Something i had not seen for long time !!

Discussion in 'Fiberglass and Composite Boat Building' started by tunnels, Jul 12, 2012.

  1. tunnels

    tunnels Previous Member

    Anyone seen this in there gelcoat before ?? usually starts as a patch thats has a strange look about it !
    So first thing is to polish it !!then the cutting compound comes out but still doesnt come off just gets a little more noticable !so 1200 sand paper and another buff and oh S*^t its even worse than before !!,
    It was a small patch now its grown in size and you begin to see even more the more its rubbed .
    Where did it come from and what are some of the causes ??

    Its hard to impossible to see on white or very light colours.things have got better over the years and i have not seen it for long long time!!
    Was quite common to see this years ago , you cant sand it out and if you know what it is better to take a walk and leave alone .

    I did a twiddle on the photo program to enhance and highlite so could be seen easyer ! that why the colours are differant in each photo ! its actually a dark brown !!.

    Attached Files:

  2. davhill
    Joined: May 2012
    Posts: 20
    Likes: 3, Points: 0, Legacy Rep: 28
    Location: Massachusetts

    davhill Junior Member

    Looks like a thin spot in the gelcoat, letting matt show through. Polishing just makes it thinner and brings out the under layer even more.
  3. garrybull
    Joined: Nov 2010
    Posts: 508
    Likes: 16, Points: 18, Legacy Rep: 143
    Location: portsmouth england

    garrybull Senior Member

    not sure if thats the mat showing through but it could be air bubbles that were in the gelcoat.

    it will show up more when you polish it as the polish will get in to the tiny holes and then you can't get it out.

    is the finish still smooth or can you feel any little holes in it?
  4. tunnels

    tunnels Previous Member

    Not even close with the guessing .

    Gelcoats are interesting to play with and like i said i have not seen this in many a long day . I would say not many of you have ever seen it before either !
    With Older gelcoats happened now and then but with time and constant improvements with products and spray equipment its hardly ever seen these days . Some of the old hands that are still alive should be able to recognise it straight away !
    theres about 4 main causes of this problem and things we do every day believe it or not !.
    Again it almost impossible to replicate to show anyone , its the reason i carry my camera all the time as you only get one chance to see these things .
    Keep guessing !! its not thin gelcoat its the opposite !!Hint hint !!but there are other casues as well that contribute !:confused: back this afternoon !.
  5. masalai
    Joined: Oct 2007
    Posts: 6,823
    Likes: 121, Points: 0, Legacy Rep: 1882
    Location: cruising, Australia

    masalai masalai

    Hi tunnels, set your camera to "macro" which conversely means "close-up" and zoom as much as possible with as small a shutter opening as possible (to achieve some depth) - to my tired eyes, it looks like tiny bubbles in the surface and just below the surface?

    Is that your hand visible and reflected in the third image? - - set some lights 'behind your ears' move around to fairly close to 10degrees to the surface, bit of trail & error, to minimise the light reflected onto your hands and still achieve greater definition for the camera (turn the flash off)...

    Certainly got me going and curious... My feeling is that garrybull is on the mark... My guess is either very fine (not readily visible to inexperienced workers) dust or water condensation settling on the gelcoat but before the glass was laid up?
  6. tunnels

    tunnels Previous Member

    good for you

    Good guess and you are on the right track it looks like tiny bubbles in the surface and just below the surface?
    They are not only on and close to the surface but ususally all the way through ! so when you polish and sand it gets worse !!
    Whats it called ---------??? any one ??
    and what are the most common causes ?? -------any ideas !! come on think alittle ! how well do you know the materials you use !!! how well do you understand them ??
    if you do this ,that will happen!, and if you do that ,this will happen ! come on !!

    Yes i had the sun behind me and it is my fingers you can see the camera was about 15 mm off the surface to get that picture , but i did play with it on the computer to make it standout more and easyer to see !!.

    Good for you !!:D
  7. masalai
    Joined: Oct 2007
    Posts: 6,823
    Likes: 121, Points: 0, Legacy Rep: 1882
    Location: cruising, Australia

    masalai masalai

    Well if there is depth to the bubbles then slight cooking may be the cause.. - i.e. The epoxy is too thick - a common trait in building in China and India... I inspected a builder in India where he was making ships lifeboats and was proud of the depth of epoxy (no reinforcing layup) in core samples for QC :eek: :eek:

    He would not believe that strength was achieved by a relatively thin layer of grp where the layup cloth represented more than 50% and epoxy the rest (including the surface layers)... Jeeeees I am a rank amateur... I am surprised at there being no other wise men responding - I am just guessing as I have never seen that before...
  8. tunnels

    tunnels Previous Member

    Any one ?? 3 hours to go !!

    This is gel coat and nothing to do with epoxy ,cooking has nothing at all to do with it !! personally i dont ever work with epoxys at all !
    But thickness and bubbles all the way through yes !! and a couple of other things as well !! :confused:
    Come on !! whats it called ?? :?:
    and what can be the causes ???

