Trojan Boat Forum

I painted the bottom of my boat for the first time and noticed tiny pin holes every where,

It appeared that the previouse owner striped the haul down to the fiber glass .sanded smooth, primed and put twon coats of alblative one black and one red ,
there was no bubbleing what so ever in fact it needed only a light scuff , but I am wondering what the deal is with the pin holes
I have never seen that before



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A bit hard to follow this... but if I am understanding correctly previous owner had the bottom down to raw glass (for who knows how long), but it had pinholes in the gelcoat.... you sanded, primed, painted and all looks good for now... is that right?

If so, the holes were probably from osmosis blisters that occurred, then popped.

Over time the hull has absorbed water. Gelcoat is not waterproof, so water leeches through it (via the 'osmosis' process) and gets between it and the actual fibreglass/resin construction - this happens in all glass boats to some degree, but is worse if there is no bottom paint to help as a barrier coat. There is a chemical reaction that occurs between the penetrated water and the glass/resin/etc, resulting in a collection of fluid that is like a solvent or acid at a particular spot. The fluid collects, pressure builds, and acting as a solvent it softens the gel and you get a blister.

When a boat is hauled and given time to dry thoroughly, the blister may shrink and go away... but if pressure builds up enough the blister will pop, releasing the fluids that were behind, and leaving a 'pin hole' where the gel was dissolved or blown away. If the water intrusion and blister were big enough, you might end up with more of a crater than a pin hole - where the gel is gone and the underlying laminate has been dissolved.
Severe osmosis can affect the integrity of the hull (if it dissolves enough of the fibreglass/resin compound behind the gel), so severe blistering is usually addressed by grinding out blisters, filling the resulting craters, and re-gelling. Minor osmosis is expected on most older boats and isn't a problem.

Pin holes everywhere is better than craters everywhere, but if it was me I would be getting someone to check things out with a moisture meter to find out how saturated the hull might be... Water = weight = poor performance and gas mileage, plus possible integrity issues depending on how wet things are.

Painting is better than unpainted gel... if needed, an epoxy a barrier coat (such as Interprotect 2000) applied before painting can help seal the bottom and reduce future water penetration issues.

captainmaniac wrote:A bit hard to follow this... but if I am understanding correctly previous owner had the bottom down to raw glass (for who knows how long), but it had pinholes in the gelcoat.... you sanded, primed, painted and all looks good for now... is that right?

If so, the holes were probably from osmosis blisters that occurred, then popped.

Over time the hull has absorbed water. Gelcoat is not waterproof, so water leeches through it (via the 'osmosis' process) and gets between it and the actual fibreglass/resin construction - this happens in all glass boats to some degree, but is worse if there is no bottom paint to help as a barrier coat. There is a chemical reaction that occurs between the penetrated water and the glass/resin/etc, resulting in a collection of fluid that is like a solvent or acid at a particular spot. The fluid collects, pressure builds, and acting as a solvent it softens the gel and you get a blister.

When a boat is hauled and given time to dry thoroughly, the blister may shrink and go away... but if pressure builds up enough the blister will pop, releasing the fluids that were behind, and leaving a 'pin hole' where the gel was dissolved or blown away. If the water intrusion and blister were big enough, you might end up with more of a crater than a pin hole - where the gel is gone and the underlying laminate has been dissolved.
Severe osmosis can affect the integrity of the hull (if it dissolves enough of the fibreglass/resin compound behind the gel), so severe blistering is usually addressed by grinding out blisters, filling the resulting craters, and re-gelling. Minor osmosis is expected on most older boats and isn't a problem.

Pin holes everywhere is better than craters everywhere, but if it was me I would be getting someone to check things out with a moisture meter to find out how saturated the hull might be... Water = weight = poor performance and gas mileage, plus possible integrity issues depending on how wet things are.

Painting is better than unpainted gel... if needed, an epoxy a barrier coat (such as Interprotect 2000) applied before painting can help seal the bottom and reduce future water penetration issues.

The previous owner did the barrier and 2 coats of paint . no signs of blisters of any kind no cracks and no signs of blisters that have popped and the pin holes are filled with the three coats the aside from the pinholes it is in great condition . you can tell when a bottom has been scrapped and painted this bottom was obviously stripped down to the gel coat previously,
I don't see any signs of trapped water or delaming of any kind it seams to be more on the surface,
This however might dictate how i will paint it in the future . my thought is I will stay with the soft ablative paint as opposed to a hard paint so it wears back off each season with less paint build up and potential blistering down the road .
I think

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contact the manufacturer of the paint you used to paint the bottom of the boat, it almost sounds like you have incompatable paints, and there is teflon / silicone in the exisitng paint.. (high speed racing paint)
Ask the MFG what types of paint yours is compatable with.

gettaway wrote:contact the manufacturer of the paint you used to paint the bottom of the boat, it almost sounds like you have incompatable paints, and there is teflon / silicone in the exisitng paint.. (high speed racing paint)
Ask the MFG what types of paint yours is compatable with.

