Bog Recipes?

[CatBuilder]

Bog can be used in a few different ways:

1) As a fairing compound

2) As a filler


What are some good bog recipes for both situations?

Specifically, if I choose to bog the inside of my hull, is bog strong enough to take the loads from the bulkheads?

Would you use a different bog recipe for the inside of the hull vs. the outside, since the inside has structural loads like bulkheads, while the outside is mostly for show?

[Herman]

It is good practice not to use any bog on the inside, before the bulkheads are installed. Tabbing needs to land on bare laminate.
After that, you could scrape things smooth with some commercial product, or with a mixture of epoxy, microballoons and perhaps a small amount of silica. When scraping, dont worry about minor imperfections, they can be fixed in the second round of scraping.

For the outside you can do the same. After you are 95% fair, roll some layers of epoxy over it, then correct the small problems still missed (usually some dents, scratches aso) with fine fairing filler, usually available from your paint supplier.

[CatBuilder]

Ok, no bog inside.... I had suspected that. Thank you.

Excellent advice, thank you very much, Herman.

[AndrewK]

When you run out of peel ply or you dont like using it then fill the weave where you have structural bonding with a runny resin and silica only bog.

For a fairing bog I like consistency so weigh all of the components, will get back to you with the recipe as its on the wall of by shed.

[Herman]

Be careful, particle size is very important. If you do not have the exact same materials as Catbuilder, then he might end up with runny product, or something too stiff.

Still, it is nice to see what others use, and it can definately be a guideline.

[PAR]

I divide fillers and fairing compounds into three basic categories, light structural, heavy structural and cosmetic.

The structural mixtures often are application specific, for example I'll use milled fibers for bonds on 'glassed surfaces, or wood flour for color or on wood surfaces. I generally use silica to control viscosity and use calcium silicate (West 404) and/or cotton flock (West 403) and/or milled fibers in heavy structural mixtures. Talc can be added to these heavy mixtures to help smooth them out, particularly if milled fibers are used and you want to make reasonable clean fillets that will be taped over. A heavy mix is almost always taped or otherwise skinned with fabric.

The light structure mixture can often stand alone, so it'll have a higher "non-fibrous" material percentage. This would be again talc and/or balloons and/or spheres. As a rule the material used in structural mixtures are quite fibrous when view under a microscope. This is why they're so tough, they physically interlock within the cured matrix.

For example a moderately heavy mixture would be West 405, which is wood flour, silica and cotton flock. There's not much wood flour in this mixture and it's there for color mostly according to the chemists at West.

Fairing compounds use materials that are generally smooth and round under the microscope. They have less surface area for the resin to grab, so they're easy to sand. Phenol balloons, micro spheres, talc, etc. These materials shouldn't be used in structural mixtures, as they're just bulking up the resin, but offering little in terms of strength, stiffness, etc.

Ultimately, you'll just have to develop a set of mixtures as you gain experience. Each mixture will be governed by the environment and the application. Some will need to be thicker, stronger, easier to sand, non-sagging, smoothly applied because it's difficult o get in there and sand it smooth, etc. Lots of stuff will affect the content of your mixtures.

Some just buy pre-mixed fillers, but you pay through the nose for this luxury. Buy the basic filler materials in bulk, big tubs of the stuff, you'll use surprising amounts of it. You can pre-mix some if you like. I have a few gallon jugs with pre-mixed materials in them, at the proportions I usually need. Of course they get "doctored" up as I use them to improve viscosity, adhesion, etc., but the basic mix is there. It's so much cheaper to do it this way too.

[Herman]

For storing the fillers these IKEA boxes come in handy. They come in 2 sizes, this is the larger one. The lid keeps the fillers clean. The name is "Sortera" (at least in Holland)

[PAR]

I prefer to store bulk materials in sealable containers. This keeps out air, with it's captured moisture, which can cause some of these materials to clump and even rot. At a local veterinary supply store, I was able to find 2.5 gallon wide mouth plastic jars. I also have 1 gallon plastic jars that pretzels came in. Both work well and can be sealed down tight enough to drop in a pool without worry they'll leak.

[AndrewK]

For fairing I use QCells, Phenolic balloons, and Silica.
Internally I use the cheaper Qcell and externally phenolic balloons.
If the budget can stand it then adding West Microlight to the mix is nice as it makes the bog smoother to apply and easier to sand.
The reason for weighing the components is to have consistency from batch to batch so that it's all the same hardness.
Our climate is hot so usually only make 1kg resin batches or less in a 9L bucket, if the components have gone lumpy I push these through a sieve as I add them.

Resin mix grams x 0.27 = g spheres + x 0.01= g silica

This is a basic recipe for the resin I use that I fine tune only for the day time temperature.
Viscosity of your resin mix and particle size of the spheres will influence this.

The nicer expensive mix is:-
Resin mix g x 0.1 spheres, x 0.01 silica, x 0.06 microlight
Also happens to be a very easy formula that you can do in your head, for my resin viscosity that is.

I apply the bog with the standard plasterers trowel that I round off the corners on one end so that you can trowel right into your coves.

After long boarding I fill and screed the hollows.
Then spray with neat high build followed by second heavy coat of high build to which I add 25% vol phenolic balloons or microlight.

Repeat with home made spray bog until happy with the surface and then apply final coat of neat high build.