Polyester for wood waterproofing

[ondarvr]

Re: Polyester for wood waterproofing

In your test I would expect the C side of the A/C plywood to bond better than the A side and without letting the first coat of resin soak in and then start to harden both bonds would be poorer than they could be.
Sanding the surface of the wood will also improve the bond a little
We do testing like this on plywood frequently and one of my customers does it on every panel they make to ensure the bond is good. To pass the test the entire failure needs to be in the plywood, if the bond between the two comes apart, it fails. They use unthinned standard resin catalyzed at 1.5%. You should've had both samples rip a great deal of wood up with the laminate, it should cover almost the entire bond line between the two, if you only had some wood pull up on one panel then something went wrong. The other problem with this test is the cloth, cloth has poorer bonding properties than mat, if you do the same test on a well sanded fiberglass surface cloth will pull off much easier than mat also. The bond is really the same as far as the resin is concerend, but there is a resin rich layer between the cloth and whatever the substrate is and it's this resin rich layer that fails. With mat the glass is right at the surface, so there's less chance of the resin failing between the glass and substrate.

 

[Stoutcat]

Re: Polyester for wood waterproofing

Hi all,

Just .02 from a wooden boat guy...

Ummm, I'm not a fiberglass boat guy, I'm just an engineer who's built a few FRP boats using every resin imaginable including prayer... I'm also a mod for a couple of wood boat forums and we see these types of questions all the time... Thoughts...

* From my experience, I think ondarvr is dead-on right. Maybe you can tweak a mix a bit... But I'd want to test it to the max.

* Companies like WEST, (and no doubt the folks ondarvr deals with) have pretty good chemists and engineers on board...

* Every time I tried to take a shortcut, sooner or later I got burned. After 30 years of messing with both polyester and epoxy, I've finally learned to simply follow the directions.

* In the case of "my" forums the designer is in his eighties, and the prototype builder is also in his eighties. The designer has drafted over 600 plans, and the builder has built over 600 boats. Both are prolific authors of both books and magazine articles. If there was a secret for the manipulation of polyester and/or epoxy, I'm pretty sure these guys would have it nailed to the wall.

* Anyway, my advice to those who ask these types of questions on the wood boat side is just to follow the advice of guys like ondarvr, (and the instruction on the can for that matter...)

* If you need brute strength (as in building a boat from scratch using plywood, or reinforcing a key structural member in a fiberglass boat), use epoxy. Otherwise, use poly and follow the directions.

* We see some problems analogous to positioning glass on pre-wetted surfaces on the wood boat side... There is nothing on earth like practice, practice, practice, and more practice. Right now we've got at least two first-time builders who are building small "throw-away" skiffs just so that they can learn the "ropes of goo".

* One last thought... With practice comes insight... Some years ago, I finally learned that to slow down the "kick" of epoxy, mix it thoroughly, then pour it into a large flat pan... The cure of epoxy is an exothermic reaction... Expand the surface area and the mix doesn't get as much of a chance to "cook in its own juices". I also learned that I'm lousy with resin and glass... My wife and I build together. Without words, she mixes the brew, splits it between us and we each attack our own side of the boat. As soon as she's done with her side, she comes over to my side and tries to fix the breath-taking mess I've made. Practice, practice, practice.

* One last, last thought... To come full circle... IMHO, there is absolutely nothing that is waterproof. Not polyester, not epoxy... Nothing... As the saying goes, time and tide... The trick in building (or repairing) is to take into consideration inevitable moisture, and the appropriate venting/inspection to deal with it. To borrow from "Jurassic Park", water finds a way.

Like I said... Just two cents...

Alan

 

[jonesg]

Re: Polyester for wood waterproofing

Well, I did an experiment. I took a scrap piece of AC plywood, untreated and dry for the test.

On one side of the plywood, I laid up 1 ply of fiberglass cloth using polyester resin mixed as the can instructions said. I first painted the unthinned catylyzed resin on the wood and then laid the glass cloth down and used the brush and additional resin to fully wet it out. I left a tab of cloth so that I could peel it off later.

On the other side of the plywood, I first brushed on the thinned catylized resin. The mix I used was 2 ounces resin, 2 ounces acetone, and enough catylyst for 4 ounces(32 drops total, 8 drops per ounce). I was told to do it this way so that's what I tried. Once the thinned resin was painted on and had soaked in I brushed on some unthinned resin, laid the cloth and wetted it out using more resin and the brush. Incidentally, I used a different brush for the thinned resin and the unthinned resin.

