Epoxy and what?

Clyde_Wanderer

Clyde_Wanderer

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Was just about to post a question about what laminates to use with epoxy resin to strenghten up my hull at keel and bilge area, ( inside hull) when I read last post stating that epoxy and csm dont work well.
So what should I use?
I had been considering unidirectional roving, alternated with csm, and am hoping to add aprox 3/8 to 1/2" thickness, and will also be laminating in new epoxy prepared plywood floors (cross members ) on top of the new laminate.
I have practically rebuilt a grp boat in the past, with polyester and csm/udroving. but have never used epoxy resins.
Any ideas or advice?
Thanks.
 
Chopped strand mat contains a styrene binder that is broken down by polyester resin during the lay up process, presumably so that the fibres can interweave properly or something like that. Epoxy doesn't dissolve the binder, so the mat doesn't get wetted out properly. Bidirectional cloth seems to be recommended by a lot of people here, and is what I've used with epoxy. I haven't had much success wetting this out with a brush though - I use a plastic spatula (like the one you get with Isopon), which really seems to force the resin into the weave of the cloth.
I can't remember the name of the forum member concerned, but there's a resident expert on this topic, and if you're lucky he'll step in and give you the full and complete answer.
 
I would suggest that if you are doing a layup of 1/2 inch thick then ployester will be fine and far cheaper (easier also in cold conditions just use more hardener) Epoxy does stick better and this is important if you are doing a layer of just a few mm which can flex and get water under but with 1/2 inch thick it will be quite solid with out that flexibility so will stick better ie polyester ok. (so chopped strand mat ok) although I imagine woven rovings would give more bulk with less layers. good luck olewill
 
You can get CSM suitable for epoxy but its a nightmare to use. The resin is so sticky you end up with a resin brush that looks like an irritated hedgehog, and fibres sticking out in every direction from the job you are doing

I use woven cloth with epoxy
 
Nice to see Boatbuilders post ...

I too don't understand this obsession with epoxy ...

Years of repairs / strengthening / additions using Polyester ... have shown me that it works. The trick is preparation and laying out all you need before starting.
 
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I would suggest that if you are doing a layup of 1/2 inch thick then ployester will be fine and far cheaper (easier also in cold conditions just use more hardener) Epoxy does stick better and this is important if you are doing a layer of just a few mm which can flex and get water under but with 1/2 inch thick it will be quite solid with out that flexibility so will stick better ie polyester ok. (so chopped strand mat ok) although I imagine woven rovings would give more bulk with less layers. good luck olewill

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I would suggest nicely ... Do NOT increase hardener in Polyester mix ... it is possible to "scorch" not only the mix but also the material bonding to. In fact Polyester mix with too much hardener is unstable and becomes brittle. It can also in extremes actually catch fire ... try it if you don't believe.
If its cold and resin is curing slowly ... then basically you are working in unsuitable "climate" conditions. The thing to do then is to have fan heater blowing over work area ... but be careful as resin fumes are flammable when confined - so make sure area is well ventilated.
 
Why use an Epoxy:

The question of why some prefer epoxy for some particular projects over standard Poly resins is raised on a regular basis on this and other forums. This is not the full answer, just an attempt to clarify a few observation I've made over the years.
I'm no expert just a daily user.

It's important to understand that a standard poly resin sticks to itself very well in most conditions, however, it relies on the surface being very clean, dry and with a good key. Given that it's clean and dry, it's the key (roughness of the surface) that the resin will bond too. This is referred to as a primary bond.

An epoxy resin needs the same conditions as above for poly resins, the only real difference is that the epoxy not only forms a primary bond to the keyed area but also a secondary 'Chemical bond'.

There is no reason why some projects can not be constructed using a poly resin than attached using an epoxy for high bond strength and better joint water resistance.

Other points of interest are:

Poly resin is less water resistant than an epoxy.

Polly resin requires a ratio of 3 resin to 1 mat, epoxy resin needs only a 1:1 ratio. This can be important if you are looking for high strength and water resistance with less weight.

Poly resin has a shorter pot life when mixed with the minimum recommended 1% catalyst, and a lot shorter when mixed at the maximum recommended of 2%, you can add more than 3% if you like sudden fires.
Epoxy resin has a pot life between 30 and 45 minutes stock standard, however slower curing and faster curing epoxy resins are readily available.

Many complain about haw difficult it is to wet out epoxy cloth, I use Poly and epoxy resins every day and only ever use a roller suitable for use with resins, when using epoxy I apply with a soft roller then roll out the excess resin with a steel threaded or grooved roller, no problems.
If you time it right you can pull a squeegee over the surface and get a very smooth and flat finish that will reduce ans sanding time later.

No doubt I will get flamed for posting this by the Poly Only Brigade, but the point of all this is to point out that each resin type has it's own advantages / disadvantages.

Avagoodweekend......

Only 12 days to go and I'm off sailing.
 
Whilst I agree with you on the whole, I try to maintain a 1:1 ratio with polyester and cloth. The only exeption is of course CSM wich will allways need 3:1 and a good consoldating roller.
 
G'day Boatbuilder,

You are correct I was referring to Chopped Strand Mat (CSM) resin ratio at 3:1, though I have never had roll it out after application with a 10mm nap roller and only very light pressure during application.

Thanks for you comments it will have made the point clearer, I should have noted I was referring to CSM.

Avagoodweekend......
 
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Here in England it is tought that all layups must be consoldated hard with a washer roller. The excess resin is then taken up with a dry fluffy.

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Try layiong up a small sample on a sheet of glass or plastic, take note of the weight the CSM was prior to rolling with a washer roller, do a second sample with a standard 10mm nap resin roller appling only a light pressure to finish, when cured drop the samples onto a scale and see for yourself what ratios have achived.

A washer or threaded roller in common if not a requirement with epoxy resins but not for poly resins, though I have used a slotted roller to bring extra resin to the surface in some applications where a thicker covering is required.

Let us know your findings.
 
Hi Oldsaltoz, I thought you were already sailing of the Barrier Reef somewhere!
No I haven'y got any where with my Keel area as I am recovering from a slipped disk!
As I am going to be doing the job you have outlined and have taken a lot of advise from Oldsaltoz and read a few books and totaly confused my self, I believe that I am right in saying that Powder Bound CSM is ok for epoxy but NOT emulsion bound CSM. The emulsion is disolved by the styrene in the Polyester resin but epoxy dosen't have any styrene to desolve it so the CSM cannot work properly.

Derek
Konsort 'Rhumlady'
 
G'day Derek (rhumlady),

There are some (very few) applications that require epoxy and CSM, the main reason being that the large voids in CSM use a lot of epoxy resin without any advantage, ending up in a more expensive, and some cases a weaker finish that will be very brittle.

I avoid CSM with epoxy resin as it's such a waste. As I said very few applications would require a brittle finish in the boating industry; this combination is more likely to be specified by an engineer to control panel break points on a high performance/racing car shell, or a control break point on a structure.

Though the same can be achieved by other means like adding filler to resin mix prior to laying up cloth, and, depending on the type of filler making a section more or less flexible without a change in layup thickness using standard or epoxy resins.

The fact that someone produces a CSM that they advise is OK with epoxy resins is not an indication that it's designed to replace epoxy cloth.

I hope this helps,

Avagoodweekend......
 
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