Author Topic: polyester resin??  (Read 6110 times)

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Jim

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polyester resin??
« on: September 04, 2011, 02:40:17 PM »
OK, so polyester resin is not optimal, I understand it isn't really waterproof and has other drawbacks.  But can it be used to reduce cost?  Epoxy is pretty spendy, normal "fiberglass" resin is pretty cheap.

My thought is about using the polyester for under layers, initial wood soak, between 3/8 ply layers, between transom layers, some above deck use, and using epoxy for all outer layers or where strength is needed.

I recently built new floor boards for an inflatable, had a lot of polyester resin around so I used that.  Thinned with acetone it soaks into the plywood real well... cheap fix.  of course, there is no strength needed, nor is a real waterproof situation needed, just a real good water resistance in this case.  The thinned polyester soaks in a long way, so a deep gouge in the floor still will not readily allow water penetration.  I have not had epoxy soak so deeply.

On a completely unrelated side note:  I have a lot of this resin I need to use up.  I was going to do my garage floor with epoxy, but I spilled some of the thinned polyester resin on the floor.  It seems to show that putting polyester resin on the concrete floor will make for a very nice sweepable surface, oil resistant, and cheap!  So I'm going to apply it to the entire floor and use my floor for a test bed.  I can always rough it up and go over it with the originally intended floor epoxy in the future when I want to spend a lot more money.


Striper

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Re: polyester resin??
« Reply #1 on: September 05, 2011, 10:13:02 AM »
Jim,

It is your boat you can do anything you want. That being said, I would not put all the time and effort into a boat building project and use inferior materials. It is my understanding that polyester resin is a pretty poor glue, I would not want to be pounding though waves and have a glue joint failure.  In my opinion, if you want to spend less money, build a smaller boat. Never compromise quality on something that could get someone hurt.(worst case) or cause future costly repairs that would be more expensive than doing it right the first time.

You mention using polyester for underlayers, if you use epoxy for all layers you can get a chemical bond (stronger). There are many good epoxy systems on the market that are less expensive than West or System 3 and work as well.

Check out this link.
http://www.oneoceankayaks.com/Epoxtest.htm

Brian.Dixon

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Re: polyester resin??
« Reply #2 on: September 22, 2011, 11:58:20 AM »
Striper's right ...I do not recommend using polyester resin.  This boat requires the resin to act as a gap-filling glue and as a waterproof matrix for the fiberglass.  All strength calculations were made for epoxy, not polyester, resin.  Rather than switch to a non-epoxy resin, shop around for a lower cost marine epoxy such as RAKA or Basic No Blush from Progressive Epoxy Polymers:

http://www.raka.com
http://www.epoxyproducts.com/noblush.html

Any non-shrinking (no volatiles) marine epoxy will work for this boat.  If a company sells more than one type, then make sure you compare the viscosity to something like System III's General Purpose (or SilverTip) epoxy.  If they don't advertise their viscosities, then look for "laminating" epoxy that is designed to wet-out fiberglass.  Note also that low-ratio epoxies are generally more forgiving of measurement mistakes as well, e.g. look for 2:1 resin to hardener ratios rather than 5:1 or 7:1 like some companies offer.

Brian


pjitty

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Re: polyester resin??
« Reply #3 on: September 23, 2011, 07:04:02 AM »
US Composites has Epoxy for about $55.00 a gallon. Do a Google search. I've used this Epoxy for several boat builds and am completely satisfied. Polyester Resin has it's place, and used in Fiberglass boats for several years, but I'm not sure if I would use it for bonding a wooden boat together. If your looking to save money, I don't think bonding the plywood is the place to do it. Some may argue with me, but that's my opinion...

Joe D

Brian.Dixon

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Re: polyester resin??
« Reply #4 on: September 23, 2011, 12:21:53 PM »
US Composites has Epoxy for about $55.00 a gallon. Do a Google search. I've used this Epoxy for several boat builds and am completely satisfied. Polyester Resin has it's place, and used in Fiberglass boats for several years, but I'm not sure if I would use it for bonding a wooden boat together. If your looking to save money, I don't think bonding the plywood is the place to do it. Some may argue with me, but that's my opinion...

Joe D

Polyester fiberglass boats (the typical fiberglass boat) gain strength from structure, shape, and thickness.  The polyester impregnated fiberglass by itself is not very strong, so box beam structures combined with lay-ups thick enough to become structural are used in order to make up it.  Sheathing a boat in glass and building seams is a whole different method of giving a boat's structure enough strength and is why epoxy is suitable but polyester resin isn't.  Maybe it seems expensive, but what you should compare to is not the resin cost, but the total cost of resin in the boat ...glass boats have MUCH more resin in them and that's where their cost comes in.  And in glass boats, the requirement to have structure (box beams or equivalent) is why glass boats have a lot less interior space in them than a wood/epoxy composite boat.  You do get more for your money when building with wood and epoxy.

Brian

pjitty

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Re: polyester resin??
« Reply #5 on: September 25, 2011, 03:08:19 PM »
Thank you Brian, you really know your stuff. I am not a Naval Arch. and I don't pretend to be, and I know that Polyester Resin is hit or miss with it's bonding ability on plywood, I've tried it several times, but with epoxy, I've never had a failure. Just to give you a little insight, I'm not a professional Boat Builder, [I'm on my 4th build right now, at 19' it's my largest],just a guy who love's to build stuff...

Joe D

Brian.Dixon

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Re: polyester resin??
« Reply #6 on: October 05, 2011, 06:32:03 PM »
I've seen epoxy fail in two ways.  On one boat (not built by me), the person who did the build wasn't very careful about cleaning up before coating and gluing, and one of his glue joints that was made on dusty/dirty wood failed.  I also saw the fillet and glass crack in the transom corner when the boat owner drove over a curb with his motor up and bounced it really hard.  This is why my construction manuals stress cleanliness, pre-wetting of the wood with unthickened epoxy, and using high-strength wide-radius fillets in areas where high stress could occur ...like milled glass fiber + wood flour + colloidal silica (Cab-o-Sil or Aero-Sil) fillet mixes used in the transom corners on the GA.

Brian