My 1st time epoxying,.(fiberglassing)

[Chipper1959]

My 15ft Hiawatha got to the fiberglass stage this w/e and the actual laying down of the fabric went quite well. I really surprised myself. I even managed to do the stems without having to cut out any creases.
I'm using West Systems with the 207 hardener. The 2nd coat of resin left me with quite a few runs which I managed to sand out..(24hrs later). I had used a combination of a brush and a roller. I'm thinking I put it on too thick so I went easy on the 3rd coat, with a roller, and the weave was still showing...a lot. I just put on a 4th coat and I can still see the weave. I'm doing something wrong, obviously.
I'm wondering about the temperature in my basement....it's around 68 deg.

Any thoughts ? I included a picture of what it looks like after the 4th coat.

[fonz]

Hi Chipper. First off I don't feel the temperature of your work area is an issue. Before making an educated guess I would like some more information. Such as: How long between the first and second coat, did the first coat seem so soak into the wood and glass well, can you estimate how much of the second coat you may have removed by sanding out the runs ? In the picture I'm not sure if I am seeing the weave to badly or just a build up of epoxy because of the angle of the shot. Sorry I know it's a lot of questions. If I was to guess at this point I would look at the first coat.

[Chipper1959]

The time between the 1st and 2nd coat was about 24hrs...the 1st coat was no longer tacky. The 1st coat seemed to soak in well,(although it's my first attempt so I can't really compare to anything).
I didn't sand between the 1st and 2nd coats,(the 1st coat didn't have any huge runs). I only sanded the runs after the 2nd coat.
I looked at it this morning and it seems to have flowed a bit and hidden the weave a bit more but the flat bottom ,(horizontal), part is almost perfect, seeing as I didn't have to worry about runs. Down towards the sheer line, the weave really shows because I was afraid to put it on too thick where it got vertical.
I'm almost tempted to really slop it on, let it run, then simply sand everything smooth.

[fonz]

Hello Chipper, Just for future reference if you leave 24 hours between coats you must sand. To get a chemical bond with the epoxy the second coat should be applied 5 to 8 hours after the first coat of when it is no longer tacky which should be around that time. If you wait 24 hours you must sand to have a mechanical bond with the epoxy. Having said that you not sanding between the 1st and 2nd should not have caused your weave issue. If you can't feel the weave but only see it I don't feel more coats will solve the problem. Just like a blemish in the wood you can apply as many coats as you want but you will still see it. I still feel something in the first coat is the issue. If do apply more epoxy don't slop it on but use several light coats. Don't sand out your runs but use a cabinet scraper on the individual runs and lightly sand the remainder with 220. Just keep in mind every coat you add adds several pounds to you finished project. Don't get frustrated, you will do just fine. Good Luck!

[Chipper1959]

Thanks Fonz..

I was under the impression that the chemical bond would take place up to several days....and that the epoxy didn't cure completely until 5 or 7 days....(but then again...I'm a newbie).

The scraper idea is great. I had one which I hadn't really used much and decided to give it a try....the runs peel right off !

[wb9tpg]

...the runs peel right off !

That statement really worries me greatly. If you had a good chemical bond, I would not have it to peel off.

[Chipper1959]

I guess I should have phrased it differently..

The scraper removes the runs with only a few strokes, just as if I was scraping hardwood....nice curly shavings.

[Patricks Dad]

I was under the impression that the chemical bond would take place up to several days....and that the epoxy didn't cure completely until 5 or 7 days....

Not sure where you got this impression but I think it's very wrong. You should only plan on "Not" sanding if the prior epoxy layer is just past the tacky stage (a few hours). Over 8 hours or so, you should plan on sanding.

Please clarify your comment about the run "peeling right off"... if you really meant that it came off easily (as in the bond between the first and 2nd coat was weak) then there may be a big problem here. If you instead meant that "it worked really well" and the scraper was able to scrape it off easily (a thin layer at a time until the run was gone), then the bond may be OK. I've seen a 2nd coat applied to fully cured epoxy be "OK" (but I've never really stressed such a bond).

[Chipper1959]

I have the book "Illustrated Guide to Wood Strip Canoe Building" in which the author says it's safe to reacoat up to 3 days later without sanding. She used System 3 brand epoxy.

Here's what System 3 says on their blog...

"When this first coat is cured to at least a soft set tack free stage it can be recoated. Subsequent coatings applied at anytime between this soft set stage and 72 hours do not need to be sanded and will chemically bond.

Subsequent coatings may still bond well after 72 hours without sanding but the proposition gets riskier. An amine cured epoxy surface is quite alkaline and can react with any acidic material such as moist carbon dioxide or silicates. Further epoxy coats may not bond well to some of these reaction products. Sanding, in addition to providing some “tooth” for mechanical bonding, also cleans since it exposes new, uncontaminated surface. If in doubt, sand enough to kill most of the gloss."



As for the Scraping...yes, with a well-sharpened scraper, the epoxy works very well....I'm able to scrape a run off , in thin layers, with very little effort.

[Glen Smith]

But you used West System epoxy which does not have such a generous "recoat window".

[Patricks Dad]

I may have misunderstood your original post. I assumed you were using West System 105/207. Your last post referencing System 3 confuses me. I don't have very much experience with System 3 (I have used West System much more) so I can't comment on re-coat policies on System 3 (I fully trust your reading on that subject). But if you are actually using West System 105/207, I suggest you read their manual and follow their guidance rather than System 3's guidance.

You might look here: http://www.westsystem.com/ss/assets/How ... 0Part1.pdf

Of particular interest might be:

The mixture will become tack free about
midway through the initial cure phase.
While it is still tacky
(about like masking tape), a new application
of epoxy will still chemically
link with it, so you may still
bond to or recoat the surface without
special preparation. However,
this ability diminishes as the mixture
approaches the final cure phase.

Solid—Final cure phase
The epoxy mixture has cured to a
solid state and can be dry sanded.
You will no longer be able to dent it
with your thumbnail. At this point
the epoxy has reached most of its ultimate
strength, so clamps can be removed.
A new application of epoxy
will no longer chemically link to it,
so the surface of the epoxy must be
properly prepared and sanded before
re-coating to achieve a good mechanical,
secondary bond.

Under nominal conditions, the "Cure to Solid" time is listed as 10-15 hours (longer than I recall but certainly less than 24 hours). If you wait until it's just beyond tacky, you will be certain to have a chemical bond. 10-15 hours is probably a questionable wait time to avoid sanding. I've always followed the first coat with the 2nd and 3rd coats on the same day as quickly as possible and got the job over with...

Best of luck on the rest of your build (enjoy it!).

[Chipper1959]

I made the mistake of assuming that all epoxies would have the same basic chemical properties, as far as cure times are concerned.
I finally gave the entire boat a real good sanding with my RO sander and laid on 2 more coats,( 3 hours apart this time).....it's looking pretty good.

Thanks to all for setting me straight...