Epoxy Method and Protection of Epoxy

Discussion in 'Boatbuilding' started by tontoOx, Apr 25, 2021.

  1. tontoOx
    Joined: Feb 2021
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    tontoOx Junior Member

    Folks,

    The dinghy I am building will be made out of Okoume (gaboon) marine plywood with kiln dried spotteed gum (or similar) for the square and rectangular section solid wood pieces.

    I will coat all of the wood in epoxy resin (espcially end grains) and apply woven fiberglass tape on all seams and apply woven fiberglass cloth on the hull underside and maybe the hull interior bottom too (seems like a good idea?).

    Q1. I have read that epoxy resin can take up to two weeks to fully cure even if it feels dry. If that is so, can I leave it up to, say, five days before applying the second coat of epoxy resin, and then a further five days before applying the third coat after that, would the three epoxy resin coats still stick to each other "chemically" with such intervals between epoxy resin coats?

    Q2. Should I sand in between epoxy resin coats and if so how long should I wait before sanding and then apply the next coat?

    Q3. I gather it is possible to apply a coat of epoxy resin to cured epoxy resin provided that the previous (cured?) coat has been sanded to provide a mechanical key. Would a mechanical key provide an effective bond for the next new coat of epoxy resin? Wouldn't a chemical bond provide a better bond?

    Q3. I have read that epoxy doesn't like UV. In Australia we have a lot of sun! What would be the best way to protect the epoxy resin and epoxy fiberglassed dinghy from UV etc?

    Q4. Teredo shipworms, is this a potential problem for a boat that is on the water for a day at a time, should/can anything be done to mitigate?

    Thanks in advance.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    What are all the coats needed for ? You should be able to seal the timber, complete the glass work, and then proceed to paint.​
     
  3. gonzo
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    gonzo Senior Member

    All bonds are chemical. However, if you laminate over resin that is still tacky, there will be crosslinking which is a stronger bond.

    All bonds are chemical. There is no need to sand the resin, only to remove the amine wax. Warm water and detergent will do that better. Sanding can smear the wax instead of totally removing it.

    Any paint will provide UV resistance. A good quality alkyd enamel is an economic product.

    They won't be a problem in a day or even a week.
     
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  4. fallguy
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    fallguy Senior Member

    typically the epoxy manufacturer will tell you the maximum no sand or no key window, 5 days is too long


    typically sanding can be done next day as long as cure temps are 65F or higher, cures below 65F may retard and take longer, gumming or corning will tell you if it is not ready if your temps are an issue


    yes and yes, there is no reason to sand if you are within the epoxy manufacturer's bond window unless the surface has high spots other than weave, the best approach is to apply 'neat' coats next day


    paint or 8 coats varnish on areas in shade and 15-20 coats varnish on sun exposed areas


    no need
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    The Teredo "shipworm" is actually a kind of mollusc, and is regarded as a delicacy. Eat them if found !
     
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  6. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    Others have already replied with correct information but I will summarize anyway.
    The "fully cured" of a 2 weeks probably refers to achieving fin strength inside out. It is much sooner that the surface gets waxy and hard enough that you do not get cross linking (as you refer chemical) bond. Some reins don't get waxy residue and need no wash other should be washed with mild detergent and if the surface cures past certain time. So typically your options are a) next coat soon enough when still tacky b) wait for day extra and wash and sand

    If you are smoothing out glass cloth weave it depends really whether you need to sand for other reasons (to get rid of bumps etc).

    All times are dependent on products and conditions.

    The "bible" for epoxy + wood boat building is available as a free pdf here:

    https://www.westsystem.com/wp-content/uploads/GougeonBook-061205-1.pdf
     
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  7. latestarter
    Joined: Jul 2010
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    latestarter Senior Member

    Read the safety section in the Gougeon Book ^ and get good protective gear. Sanding cured epoxy is a hazard, sanding part cured epoxy is significantly worse.
    Quote from page 79
    "Partially Cured Epoxy Dust. Sanding partially cured epoxy produces airborne dust,which increases your risk of exposure by skin contact,inhaling, or ingesting. Although epoxy may cure firm enough to sand within a day, it may not cure completely for up to two weeks. Until then, the dust can contain unreacted hazardous components. Do not overlook or underestimate this hazard."
     
