Pinholes in Gelcoat

[jay]

Policsing my hull yesterday i discoverd a rash of tiny pinholes in the gelcoat above the water line - seem to be all over the boat at a density of 4-5 per sq foot. No idea how long they have been there as this is the first time I've been ths close to the hull.

Any ideas on whats causing them. Are they going to be a problem - and if so what I can do about them in the 3-4 days before I relaunch?

PS the glecoat is 29 years old

 

[oldsaltoz]

G'Day Jay,

Pinholes in gelcoat can be formed if too much glass was applied with the chopper gun causing high temperatures, others are caused by poor application of the gelcoat to the mould, and again can be made too hot so small bubbles form. After almost 30 years of weathering and no doubt a polish or two, you may have worked your way to the voids.

I doubt there is a quick fix that could be applied in the next 3 to 4 days that will last long. However it is also doubtful that any major damage will result in using her for another season and planning a proper fix when you lift out next.

Anything you apply as a temporary cover will have to be removed later, and if it gets into the voids it may be difficult to remove as part of the preparation for the long term fix, depending on what you use may do more harm than good, like applying a coat of polish that has a silicon base would make it almost impossible to treat later without some major chemical silicon remover.

The best looking cure is a 2 pot polyurethane coating, that will last for many years.

Avagoodweekend.

 

[boatmike]

If they are above the waterline and not accompanied by blisters they have probably always been there and after 29 years should not be a cause ofconcern.

 

[heerenleed]

As Oldsaltoz points out, they have probably always been there. It is a well known fact. We repainted an elderly hull twice. The forst time on our former boat, a Nicholson 35,and two year ago on our actual boat, a Nicholson 48. When repainting a GRP hull, you always need to use a special primer to fill the pinholes. After it has cured well, you sand this off completely (rotten job) but it will stay in the pin holes. They only are a problem if not well filled before applying new paint. The trapped air will eventually cause the new paint to blister. If you do not plan to repaint, leave them as they are

happy sailing

 

[jay]

thanks gents - will tell swmbo to get on with the polishing and worry about it when we repaint!! /forums/images/graemlins/smile.gif

 

[JAYEL]

Whist polishing the hull yesterday, just above the waterline I noticed a rash of tiny (about the size of a pinpoint) spots in the jelcoat. I only noticed this because these tiny points were picking up the polish I was applying. Is this the same phenomenom or is it the start of the dreaded Osmosis? Your thoughts please.

 

[oldsaltoz]

G'Day John,

If your trapper 300 is more than 10 years old there is a very good chance it's the same thing, but as I said it's not going cause any major failures, so don't worry too much.

When you do decide to fix it just make sure all the polish is removed form the pin holes or your new finish will develop blemishes.

A good pressure clean or steam clean will remove most of it, then a wash with wax and silicon remover followed by another pressure clean does a pretty good job, check for water beading on the surface to show any contaminated areas still left.

Do a second check after the first coat of primer as well and you should be ok.

Avagoodweekend.....

 

[Avocet]

I had exactly the same thing - a small rash just above the water line. None of them were big enough to have any fluid in and most of them were open anyway. Interestingly, I tried sanding a few out and the gelcoat seems to be quite thick - about 3mm in places. None of the blisters / pinjoles were more than about 0.5mm deep. As they were only about 1.5" above the waterline, I just extended the epoxy that I used below the waterline to cover them and now paint a boot top line in that area.

I do, however, have a big problem now with pinjoles well above the waterline. Again, these are all shallow and all of them are open. In places, there are very fine cracks connecting them together. I think these might be ultra-violet damage for several reasons:

1. They are mostly in areas that get a lot of sunlight. i.e. on any vertical or upward facing surfaces. As I go down the topsides towards the counter under the stern, the gelcoat looks like it came out of the mould yesterday.

2. They are worse on the starboard side -which on our berth is the side facing the sun for most of the day.

3. There are none at all under a small area which used to be covered by a stainless plate for some drying out legs.

4. In one place, there is a small chip missing out of the gelcoat on the rubbing strake. The chip (only about 1/8" diameter) is right in the middle of three of these hairline cracks joining two pinholes and it has gone right through them and into fresh gelcoat again.

