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FAQ - Reducing labor and waste when using epoxy.

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There are a number of labour and materials saving techniques that are applicable when using epoxy. 

Contents of this section
  • Filleting and Gluing using “Snap Lock” Plastic Bags
  • Snap Lock Bags - Method 2
  • Precoating Plywood Panels before Assembly.
  • Wet-on-Wet Coating and Dewaxing Cured Epoxy.
  • Building strong lightweight boats - a note on the use of epoxy
  • One Hit coating and gluing

Filleting and Gluing using “Snap Lock” Plastic Bags


Most supermarkets have varieties of “snap lock” bags.  They have a seal across the opening of the bag that can be pressed  together with finger pressure.  They make it a lot easier to keep epoxy glue away from areas on the boat where you don't want to put it.  And also areas on yourself where you don't want to put it!

Make up some epoxy, thicken it to the consistency of peanut butter.  Put a "snap lock" Glad plastic bag into a tin and fold the top of bag over lip of tin (like a garbage bag in a garbage bin - trashcan).  Scrape epoxy into the bag.
                            
Take bag out of tin, seal opening and cut one corner out of bag to make a hole a few mm (approx 1/4") across - size will need to vary with consistency of mix.

By gently squeezing the bag a bead of epoxy will ooze out of hole in controlled way from the hole.
Pipe a bead of epoxy down the right angle between the two plywood panels.

Use a filleting stick of a radius three times the lesser ply thickness to smooth down the fillet.  Practice getting it smooth and even.  Sometimes I use a flat edged stick which gives the fillet an even visual width and can also be useful where a radiused fillet is getting too thin over the join in the plywood.

Remove excess from either side of fillet with a stirring stick that has been sharpened to a chisel point.  It is possible to lay masking tape down either side of the join in the first place so that the excess can be removed with the tape.  

If you find the supermarket bags are too weak find a wholesaler or manufacturer of plastic bags on the net or in the phone directory.  Their prices are usually very reasonable.

Snap Lock Bags - Method 2


This method is used by Duck Flat and has the advantage that very little of the powders that are added to the epoxy for filleting or gluing can end up in the air.  Much better for health.

Do the mix in the bag from the start.  Pump the measured quantities of resin and hardener into the bag and mix very carefully by massaging the bag.

Add the powder filler and massage it through.

Don't be tempted to try and mix resin and hardener and powder in one step.  It won't work very well.



Precoating Plywood Panels before Assembly.

I find this the best method, where possible.  It saves the effort of sanding between coats of epoxy and prevents any waxing problems between the wet-on-wet coats.

Mask off all areas that you don't want coated.  (Especially any areas you are going to glue to later - not strictly necessary with the Eureka.

Lay surface flat where possible.

Mix resin and hardener.  You don't need to add any powder when you are coating - they are only used when gluing one piece to another.  Apply first coat.

NOTE - If doing large areas the epoxy will go off too quickly if left in the mixing tin.  You will have much more working time if you pour most of it out over the surface first and roughly spread with a squeegee, before going back with a roller to spread properly.

When it is spread hold roller so it cannot rotate and pull gently along surface of epoxy.  It slicks the surface smooth and pop any air bubbles.

When first coat has become quite tacky, roll on second coat.  Slick the surface. 
    
When second coat is tacky roll on third (if required) and slick it down.

IMPORTANT - Remove masking tape when third coat is still tacky.  You don't want to glue it down - forever.

When epoxy is fully cured turn the panels over, sand off any drips that have come from the other side and repeat process if required.

When the epoxy has cured sand the panels smooth using a random orbit sander (these tools are a very worthwhile investment but hand is fine too). 180 grit paper is about right.  Sand enough to remove gloss.
If you have problems getting a good finish speak to your epoxy dealer.


Wet-on-Wet Coating and Dewaxing Cured Epoxy.

As epoxy cures some of the unreacted components migrate to the surface, leaving a waxy residue. 
This can reduce the adhesion of following coats, whether epoxy or paint and make them go "fish-eyed" (the surface finishes pitted). 


