RIB outside print through

Yersterday I released hull from mold, found the surface is very smooth and glossy. I put the hull back to mold then laminated the RIB and keel on, just now I released the hull again found some print through and small distortion on the RIB outside
Who can tell exact reason ?
I am thinking maybe I mixed too much MEKP, about 3.5% . all polyster resin

 

Polyester resin shrinks; glass fibers do not. There are a few ways to minimize this--kinda late in the game for you, I know. Some guys skin the gelcoat with veil and minimal resin. I sidestepped printthrough by using vinyl ester (shrinks less than polyester), and I mixed in plastic microspheres to displace some of the resin. Microspheres don't shrink, either. And I used only as much resin as necessary to wet out the 'glass. If it doesn't take you at least 30 seconds with a roller to wet out all the dry spaces, you're using too much resin.

Of course, you're already screwed. Don't be in too big a rush to sand it out--it's gonna keep shrinking for awhile. Make it a winter project. Or just live with it. I've seen some awful printthrough on pricey production boats.

You'll notice resin shrink where pieces are bonded together, too, like where seats are bonded directly to the sides of rowboats, or the flotation chambers are bonded into the ends of canoes. Where there's extra resin--including extra layers of 'glass--there's gonna be shrink. If you look at the outside of these boats, you can see exactly where the extra 'glass was laid on the inside.

 

OH dear'y me !!

Hot brews !!!! Never make hot brews for any reason at all its really not work the heart ache and disapointment !!
Using polyester with 3.5% is a hot brew in any country .Check with you resin supplyer for the type of catalyst to use and the range of the Ratio's that is recomended to work within !!!, 1% to 1.5 % is normal but its not the whole range that can be used .
The amount of glass (number of layers ) is another factor , High catalyst with a single thin layer like 225 gram csm is not so bad but 4 or more layers of 600 gram csm glass at a high catalyst will produce lots of heat and massive amounts of shrinkage .
Have to think a bit more about what you are doing !!!!
The resin gets hot and shrinks plus it looses some of it strength because it goes brittle and breaks more easly .
On the other end of the scale not enough catalyst the resin stays weak and semi flexable and no mater how you try to bake or heat it, it will never reach anywhere near its potentual strength and hardness !!.
Most polyesters are some where in the range of .75% ranging through to 2.25% tops !! reguardless of what catalyst you are using !

Vinylester is differant animal and has a much smaller range between the hi"s and low"s.

Always use scales and weigh your glass ,then you know how much resin you will need !! use a accurate measure for your catalyst will be needed !!, do this always and your problems will all go away !!

Learn from your mistakes ! you have seen what happens when you make hot brews ! Its really just not worth the hassles !!
OH DEAR !!

 

Don't use a hot mix. Let skin coat cure somewhat before following with hull laminations. Let hull laminations cure somewhat before installing reinforcing structure. Don't take the product out of the mold before putting in the reinforcements. Make the hull thick enough to resist print through. Don't have hard edges against the hull. Stagger and layer all tabbing to spread loads. Maybe switch to a better poly resin. Don't cure in the sun or high heat.

 

How many layers of glass and what type did you use on the hull and then the same question for the other components you glassed in later?

Like others have said 3.5% is far above the recommended amount, typically half that would be more than enough.

It also depends on the type of resin used, not necessarily meaning good or bad, just the correct one for the job. Do you know the type (ORTHO, ISO, VE, or one of these blended with DCPD)?

 

Should I sand more ?

I have repaired the print, sand with ＃1000 sandpaper then ＃1200, polish with 3M. looks good
But my friend said I should sand to ＃1800 sandpaper, that will be perfect
Should I do that ?

 

The better the shine the more defects you will see !!
I personaly do not like shiney boats because it always reminds me its been repaired for some reason
Just match the same shine as every where else !!

 

fade ?

My friend said if only sand to 1200 the gelcoat will fade easily, sand to 1800 will be much better.
I am really confused :?:

 

As for going to 1800 grit paper, it sort of depends on the gel coat, the buffing compound, buffing pad and quality of the sand paper.
On some gel coats you won’t see a difference after 1200, so going further won’t help. The buffing compound needs to a very fine grit too, a coarse compound won’t yield a high gloss, you need to use the right buffing pad with the compound too. Uniformity of the grit on the paper will also affect the results.

 

What a load of rubbish !! never heard of anything so ridiculous in all my life !!
To much home brew or wacky bac-y maybe !!
Honestly how can using a finer sand paper stop gel coat from fading !!

 

....hot, gees mate, you are lucky it was not buggered.....why in the world did you feel the urge to double the manufacturers spec......please explain.

