off but course the 300mm surrounding the area. Apply styrene as above with a lint free rag.

Wait 10 mins,

Paint the area with resin. Pre-wet a piece of woven ie 300g that will cover the hole. Place over the hole, but make sure it is relative close to the shape - it should not bulge out on the outside or take shortcut on the inside, you may need to nurse it a bit. check that there is no cavities around the hole edges and the woven you're applying. Remember woven stretches or schrinks in only 2 direction. Allow to set. For the resin you put on the cloth you could add a bit extra hardner so it wil set quicker.

Once it's hard enough to do layups on, paint the remainder of the coursed area around the hole and over the glass that you just put in. Do the layups untill at least the same thickness as the hull is achieved.

Mix some gel coat and apply on the outside, matching color of course. Allow to cure enough to sand off... next day, If any cavities, repeat. Islands, sand them off. Use fine paper when you get close untill you can buff.

Good luck, it's a pain in the butt.

 

Don't over think the repair, just use one or the other and forget about it. I don't say this to be rude, it's just that either product will work and they've been used to do exactly what you're talking about for many many years. The failures are due to poor techniques, not the products themselves.

Epoxy is better, but the rest of the boat is made from polyester and on larger boats there are many mechanical bonds because they're too large to make all at once and they don't fail or fall apart.

Don't rely on styrene to do more than clean the surface you've just sanded with 36 grit, it's not a miracle product.

The resin you buy retail is typically of better quality than what the boat is made from originally. The resins used to make most boats are DCPD blends, they cost less and are very easy to use at the lower styrene levels now mandated by the Feds. The problem is they're not as strong or water resistant as most straight ortho's or iso's. Plus the shelf life is shorter, so for a resin that may sit on a store shelf for a long time, the DCPD blend is not as good.

Most builders do use a skin coat of a higher quality resin that is more water resistant on the hull, after the skin coat they use a resin (DCPD blend) that costs less for the rest of the laminate.

 

kk,,, talking bout big boats,,heh, and mechanical bonds, in fact big boats usually only have a FEW mechanical bonds, but they major ones,, like putting the 2 halfs of the hull togather, deck onto hull, and sometimes the transom onto the hull. and YES those big boats also have catastrophic UNBONDING, ie: that yacht a few years ago that lost its whole TRANSOM off the boat ( should of been sailing a boston whaler lol) but again, i think with all this on this post proves my point,, stay with what the boat is made from, is WAY easier

 

1Much, I posted a question that a guy emailed me. About cold tempatures and awlgrip. I thought you would know better then us southern boys. See the "upnorth painter" question. thanks

 

I couldn't agree with Ondarvr more, it's a simple enough repair.

The styrene comment is correct, it's a solvent, doesn't soften cured polyester and is used as a cleaning agent, during surface prep for a repair.

The usual course, for such a large hypothetical hole as mentioned, would be to provide a backer, typically a piece of thin plywood covered in Visqueen or plastic packaging tape if much compound is there. The plywood is wedged tight against the hull from the inside. From the outside, the pre tapered edges (3" would be pretty small tapers, 6" or more would be better) are wetted out with the resin of choice then fabric applied. The fabric will likely be mat or combi-mat with polyesters or cloth with epoxy. The first layer being the smallest, with progressively larger layers placed over and wetted out.

The backer provides a uniform surface for the fabrics to be pressed against and prevents spillage into the hull, plus the added benefit of a clean, smooth interior surface. The outside then can be filled and faired as a normal cosmetic repair. Of course, the backer is removed and the access hole filled.

These are repairs that happen every day in marinas around the world. It's not rocket science, just technique, proper prep and materials.

Most all manufactured hulls have a complete layup in less then 24 hours, many in 16, which means chemical bonds. Mechanical bonds are often supported with sealants, gaskets, metal fasteners, etc. These would include hull halves, liners, deck caps, etc.

 

Yes, on smaller Boats of less than 40' or so, the hulls are completed fairly quickly, on larger hulls it can take months to finish. Then it may be cut and lengthend, with bulkheads, stringers, decks and many other things being glassed in later, with grinding to prep the surface and standard laminating resin used to glass them in place. While there are failures, there are hundreds of these yachts being made this way every year and very few have problems.

Secondary bonding issues became more of a problem when DCPD resins came into the market place. DCPD resins surface cure much faster than other types of resin and the industry didn't change their methods of production when it started using them. There were many problems with products made during this transition. The other reason for the "polyester doesn't stick well" line of thought, is many inexperianced people do a poor job of surface prep, as in little or no sanding, leaving dirt, oil, and other contaminates on the surface and then when the bond fails they blame the resin. Epoxy will do a much better job of staying in place with less then ideal surface prep.