Great improvements have been made to Bote Cote (Australia) brand epoxy in regards to this problem.  It is very unlikely to occur at all.  All the preparation you need for the next process is to sand the hardened epoxy surface.  The wet-on-wet application method is still the best so you don't have to sand between the epoxy coats.

However other brands of epoxy may suffer from wax.


This is why I always use a "wet-on-wet" epoxy application method (see "epoxy coating" above).  If the surface is allowed to cure it will have to be dewaxed (not Bote-Cote) and sanded (Bote Cote too).
Dewaxing- When the two to three coats have cured I always de-wax the surface using a plastic domestic scourer (Scotchbrite) and water with some cloudy ammonia added.  Scrub very thoroughly.
You can then sand the surface to key it for further painting, epoxying or gluing.

For example

Bare sanded wood



Lay glass over top dry and trim to approximate size



First coat of resin using a squeegee made of scrap ply (sand the working edge smooth and round off the corners so they won't catch the weave of the cloth).  Additional coats are applied with a roller as each successive coat goes tacky.



Epoxy coats are all cured the next day - glass can be trimmed with a stanley (carpet) knife.



Sanding the surface smooth - be careful not to go through the glass - you will start to see the pattern of the weave while sanding if you are about to go too far.  The centreboard on the right is already sanded to remove the shine of the epoxy surface.  I have done a little bit of sanding in the middle of the rudder on left - see the difference in the colour.



Both fully sanded and ready for a thin sealing coat of epoxy - to protect the fibreglass in any areas where the weave has been exposed.



The trick for getting a good end result with the final sealing coat is to
1/ get the surface sanded smooth to remove all the shiny epoxy surface (or make 95% of it non-shiny).
2/ apply a thin coat of epoxy with a roller - work the epoxy out over a large area.
3/ finish off the surface by holding the roller so it can't spin and sliding it lightly over the surface to pop bubbles and slick off the texture left behind by the roller.
The end result should be something like this...



Now they are ready for a really light sand and to be varnished or painted to protect the epoxy from UV deterioration.


Building strong lightweight boats - a note on the use of epoxy

Epoxy is expensive stuff, so when there is a bit left over from a process there is a temptation to use it somewhere. 

Don't do it!  The boat has been carefully designed to be strong enough already - all you will do is add weight and ruin the boat.  Where you can use it for a legitimate step, do so - but think about it first.

Another time it is best to throw out epoxy is if it is starting to go off in the bag or tin.  If it is starting to get too hot to comfortably hold it is going to be hard very shortly - you are unlikely to have enough time to put it into place.
Furthermore, hot epoxy fillets slump badly, hot coatings wax and get fish-eye pitting, and hot glue joins end up with lumps that stop clamping.  Make up a smaller mix next time and get it out on the surface earlier - straight after careful mixing in the tin or bag.

One Hit coating and gluing

An extension of wet on wet epoxying is a method for coating areas that are easy to get at now (plain plywood compenents) may be hard to get at a bit later when other parts are attached. A couple of examples are fitting the bottom, fitting the side decks and fitting framing to the bulkheads.

For example if gluing the bottom panel in place it is easy to coat the inside of the bottom at the same time. For major gluing processes like this it is important to make sure that everything will work smoothly – do a DRY RUN without the epoxy to make sure that you have enough screws etc to hold the bottom on OK – you can use the same holes again when you are putting the bottom on permanently.

This is the method (put on your disposable gloves!!!).

1/ get all the framing that the bottom will be attached to bevelled and ready to accept glue

2/ put three coats of epoxy “wet on wet” on the inside of the bottom as per the mehod in the appendix above.

3/ immediately put glue (epoxy plus the gluing thickening powder – make up to a peanut paste thickness) on all the framing of the hull that the inside of the bottom will be glued to – spread it out ready to take the bottom.

4/ drop the bottom on with its wet face in contact with the glue in the previous step and screw the bottom in place.

5/ clean up any excess glue that has squeezed out of the joints about 20 minutes after the assembly. If you wait till tomorrow you will be sanding forever. Use a flat piece of timber sharpened to a chisel edge on the end with a sander.

The same method can be used when putting the framing on the bulkheads. Coat one side of the bulkhead immediately before gluing the framing on that side.




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