Strange epoxy wetout

Hi all

Doing the insides of a canoe with West Systems Epoxy and 6oz cloth over WR Cedar strip. I am using the 'dry' method, laying the cloth on then saturating it.

The last bit I did I can still see the cloth threads *except* where I poured or flooded the cloth with epoxy before spreading it out. Where I merely brushed it on, no matter how hard I 'worked' it in, the threads show through. I am wondering why ???

I used peel ply over the cloth, and so the resin got a thorough working over, but the threads are still showing through now it is cured.

I am aiming at a clear finish, so this is a nuisance if it is going to happen with the more noticable parts of the interior.

Any Tips ?

Cheers

Ray

 

This is normal (to see the weave) after the wetout cures. If you don't see the weave, you've applied too much goo and the fabric is likely suspended over the wood (still glued), not directly bonded to the wood. these high resin to glass ratios make for heavy and brittle laminates. You want just enough goo to wetout the fabric but not enough to flood, float or fill the area. The weave can be filled on subsequent coatings of epoxy. This is especially important on bright (natural) finishes.

Fabric weight also has a large bearing on how much is visible. Anything much over 4 ounces will be visible, after filling the weave and varnish. 6 ounce is just barely visible, but noticeable in bright light conditions.

The key is good contact (wood to fabric) and this is done with the first coat of resin. Then fill the weave (one or more coats, depending on resin viscosity), then the top coat of UV protection (varnish, polyurethane, etc.)

 

The problem is most likely resin starvation--- not enough, and possibly attempting to fix that, you may also have entrained air into the resin.
Remember next time that once it begins to kick, it isn't going to look better in a few hours. It will just be harder, so cut it out immediately!
I've found that using a slow hardener and not overworking any area all at once works best. Many times the resin will cough up the air by itself given some time. I don't use any peel ply though. There will be other suggestions, I'm sure, regarding that method.

I'm editing this to note that what you meant by "see the cloth" is likely better answered by PAR's response. If it's only the texture you see (without any lightness), then it is ideal, and in the future, you will gain a mastery of the process, so that the result is a more uniform cloth-like texture.

Alan

 

Thanks for the ideas guys.
What I see is actually veeeery fine threads, not pronounced, but visible.
The thing that intrigues me is why some areas (the ones that have been 'dripped' or poured on) don't show any threads, but the other areas do.
PAR's comments about high resin to glass I understand.
I have just done another section today, and it has turned out the same. Its definitely not air entrapment, as this time I also used a ribbed metal roller before the peel ply, and in the peel ply process, the squeegee really forces the cloth onto the wood, and of course ensures a uniform and minimum depth of resin.
I guess it is the weight of cloth that makes it happen as PAR says. I dont feel like wasting a lot of epoxy by sousing the cloth all over before rolling it, just to get rid of a relatively minor effect. If I was doing something like some exotic brightwork, it might rate more investigation.
Still, dropping resin from 3 inches definitely makes for a better (visible) result than thorough rolling and working.
Maybe I should play with vacuum bagging a bit to see if that emulates the slightly higher application pressure (if thats what is causing the phenomenom)

The mystery continues ..

 

See this. http://duckworksmagazine.com/03/r/articles/glass/bottom.htm

Pericles

 

like others have said about you should see it is right on, if you cant you've used too much resin,,and does those spots happen to be on the top of ya sides? or on flat bottom?,, if its in a high vertical area its that the resin is "sagging" and running down to the bottom where it collects and becomes "too much" resin and you cant see any fabric

 

when you put the resin on ....you have to wait a bit before you spread it out thinly ...sometimes ..you are at the point where you think you should be spreading the epoxy around ...and the wood underneath the glass is still absorbing it ...what it sounds like is ...you put the epoxy on ...and where you poured it ..the wood underneath reached saturation point..the other areas ...where still drinkinng in the resin ...thereby " starving" the cloth...you really have to goop it on ...allow it to saok in ...and then thin it out...it just takes a bit more practice

 

if you haven't already ....read Ted Moore's " canoecraft" book ...he is pretty good about telling you the proper wetout techniques over cedar

 

If you can see the white glass fibers it means that they have not been wet out thoroughly. This is partly due to technique and partly due to the chemical treatment of the fibers. I have experienced the same thing with a particular glass cloth, vacuum bagging helps but does not eliminate it. The only way I can achieve a perfectly clear laminate with this cloth is with resin infusion.
My recommendation is to change to a different brand of cloth, get samples and test first.
But if you have already purchased all your glass then the best you can do with that cloth is to pre wet the surface first before you lay the cloth down and do not over work it.

