Epoxy and CSM

[laika]

My rudder had extensive blistering. I was advised by the pros in the yard to grind out the blisters (which I've done) and laminate epoxy with csm into the voids. Most of my knowledge so far has been book learnin' which I'm aware often aint how it's done in the real world. I questioned use of CSM, citing the binder not being soluble in epoxy but was told that's how they always do it, not tape or similar.

I did read an article on the west site saying that actually you can use csm, and although you can get (rarer and more expensive) csm without powder binding, there's not really a significant problem with with CSM binder not dissolving in the epoxy..

I'll take generous advice of people who do this for a living over what I've got (with possible misinterpretation of emphasis) from a book and the CSM and epoxy route is what I'm planning, but what do the forum think?

 

[pvb]

You don't say how big these blister voids are, but what's the purpose of the CSM? It won't do much in terms of structural integrity.

 

[laika]

You don't say how big these blister voids are, but what's the purpose of the CSM? It won't do much in terms of structural integrity.

Go easy on me: I'm a beginner at this
The ground out areas vary from 8cm across and 1cm or so deep to about 20cm across and 4cm deep in areas where soggy filler was still being ground away the more I ground. The CSM was advice from the yard boatwrights whose advice was that epoxy filler except on the surface was bound to absorb moisture. This seems to be supported by an examination of the exposed areas: the deeply filled areas were wet. Areas that looked pretty much like pure epoxy had cracks which had water behind. I guess with the larger voids the CSM is providing structural integrity

 

[pvb]

They're quite big voids!

 

[Daydream believer]

Do not want to teach you how to suck eggs but some may find this of use:-
When you do the fitting get a piece of polythene & mark the shape you want with felt tip pen lay it on a flat hard surface
Lay the matt on this which is a little bigger all round
Pour on plenty of resin. Enough to soak the matt. Try a small sample first to get the experience.
Lay another layer of polythene on top
Using a small plastic roller ( a wallpaper edging roller about 1-2 inches wide) roll the resin around between the polythene layers until the matt is wetted out fully
Roll excess resin out of the pattern area
Using a pair of scissors cut the shape you want ( you will be able to see the felt tipped pattern)
Chuck the excess away. Sensibly
Take one layer of polythene off. Top or bottom one will come off first
Put a coat of resin on area to be bonded. Just enough to wet the base
Apply the matt & roll on to get good adhesion
Leave the polythene on to get a smooth finish (but this delays set & restricts vapour ejection a little and depends on setting time of epoxy)
Or carefully remove polythene and gently roll matt to get good adhesion
By having the matt on polythene it will not hang & tear etc & is easier to handle

This method ensures you do not get great blobs of matt & resin & is great for areas where you want a thin finish
I use it in model making with very thin matt but it works with thicker weaves as well& will probably help op with the last couple of layers once the main gaps have been filled. Successive layers can be bigger to get a tapered finish

 

[macd]

You don't say how big these blister voids are, but what's the purpose of the CSM? It won't do much in terms of structural integrity.

+1
Unless the voids are humongous, presumably you're just looking for a filler? Epoxy and microfibres is the strongest but I imagine you'd be relying on the integrity of the rest of the rudder for overall strength, so that might be overkill. A photo with some sort of guide for scale might help.

Sorry, laika: my post took so long to arrive via rubbish connection, it was answered before it docked.

 

[Tranona]

If you are going to fill them that way use the proper glass cloth. Much easier to use as you can cut it to shape and it does not fall apart. Wets out more easily with less chance of voids. Build it up in layers rather than all at one go to avoid exothermic reactions. Finish with epoxy and a sanding filler.

The moisture in the foam core does not sound good and you may find whatever you fill the holes with will come out anyway. Get somebody experienced to look at it before you do a lot of work only for it to fail again.

 

[laika]

A photo with some sort of guide for scale might help.

View attachment 34748View attachment 34749View attachment 34750
The general situation, the biggest, and one of the not so big. Maybe I got carried away but I kept grinding where things were wet. The middle one was definitely angle grinder, much as it looks like sasquatch.

If you are going to fill them that way use the proper glass cloth

Actually this was what I suggested to the yard guys. They are adamant that they always use CSM and I shouldn't use cloth.

The moisture in the foam core does not sound good and you may find whatever you fill the holes with will come out anyway. Get somebody experienced to look at it before you do a lot of work only for it to fail again.

You're completely right but the bottom line is that I don't have the cash at the moment to have the rudder dropped and the thing professionally done with infra-red lamps. I am asking the pros, but it's only informal advice. I was hoping it would dry out through being out of the water all summer. I also desperately want the boat back in the water for at least a couple of weeks of sailing before summer ends and I absolutely have to find a job which will make me time poor again

 

[RAI]

Are you using epoxy or polyester resin? I understood CSM works well with the latter, not so well with the former. CSM will fill the indents faster than glass cloth.

 

[laika]

Are you using epoxy or polyester resin?

Epoxy. Wouldn't have asked the question with polyester. The trouble is the conflict between what I've read (don't use csm with epoxy because the binder isn't soluble in it) and the advice I'm being given by local boatwrights. They are undoubtedly right, but I just want to understand *why* CSM is the right thing in this case. Maybe a bulk thing as you say and the lack of the binder dissolving being actually of minor import in this situation.

 

[Quandary]

I use epoxy with CSM, the difference is that the matt is powder bound not the more common resin bound stuff that you use for polyester. If you use the correct type of mat it laminates every bit as well as polyester, holds the resin well and is a very strong, water resistant job that adheres to any sub strat. Powder bound mat is available from most grp retailers as they will know you need it if you are buying epoxy resin. If you are reskinning something like a damaged rudder you can be confident that the epoxy lay up will adhere properly to any old polyester lay up, to the foam core and to the metal tangs. Polyester resin may not do that. If you are filling voids woven rovings is not good as it does not deform sufficiently well to take up irregular shapes, I suspect that is why the CSM is being recommended.