  8. Ilan Voyager
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    Ilan Voyager Senior Member

    The information is from the eighties (the was written around 1980) when there was some ferocious amine hardeners in a some resins for epoxy wood building, including West Systems.
    Nowadays all the epoxy resins for wood boat construction are pretty safe and the cases of severe allergy are extremely rare. It's not the same with the resins used in composites, and specially the high tech composites. Some are very nasty.
    That does not mean that's as safe as milk (good song by Captain Beefheart). Even milk can be harmful for some guys, hen eggs can kill, peanuts can send you to hell...So like always with any product precautions must be taken. The habitual ones (work clothes changed every day and washed separately from the normal clothes, gloves, masks for the dust all dusts are harmful, good soaps etc...
    About the paint the best ratio quality/easiness/price paint for small boats are the ordinary acrylic ones with hardener for cars. In hot climate you can make the 3 coats in the day with a simple cheap airgun and a simple paint mask. They dry in minutes. These paints are very resistant to UV and are very easy to repair (they are made for that purpose...). With the hardener one day exposed to the sun makes then harder than tiger nails.
    Alkyd on epoxy gives ugly results and are pretty long to dry. Polyurethanes are expensive and can be very harmful when airbrushed.
     
  9. latestarter
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    latestarter Senior Member

    ^ You make a valid point that the risk may be less from modern chemicals however the advice is almost word for word now as it was then.

    "Sanding partially cured epoxy produces airborne dust, which increases your risk of exposure by skin contact, inhaling or ingesting. Although epoxy is firm enough to sand within two hours, it may not cure completely for up to two weeks. Until then, the dust can contain unreacted hazardous components. Do not overlook or underestimate this hazard."

    Overexposure to Epoxy - WEST SYSTEM Epoxy - Safety basics https://www.westsystem.com/safety/understanding-overexposure-2/
     
  10. tontoOx
    Joined: Feb 2021
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    tontoOx Junior Member

    Thank you all for your help, very informative, particularly from:

    gonzo
    fallguy
    kerosene
    latestarter
    llanvoyager

    Regarding safety precautions I have a P3 respirator and the Makita LXT random orbital sander will be connected to a Makita vacuum with HEPA filter. I also have some Type 5/6 disposable overalls too and rubber boots. The jigsaw can also connect to the Makita vacuum for when I cut the plywood. When applying the resin I also have an extractor fan which is one of these:

    ITM 200MM PORTABLE VENTILATOR SET https://www.industrialtool.com.au/product/3459-itm-200mm-portable-ventilator-set

    To answer Mr Efficiency's first post response to my thread; when I was learning how to renovate bathrooms it was drummed into me to do a minimum of two coats of the liquid waterproofing membrane, a horizontal coat, and a vertical coat after first coat has fully cured, this was to avoid pinhole gaps. I admit I am (very) new to epoxy wood boat building although I have worked with wood a lot and many years ago I helped my father build a mirror dinghy which used glue stitch and (I think polyester resin i.e. before epoxy became popular). To my thinking at least two coats of epoxy resin are needed to seal (I have seen the word "encapsulate" used on this forum which I take to mean the same thing?). I also think I need woven fibreglass on the bottom (weight?) both interior and exterior because that would improve durability of the boat. The plans I am working from were based on using a Titebond III glue with drywall fiberglass tape etc. While interesting, I wasn't sold on that approach. The plans mentioned that the dinghy could be fiberglassed as an alternative method but gave no information to help someone wanting to do that hence my newbie/rookie questions on this forum. I think I would like to use epoxy and fiberglass mat on bottom (interior and exterior). Sure it is a lot more expensive to do, but will hopefully create a durable boat that can be used for many years. I have now got the gougeon book (thanks kerosene) which is going to be quite a read.

    Q1. Can you cut woven fiberglass mat with scissors and do you need to take any precautions with it?

    Thanks again, greatly appreciated.
     
  11. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Fiberglass mat can be cut with scissors. But mat isn't woven. It is like felt or a plate of spaghetti. Fibers running every witch way. Usually it is torn to avoid lumpy edges.

