Differences using epoxy and polyester.

[rhumlady]

When using Polyester with glass mat you put the smallest layer down first and work up to the largest but with epoxy you put the biggest down first and work down to the smallest. Why the difference. When using epoxy and cloth it would be good to be able to do it the other way round as then all the ends of the smaller pieces would be covered by the largest piece. Does it realy matter which way round you do it?

 

[pollygonforty]

where did you get this information from?

 

[rhumlady]

For epoxy it is listed in the West Systems handbook and for polyester it is in other books I have read. It is also stated here on the forum on a number of occasions.

 

[William_H]

I don't believe it really matters. Of course you havn't said if you are laying up a in a mold so exposed outside layer goes down first or if it is a repair where the exposed layer is last. If using mat it is usual to put a layer of cloth fine weave over the mat being smoother it will look better / be easier to fair off.
If you are filling a hole then the smaller area pieces go in first so that subsequent larger pieces follow the chamfer you have ground.

However I can't see and have never been told that it matters on say a flat sheet of fibreglass with thinner edges which layer goes on first. Certainly no difference with epoxy or polyester. Perhaps they had some situation in mind where it does matter. olewill

 

[Refueler]

I cannot agree with that at all - it all depends on job you're doing.

Logic tells you that larger first in most cases would result in a poor structure and shape to repair. In case of hole or filling a pit - it would increase localised stress. Larger last would spread the load bearing and be far better whatever you use - Epoxy or Poly.

One point I would make about them - Epoxy is generally more tolerant of incorrect proportion catalyst ie too much. Too much with Poly and you can have such heat generated that it can damage itself and surroundings ... even to catching fire in extremes.

 

[boatmike]

Correct William, It does not matter. Properly consolidated it only matters that the "patch" if that's what we are talking about tapers off to avoid a sharp change of section at the edges. The same applies to boundary angles or anything else similar where one section meets another. What layers you put down first is immaterial but it's sometimes useful to lay down about 3 or 4 layers only and consolidate them properly and allow to harden before building up further, thus avoiding mass effect which causes exessive heat and possible distortion. When using epoxy this is also useful as it is more difficult to "wet out" than polyester. A good tip is to always apply resin to the surface and roll thoroughly to draw resin up from below rather than applying resin to cloth from above if you can. That way you avoid voids and air pockets.

 

[wotayottie]

Dont agree Refueler. Since the job is most likely done in one session, the whole lot of the added layers chemically bonds together to make a single structure, so there cant really be any difference between the two approaches.

 

[Refueler]

[ QUOTE ]
Dont agree Refueler. Since the job is most likely done in one session, the whole lot of the added layers chemically bonds together to make a single structure, so there cant really be any difference between the two approaches.

[/ QUOTE ]

Sorry but if you have a hole or pit to fill ... you start by tapering the sides in so that it's smaller at depth. Laying up then is filling the pit such that you have larger pieces as you come out to top ... with last overlying the surrounding structure.
This a) reduces possibilities of voids deep in, b) creates a uniform reapir build up.

If you used large first ... I assume this would be larger than the pit or hole to be repaired ... you have immediate overlap and chance of voids created. As the matt reduces in size - you end up with a tapered pillar where it should taper other way.

Matt may 'meld' into layer below but only as far as wetting out - it does not interweave and become one matt at all .. It may cure and become one repair, but still the matt has it's physical thickness and size.

Personally - for this sort of repair - I prefer chopped strand filler type resin to build up a base in the pit or hole and then once sufficient in and semi cured - to then overlay with matt and finally matt tissue to form a neat finish. The matt layers getting larger to final.

You only have to minds eye imagine the side view of a pit or hole to appreciate my suggested method.

 

[boatmike]

That would only apply to a patch on a small hole. Anything else, it does not matter and is often more convenient vice versa. Certainly I always do boundary angles (bulkhead fixings etc) the other way around having "tacked" them first.

 

[Refueler]

[ QUOTE ]
That would only apply to a patch on a small hole. Anything else, it does not matter and is often more convenient vice versa. Certainly I always do boundary angles (bulkhead fixings etc) the other way around having "tacked" them first.

[/ QUOTE ]

Agreed ... but most times people are repairing holes or pits. In event of flat repair etc. then it becomes academic as you would usually cut your matt up into workable squares / strips etc. to make it easier to use and wet out. Large pieces as you see some struggling with are in fact unnecessary if lapped in well.