Laika,I began to doubt my advice after re- reading you first post so checked again, powder bound is indeed the stuff for epoxy so I was not giving duff advice, the commoner chopped strand matt you buy in the car accessory shop is resin or emulsion bound and that binder does not dissolve in epoxy so that the matt does not relax into the shape you are filling, for complex shapes or smaller cavities you want 'short strand powder bound csm, a look on google will show you where you can get it, it is not that expensive though you may have to buy more than you might need.

 

[Lakesailor]

Yep. If the binder doesn't dissolve you are going to have a hell of a job wetting-out the csm. Either get the correct csm for epoxy or use polyester resin.
If the rest of the rudder is polyester there isn't a lot of point in having some dobs of epoxy here and there.

 

[TradewindSailor]

Epoxy and csm ...... CSM uses up lots of resin. Seems a pretty inefficient way of doing the repair.

I would be inclined to clean back to bare laminate. Work up a BOG .... csm and POLYESTER resin ..... and fill the holes. Grind back to flat and then put 3-4 of layers of bi-directional stitch mat with csm attached using polyester resin over the entire rudder blade. Then coat the lot with gelcoat with wax to allow it to cure properly in air.

If you want to go to the expense of epoxy, fill the holes with a filler made from epoxy resin and microballoons, fair it, and then laminate the entire faces with 3 layers of bi-axial 45-45 stitch mat with no csm backing. Use two squeegies (plastic scrapers will do) to apply the resin and saturate the cloth). Wash off the amine and apply the anti-foul. Reasoning ..... the face of your blades are so badly damaged that epoxy cloth will not add anything to the structural integrity. Just make fair and then add a new structural layer over the top.

Frankly I wouldn't bother going to the expense of an epoxy resin repair because that rudder probably needs renewing. If moisture has got to the stainless structure, it is probably suffering from crevice corrosion.

 

[laika]

Quandry: Thanks for that. I was aware of the latter suff from this which hopefully should be of interest to anyone else landing on this thread while researching:
http://www.westsystem.com/ss/chopped-strand-mat-epoxy/
The key phrase I didn't know was "powder bound". The above article suggested it was hard to come by but I'm sure I've seen "powder bound" in force 4 (2 mins walk away). Don't know what the stuff I have in the locker is that I normally use with polyester resin. Anyone knows how to tell powder binding from emulsion by visual inspection, please let me know.

I understand the reason for not using glass cloth alone in polyester work is that it is more prone to delamination unless alternated with CSM but my research also suggests that this doesn't apply when glass cloth is laminated with epoxy as the epoxy layers stick to each other better. guessing that either approach would probably be ok and certainly better than sitting here overthinking and not doing. Many thanks to everyone.

Edit: just saw the other two posts. Thanks again. Actually the rudder isn't as bad as it looks and is perfect on the other side. All the damage there is from the angle grinder and I was probably over enthusiastic. I will probably go with the epoxy..

 

[VicS]

My rudder had extensive blistering.
..........
but what do the forum think?

I have done enough work with polyester and CSM and with polyester and tape to be happy with using polyester ( Several small boats with tape and my Sea Wych with CSM.

For a recent job I wanted to use epoxy ... very apprehensive about it for no really good reasons.

I discovered that there is a grade of CSM, without the binder, suitable for use with epoxy but also came across a suggestion that it was difficult to work with.

For my job biaxial cloth was, I decided, the appropriate material ...... also some thickening and colouring of the resin.

The Wessex resins website is a very good source of detailed help and advice on working with epoxy and the associated materials. I recommend you take some time to study it if you have not already.

I bought the epoxy and all the materials and some tools and other equipment from http://www.ecfibreglasssupplies.co.uk/.


Bought far too much of every thing!

 

[maxcampbell]

I don't see what the csm is adding. I'd just mix up some stiff epoxy / microfibres & trowel it in. I may layer a bit of csm wetted out with epoxy over the top afterwards. Tidy up as much as poss while its wet, it ain't half hard when it goes off.

 

[Lakesailor]

I can't see the point in using epoxy if the rest of the rudder is polyester. It's just sticking some hard points to a softer substrate.

 

[VicS]

I can't see the point in using epoxy if the rest of the rudder is polyester. It's just sticking some hard points to a softer substrate.

You are probably right. Its hellish expensive compared with polyester too.

If any structural strength is required epoxy is a better choice because it supposedly sticks to the existing structure better than polyester. That's one of the reasons I used it.

Underwater perhaps also a better choice because it's more water resistant and does not need a gel coat to be applied. That's the other reason I used it.

 

[laika]

The rudder has been filled before in patches with epoxy. I'm guessing that adherence to multiple materials (including epoxy) is sufficient reason to use epoxy rather than polyester. Also I'm grateful to the blokes in the yard for their advice so would rather try things their way unless I have a really good reason not to. My main issue was resolving their advice with apparently contradictory advice in books. Further research and everyone here's kind advice has made things clearer and offered me other approaches which if I don't try on this occasion, I may well use next time.

 

[JumbleDuck]

I can't see the point in using epoxy if the rest of the rudder is polyester. It's just sticking some hard points to a softer substrate.

New polyester doesn't stick well to old polyester; epoxy sticks better. Mind you, it's only a rudder skin, with very low stresses. I'd wodge in a bit of filler and stick a layer or two of cloth and epoxy on top to seal it.