    Have said this a lot recently >
    Know and understand the materials you are working with !!
    Last edited: Jul 13, 2012
  9. masalai
    Joined: Oct 2007
    Posts: 6,823
    Likes: 121, Points: 0, Legacy Rep: 1882
    Location: cruising, Australia

    masalai masalai

  10. tunnels

    tunnels Previous Member

    Come on ,some one must know !!

    Osmosis is something completely differant !! you not even anywhere near getting it !!:eek:

    This is a brand new boat and the closest its been to water is the creek 100 metres away from where it was sitting . Plus its in the topsides of the boat not the bottom ,osmosis looks nothing like this :confused:

    Another 90 minutes to go
  11. tunnels

    tunnels Previous Member

    your partly right and yes some of the causes are there and if you find the chart of problems its there and the causes . so what is it ????? its not osmosis ,its---------??????:D
  12. masalai
    Joined: Oct 2007
    Posts: 6,823
    Likes: 121, Points: 0, Legacy Rep: 1882
    Location: cruising, Australia

    masalai masalai

    "Pinholes / Porosity" at one place, (the links are not active as url's - possibly disabled by jeff et al) and that is the only link that does not giva a "404 error" - - Where are all the knowledgeable ones? - busy pontificating on the size of their ****************** :eek: :p
  13. tunnels

    tunnels Previous Member

    Yahooo !!

    Took a while !!
    Ok take a long hard look at it !! may never see it again but remember any way !
    Causes > mostly gel coat sprayed to thick to fast and the catalyst producing the gas and the gas isnt able to come to the surface . and the catalyst ratio could be to high and gelling before the gas escapes , or the wrong catalyst being used !!
    Had this some where a while back about hand brushing gel coats .

    During the early times before everyone sprayed gelcoat there was only brushing grade gelcoats !! dont think any one makes it any more !! nice and thick and when brushed gave a nice coat and covered really well . Later could buy spraying grades gelcoats thinner viscocity and more runny and hard to brush and get a decent thickness and when sprayed used to run a lot so like all new things there was a ooops we had funny marks !! what the hell is this how did that happen and what caused it ?? they later gave us better thixo system to stop the runs and so it would hang better on a vertical surface .
    Its one of the reason i try never to modify any products unless i have the right increadiance to do the job properly .
    The more you sanded the worse it gets most times . becasue the bubbles do go all the way through from mould to the inside surface and some places the bubbles combined and enlarge in size .
    Like i say know the products you use and what they wil do .
    Chemist they got on the trollies and looked hard why and what and how do they fix this . air releaseing agents got added to the gel then endless testing of a load of differant catalysts ,Remember not all catalysts are equal !!
    Its why when you buy gel you should always ask and get the right catalyst for that product and you will find it on there spec sheet if you take the time to look .
    Then fingers got pointed at the operater and how could he help the system as well . After all hes the man applying the stuff and always the last to know whats new !!.
    Hight pressure spray like venus and fine nozzels but was still possible to get porosity so yet more exsperimenting and then the technique of a flick coat first and then a fine thin coat and another thin coat till eventually you get the required wet film thickness . The time between each coat is enough to allow the gassing to take place before the next coat covers the one or ones below . with the mix in or at the gun the catalyst when mixed needed a few short seconds to gas a lot then subside quickly hence the thin coats and small delay between coats !!!
    Also the catalyst ratio almost anywhere in the world i have worked is 1.5% of the recomended catalyst by the manufacture. .
    This allows enought time to work with the gell and get it on to the job and completely covered specially on big jobs the chemical reaction of gassing is kept to a minimum.
    Temprature playes an important part in all this as well . cold its slow to gel !!hot it gels quickly so be carefull and know the limits !! but there again the manufacture has taken all this into account and has a wide range of tempratures to work within safely !.
    Then along came the pressure pot and the heavy handed operater and the problem came back for those guys !!,so had to teach him to use his brain and lower the air pressure and adjust the volumn being applied to get a nice fine but even spray and multipul thin coats .

    Our local manufacture used to come to the factory where i managed the glass shop and worked beside the guys and formulated there gelcoat to suit our equipment . We did lots small test panels when we did spraying and they took away and disected then grain by grain this was 1990s that was about the last time i saw Porosity on anything , untill a couple of weeks ago !!.
    So thats me till the next problem comes along :p
  14. SamSam
    Joined: Feb 2005
    Posts: 3,900
    Likes: 199, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member

    I'm slow and not too bright and try to limit my time spent solving riddles pertaining to very unlikely and unusual events.


  15. masalai
    Joined: Oct 2007
    Posts: 6,823
    Likes: 121, Points: 0, Legacy Rep: 1882
    Location: cruising, Australia

    masalai masalai

    Thanks tunnels,
    Old farts are not beyond learning new stuff - even those heading for dementia and feeling that handicap... I am constrained from giving points to you for the time being :eek:
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.