Elastomeric on top of gelcoat?

Discussion in 'Boat Design' started by nopeda, Aug 7, 2013.

  1. nopeda
    Joined: Aug 2013
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    Location: GA

    nopeda Junior Member


    The roof of my houseboat is covered with decades old gelcoat which is cracked and leaking. I would like to cover it with elastomeric and I've seen roofs where people have done that. One of the roofs looks fine like the elastomeric did great. On another one there are spots where the rubber is pealing off. I had thought that elastomeric and rubber roof stuff were the same thing and elastomeric is just a brand name, but in another thread I saw where a person specifically said that elastomeric is good but that rubber roof stuff will peal off. What's the difference and what to look for? Is it true that elastomeric works well, but the rubber stuff does not?

    Thanks for any help with this!
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    If it is a flat roof, a membrane glued on may be better. They sell it at building supplies and looks like the material used to make inflatable boats. It is glued on with contact cement.
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I've done just what you're thinking about and it does work, though there are a few basic types of elastomeric coatings, which you'll need to sort through.

    Elastomeric isn't a brand name but a semi-descriptive category or coating type. Again, there are different formulations and bases, so you'll want to do some research. The stuff you'll find at Lowe's/Dept will be a polyurethane or modified acrylic. The acrylics are cheaper, but also don't last as long. Either of these products hold up very long in tropical environments.

    Polyurethane: this covers a fairly wide range of products. Not perfectly waterproof, particularly the single part versions. The LPU versions are more durable (and costly), but most of the polyurethanes tend to chalk, but can be over coated. The solvent based versions will be more durable and priced appropriately.

    Silicone: has limited uses and is difficult to top coat, but useful in places you might need things to breath.

    Neoprene: a DuPont synthetic rubber, chalks and degrades in UV, but can be top coated.

    Hypalons: a wider spectrum synthetic rubber, than neoprene.

    Butyl Rubber: very water resistant, but soft and will chalk.

    EPDM: a synthetic rubber, very compatible and durable, but you pay for this.

    I've not mentioned asphalt or the other more common land based roof coating,s mostly for obvious reason.

  4. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    I'm not sure if you are talking about installing a rubber roof membrane, or are thinking about using an elastomeric roll-on coating. A white EPDM 60 mil sheet would work, but you are looking at something like $2.25 a SQFT as a do-it-yourself job. And there is a fair amount of fussiness and specific glues and caulks and primers and prep that goes with it. Prepping and re-gelcoating would be easier and cheaper. You probably want a very smooth finish on a houseboat roof unless you are in the boonies and nobody else has to look at the thing. Mopping on the roof coating goo that comes in a five gallon pail at a big box isn't going to get you there. Careless applications forms little lakes that persist long after the rain has stopped and water then works into the cracks and forms a much worse problem. If you are set on a roll-on fix, prep the roof with a DA, and used a rubber roof coating such as Hengs, to name one of many. You need to mend cracks first. You need to make sure there aren't any craters or dings that will puddle water. You need to deal with any vent repairs and other roof appliances first. Then roll the stuff on with a smallish roller, say 7" ultra smooth 1/4 cover. The stuff does not self level. Put 2 or three coats on just as thin as you can manage. Then a coat about every five years will keep it up. It does chalk up and it does let that lousy black bacteria/mold stuff grow on it which leaves streaks down the side of the walls, so keep the rest of the boat waxed. So it's about the usual routine- a solid week of prep work then a day of coating. The purpose of the roll on coatings is not fix cracks, it only really replaces the stuff that is wearing away due to oxidation and crud-critters.

    for those not in the southeast, one of our pests that is rapidly expanding its range- http://en.wikipedia.org/wiki/Gloeocapsa_magma
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