....and the gelcoat certainly will not fade quicker no matter what grade you dsand with, however maybe you misunderstood what he was saying, in that the lustre would mayve different, showing an apparent "fade" in the gelcoat.

 

About polishing:

Use whatever system your supplier can recommend. Most systems have a nice schedule of what the sequence should be.

In general, the finer you sand, the less you have to buff. The courser you sand, the more you have to buff, probably even using 2 or 3 different buffing materials (course compound, fine compound, glaze compound, or whatever your supplier calls them)

About your print through:

Adding a lot of MEKP curing agent is not a good idea. Most resins are targeted for a 1%-2% MEKP level. There is a lot of phlegmatiser in MEKP, so that can cause trouble. If you need faster resin, ask your supplier for faster material, or add a bit of cobalt solution. (and again, this usually contains phlegmatiser, so I like the 6% or 10% cobalt solutions over the normally available 1% solution, as you only need 1/6 or 1/10 of solution.) Your supplier should be able to help you with the amount needed, but as a general guideline 3% of a 1%solution is added in production, and you can up that in 0,2% steps. (divide by 6 or 10 if you can source high-concentration cobalt)

Back to your printthrough:
Polyester can shrink for a considerable amount of time after initial cure. Some hints to prevent shrinkage:

-use different resin. Some shrink more then others. So called "low profile" resins shrink less.
-use recommended and conservative catalyst and curing agent levels. If it takes half an hour more to cure, so what?
-use different curing agent (MEKP). Check the availabilty of these in your part of the world. MEKP is not just MEKP, it has a great influence on curing.
-use the right thickness of gelcoat. 0,7mm is recommended, and is usually reached with 2 layers of rolling. (ask your supplier for a wet film thickness gauge, and read my comment on them below this post). Check regularly with the gauge.
-use a barrier coat between gelcoat and laminate
-use a veil between gelcoat and laminate
-use a skincoat between gelcoat and laminate
-use a light CSM, low tex, then a layer of Lantor Soric TF (print blocker), and only afterwards your laminate.
-make sure your gelcoat, skincoat, or whatever you use to block print, is cured well enough to actually work as a print blocker. It really needs to have developed a good cure, before you can throw in your laminate. A barcol hardness meter helps to determine cure development. (although it has its limitations)
-be conservative with your layup, so no thick layers in 1 go. This does not count for infusion, where surface quality can be a challenge. Although high fiber volume ratio helps reduce shrinkage.

A research institute in NL did a couple of tests, and they found out that all of the above helped reduce print. They also found out that combining above options even reduced print more. They must be geniusses...


Comment on wet film thickness gauges:
I have had the situation where a client was experiencing problems with his gelcoat. I asked if they checked film thickness. They were on the high side, but not so high that it could cause problems (shrinkage and prerelease). They showed me with their wet film thickness. We experimented a bit further, and at a certain stage the gauge was gone, so I took one from my collection (I have several, from several gelcoat manufacturers). It showed the gelcoat was about 25% too thick! So I checked with other gauges, which showed the same.
We then traced the gauge used by the company (it was hiding under a piece of cardboard) and it showed 25% less. It was given to that company by another supplier of gelcoats. These guys must have seen a dramatic increase in gelcoat sales! So cross check your wet film thickness gauge...

As a complete side-step, I once checked a vacuum bag with a vacuum gauge. There was a leak somewhere, but I could not find it. Check the whole bag for mor ethen an hour, using a leak detector. It took a while to find out the vacuum gauge was leaking...

Things like this you just need to encounter once, to be able to react quickly on it.

 

not fade buy only hide.

This is my friend's point of view--------- after sand to ＃1200 paper use a magnifier you will see much very small scratches, those scratches will hide dust and let the gelcoat looks obscure. Dark blue will become to paleness color. Sand to ＃1200 surface will like a cloth, sand to ＃1800 surface will like a mirror,dust will hide cloth color but never hide mirror. Is this right :?:

 

Your friend has a problem !!
1200 buffed gives a magnificent shine once its waxed and even with 1800 or 2000 makes no differance .
Why are you wasting time on such a trivial matter .
The shine of a mould increases as time goes by as coats of wax get added and polished each time .
Some old moulds have a chrome shine look about them . if they need to be repaired its impossible to get back to that shine so the whole mould meeds to be dewaxed , recut and buffed .
I spent 2 years doing mould maintinance and repair work for a shower manufacturer and there moulds were pushed to the limit with 2 pulls off some of them 6 days a week almost every week of the year .