4. The hull has never been painted and is 33 years old.

I'd be grateful for anyone's thoughts on this - especially Oldsaltoz! I'm thinking of painting over a couple of them for a few inches in an unobtrusive area this year just to see if they show through the paint at the end of the year. I really can't face sanding through all of them!

 

[JAYEL]

Thanks for that re-assurance Brian, I shall have to keep an eye on it and monitor further developments

 

[Kurrawong_Kid]

I too have noticed these on my boat. I wonder if its anything to do with too vigourous attack by pressure washer? If there were very small voids behind the gelcoat a modern pressure washer could implode them and wash the evidence away! The thing tha ts puzzled me is how regular the pinholes are in size, not a ragged edge to be seen. I stupidly tried to fill them with gelcoat which did not match, so now I've a patchwork quilt of a boat!

 

[oldsaltoz]

G'day Ian,

If you only have a few pin holes in a small area you plan to coat; use a small tip on a Dremal or small drill bit to clean the holes, just deep enough to clean out any contaminants, apply a mix of epoxy and closed cell balloons or spheres and let it cure overnight, sand with a 250 grit over a block (it's soft and very easy to sand).

You are now ready to coat it.

Andavagoodweekend.......

 

[DrBob]

In my previous life, I spent a number of years as a development chemist for one of the big UK resin manufactures - and one of the areas I worked in was gel coats. Probably 25% of UK built boats at that time used our gel coats. One of the biggest challenges was to get good resistance to water, good response to pigment (ie good uniform colour from the solid pigments) and bubble release.

I am not sure oldsaltoz is right in his theory of heat causing the bubbles - the action of brushing on the gel coat causes the bubbles - the trick was to make sure they came out quickly before the curing increased the viscosity so they couldnt come out.

Any way - bottom line is that a badly formulated gel coat - or perhaps one with extra catalyst added to make it cure faster - could have bubbles in the layer which over time will be seen as the weather / polishing / etc exposes them. I would blame the resin manufacturer rather than the application.

Any way - oldsaltoz is spot on with the remedy.

Dr Bob

 

[oldsaltoz]

G'day Dr Bob (Andy)

<<I am not sure oldsaltoz is right in his theory of heat causing the bubbles - the action of brushing on the gel coat causes the bubbles - the trick was to make sure they came out quickly before the curing increased the viscosity so they couldn't come out.>>

I presume you meant before the curing decreased the viscosity Andy?

<<Any way - bottom line is that a badly formulated gel coat - or perhaps one with extra catalyst added to make it cure faster - could have bubbles in the layer>>

A common example of this is pin holes on the corners of cabin tops and the edges of gunwales; because gelcoat has to be applied a lot thicker than paint it tends to flow down and collect in pools and the extra depth of resin causes more heat to be generated, thus more bubbles form in these areas.

Even when gelcoat is sprayed on areas that are 'U' or 'V' shaped are sprayed from both sides to get coverage and some will flow to the bottom, as you say Andy any extra catalyst added will only make the problem worse.

In the early days of fibreglass boat building 'some' manufacturers would start spraying with a chopper gun as soon as the gelcoat was tacky, this would not only trap any heat in the gelcoat, but add to it if the chopper gun was set up with a high catalyst setting or the coating was too thick; and the problem of too much product in 'U' or 'V' shaped areas also applies to the use of chopper guns.

As we all know many older hulls were very thick and heavy in the early days of glass boats and the use of chopper guns, this improved when rope feed for chopper guns has a dye added about every 3 feet of rope, this gave the operator some indication of how much material had been sprayed on a given area, by covering say a square metre (or yard in those days) and moving to the next square metre as soon as the red or blue strands showed.


Avagoodweekend............

 

[Avocet]

Thanks for that Oldsalt! Unfortunately, although the pinholes are relatively few, the cracks connecting them cover the vast majority of the topsides (at least on the port side). I'd like to e-mail you a few photos for your opinion if you wouldn't mind....

PM me if that's OK!