Help with Print-through Problem In The Hull

Hi, Everybody:

We have one boat just finished and shortly after its completion print-through in the hull turned out as a serious problem.

We worked very hard to figure out the solutions to the print-through without any success in the end. It seems that what we can do only was to water sand the print-through in hull which we know is only a temprary remedy.

Does anybody know how we could avoid the print-through in the hull during the lamination and construction?

Thanks a lot for your help in advance.

 

Hi genuineyachts,

The print through could be from the mold, the hull outer skin, the hull core, bulkheads/stringers, incorrectly applied resin/gelcoat or a combination of these.
Identifyng it's cause depends on what it looks like. Or possibly an obvious error -ie a heavy laminate hard against the gelcoat/paint.

Your best bet to a remedy is probably to have your suppliers look at it.
(unless you want to publish to the web sensitive (company) information like your laminate schedules, build prosesses, times, temperature's etc)

Rob

 

I know of builders who use a non-woven fabric to prevent print-through.
This is one brand I know, but there are more ofcourse:

http://www.lantor.nl/composites/fr_comp/frame_comp.html

 

Hiya

Did you use a "plastic/foam core instead of basla.......

 

Hi, Darren,

We use one kind of foam core called Ariex from Swizertland and any problem with it?

Yours truly
George

 

Hiya George

Sorry but I've never heard of it but we have had a lot of trouble using everything except balsa
We have had to flatten back and repolish the whole topsides of two 95ft & one 108 ft boats

Regards
Darren

 

Print Through

I doubt that any problem with print through has anything directly to do with what core you are using (except for possibly wider kerf cuts in the foam), but is a product of the resin system and it's exotherm profile. If the resin system you are using has a fairly high exotherm (say, 350F or higher in 100 gram mass) and you laminate everything at once, the high heat during cure will cause excess shrinkage of the resin, resulting in print through of the fibers or core material (the second especially if the kerfs are open wide and filled with resin).

As mentioned earlier, check with your resin supplier as they should have extensive knowledge on this subject.

 

I beleive that he is talking about Airex not ariex.

http://www.baltek.com/contactbaltek/contactbaltek.html

 

It's not a problem with the core. It's a problem with the resin (maybe too catalysed) wich shrinks. In the mold, when the gelcoat is tacky, a light chemical glass mat must applied, wetted and cured again until almost dry, very little tackying,: this screen will control the print out.

In molds, it's better to use very little catalyser (peroxyde or other) as the resin, having a small surface for cooling compared to its mass, may become too hot, and may cure too fast with a lot of shrinkage.

Ask your provider what resin is convenient, and what are the ratios of accelerator and catalyser when making a thick laminate in mold. Maybe, In tropical climate, you'll have to think over an schedule permitting the cooling of the composite between the layers, but assuring a good chemical bond.

For the actual hull, let it cure 2 weeks, until the chemical reaction is done at 90 and some %. After it's a big job: sanding of the gel coat, laying a light mat, light sanding , filling, application of a new gel coat. Long term results are not guaranteed.

 

Ilan Voyager, we meet again. Your advise on preventing through-print is correct (of course...). But your talking about polyester/vinylester. Epoxy should have no shrinkage and therefor no through-print. Should, I say. Because in fact it does. Especially on dark hulled boats.
We just finished a super lightweight 35' racer, using only about 5 kgs of filler on the hull (epoxy) and sanding of a lot again. It is a very nice boat, but on hot days the outer glass mat (woven roving) of only 150grams is printing through the blue paint a little.
The only way to prevent this is to use a little more filler (gelcoat thickness - 600gr/sqm) and not to sand off too much. Extra layers of very fine woven mats on the outer skin also helps.
If you want to build as light as possible it is unavoidable to have some through print.

Do you agree or do you have a good solution ?

Lucas

 

Epoxy print through..

I believe what you are seeing with a dark colored epoxy hull is that the surface temperature is exceeding the epoxy's Tg (glass transition temperature), not an issue with shrinkage. This is a fairly common problem with epoxies on large non-post cured parts (assuming that it has not been post cured). If the surface temp of the hull exceeds the material's Tg, the epoxy will become soft and allows the fibers and in many cases the core material to print through..

 

AVMAN, I reckon it is not shrinkage indeed, as this should not really be possible with epoxy. My guess it has to do with differences of expanding in glass and epoxy. (your Tg's ?) There also is a big difference of expanding between lightweight fillers and finishing (heavier) fillers. And even between thin an thick layers of the same type of filler.

But the boat has been postcured, though in an economically interesting way. We put it outside in the sun for several days. Getting the hull temp up to 45 °C for a couple of hours every day (average temp per day was about 35 ° C for 7-8 hours).
There is no sign of through print on normal days, probably because if this postcuring , but midsummer on hot days there is (very fine, but visible when looking closely).
By the way, the epoxy on the outer skin is a special one for this use (dark hulls - higher temps) and should do the trick. But apparently you still need a little more finishing filler than 0,5 mm to really cover it.

 

...If I am getting things right,,you have standard gelcoat with an epoxy build.If this is the case,,it's probably shrinkage in the gelcoat itself--there are vinyl-esther gelcoats,which reduce shrinkage substantially.,not to mention better bonds-which are also at issue when building epoxy over gelcoat.

 

Hi Lucas,

I've never experimented myself this problem as all the hulls we have built were in colors like pearl.

The print out comes from softening by the heat of the epoxy resin. It's a well known and old issue with dark color hulls.

With room temperature curing epoxies, the softening may happens at temps as low as as 50 celsius degrees. Post curing (specially at low temps) has no effect; the purpose of post curing is to get immediately the 100% curing of the resin (that last weeks if the temps are low), but won't change the inherent characteristics of the resin as high temp softening.

Solar post curing may be nice but it not insures an even temperature on and in the hull. Even the whole structure may deform is the boat is kept in a very hot hangar during a long time. I'ts similar to the deformation of wood by a stress applied during a long time (look at the old roofs...no more straight)

It's good to get all the characteristics of the resin you'll use.

The solutions range from very expensive to cheap:

- High modulus resin which has to been cured in oven at least at 90 degrees celsius.
- Special ceramic paints.
- Painting the hull in a light color like white...

Dark colors may rise the temperature of surface hull to 90 degrees locally... it is not good on any material.

Look at the pics of high composite multihulls (mainly french) ; almost all are painted in light colors. We have never used gelcoats of any kind on epoxy boats (too heavy) : finishing with a complete line polyurethane bi component and epox primary.

 

Seamonkey, no we never use gelcoat on an epoxy boat ....

Ilan Voyager, thx for the reply. Just to update you on the European fleet (west & north) nowadays about 25% of the sailingyachts are blue. That's what people want ...
We have built several and that's the reason we have been using this special resin for this purpose. Our supplier states that the used epoxy resin and hardener will not soften under 70° C.
On a sunny day in summer the hull acumulates heat, but not exceding 45° C. The foamcore (Divinycell) should not be heated higher than 70 when postcuring. So 90 is out of the question here. The 'sunny post-curement' has been timed to last no longer than 48 hours over 6 days. No rooflike deformation..... (which comes from drying out unevenly)

Still, it is strange that there is so much (uneven) expansion in epoxy filler (the thicker the more it expands). And there are plenty of very dark hulled yachts in Europe that were built in epoxy (wet), without post curing. So .... ?

The boats with an epoxy layer 'as thick as gelcoat' (that means 600gr/m² evenly applied, not actual gelcoat, Seamonkey) seem to have no throughprint.

See ya
Lucas