Fillers for bonding

[smacrae]

Where fillers are specified to thicken epoxy for gluing, what fillers are suitable? Specifically, can Q-cells be used in this application?

[Tom Lathrop]

Q cells are fine for fairing and filets that are not heavily stressed. I would not consider Q cells suitable for glue. Wood flour, sanding dust or even sawdust are all better, along with cab-o-sil as a thickening agent of course. A good mix is equal amounts of cab-o-sil and wood flour by volume for glue or just cab o sil alone.

[smacrae]

Thanks Tom, cab-o-sil it is.

Of course the other thing thing I need to learn is to take care with my resin to hardener proportions. Because I used the wrong sized measuring cup for my hardener, the proportions turned out to be 7:1 rather than 5:1. :cry: I was easily able to split the boards apart after 3 days of curing. Never thought I'd have to use a machete to build a CS17 :?

[Frank Hagan]

The 5:1 ratio can be surprisingly tricky. I have always used a 2:1 epoxy because I'm severely "math challenged".

[smacrae]

I was given 24 sets of measuring cups each containing 1/4, 1/3, 1/2 and 1/1 cup sizes. My erroneous mix was 5 x 1/3 to 1x 1/4. I have since colour coded them.

But you are right Frank, one must fully concentrate when tallying 5 measures - it is surprisingly easy to miscount. Pity I wasn't given some 1/5 cups.

[Arnie Eaton]

I only get the 1:1 ratio type epoxy. Makes it much easier to mix. I just use paper cups in various sizes depending on the job. Just be sure that both are the same size. I have some putty type epoxy that mixes 1:2 by weight so a small electronic scale is a must.

[PAR]

I solved this problem years ago by buying several cases of plastic mixing cups. They are smooth bottom and sided 16 ounce versions and I made masters cups that I use to mix with.

The master cups have a line on them, ratio and epoxy type is also marked. The master cups were very carefully arrived at through measurements to get the desired ratio.

When I mix a batch of any epoxy, I find the two masters that go with the epoxy type (5:1, 3:1, etc.) I insert a clean, unmarked mixing cub inside the master and fill to the line, for each part. I then move the masters back to their save location and begin mixing. Every once and a while I'll get one of the masters dirty or contaminated, so I make a new one and put it away.

I have a two different masters for each epoxy type. A small batch of just a few ounces and a larger that will make about 6 ounces. Larger batches require I refill and dump into the mixing pot, which isn't much trouble, just maintain the count and you're fine (okay, I've screwed up the count more then once)

I developed this method because I had a set of pumps that became inaccurate, which drove me nuts until I finally questioned their accuracy and checked them. I've since learned this isn't an unusual problem and many who use a lot of epoxy mix by hand rather then trust the pumps (they've been screwed too)

Procedure and routine are the hallmarks to successful epoxy runs.

[Tom Lathrop]

Many knock the plastic pumps, but I check them regularly and use new ones is the give trouble. Measuring in cups is fine for larger batches but I find that I'm using mixes far too small for cups in the 5:1 ratios very often. Large syringes are good for really small batches. I use the 2:1 ratio epoxies.

[Charlie Jones]

You can also use a marked stick and a STRAIGHT sided container. Mark the stick for resin, then go up as needed and mark for hardener. Fill with resin to the line, fill with hardener to the second line.

As just one example, for a 5-1 mix, mark at 2 1/2 inch for resin and then another mark at the 3 inch point, for the hardener.

Using WEST Sys epoxy with it's 5-1 mix, I commonly use the inner part of the cap from a spray can of paint. It's about 1 inch in diameter, straight sided and about 1 inch tall. I use as small as 5/16th resin and 1/16 hardener. Been mixing tiny batches like that for years with never a failure. With a 2-1 mix it's even easier. Vary batch size by both the size of the container and the spread of the marks.

Another nice thing about using the stick- when doing a big job you can pre fill containers ( I often use cleaned out metal cans from the kitchen) with resin and line them up waiting. Then you just need to pour hardener, mix and use. Cuts down on wait time between batches. When you are doing something like glassing the hull of a 35 footer, it's NICE to speed things up

Meade Gougeon taught me that trick at an Experimental Yacht Society meeting in St Petersburg Florida, back before the EYS folded up. Last meeting I went to we had Meade and also Jim Brown in attendance. That was the year Jim introduced the Cylinder Molding (*) technique, using a scale model of Simple Sib, the first cylinder molded boat. 1978 or 1979. Can't remember any more.

(*) Should read "Constant Camber" not Cylinder mold. Cylinder molding is a development by Kurt Huges for his multihulls.