Epoxy/Mahog lamination

[bjl_sailor]

Hi:

I'm about to assemble my 20 foot long keelson made of biscuit joined strips of meranti mahag. It is a series of 2 x 3/4" strips so that it will be flexible enough to follow the boat's lines. My question is this: I've joined the edges and put biscuits about every foot. (At it it's wides it is 6 strips wide) when I epoxy it with with West System should I thicken the epoxy at all -- and if so how much and with what. Everything is dry fit tight and it will be a bit of a task to wet it all out, reassemble it and clamp it down within a 30-40 minute pot life.

[PAR]

Biscuits will provide little by way of strength, to the joint and epoxy as a rule, requires not so tight fitting joints and little pressure during the cure to work as an adhesive. The only advantage to using them (biscuits) may be in alignment of the pieces during assembly, which is the key to good epoxy work. Setup for an epoxy run is critical for success. Epoxy is slippery stuff and fitting many pieces in an epoxy run is difficult if setup isn't sound.

You have a limited amount of time to work (205 hardener will increase your working time) and the pieces need a jig or form or some device to manage the movement while you arrange the parts. A dry run is highly recommended, testing your setup and timing the effort to get the assembly in place before your goo kicks off in the pot.

Why did you build the keelson (or is it a keel?) this way? What was offending about the designer's ideas on the plans that this change was necessary?

I ask, because it seems like a lot of extra work milling little pieces to shape, just to make them one glued piece in the end. Sure it's difficult to get stock the sizes we need for some projects, but the simplest methods are usually the shortest way to the goal. Personally I'd skip the biscuits and use a good setup (be a jig, dowels, clamps or whatever works fast) I use dowels a lot during epoxy runs as they allow me to set the parts in an assembled state and control the goo line, by sliding the parts in and out on the dowels. I use as few as possible. I also use lots of course thread drywall screws during setup, which are removed after the cure and filled.

Log onto the www.WestSystem.com site and look up the "how to" sections. Also order their construction manuals (most are free) and I strongly recommend their book on boat construction. Epoxy only works when you follow the rules and you need to learn about these. There are many types of "reinforcements" used in epoxy work. Some are powders others material and fabric, I've used all sorts of things mixed into epoxy to provide an additive giving me the requirements I need in the matrix, including paint dust from the belt sander dust collection bag.

Epoxy and 'glass work are highly engineered materials, it's not a time for a good guess . . .

[pungolee]

I would use it unthickened.Make small batches.Use a lot of acid brushes.Have a lot of vinyl gloves that fit.Have a case of empty 1 quart plastic tubs.(At least 24)Get a whole box of wooden stir sticks(100)A 1 gallon waste/scrape bucket.Line up the whole mess where it is efficient,where the work will flow.Since you can't pre-wet out the parts don't be afraid to throw the glue to it.Epoxy is a wasteful,expensive,but very effective process properly used.Make sure you stir the batch properly,I count 100 strokes for two squirts before adding thickeners,which may require an additional 20 to 50 strokes.I have no comment on your joint system.

[bjl_sailor]

I managed to get it together last evening. I did a dry fit with all the biscuits in place and it all aligned properly. Since the temp was about 65 degrees i was able to use the West System unthickened. I had micro fibres but the viscousity of the epoxy seemed ok. I brushed epoxy on everything and assembled it wearing rubber gloves. Without the biscuits to align everything I never would have gotten it together. I was carefull not to over clamp and and squeeze out the double applied epoxy. There was a considerable sheer to this peice and in places it is nearly 10" wide. I never would have gotten the piece in place without out cold molding it of small (1 1/2") strips.

[Not A Guest]

bjl_sailor ---

Let your work cure for a week or so. Then bang it hard with a big hammer several times all over.

This procedure may not find all poor work, but you really should test your work.

[bjl_sailor]

Wow! I'm presently rather surprised by the relative ease of using epoxy for stripping my hull. I had great misgivings about having to epoxy the entire hull but 1 weekend and 1/2 gallon of epoxy and milled fibers /micro baloons later I am very please and relieved. The keelson/backbone went together well prefitted and biscuit joined (just to hold the assembly together). With that cured and cold molded I started stripping using 1/2" thick by 3/4" bead and cove western red cedar. I got apporixmately 60 19' long strips on. I was using rubber gloves and mixed '3 pump batches' with 1/2 micro filaments and 1/2 micro balloons to a peanut butter consistency. This was then carefully applied to the cove and then tacked in place with partially driven #6 finish nails and a few clamps. A real confidence builder! I'm sure I have a lot more to learn about epoxy work but I feel alot better about using it than previously.

[pungolee]

Study "Fillets" in the Guegeone Bothers book "Wooden boat restoration"It applies to new boats as well,this is the secret for strong construction, epoxy fillets.Get good at them.Real good,your boat will be strong!