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Epoxy and Fillers



MAS Epoxy Resin MAS Epoxy Hardeners MAS epoxy Fillers

These are the same MAS epoxies we use at Devlin Boat to build many of our stitch and glue designs. We offer MAS low viscosity resin, MAS FLAG resin, MAS slow hardener, MAS medium hardener, MAS fast hardener, wood flour, micro-balloons and cab-o-sil. With these products you can build a7' dinghy or even a 45' motor yacht.

The MAS slow viscosity epoxy resin easily saturates fiberglass and can give you a thin, even coat of epoxy over sanded fiberglass or wood. If a thicker epoxy resin is desired use MAS FLAG resin or you can simply add cab-o-sil and/or wood flour depending on the application.

There are three MAS epoxy hardeners fast, medium and slow. They are mixed with the epoxy resin at a ratio of two parts resin to one part hardener. The hardeners can be mixed together to speed up or slow down the cure time. If you mix the hardeners, it is still two parts resin to one part of mixed hardener. The fast hardener cures quickly, but creates a by-product called "blush" which is a thin waxy layer that develops on the surface of the cured epoxy. It is a nuisance but is easily removed with water. If the climate is hot and dry, it may not be noticeable, but in cool and damp climates it will appear and need to be washed off with water prior to sanding, and re-coating. The slow hardener does not create blush and can be re-coated the next day without washing or sanding. The medium hardener is blush resistant, you will generally get no blush, but in very damp and cold conditions a little blush will form.

There are many fillers but all you need are two, wood flour and cab-o-sil. I like to mix the two (50/50), which makes a good all-purpose filler. For making fillets and general filling, the wood flour alone will work, but with cab-o-sil added you will get a filler that spreads much much smoother. For thickening epoxy resin for bonding or cold molding you can use both fillers, the 50/50 mix works great. To thicken epoxy for sealing or flow coating you should use only cab-o-sil. Micro balloons can be added to epoxy to make a sandable fairing compound.

If you have any questions about epoxy and fillers feel free to contact us at randy@boatbuilder.org or call Randy Foster at 360-870-2526.

Joel Mill


Working With Epoxy and Fillers


Working with epoxy requires only a few very basic tool. Measuring and mixing are the two most important steps to any epoxy job, get it wrong and it does not matter how well you do everything else. I use 14 ounce graduated cups for measuring and for batches over 6 ounces I pour it into paper buckets to mix. If the mixing container is to full, a good mix is hard to do. I like to stir the epoxy with the mixing container on edge a bit while working the mixing stick, much like you would an egg whip. Mix for about two minutes occasionally scraping the bottom and sides of the mixing container.

The two most used tools are the roller and squeegee. In addition to the roller cover in the picture below, I also use 1/4" nap foam roller covers. The squeegees are used for wetting out glass lay-ups, applying fillets and spreading epoxy when cold molding.


Epoxy and Stitch and Glue Construction

For sealing bare wood, glass or Dynel a roller and brush are used. Whenever epoxy is rolled on there is a textured surface left behind with small air bubbles and therefore it needs to be tipped off. On small areas a bristle or foam brush will work fine, but on large areas I cut foam roller covers in half in slip them into a notch that is cut into a piece of wood with a bands saw.

Epoxy is relatively thick and needs to be worked with the roller or brush to get an even coat. Is is very easy to get to thick of a coat and you will end up spending a lot of time sanding out runs and sags.


Epoxy and Stitch and Glue Construction

The squeegee at the left has been rounded for making fillets, and the notched one to the right is for spreading epoxy during cold molding. This one was used for a specific job and generally the notches are shallower and spaced closer to together.
Epoxy and Stitch and Glue Construction

For fillets, a "peanut butter" mixture is made. The epoxy is mixed first and then wood flour is mixed in. I also like to mix in cab-o-sil to make it a bit smoother but it is not necessary.


Epoxy and Stitch and Glue Construction

There is tendency to make the peanut butter to thin, if you can't scoop a big wad of it on the stir stick without it sluffing off it is to thin. You can lay down a perfectly fine looking fillet only to come back in 10 minutes and find it sagging. Re-working the fillet will only make the material become thinner.