Good luck
Andrew

 

I am fairly new to epoxy use but here is my thought, please correct me if I am wrong.The cloth will float so if your resin is slow enough to harden using the dry layup technique you speak of, the resin can go thru and float the cloth giving you the visable weave look (like you want) but be resin rich. The drips are staying on top because the surrounding cloth is being held down keeping it from floating in those small areas. If you see milky strands of cloth, they are not wet out all the way.

I dont know if the epoxy guys here would approve but my technique evolved to this: Wet the area with a thin coat of epoxy, let it kick and then put your cloth down. The tacky resin will hold it very well even in the corners and keep it from floating. Then wet it out. I used RAKA epoxy with slow hardner which is very slow giving me a long work time.

 

Sbklf, you've described the wet on wet method and it works well. Regular fabric doesn't float, but can be forced to do so if you apply enough resin. Other fabrics can float, which you have to be careful of, but regular 'glass doesn't naturally. If you see weave after the wetout, you've done okay, if not you've applied too much resin. Weave gets filled on the next pass of goo. Milky spots are a clear indication that you've got air or not enough resin. Work these areas again to remove the spots.

 

The difference between pot life and working time with epoxies can cause misunderstandings. Pot life is a standard test, common to all manufacturers of epoxies and determines the speed of the hardeners. An example would be West 105 resin and 205 standard hardener. correctly dispensed at 5 : 1 ratio and thoroughly stirred. The 100 g sample in the mixing cup will go off in 6 1/2 minutes at 25 degrees Celsius. At 18 degrees Celsius pot life is extended to nearer 22 minutes. With the same resin and 206 slow hardener, pot life at 25 degrees Celsius extends to 23 minutes and at 18 degrees Celsius, nearly 40 minutes.

However, the working life depends on what is done with the mixed epoxy. If it is poured into the roller pan the heat generated is dispersed and the epoxy says workable for much longer than the pot life would suggest. The viscosity of the epoxy is affected by heat, the warmer. the runnier! The greatest release of heat comes at the moment of gel and the thicker the film of epoxy, the runnier it is. This fact explains the mystery of runs. If too much epoxy is flow coated onto the glass cloth in an effort to fill the texture, pools of epoxy can form where the glass cloth has slightly floated off the wood surface below and they are not easy to see. The applicator goes for a break, the pools of epoxy heat up more than the surrounding areas and the runs form and then go off more quickly. Bugger!

The answer is more thin coats applied, wet on wet, as the underlying coat tacks off. Therefore, a slow hardener approach, as suggested by sbklf, can be counter productive, as the waiting time between thin coats is too long.

Hope this helps,

Pericles

 

Its been interesting to get some insights into the epoxy process.
I took a photograph of the effect to clarify what I was talking about.

Of some points, I am sure
1) The fabric has not floated off the surface.
2) There is no thicker layer of epoxy resin over the clearer sections.
3) The fabric was throughly wetted out.

I hope its not too hard to see in the photo, but there are sections where the silvery outlines of the fabric can be seen, and some irregular patches where they cannot. The sections where the silvery outline cannot be seen are where the epoxy was poured on, or ran down from the initial pour.
The bits where the fabric outlines can be seen, are where I subsequently brushed AND squeegeed AND rolled with a grooved metal roller.

To deepen the mystery, if I run my finger over the surface, the less visible sections appear slightly *lower* than the bits where the fabric is seen.

The bit that puzzles me is what happens to poured resin that the full brush on, squeegee and roll cannot do?

My best guess is that something to do with air entrapment occurs (I have repeated the process twice) and no amount of working removes the minute bubbles.

 

The minute bubbles might be out gassing, caused by warming epoxy poured onto cold wood. The wood is heated up by the epoxy and bubbles are created. The wood should be previously warmed with an infrared electric patio heater or a hot air gun (carefully).

Good luck,

Pericles

 

Hmm, no I have had outgassing, and thats much bigger bubbles - and the the fact that it only happens where the resin isnt poured is the key.
I am working on the theory that brushing the resin across the top of the fibres 'locks in' the air around the fibres.
Apart from infusion (as suggested) , I cant think of a way to force the resin right through the fibres. Thougn I have a big plastic bag of water that I am going to experiment with tommorrow.