Epoxy coverage data . .

[Pete McCrary]

I thought it would be useful to share some data that I've recorded over several "builds" regarding how much epoxy is needed for several tasks -- such as simply sealing out moisture, application of FG, etc.

Most recently (for my "Chessie," a CS20.3) I covered one side of each sheer strake and 4 cabin knees using a 4.5" roller with about a 1/8" foam nap. The first coat required 8 squirts (sqts) each of epoxy and fixer. For the 2nd coat I mixed 6 sqts, and estimated that I had about 1 sqts left over, for a net requirement of 5 sqts. The total area measured (approximately) 38 sqft.

4/24/16, 8 sqts / 38 sqft = 0.21 sqts/sqft for 1st coat on bare marine plywood (Okoume)

Same date, 5 sqts / 38 sqft = 0.13 sqts/sqft for 2nd coat ...

This is fairly consistent with 0.20 and 0.12, respectively, measured on 11/27/15 on a smaller sample.

For application of the

1st coat when covering plywood with 10 oz FG -- requires about 1.1 to 1.2 sqts/sqft.

2nd coat (filling the weave) -- about 0.2 to 0.3 sqts/sqft.

For filleting (r= ~ 3/8") -- about 1.5 sqts/linear ft. More for > radii.

For glueing -- about 1.0 sqts/sqft

Such numbers are, of course, approximate and vary according to materials, the brush or nap of the roller, and other factors.

To save epoxy for small jobs, I've found it useful to mark the pump shafts at 20%, 40%, 60%, and 80% of their full strokes. It seems to work pretty well -- at least no problems so far when mixing small batches.

I also [sometimes] mark the epoxy level (on bottle) before & after a multi-squirt job.

I keep a "build" note book and try to remember to record such epoxy data so that I'll eventually get a fair idea of what's needed for any particular job. But memories fade, and the note book has proved useful.

[meester]

Love it, love it, love it.

 

I've been sort of wondering whether I need to order more epoxy before I eventually flip and start on glassing the hull.  Your measurements will be very helpful.

 

Just for clarity,  1 sqrt  is shorthand for a batch of 1 sqrt of resin plus 1 sqrt of hardener, right?

Also, are your pumps the typical 1 oz pumps?

 

Bob

[Pete McCrary]

Bob,...

Yes, one squirt (sqt) is one each of epoxy and fixer. The pumps were supplied by B & B with their kit materials. I don't know their capacities. Could be "... the typical 1 oz pumps."

[Alex]

I will never use pumps again. They spit and splatter and are pretty useless in the cold. I only use syringes now. Much faster and a lot more accurate. Also easy to mix up a very small batch so very little waste.

[Pete McCrary]

I'd say pumps are OK, with certain precautions. You do need to keep the fluids fairly warm, say at least > 70 dF. In my unheated shop I made a HOT (i.e., warm) HOUSE out of 1" styrofoam insulation heated with a 40w lamp. I've never had splattering. Occasionally, the fixer punp needs to be primed if it hasn't been used in a while. Cleanup just needs to have the spouts wiped with a shop paper towel on the outside and a pipe cleaner on the inside.

You can see there's room to keep extra epoxy and fixer warm so that they don't chrystalize. Occasionally, the pump shafts need to have the percentage scale remarked as the old marks fade. I first tried a 25w bulb, but it didn't add enough heat (Nothern Virginia). The 40w adds about 20 dF to shop temp. I have two remote temp sensors inside the HHouse -- one transmits to the receiver on its top and the other to a receiver in my kitchen.

Although my shop is not heated, I have two 1500w electric space heaters that together can add about 10 dF (to the outside temp) for the whole (3-bay) shop/garage combination. I can drop an insulated roll up curtain to separate the 2-bay garage from the shop. In that arrangement I can add as much as 25 to 35 dF (to the outside temp) for the shop alone..

[Chick Ludwig]

I have a "hot house" similar to Pete's. It works well. i'll get a picture of my "resin cart" onto my Summer Breeze thread next week.

[meester]

I like my pumps, but true, they are a pain when the stuff gets cold.   My favorite for half batches, the dregs of the bottle, and for situations when there could be bubbles in the pumps is to use a kitchen scale.  They're very accurate, and there's no cleanup.  You can get a small kitchen scale for about $10 to $15.

 

Note that a 2:1 volume ratio is not exactly the same as a 2:1 weight ratio because the densities of the resin and hardener are different.  You can figure out the ratio using densities from the manufacturer, or you can go quick and dirty and just weigh while measuring out a batch using your old method.   

[PAR]

A syringe is the best thing I've found for small batches and you can get really precise too. I use the bigass ones from a veterinary supply store a 1/2 mile away. They're cheap and I get them by the case, so they're cheaper.

[Howard]

Not to put too fine a point on it, but a "squirt" isn't a reliable measurement. It might be for the person using it, but that does not port over to anyone else, unless the pumps are known to be the same.

 

I seem to recall the B&B pumps are in the 30 ml per stroke range, with the side B having the "restrictor" plate on it so it only gets half a stroke........so 30 + 15 = 45 ml per stroke or "squirt". I mention this as I have pumps from two other sources that give different results. One is 12 and 6 for 18 ml......the other does not have the restrictor plate on it, so that delivers (30 + 30 A) + (30B)  or 90 ml.  Then there are the West System pumps. I have no idea what they meter out per stroke.

 

So what would be helpful would be an estimate of the amount of coverage in either square inches or square feet (or if you want to stick to metric........square centimeters or some such thing) per 45 milliliters. This applies not only to coverage to coat and seal plywood, etc, but also to glassing schedules and even fillets and such. So you have 10 linear feet of fillets and you want a 1 inch radius? How much to mix up? (and then decide if you can you get that much fillet mix out of your mixing cup before it heats up and goes off in your hand)?

[Steve W]

I don't have much to add except that a digital scale works well, once you make a chart to convert the volumes to weight. I's not 2:1 by weight. SG is different. Then you can mix precisely what you want. Also, if you have material get crystallized as I have often, par-boiling the material makes it good as new. Just be sure if the pump crystallizes that you leave it attached and as it gets up to temp, just pump some through the pump until it's running good and pour what was just pumped into the gallon and you are back in business.

[meester]

Hi All, Y'all, all y'all, yous guys, y'uns 

 

A little browsing last night turned up this gem from West Systems for estimating epoxy needs:

 

Gallons = square_feet x [  oz_fg_cloth x 0.00085 + .0075 ]

 

The original article with an example of calculating epoxy for an Optimist is here --

http://www.westsystem.com/ss/estimating-epoxy-amounts