In both cases, the brushed area of resin was made larger than what was covered by the cloth. On the side with the thinned resin the area outside the cloth was then only the unthinned resin painted area.

What were the results?? After about 24 hours cure, I very unscientifically peeled the cloth pieces from the wood. The unthinned sample was noticeably easier to peel off than the side that had the thinned resin painted on first. The side with the thinned resin had a few bits of wood fiber hanging on here and there to the cloth when pulled off. The unthinned cloth did not. Again, unscientifically, there was no noticeable difference in the stiffness of the two pieces of cloth once peeled off the wood. All of the resin painted on the wood was dry to the touch with no tackiness. The side of the wood that had the thinned resin had the coloration like it did after painting the resin on. The side with the unthinned resin looked like bare wood once the cloth was peeled up. The unused unthinned resin in the cup was hard and could be scratched with a screwdriver. The unused thinned resin in the cup was a bit rubbery when I tried to scratch it.

There it is. My unscientific experiment. Take from it what you will. I have made my decision as to how I will proceed.

Covering the thinned resin with unthinned before it cures isn't the way I do it, let the thinned resin go off first, it will cure hard and can be sanded without any balling up on the sander.

The thinned resin in the cup will harden but because its in the cup and over thinned it will take longer .

50/50 is also a lot of acetone, I just add it til its thin enough, its more of a method...not a recipe. But at a guess I'd say I use 1/4 cup acetone to every pint of resin, it doesn't take much.

can't imagine such drama over adding a bit of acetone to resin.!

 

[ondarvr]

Re: Polyester for wood waterproofing

Thanks Alan, it's always nice to have experts from other sites add their knowledge to the mix.

Like Stoutcat said, if you're looking for high strength in wooden construction, epoxy is the way to go, I left that out of my list since we were discussing FRP boats.


I was looking for a pic of undercured resin and/or gel coat, what it shows is the effects of poorly crosslinked and weakened polymer chains, there are some here in iboats, but I couldn't find them fast enough. Crazing on the gel coat is a common side effect of adding too much solvent and/or the incorrect amount of catalyst, either higher or lower than recommended. In the beginning the gel coat or laminate looks fine, but after a period of time, and it can be from a few weeks to a few years, you start to see crazing on the surface. Part of it is due to the continued cure and shrink, but most of it is due the poor physical properties of the resin and or gel coat. Many of the problems found in finished FRP products can be blamed on polyester's very forgiving chemistry, many things can be done poorly or incorrectly and you still end up with a part that looks good for at least some period of time after it's been completed.

The drama over just adding a little acetone is mainly because of the what opps! refered to in his post "all too often 3% turns into 30%". You said you added "some" acetone to the resin and reported it helped what you were doing, the next person that read it more than doubled the amount you used.

Building and/or repairing boats is all about the small details, doing these small details right makes a big difference in how long the boat will be in service.

 

[oops!]

Re: Polyester for wood waterproofing

stoutcat........welcome aboard bud !

good to have ya!

 

[oops!]

Re: Polyester for wood waterproofing

btw....im donna do a few casting experiments today....ill add some thinner....and post the results here so ya'll can see em

 

[Stoutcat]

Re: Polyester for wood waterproofing

Hi Oops,

Thanks for the welcome! It's interesting to come over to a new boat material... Yet the discussion follows similar lines. This business of waterproofing wood is an old one for us wood boat guys, and after decades of messing with the stuff, the general consensus (and my opinion too) is that water always wins. Sooner or later it's going to get where you don't want it to go. While a primarily a rowboat guy, my wife and I built a kayak a few years back, and the kind folks on the CLC forum held my hand through the process. Those folks were the ones that finally got me to understand that there's no way to stop water when it wants to get to wood... About the best one can do is use marine ply, seal as best you can and inspect...

One thought... I've been reading a lot of posts on iboats.com and have noticed bunches of people rebuilding alum and fiber boats... In the process, they install new stringers and then deck over permanently. Next comes the carpet... Ouch. I live on Cape Cod, and try to watch how commercial fisherman deal with the issue of wood and water... In general, some seem to take the "removable deck approach" or the "deck plate approach". My best friend just bought a used 40+' fiberglass commercial fishing boat. (The boat mortgage is more than the mortgage on his house.) It has large deck panels that are latched down. Part of every day's dock work is to pull the panels and dry it out... The system must be working... The boat was made back in the '70s and all is still sound. Just an observation...