Epoxy and Stitch and Glue Construction

To make fillets I grab a handful of peanut butter and smear it into the corner. Lightly run the squeegee at about a 45 degree angle along the joint then again firmly and at less of an angle. There is usually at least one sharp edge on a squeegee, use it to scrap off the excess peanut butter.


Epoxy and Stitch and Glue Construction

Fiberglass lay-ups consist of one to three layers of biax and two layers of tooling cloth. The two layers of tooling cloth are the same width and the first layer of biax is two inches narrower with each other layer of biax being two inches narrower than the previous. This makes the glass easier to grind smooth later. I do not use peel ply with the lay-ups, the job goes much faster without it and I think the end result is better as well.

I will explain applying glass lay-ups later. For sheathing a hull, decks, soles, cabin roofs etc. I use tooling cloth or Dynel. Most of the time Dynel is used, I only use tooling cloth on small skiffs and dinghies. With tooling cloth you can lay it down over dry wood and pour epoxy over it working the epoxy in with a squeegee. It wets out fairly easily and pre-coating the surface with epoxy is not necessary. Avoid using to much epoxy, the surface should have a texture to it and if there are glossy areas work out the excess epoxy with the squeegee. For applying glass to a small area or working it into inside corners, a 2" bristle brush is the tool of choice. When using small patches it is easier to pre-wet the surface so the tooling cloth will stay in place as it is worked.

Dynel is a bit more difficult to work but the end result is a thicker layer of protection because the Dynel tends to swell a bit. Dynel also has better abrasion resistance than tooling cloth as you will find out when you grind and sand it. Dynel requires more epoxy to wet out than tooling cloth and it is slower to saturate. I always pre-roll the surface with epoxy, lay down the Dynel and roll more epoxy on. It probably requires twice the epoxy, if not more, and takes twice as long to apply than tooling cloth but well worth the protection the boat gets. The big bonus is that it does not itch when you sand it.

Biax is applied like Dynel; wet out the surface with a roller, lay down the biax and roll it again until it is saturated. For multiple layers just keep adding and wetting out one layer at a time. Always cover biax with a layer of tooling cloth or Dynel. It does not have a smooth surface when wet out and you will spend a lot of time filling after it has cured.


Epoxy and Stitch and Glue Construction

Glass tapes are convenient but come with a selvage edge to keep it from unraveling, but I have found that it can cause air pockets when it is over lapped, so I cut the widths I need off of a wide roll with a razor blade and straight edge.


Epoxy and Stitch and Glue Construction

Lay-up trays are made out of plywood, a 6' x 20" tray will do just about everything you need. In the pictures below the trays were lined with plastic because they were used earlier in the day and became very tacky. When the trays get to sticky it makes it difficult to pull off the lay-up cleanly.

To wet out a lay-up lay out the tooling cloth first, pour on some epoxy and spread it out with a squeegee. Then add the biax layers wetting them out one at a time. It will take a bit of practice to get the right amount of epoxy in the lay-up. If you pull it off and epoxy is dripping off it... to much epoxy. If the lay-lay-up is to dry it will take a lot of extra work to get it properly applied to the wood.


Epoxy and Stitch and Glue Construction

When the glass is set in place it is jus a matter of working all the air out from underneath it. There is a wide assortment of rollers for doing this, but prefer to us the side of my thumb. I only apply lay-ups over uncured fillets so care is taken not to push to hard into the corner..


Epoxy and Stitch and Glue Construction

The hardest areas to sand and do body work to are corners, they are also the areas that are most difficult to do neat work in. A corner with multiple lay-ups, each with multiple layers of glass and each of those with multiple stray strings, the corners can become a damn mess. The picture in the lower left has three lay-ups meeting in the corner, but I added several 2"x2" tooling cloth patches which holds all the loose ends in place and keeps the fillet smooth. This is the best spent two minutes in all of boatbuilding. Your finger tips will love you when it is time to sand.


Epoxy and Stitch and Glue Construction






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