need help - 1978 Thompson 18 spider cracks - gelcoat or paint

Discussion in 'Fiberglass and Composite Boat Building' started by boater1, Aug 18, 2011.

  1. boater1
    Joined: Aug 2011
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    Location: ca

    boater1 New Member

    Hi I just bought a 1978 Thompson 18' boat and I want to restore it but I don't know if I need to re gel coat it or just paint it. There are spider vein cracks everywhere and there are scratches and on the bottom some chips but not deep enough that you can see the hull. Any suggestions?
     
  2. tunnels

    tunnels Previous Member

    the spider veil is stress cracks in the gel coat !! If you simply sand a regelcoat or paint over it they will come back very quixkly and you will be back where you started !!Dont like to say it but need to sand the gel coat off to the glass underneith . Then re paint using the whole process of primers and undercoats to a top coat . You could try to find some DURATECH PRODUCTS these are poly and are really good build up and easy to sand can gelcoat over the top or paint anything over the top .
    Post some pictures it easyer to see whats there . :D
     
  3. boater1
    Joined: Aug 2011
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    Location: ca

    boater1 New Member

    Here are some pixs
     

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  4. boater1
    Joined: Aug 2011
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    boater1 New Member

    so if I need to sand off the gelcoat what tools do I need to do that and do I have to take all the hardware off the boat? Also all the cracks are mainly from the blue part of the boat and up nothing on the bottom so would I have to take all the gelcoat off everything or just the top?
     
  5. ninetogo
    Joined: Aug 2011
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    Location: Fayetteville, Ga. USA

    ninetogo Junior Member

    The problem with stress cracks in gel coat is that polyester gel coat and the underlying fiberglass have different coefficients of expansion. Gel coat is semi-rigid and fiberglass has some flex under impact. Under impact the fiberglass moves and the gel coat does not, hence the spider web cracks.

    Have had good results with a water based, thixotropic material by the name of "Captain Tolley's Creeping Crack Fill". I did not name this material, just use it. The spider web cracking will continue to run unless you create a stopping point; the best artificial stopping point can be made by using a 1 MM drill bit to drill the end of each crack. I choose to run the bit into the fiberglass about 1/8" and later fill with fairing material.
    Heat the surface of the gel coat with a blow dryer (around 135 F) and apply the Capt. Tolleys which will be sucked into the crack surface. Use a wet rag to remove any excess. Repeat the process 4 to 5 times and the crack will be filled. The water base will dry, which leaves the thixotropic material inside the crack and the crack totally filled. Use 400 to 600 grit DA paper to remove any traces of the Capt. Tolley's on the surface of the repair area and additionally prep the repair area for paint or gel coat.
     
  6. tunnels

    tunnels Previous Member

    Spider cracks and star cracks are telling you something !!!Can you guess what ? Its been damaged below the surface of the gelcoat . The gel coat is like a egg shell in the surface . Hit from the outside and you have a star crack the crack up forward are where its been hit into a pile or a wharf or something simular . Crack in the back wheres theres boats and things mounted is its weak , Take off what ever is there and fit a proper mounting pad and repair the weak and damaged delaminated glass underneith . I theres wood inbeween the layers of glass it possibly rotted or delaminated or need replacing .
    Trying to repairing the cracks is going to be a ongoing endless job forever more !! Know what the causes are and fix them !!,then finish off with repairing the Gelcoat cracks and they wont come back any more !! :confused:
     
  7. ninetogo
    Joined: Aug 2011
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    Location: Fayetteville, Ga. USA

    ninetogo Junior Member

    We both agree that "star cracks" and "spider web cracks" in the gel coat are typically caused by some form of impact to the outside hull. My previous post was based on the thought that the underlying glass was intact, with no glass delamination or other damage beneath under the gel coat. Thanks for pointing it out. Again, the gel coat cracks must be stopped or they will continue to travel.
     
  8. tunnels

    tunnels Previous Member

    only travels if the gel coat is thick or the panel is weak !!! in older boats its a case of both normally , delaminated panels that has losst there support from strengthening pads behind ! If the pads were plywood they will have got wet through screw holes leaking and delaminated and rotted in most cases . :eek:

    About every 2 to3years pays to check the sealent under fittings !! specially screwed on fittings ,most times thescrews will have lost there tension and have movement so the rain water gets in down past the screw of from under the base of the fitting .
     
  9. pauloman
    Joined: Jun 2010
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    Location: New Hampshire

    pauloman Epoxy Vendor

    yep - the hairline cracks are filled with air and or water and just painting over them will bridge the gap until the next hot day, etc. Also the hairline cracks have curled up edges that you may need to sand down smooth for a nice end result/finish.

    The capt tolleys mentioned above is also my recommendation. It looks like watered down elmers glue with something to reduce the surface tension so it literally sucks right into the tiny cracks. It is milky white and dries clear.

    By the book repair is to sand the gel coat and cracks away or open up the cracks more so that standard paints/epoxies/putties can get inside and fill them.
     

  10. tunnels

    tunnels Previous Member

    Gel coat is like a egg shell!! if its cracked and the laminate below is not damaged you need to stop the panel from bending!!.
    Glass will bend!, gel coat will crack !! If the gel coat is thin its less likely to crack !
    or use semi flexable gel coat that will take the flexing .
    If you spend hours repairing the gel coat without stiffening the panel you are wasting your time . :eek:
     
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