    Mat is not the best choice of FG for your protect.

    Look for 6 to 10oz (sorry, I don't know the metric equivalent) twill. It is woven with two ot three glass yarns paired together. It looks a lot like duck canvas.

    Roving woven with six to ten parallel yarns will be too heavy.

    Unwoven bi-axial is expensive.

    The weight of FG cloth you need can easily be cut with sharp scissors.


    As a side note.
    Block planes can remove lumps and bumps from firm epoxy with less risk of inhaling particulars.
     
  12. tontoOx
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    tontoOx Junior Member

    Thanks. I guess mat means something else. So by 6 to 10 ounce twill I presume you mean a lightweight woven fiberglass cloth? The dinghy is under 8 foot long so would one layer on the hull bottom interior and one layer on the hull bottom exterior be okay? Also, is it possible to get the same 6 to 10 ounce twill as fiberglass tape for the seams? In terms of role what is the difference between plain and twill woven fiberglass cloth?

    Thanks also for tip on tearing the cloth.

    You twill comment helped me just now to find a supplier who sells the following fiberglass cloths in Australia. 200gsm is the same as the 6 ounce weight you mentioned. Would one of these cloths do?

    25 gsm Plain Weave Fibreglass Cloth 1270mm wide, per lineal meter
    extremely light almolst gosamer like woven cloth. About 1 oz per square yard in the old measurements. It is much used by modellers. Cloth width is...

    85 gsm Plain Weave Fibreglass Cloth 96cm wide, per lineal meter
    Cloth width is 965mm. It is sold by the metre. The roll length is 50 metres approximately. Click here for the Data Sheet.

    125 gsm Plain Weave Fibreglass Cloth 1m wide, per lineal meter
    Cloth width is 1000mm. 125gsm is approximately 4 oz per square yard in the old way of measuring. The Plain weave 125gsm cloth is popular for general...

    135gsm or 4 oz HiTensile EGlass 76cm Wide Plain Weave Cloth
    Cloth width is 76 cm. Price is per metre. We will cut a piece to your desired length. This cloth is 135grams per square metre or 4 oz per square...

    200gsm or 6oz HiTensile EGlass 76cm Wide Plain Weave Cloth
    Cloth width is 76 cm. Price is per metre. We will cut a piece to your desired length. This cloth is 190grams per square metre or 6 oz per square...

    195 gsm Plain Weave Fibreglass Cloth 1m wide, per lineal meter
    The cloth width is 1000mm. 195gsm is approximately 6 oz per square yard in the old way of measuring. This is the most popular general purpose...

    200 gsm Plain Weave Fibreglass Cloth 1.4m wide, per lineal meter
    Cloth width is 1400mm. 200gsm is approximately 6 oz per square yard in the old way of measuring. It is sold by the metre. The roll length is 100...

    287 gsm Plain Weave Fibreglass Cloth 1m wide, per lineal meter
    Cloth width is 1000mm. 287gsm is approximately 10 oz per square yard in the old way of measuring. It is sold by the metre. The roll length is 100...

    FibreGlass 185gsm Crowsfoot Weave 1 m wide per metre
    The crowsfoot satin weave makes the cloth considerable more conformable. It will drape over difficult shapes more easily than plain weave cloth. It...

    Fibreglass 2,2 Twill Weave 285gsm 1.27m wide, per lineal meter

    The twill weave makes the cloth considerable more conformable. It will drape over difficult shapes more easily than plain weave cloth. Cloth width is...
     
  13. fallguy
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    fallguy Senior Member

    200 gsm @ 1.4m wide

    typ 2 layers bottom for abrasion, can be two inside bottom same reason

    Sides one.

    somewhst depends on beam
     
  14. Blueknarr
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    Blueknarr Senior Member


    I don't know the price difference between the last 5ish choices. Or how complicated the shape of your boat is. I suspect any of the last options would work. But I don't know which would be best for you

    Also ask the supplier about 'fumed silica' and micro-baloons. I recommend you get a couple of kilos of the fumed silica (cabo-sil) and about half a kilo of micro-baloons.

     

  15. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    inside probably one layer is enough. most places carry tape 200g or 300g.
     
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