Na its below the paint there is no capability issues the paint has no signs of bubbles peeling or separating has excellent bond and is in very good shape . I believe its inter protect primer and to coats ablative , that is done by the book from what i know I will try to post some pics today
one thought I have is maybe they re gelcoat the bottom and there was air bubbles that popped not sure since I did not do it ,

usually from what I have seen in the past is when bubbles from osmosis occurs they blister a bigger spot around with some spider cracking this is nothing like that ,they are perfect small pin holes .


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I have poweder coated equipment in the past that somewhere in the process of manufacture / modification there was WD-40 or some sort of silicone spray used as a cutting fluid or cleaner, and when the part went into the oven after the poweder was applied, the part would be covered in pin holes, like you are describing. I was told by the powder coat company what was going on, while bottom pain and powder coating or two different animals, there are similarities.

If the previous epoxy barrier coat was applied correctly, which it sounds like it was, and the previous bottom paint had no issues, and the pin holes occured only after you painted the bottom, it would make logical sense that the problem lies with incompatability or there is an issue with your paint, did you check mfg date?. was it mixed thouroughly, did you add Tributyle tin?, did you wipe down the bottom thouroughly prior to painting, if so what with? paint thinner takes forever to dry and is "oily" , was there oil or wax on the rags, sand paper or rollers?

I know these all sem obvious, but sometimes it's the most obious that we miss, I know I have.
I think I would still contact your paint manufacturer and ask them, I know a guy who worked for Interlux and he is a wealth of paint knowledge.

this is after my first coat all these pin holes where there before I did no scraping only a light sand as you can see the the hull is smooth no signs of chipping paint ,blisters or anything like that . just pin holes
this is at 20x zoom so they look bigger that they are






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Now that is just wierd. They almost look like punctures. looks like it was blocked on a bed of nails!

Are they very deep? When you say pin holes are they really that small? I know photo scale can be deceiving but some look quite deep to me and using your 20x guide they seem larger than I would expect pinholes to be.

I have to agree they look more like damage rather than voids due to trapped gas bubbles which is often the cause of pinholes in gelcoat. Of course if it was sprayed on too quickly then you could end up with large pinholes after the gel set.

ready123 wrote:Are they very deep? When you say pin holes are they really that small? I know photo scale can be deceiving but some look quite deep to me and using your 20x guide they seem larger than I would expect pinholes to be.

I have to agree they look more like damage rather than voids due to trapped gas bubbles which is often the cause of pinholes in gelcoat. Of course if it was sprayed on too quickly then you could end up with large pinholes after the gel set.

that is exactly what i was thinking


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Is there any regularity to the pattern of them, or just completely random? If there is a pattern, any chance it is a sign of a previous repair? If random, I would have to say either the hull has been on the ground / gravel (but would expect to see even more markings on the edges of the strakes) or stick with my original diagnosis of popped osmosis blisters.

However, not being a salt water guy I don't know, but could this have anything to do with damage from barnacles ?

captainmaniac wrote:Is there any regularity to the pattern of them, or just completely random? If there is a pattern, any chance it is a sign of a previous repair? If random, I would have to say either the hull has been on the ground / gravel (but would expect to see even more markings on the edges of the strakes) or stick with my original diagnosis of popped osmosis blisters.

However, not being a salt water guy I don't know, but could this have anything to do with damage from barnacles ?

i have never seen osmosis blister like that , perfect little holes with no damage around it

I see a lot of boats never seen this

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1) Are you sure these holes go all the way to your hull and are not in just the paint ?
2) How many layers of paint ?

I bet you're looking at a bad prep job for the paint that's on the hull now. I would sand real good, and clean real good and re-paint. Haul this fall and check it again, My reason for this thought. If you have trouble with the gel-coat and need to seal it, the boat will need to set for a month or more out of the water to dry out. and if no troubles clean the hull and stick it back in.

iT LOOKS TO ME LIKE SOMETHING WAS ON THE OLD PAINT/HULL that repelled the new coat of paint in the spots where it was. Almost like drops of something was splattered on the old paint before you put the new coat on. Gettaway was on the right track with the silicone theory, tho I am not sure of the cause . I have seen contaminants make surface imperfections similar to this in other painting applications. I would put another coat on and see what it looks like.

alexander38 wrote:1) Are you sure these holes go all the way to your hull and are not in just the paint ?
2) How many layers of paint ?

I bet you're looking at a bad prep job for the paint that's on the hull now. I would sand real good, and clean real good and re-paint. Haul this fall and check it again, My reason for this thought. If you have trouble with the gel-coat and need to seal it, the boat will need to set for a month or more out of the water to dry out. and if no troubles clean the hull and stick it back in.

I got these statements of the interlux site


Some blisters occur for reasons other than osmosis. They are often evident as a rash of small pinhead blisters or swellings, either locally (often around the waterline) or over the entire underwater area. These blisters are hard and difficult to break and when broken open will be dry, with no odor evident. The likely cause is air voids. This is not a serious problem, but hull moisture levels should be checked

I believe the above statements holds true pin holes created by reasons other than osmosis and I believe also it is not a seriouse problem because judgeing the condition of the paint that was on there and a couple of spots I sanded thru ,
I have determaind their recomended procedure was followed , wich is interprotect primer followed by 2 coats of paint, some body spent a lot of money and time getting this hull to be in the condition its in , my friend just sanded off all the paint of his 81 f32 and trust me it was no easy choar

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