 

[boatmike]

Agreed ... but most times people are repairing holes or pits. In event of flat repair etc. then it becomes academic as you would usually cut your matt up into workable squares / strips etc. to make it easier to use and wet out. Large pieces as you see some struggling with are in fact unnecessary if lapped in well.
___________________________________________________________________

Glad we agree. The original post said nothing about repairing small holes.....

 

[ccscott49]

One thing nobody has mentioned, polyester goes off rapidly epoxy takes much, much longer to "set" so when repairing a vertical hole/pit, some way of holding it all together until the epoxy goes off is required. I use a piece of ply or similar, with cling film on its face, held in place with whatever I can get to hold it. Clamps, posts etc.

 

[oldsaltoz]

[ QUOTE ]
When using Polyester with glass mat you put the smallest layer down first and work up to the largest but with epoxy you put the biggest down first and work down to the smallest. Why the difference. When using epoxy and cloth it would be good to be able to do it the other way round as then all the ends of the smaller pieces would be covered by the largest piece. Does it realy matter which way round you do it?

[/ QUOTE ]

Perhaps this should have read:
Why do some say small patch first and others say large patch first and continued the basic question "Differences using epoxy and polyester".

The short answer is that it depends on what you are trying to achieve or avoid, there is no single one fits all solution, if you are in doubt about what methos to use you can consult the WWW or pose your question here.

Moving on:

Polyester resin: When combined with CSM (chopped strand mat) the binders that hold the strands together are dissolved, most people new to glassing tent to rush and try to get everything nice a smooth, flat and all well wetted. This is a mistake, by applying the correct amount of resin using a roller if possible and mixing only small batches till you improve will help.

By taking your time and applying the correct amount of resin you will find that the binders have time to dissolve and the strands move around more easily making the task of removing all air much faster and more effective.

Using a consolidating grooved or flap roller will do a much better job than a soft application roller or a brush, even if it has been cut down. CSM can almost be pushed into any shape after the biner has gone making is easy to get a level surface, it's a bit harder to do this with epoxy.

The ratio for CSM is 3 to 1, that's 3 parts resin to one part cloth by weight, any more or less will effect the strength of the bond.

Epoxy resins on the other hand do not use a lot of binders in their cloth, most epoxy resin cloth is woven or stitched so will not move around as much as CSM and poly resins. This can give you the feeling that it's difficult to wet out, it's not if you apply the resin then apply the patch, now use a consolidating roller and work the resin through.

There are 2 things you need to keep an eye on when using epoxy, the first one is make sure it is well rolled to ensure no air remains between layers, the second is make sure you roll out any excess resin.

The ratio for epoxy and cloth is one to one resin to cloth by weight, any variation will result in a weaker finish or poor bonding.

Also note: most epoxy resins need the temperature to be above 20*c for the 24 hours after application and, humidity above 72%.

Do not use CSM with epoxy resin as the voids in CSM will ensure the ratio is out of balance, you may also have other problems as the binder on the CSM may not dissolve.

I hope this helps.

Avagoodweekend......

 

[Stemar]

Also note: most epoxy resins need the temperature to be above 20*c for the 24 hours after application and, humidity above 72%.

You'd be unlikely to get that in the UK even in mid summer. Maybe UK resin is more tolerant of low temperature. A few years ago, I had a hole to fill in the bottom of my hull - an old throughhull - and the epoxy cured fine overnight with temperatures down to below 5 deg C.

 

[rhumlady]

I knew I would get an answer here. I am rebuilding my Konsort and as part of that I am replacing stringers and floors above the keel. I have followed the West Systems manual which says apply large first getting smaller but this is a right pain due to the raggy ends of the cloth. I shall now reverse this and save myself time and ripped hands. I have just switched to slow hardener which has made a big difference and although I use the pumps it is only to get the stuff into the mixing pot which is sitting on a set of digital scales. The 'calibrated' pumps leave a lot to be desired.

 

[oldsaltoz]

[ QUOTE ]
Also note: most epoxy resins need the temperature to be above 20*c for the 24 hours after application and, humidity above 72%.

You'd be unlikely to get that in the UK even in mid summer. Maybe UK resin is more tolerant of low temperature. A few years ago, I had a hole to fill in the bottom of my hull - an old throughhull - and the epoxy cured fine overnight with temperatures down to below 5 deg C.

[/ QUOTE ]

Well I did say "Most'.