Vac table surface

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, Aug 2, 2017.

  1. fallguy
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    fallguy Senior Member

    My vac table is 1" MDF, raw mdf. It is 33' 4" long by 4' wide.

    Can I run the raw surface and mold wax it 3x, or do I need to paint it with a high gloss paint first?

    tia
     
  2. jorgepease
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    jorgepease Senior Member

    You better paint that
     
  3. rwatson
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    rwatson Senior Member

    Raw mdf is a bugger to get smooth with paint. Have you thought abnout buying some melamine coated mdf sheets to glue on top ?

    It will save you a heap and work much better.
     
  4. fallguy
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    fallguy Senior Member

    Well, I spoke with a few people and I am going to epoxy the table and sand it with my 39" fairing board. Perhaps even two shots. Then I am going to use epifanes 2 part polyurethane paint over that.

    Someone also suggested I could use formica, but I decided the formica will also be subject to variances in the contact glue thickness and honestly, as of this moment, I think the top is smoother, so I am going with a ain't broke don't fix approach.

    I think the melamine idea is also not bad, but I already faired out the 4 joints, so it seems like extra work to do it again. Thanks.
     
  5. jorgepease
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    jorgepease Senior Member

    There is no variances in contact cement, you roll it on so thin it can't be any variance, it will give you the fastest best result but you would have to leave space between the laminate joints and then bog that ... or make sure to seal the wood first to make it leak free ... if we are talking a vacuum table.
     
  6. fallguy
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    fallguy Senior Member

    Jorge, you are confusing me a little. If I use formica, it would be a continuous piece, so the wood wouldn't need to be sealed under that scenario, right? I called a local store and can only get the formica in 12' pieces, so it'd have joints.

    I am going to seal the table with a quart and a half of epoxy, then sand and 2 part paint it.
     
  7. jorgepease
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    jorgepease Senior Member

    Sorry to confuse,

    Since you can't get it in those long lengths you would need joints in which case it's better to leave a gap (1/8 in) and fill with a thickened epoxy mix using microballoons. Just put a piece of clear packing tape over the jont once filled and sanded and your done.

    The sand and paint method is a lot more work and will cost about 2-3 x more. With laminate you are done in about 3 hours of work over a couple of days max, the painting way method, you are talking about 3-4 days or more depending how many coats you go. Unless you specifically want to paint, then the laminate gets you a perfect surface faster and cheaper.

    Also bear in mind that the mdf underside and edges need to be painted too because it will start to move on you. Good Luck !!!
     
  8. fallguy
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    fallguy Senior Member

    Why will the mdf underside need anything? I am climate controlled and the mdf is screwed from underneath and siliconed on edges. I can't even get to the mdf underside to paint it now. The sheets are like 125# each and there are over 4, so 500 pounds of sheet. I already put 48 oz of epoxy on it about an hour ago.
     
  9. ondarvr
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    ondarvr Senior Member

    You can use 823-A to seal the mdf, this can be used as a mold surface or cover it with a top coat, not hard to do.
     
  10. fallguy
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    fallguy Senior Member

    I don't understand the purpose of 823-A. It seems odd you'd put something on the wood prior to epoxy. Can you explain?
     
  11. rxcomposite
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    rxcomposite Senior Member

    If it is raw MDF, you need to coat it with poly or epoxy. Pour the low viscosity resin on top of the leveled surface, spread it, and place on top of the fresh resin a nylon bagging film stretched on a rigid frame. From the film surface starting from the center, squeegee the bubbles towards the sides and let the resin cure. After curing, remove the film, trim the edges and you have a perfectly level and mirror like surface. If there are still some imperfections, sand it lightly and repeat the process.
     
  12. fallguy
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    fallguy Senior Member

    I did this except for the release film and now I'm sanding like a bugger, not a boat, but a temporary table! I figure another 48 hours of sanding and it'll be flat again. (well a few hours anyway). In addition to environmental dust and a fly that failed to escape, the epoxy seemed to have a mind of its own as far as flattening out and it pretty much is like giant size orange peel. It is med-low vis epoxy and I'll not name them here because this is not the reason I purchased the brand (for glassy rolling out on a piece of wood). Someone told me to use a 2 part polyurethane paint over the top of the epoxy, only that is also going to end up with environmental impacts as well. I had planned (prior to reading this post) to put up a 35 foot drape to reduce the dust falling during the paint cure. I think he suggested the paint cure because the epoxy will break down from UV unprotected. The table needs to last at least 12 months, and I like to work with the doors open.

    I'm all for this release film idea if you think the UV won't destroy the surface in 12 months. I doubt the release film would work with paint.

    What do you think rx or anyone? paint under a drape, or just epoxy with stretched bag film on it again? and I used 48 oz of epoxy last time, it was 26 minute cure, so 2 of us were rolling like mad, and that probably didn't give it much time to level out before curing up-if you recommend just the epoxy, should I mix it to medium hardening?

    I can't wait to get done and get the table waxed, the carnauba smells really great.

    Thanks folks.
     
  13. jorgepease
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    jorgepease Senior Member

    Sanding straight epoxy is a bear! I'd repour at this stage or bog the whole table and sand it, that was my fear.

    If you repour, you could build a dam perfectly level about 1/16 to 1/8 high and fill it up with very low vis epoxy, maybe the bar and table epoxy. Warming the epoxy slightly will help get rid of air bubbles and get it to flow better, polish the bugs out later. I don't really like this system because surface tension can leave you with not a perfect surface... maybe vibrate it a bit with sander on the base of the table.

    Hopefully the seal coat won't allow the MDF to suck up too much, if any epoxy, and leave you with uneven patches. UV is not going to hurt you inside but watch out for moisture leaving the doors open, I'm in FL don't know where you are, here humidity would swell that mdf before 12 mos. It would suck to have it buckle on you.
     
  14. ondarvr
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    ondarvr Senior Member

    823 has a very low viscosity, far lower than any epoxy, it's designed to do this exact thing, soak into MDF and stabilize it, plus provide a good surface for other coatings to bond to. It cuts down on the time and cost involved in making MDF and other wood plugs and molds.

    You don't need much 823 to cover a large surface, a little goes a long way, and when you put another coating over you will use far less of that product, and the surface profile will be much more uniform. I wouldn't use paint over the epoxy, there are other coatings that can be used over epoxy that are designed for this purpose, and work much better than paint.
     

  15. fallguy
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    fallguy Senior Member

    -respectfully, the thing is already epoxied, so the 823 is too late at this point, right?
     
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