I on the other hand just bought a 1957 Starcraft aluminum 14' runabout... I just can't wait to see what thrills water and time bring to aluminum hulls...

Anyway, best of luck to 109jb, and it's good to be aboard!

Alan

 

[oops!]

Re: Polyester for wood waterproofing

yep.....carpet.......nothing like a wet sponge next to your new deck !

i guess it all just depends on the look you want.

boats are all a trade off.....stronger = heavyer.

small prop vs high pitch.....

for everything you gain....you loose somthing.....

carpet = less life of the deck

gell coat deck = hard on the tootsies and a less comfie look

 

[wca_tim]

Re: Polyester for wood waterproofing

Couple things I might be able to add... especially in the context of thinning resins for penetrating or water"proofing" wood.

crazing mentioned below is the mechanism by wich cracks in gel and many other plastics start, it the surface is 'defect free" it is much more resistant to cracking and further degredation. it's bad and it is what happens when the curing reaction doesn't happen completely at the surface.

The issue of thinning resins is somewhat different for polyester than it is for epoxy and different again for polyurethane-based products.

Polyester is "free radical" cured. The curing (the process that makes the links between the chains making them into one great big, somewhat flexible but very strong molecule) reaction is oxygen sensitive(!!!) and is dependant on the concentration of the initiator (catalyst) and reactive monomer (styrene). Before the curing reaction can really kick off, the catalyst has to chew up the oxygen that's dissolved in the uncured resin mixture. Once the oxygen is consumed and not able to diffuse in as fast as catalyst molecules do their work, curing takes off. That's why it takes so much longer for thin films of resin to cure than for thick films. Water is not much of an issue, but a fast evaporating,organic solvent like acetone is required if you;re going to thin it out. because of some of the sublties of styrene / free radical chemistry, resin is the worst cadidate of the three if you plan to dilute it.

The situation is a good bit better with epoxy - AS LONG AS YOU USE DRY ACETONE! and by dry I mean substantially dryer (less water contamination than you can buy in a paint store typicall or than is in the can once it's been opn to humid air for a while. It may not seem like much, but id intereferes with the epoxy curing chemistry. Epoxy chemistry is substantially more complex but is less sensitive to dilution simply because it doesn't have that battle to fight with oxygen. it may tak a significantly longer time for it to cure completely, and any water from solvent, the air, etc...) and other impurities such as alcohols and others (yes, alcohols will shut down epoxy chemistry hard - don't ever add alcohol!) that are present will interfere with the curing process to at least some degree. Even though you may not be able to notice, it does degrade the surface and bulk properties, but if done right can be done with much better effect than polyester / styrene-based resins.

for making tough, flexible, penetrating, long term, water barrier materials for wood (or most anything else), poly urethane / urea chemistry actually has substantial potential advantages over the others above. They're more expensive, but can be designed to react to a significant degree with the wood, etc... and tailor made for the job. since the others do their job well though... and are typically what is on hand when one want's to waterproof wood...

Like Stoutcat said, if you're looking for high strength in wooden construction, epoxy is the way to go, I left that out of my list since we were discussing FRP boats.


I was looking for a pic of undercured resin and/or gel coat, what it shows is the effects of poorly crosslinked and weakened polymer chains, there are some here in iboats, but I couldn't find them fast enough. Crazing on the gel coat is a common side effect of adding too much solvent and/or the incorrect amount of catalyst, either higher or lower than recommended. In the beginning the gel coat or laminate looks fine, but after a period of time, and it can be from a few weeks to a few years, you start to see crazing on the surface. Part of it is due to the continued cure and shrink, but most of it is due the poor physical properties of the resin and or gel coat. Many of the problems found in finished FRP products can be blamed on polyester's very forgiving chemistry, many things can be done poorly or incorrectly and you still end up with a part that looks good for at least some period of time after it's been completed.

The drama over just adding a little acetone is mainly because of the what opps! refered to in his post "all too often 3% turns into 30%". You said you added "some" acetone to the resin and reported it helped what you were doing, the next person that read it more than doubled the amount you used.

Building and/or repairing boats is all about the small details, doing these small details right makes a big difference in how long the boat will be in service.

 

[reelfishin]

Re: Polyester for wood waterproofing

Anytime I do any wood coating or deck replacement I just mix with a tad bit less hardener than normal, the minimum required to get a proper cure. That's always been sufficient and I've had no problems. I've never felt the need to cut the resin with acetone. I have done more lately with epoxy than with polyester resin though, but that has as much to do with strength as it does availability and cost.