The best way to make a waterproof hole for strong attachment is:
1) Completely paint correctly-sized hardwood with barrier coat epoxy or barrier coat epoxy paint system (Must use prep and primer!).
2) Drill rough screw holes (Push hard & fast and pull out with as little rotation as possible.), 1/16″ oversized from max. screw thread diameter.
3) Fill holes carefully down a side, making sure to leave an air escape hole, with a structural epoxy paste. While chopped fiber is strongest, it will trap air and so is not recommended here. WestSystem 406, with 422 for barrier coat is ideal. Add 20% 422 first to get a waterproof mix and then 406 until it's about the consistency of whipped cream. Slowly plunge a straw into it, pinch the straw to hold the epoxy in, carry over to the hole and blow to deposit the epoxy at the bottom, then tamp it with the straw. At no stage in this process do you suck epoxy into the straw! That is very dangerous, on a number of levels!
4) Screw carefully by hand with screw coated in grease – (Including the underside of the head!), making sure the tip is not sticking, wipe off excess and leave screw in place until epoxy sets. Try this on a test piece first.
You’ve got a waterproof, amazingly strong screw hole, custom-threaded! When you seat the screw permanently, use a lock washer: You’ve turned your screw into a bolt.
The important bit to remember here is not any oil property of wood but the roughness of the hole, as well as the hardness and strength of the wood. Almost any hard wood is just fine, as long as it’s not brittle and many are much cheaper than teak. No matter what wood or other material is used, it must be truly waterproofed. Many materials appear impermeable and aren’t, over time. Screw holes are the most obvious places for rot but any surfaces that rub are also suspect, so make sure everything’s fastened properly and watch out for later mountings: I prefer to stick, rather than screw workman’s loops, mounting plates, etc.
Showing posts with label epoxy. Show all posts
Showing posts with label epoxy. Show all posts
Monday, November 2, 2009
Monday, October 26, 2009
What Is Gelcoat and How Is It Applied?
Gelcoat is the generic name for marine exterior epoxy-based boat paint. Boat exteriors are usually completely painted with a thick layer of gel coat and bottom paint is then painted on top of that, for protection against marine growth. Gelcoat is very durable, usually lasting around thirty years but also very expensive, currently around $150 – $300/gallon, with additives.
Painting with gelcoat is straight-forward but there are lots of ways to make a mess of it and it requires a week for testing and various drying times. It’s a completely more scientific process than regular painting but one that can be mastered by a beginner with patience, the first time. Always use the same brand and type of gelcoat and ALL chemicals, as the chemicals from one are only weakly compatible with those of another. Measurements must be precise. If they are not, the gel coat will not be even and won’t match or be repeatable. Once the formulations are proven, write them in the back of the owners manual or somewhere they can be found and gratefully used next time!
This is a very brief overview of the process.
(1) Make, fair and clean the underlying, rigid surface with a tack cloth.
(2) Wipe it with an evaporative degreaser (such as acetone) on a lint-free cloth.
(3) If the surface is subject to immersion, appropriate barrier chemicals must be applied at this stage.
(4) Paint the area with surface prep liquid.
(5) Mix the epoxy primer. For relatively small jobs, I use disposable syringes and cut the tips very short, allowing me to transfer the liquids quickly. I lay them aside neatly in order, allowing for reuse.
(6) Apply the epoxy primer. If spraying, add up to 40% thinner.
(7) Mix epoxy paint in the following order: Resin, hardener, thinner, pigment, flattening agent.
(8) When barely dry to touch but tacky when pressed, apply paint, again mixing thinner – 10% for brush and up to 40% for spray.
(9) Apply UV-protective layer, as specified by paint manufacturer – This is an important step for the life of the repair and will deter UV deterioration, which otherwise will be noticeable.
(10) Wax.
Build up color first and then add flattening agent on the last pass – It’s clear, so it’s almost impossible to build the color with the flattening agent in every coat. it’s vital to use a large spare board and make and apply a number of mixes because the curing process changes color significantly, only gaining its lasting color about five days after application. Generally, use much less pigment than you would imagine. When matching old gelcoat, the last coat will be permeated with flattening agent – Read the instructions for the proper mix. Wet sand between coats, with 600 grit paper and final coat with 2,000 grit paper on a board: Do not use a palm when sanding the final coats because you want the surface to be flat with the surrounding paint. Another tricky issue is the thickness of the gelcoat and you have to guess about the amount of thinner, flattening agent and pigments to build the right thickness. Chipping a bit of loose, existing gelcoat off is a handy tool for comparison.
Painting with gelcoat is straight-forward but there are lots of ways to make a mess of it and it requires a week for testing and various drying times. It’s a completely more scientific process than regular painting but one that can be mastered by a beginner with patience, the first time. Always use the same brand and type of gelcoat and ALL chemicals, as the chemicals from one are only weakly compatible with those of another. Measurements must be precise. If they are not, the gel coat will not be even and won’t match or be repeatable. Once the formulations are proven, write them in the back of the owners manual or somewhere they can be found and gratefully used next time!
This is a very brief overview of the process.
(1) Make, fair and clean the underlying, rigid surface with a tack cloth.
(2) Wipe it with an evaporative degreaser (such as acetone) on a lint-free cloth.
(3) If the surface is subject to immersion, appropriate barrier chemicals must be applied at this stage.
(4) Paint the area with surface prep liquid.
(5) Mix the epoxy primer. For relatively small jobs, I use disposable syringes and cut the tips very short, allowing me to transfer the liquids quickly. I lay them aside neatly in order, allowing for reuse.
(6) Apply the epoxy primer. If spraying, add up to 40% thinner.
(7) Mix epoxy paint in the following order: Resin, hardener, thinner, pigment, flattening agent.
(8) When barely dry to touch but tacky when pressed, apply paint, again mixing thinner – 10% for brush and up to 40% for spray.
(9) Apply UV-protective layer, as specified by paint manufacturer – This is an important step for the life of the repair and will deter UV deterioration, which otherwise will be noticeable.
(10) Wax.
Build up color first and then add flattening agent on the last pass – It’s clear, so it’s almost impossible to build the color with the flattening agent in every coat. it’s vital to use a large spare board and make and apply a number of mixes because the curing process changes color significantly, only gaining its lasting color about five days after application. Generally, use much less pigment than you would imagine. When matching old gelcoat, the last coat will be permeated with flattening agent – Read the instructions for the proper mix. Wet sand between coats, with 600 grit paper and final coat with 2,000 grit paper on a board: Do not use a palm when sanding the final coats because you want the surface to be flat with the surrounding paint. Another tricky issue is the thickness of the gelcoat and you have to guess about the amount of thinner, flattening agent and pigments to build the right thickness. Chipping a bit of loose, existing gelcoat off is a handy tool for comparison.
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