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PostPosted: Sun Feb 27, 2011 1:43 pm 
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Able Skipper

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I am building various timber partitions, bilge floors, shelves, etc inside my boat and wanted to seal and waterproof any of the timber that goes in. Have heard various reports of using polyester, epoxy, etc. What are the pros & cons of using say thinned out polyester resin v's epoxy paints such as Evidure?? Can you paint over both afterwards and if so with what type of paints?

I think from memory one guy told me to use nomal polyester resin & catalyst thinned with 10% actone. Does that sound like the way to go?

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PostPosted: Sun Feb 27, 2011 2:01 pm 
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Use an epoxy sealer, like evidure or equivalent. This can then be painted over with and epoxy paint or varnish. Polyester doen't stick to timber very well. There are formulations on the market designed to penetrate new timber, save you thinning, made by International, Norglass, Botecote etc.
Another consideration which I am sure I will be corrected by if I'm wrong, is polyester does not stick to epoxy (or is it the other way round / :? )

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PostPosted: Sun Feb 27, 2011 4:42 pm 
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Thanks Impulse. Yes I gather from previous threads that varnish goes particularly well over epoxy.

When you say:
Quote:
There are formulations on the market designed to penetrate new timber, save you thinning, made by International, Norglass, Botecote etc.
do you mean formulations of both polyester and epoxy or just epoxy?

I assume epoxy sticks to polyester as my understanding is that the usual recommendation is to paint epoxy on a hull prior to antifouling?

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PostPosted: Sun Feb 27, 2011 5:16 pm 
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I'm not 100% on this so tread carefully. Epoxy inhibits the setting of polyester. In my mind epoxy is a far superior product to polyester. Although it is widely done most manufacturers do not recommend thinning their products.
It's been a while since I played with a GRP boat so I'm sure there are others who can correctly state the compatibility or not of epoxy and polyester. Nonetheless, to seal timber epoxy is the product of choice. There is evidure, norglass timber treatment, botecote, CPES etc etc, all designed specifically to seal timber. Whatever you use it stands to reason to use a similar product as finishing coats.

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PostPosted: Mon Feb 28, 2011 3:37 pm 
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There is a specific thinner for epoxy (bote cote) that is recommended to help the epoxy penetrate new timber.


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PostPosted: Mon Feb 28, 2011 3:51 pm 
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Thanks for the extra bits of feedback Impulse & Cruisinpete. I have a tin of polyester resin and some catalyst + acetone on hand and am trying to avoid buying the epoxy (A&B tins) + epoxy thinners. Guess I need be careful as it sounds like epoxy is the much prefered, even if more expensive, way to go.

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PostPosted: Mon Feb 28, 2011 6:24 pm 
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First of all, check whether acetone is the recommended thinner for polyester. It may clean it up but that doesn't necessarily mean you can thin poly with it.
As I said earlier, polyester doesn't really adhere to timber that well, certainly not compared to epoxy which sticks like the proverbial.
Apart from your bilge boards, and maybe even for them as macs sound like a fairly dry boat, why not simply varnish and skip the epoxy or polyester stage. :?
The only other advice I can suggest is check the specs on the varnish you intend to use to see if ther are any special requirements for overcoating polyester.

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PostPosted: Mon Feb 28, 2011 8:42 pm 
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I don't recommend you use polyester. Water tends to get behind it into the wood and can't get out easily creating a rot situation. As said previously it doesnt stick to wood that well. Plus it stinks for ages :shock:
Inside the boat I would just use varnish as this will breath a little and allow moisture to escape. Epoxy to join and seal. Varnish on top if exposed to the sun.


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PostPosted: Tue Mar 01, 2011 10:28 am 
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impulse wrote:
Another consideration which I am sure I will be corrected by if I'm wrong, is polyester does not stick to epoxy (or is it the other way round / :? )


Yes this is correct, Polyester should never be used over Epoxy, it cannott bond to it securely and will eventually fail, however epoxy is the absolute best thing to use over polyester and if it is mixed correctly once hardened Epoxy is 100% waterproof.
Always use an Epoxy filler or fairing mix anyware below the water line, Never polyester filler as it will absorb moisture.

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PostPosted: Tue Mar 01, 2011 10:50 am 
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we were looking at a 'line board' on my Careel over the weekend - it carries the cleats and stuff for adjusting stuff. I made it out of normal 3mm ply from Bunnings, five layers with Norglass epoxy glue and then bend into shape using the winches and a bit of jib sheet. I shaped it then gave it a light sand then scraped on raw epoxy, no thinning. Then I used external varnish and after about six or seven years (under cover) it still looks good. Did the same with the hatch cover for the anchor locker and that still looks good. The epoxy stops the fibres sticking up because it cures chemically not by evaporation which is the killer for any treatment because it leaves small pinholes for moisture.

look on the web, people who know don't advise thinning or using the wood treatment epoxies because they cure chemically AND by evaporation, leaving those pesky holes.

J


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PostPosted: Tue Mar 01, 2011 1:03 pm 
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jamesw wrote:
look on the web, people who know don't advise thinning or using the wood treatment epoxies because they cure chemically AND by evaporation, leaving those pesky holes.

I presume you meant epoxy here James? I assume you mean because the epoxy is thinned there will be evaporation (of the thinner) as well as the chemical reaction caused by the 2 parts being mixed - is that correct?

Just to throw in a red herring, as a matter of interest I phoned up a commercial upolsterer/cabinet-maker who was doing some work on a cruiser next to me at the marina a month or so back. We got talking and he said the best way to treat timber in a boat is to use polyester thinned with acetone. He was a pretty helpful guy and said to give him a call any time if I had any questions, so I phoned him yesterday. Basically he said he considers that Polyester resin does a better job of sealing timber than epoxy (such as Evidure & BoatCoat). Said to mix polyester resin with 10-15% (max) ACETONE (not thinners). Mix the acetone well into the resin first and then add the catalyst. He said the acetone helps to lift the wax to the surface and that helps draw the mix into the timber.

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PostPosted: Tue Mar 01, 2011 1:20 pm 
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Hi Cruiser,
My B20 is of timber construction when it was refurbished in 2006 initially I used Senseal which is a two pack epoxy application great product but very expensive. It even brought rotted sections of timber back to a solid state. I have since started using Everdure heaps cheaper but does allmost the same job. I use Everdure as per instructions, start with a thinned mixture and increase the viscosity after each coat I find three is enough with the final coat full mixture it is a 50 resin/50 hardener mix. I then apply a final coat of epoxy (I use Fibreglass International Expoxy Resin which is from memory 4 parts resin 1 part hardener) You can either leave it as finish coat or apply varnish over the top, I use Feast Watson Weatherproof Gloss.
Hope that is of help.
The Baz
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