Which MAS hardener and question on adhesive for frame

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Which MAS hardener and question on adhesive for frame

Post by brockj »

Just beginning to pick up the supplies for my build and decided to go with MAS epoxy as it seems to get good recommendations. I am also able to get it locally which is an added bonus. My question though is on which hardener I should choose, specifically because it will probably be a bit cooler in my workshop (my goal is to keep it at least 50F, but doubt it will get much warmer than 60F). I picked up the MAS low viscosity epoxy resin, so looking to match with that.

Also, I have been considering the use of titebond 3 during construction and saving the epoxy for encapsulation and fiber-glassing. Any reason it would be better to use the same MAS epoxy (I believe I would also need to add sawdust to thicken it up) than titebond 3?

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Re: Which MAS hardener and question on adhesive for frame

Post by JimmY »

Hi Brock,

Looking at the MAS website: https://masepoxies.com/faq/

At 50F the slow hardener gives you over an hour of pot life, and sets in 15 hours, but takes 15 days for a full cure.
the medium hardener gives you 40 minutes of pot life, 9 hour setup, and 10.5 days for full cure.
the fast hardener gives you 20 minutes of pot life, sets up in 6 hours, and 6 days for full cure.

If you get the temperature up to 68F, these times basically get cut in half. When you are encapsulating, you want to be able to re-coat in a reasonable time frame to build up the layers, so consider this in your decision. For bonding, pot life is less important than the cure time since you will want to glue pieces together and move on in a reasonable time. You may want to have 2 different hardeners depending on what you use the epoxy for. I would read everything you can find on MAS epoxies so you know how to work with them. For encapsulation I highly recommend a no-blush epoxy (like MAS), since it will save you a lot of sanding provided you are able to re-coat within the specified time for your epoxy.

One thing you might look at is adding heat under the hull to speed up the cure time. Even a few 100W light bulbs (if you can find them) can help. I used a small electric space heater under my hull to heat up the plywood before glassing and then turned it off to help with bubbles, but you could leave the heater on so your hull will be warmer than your shop.

Several here have used Tite-Bond for their frames with good success. Your joints need to be tight for this to work well,so I think this has been limited to applying gussets to frames. For applying the plywood skins, I would plan on epoxy, since you will need the working time and unless you have a perfectly fair hull there will be some gaps to span.
Nothing says poor craftsmanship like wrinkles in your duct tape!

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Re: Which MAS hardener and question on adhesive for frame

Post by TomB »

I am using MAS on my boat. I mix and match between low and medium viscosity and slow and medium hardener. My shop temps run from 60F to 75F. I haven't noticed much difference in reaction time because of room temps. Left in a mix cup or spread out in a paint tray matters a lot for open time, spread it out if you don't want it to cook off.

For encapsulating I use a low/slow combination and I get a good hour of time before it tacks. Brush, foam roller, or squeegee for spreading. After the first coat, rolling and tipping with a foam brush gets a reasonably flat finish.

For joining I use medium/medium or slow. The medium/medium tacks off in 30-45mins. (I'm usually working out of the mix cup). I've used silica, ground glass, and dust for thickening, and prefer dust. I use the dust from my belt sander bag. Silica cures a whitish color, glass cures bluish, and dust is a dark mahogany. I use a chip brush or an acid brush with the bristles cut down about 50%. Somebody said that chip brushes shed like an old dog. By cutting the bristles it sheds like a short haired old dog, but it makes it easier to push the epoxy where you want it. The low vis resin works too, it just needs a little more filler.

If limited to one choice, low viscosity with slow hardener.

I started out with pumps and also tried weight. For MAS 2 to 1 ratio works good for mixing by volume, mixing by weight is too much math. Pumping is too much math too, was that 10 pumps or 11. I have three sizes of graduated cups, biggest is 16 oz.. Two ounces of resin and one ounce of hardener in a small cup mixed with a tongue depressor and spoons of sanding dust for consistency works for me when joining. After you're done wipe out the cup with an alcohol soaked paper towel. I get eight or ten uses from a mix cup before they get brittle and crack.

I wear nitrile gloves and safety glasses. If I get a drop of the stuff on me, I clean it off with white vinegar.

I use TB III for gluing in bungs everything else gets epoxy. Its too easy to loose a glue up because the TB has skinned over. I have painful experience with such things. :oops: :oops:

My two cents,

In the home stretch on a Tahoe 23

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