Resin Questions

hi, I'm working on a transom rebuild on a 17' runabout. I'm going to be using 3 layers of 1/2 inch exterior ply for the core. I was thinking that I'd coat all the wood in polyester resin (no wax), then do my installation and glassing with epoxy.

Does this Sound reasonable? I'd do all epoxy but the poly is so much cheaper.

 

For as little as you're going to be using, I'd just stick with the epoxy. I might be tempted to "go cheap" if I were building the entire boat, but not just for a transom repair.


...just my $0.02, take it or leave it.

 

How much resin do you think I'll end up using? I'm doing transom and stringers. I was going to buy a gallon of poly and half gallon of epoxy

 

I'm not sure...too much depends on the total area to be laminated & glassed, plus the weight/# of layers of your glass fabric, plus how much soaks into the wood...I just don't have enough experience to tell you for sure. My GUESS would be that you should be ok with a 1.5 gallon kit of something like MAS low-vis or similar (avalable for a VERY competitive price from jamestowndistributors.com).


....just my $0.02, take t or leave it.

 

Do´nt know, or can imagine the size of the transom, nor the extra work (you are not planning but may envisage), but do NOT use Poly! If it does´nt stick as you need it to, if it delaminates after some time, if you do´nt cover it (with epoxy), you have a issue.
Pay once, buy Epoxy!
And lettuce have some measurements for a rough calc.

Regards
Richard

 

size

Its 6 feet wide, 20" high at motor mount, total height at risers is 33" pictures attached.

 

Stick with one product or the other, it will survive with either one.

 

A local glass supplier told me that new glass won't stick to old glass using poly resin...

 

GO FOR EPOXY...................................shall I write it in capitals?....... he was´nt so wrong.

 

Secondary bonding isn't as strong as the chemical bond you get when the entire boat is made in a short period of time by the manufacturer, but the difference isn't as dramatic as most people think. The reason people think polyester doesn't bond well is because of how many repairs are done. Someone with little or no instruction buys some resin and cloth and heads for the boat. They're supposed to grind the surface very well with a 36 grit disc on a grinder and clean the surface well, what they do is find an old used piece of 150 grit paper designed for wood, that's been in the garage for 15 years and then make a feeble attempt at sanding the surface. After about two minutes they give up without even breaking the surface of the old laminate or gel coat, they haven't even removed all the old dirt and oil on the surface yet. It gets the once over with a rag and that's all the prep it receives. Now they mix up a quart of resin and pour it over a 6"x6" piece of cloth, I didn't mention mat or catalyst because if any catalyst was added it was most likely no where near the correct amount. Mat needs to be used as the first layer and in between each layer of woven fabric or the bond will be poor and the first timer never uses it.

After about two weeks the resin is sort of hard so they put the part (whatever it is) into service and wouldn't you know it, that cheap polyester resin failed, it must be junk. At that point they go back to where they bought it and complain. This time they get epoxy because its supposed to stick much better (and it does) and head home. The old repair gets ground off and cleaned well, they were also told epoxy needs to be mixed accurately for it to harden, so for a change they measure it. This time multiple layers of cloth are used and the repair holds up, it must be because they used epoxy, its great stuff.

There are many secondary bonds in boats, the bigger the boat, the more there are, if the surface is prepped well these bonds don’t fail and since the prep is the same for epoxy or polyester the same amount of work is involved. Don’t get me wrong epoxy does bond better, it’s a glue, polyester isn’t, but polyester does bond well enough to polyester to make a very good, long lasting, strong repair.

In the end there’ll be no difference in how your boat performs or survives over the years with either product, you’ll never notice the difference. The difference will be in how well you do the job, make sure all wood is covered well and all the holes you drill need to be sealed. Unsealed holes, gaps in the laminate, trim that isn’t applied correctly and lack of attention to detail is where the failure starts.

 

+1, good info. Just like everything else, final product is only as good as the prep.

 

Right, and for that reason go for Epoxy............. sticks several times better, no fear about moisture or blistering, and the same hours of labour!

Regards
Richard

 

In this application there is no fear in bonding, nor is moisture and blistering an issue, so we're back to even.

The reason for blistering with polyester (and I'm including VE) is using the wrong resin for skinning the hull, if you use the wrong epoxy for a critical application it will fail also.

Polyesters are so forgiving that they can be abused horribly in production and still build a part that looks good when it goes out the door. Its a few years down the road when these abuses come back to haunt the owner. Don't blame the product for misuse by those using it, epoxies would have the same issues if untrained, careless employees were mass producing products for the lowest price possible.

 

Nothing to argue....... .....if not misused...

Regards
Richard

 

Thanks guys, I just want to do it right the first time so I'm doing lots of research. I've got the book runabout rennovation in the mail, I heard good reviews, gonna read that and then get to work.

I ran through the math on going all epoxy vs a mix, its really not even much more money. If epoxy is more forgiving, then me as a first timer will probably be better off.

I'm thinking I'll order 2 gallons, if I have extra, then I'll find myself another project to work on.