Integral fuel tanks

Forgive me for asking for information that has already been discussed, but I’m reading a lot of conflicting input, need to clarify.
I’m considering utilizing some empty spaces below the deck as integral diesel fuel tanks.
The FRP hull, stringers and bulkheads are all stoutly laid up with fire retardant resin.
Once the fittings are in place, and the baffles glassed in, what’s the proper coating for the tank’s interior?
I will bevel cut the floor out to access the tank interior, and replace it last step.
What’s best goop to reseal the lid?

 

No coating needed. What kind of resin did you laminate the baffles with?

I would use epoxy resin as a coating . Oiled composites are difficult to glue later but oily layer of FRP can be washed and sandblasted for later repairs.

 

There are quite a few VE resins that work great for this, each resin manufacturer has a list of their resins and recommended applications.

 

There are coatings available for your purpose, I don't know what names they go by.
Epoxy would be my choice for resealing the lid.

Have you considered raising the safety level by using bladders?
In this case I would use a 5200 like product to reseal the lid.

 

We used an equivalent vinylester to the one express composites sells, no sure what product lines you have on hawaii. Lid was bolt down to a flange we layed up, with an orange high density rubber that was some kind of fuel resistant (can't remember what rubber it was and was unsuccessful at searching my email to see where we ordered it). It was not reccomended to use 5200 or sika 291 for long term sealing, we ended up using some kind of permatex product that went on either side of the gasket. Fittings on two of the tanks were via stainless top plates, my belly tank has some frp fittings from an outfit in California that does frp fittings. Our baffles were some left over thin gague stainless we tigged together in a grid of sorts.

 

After more research, there are $pecialized coatings for this purpose, but I see lots of recommendations to just seal coat the interior with waxed vinylester resin.
I’ve got to cut out the top, seal up some limber holes and add baffles first.
I’m considering cutting out the floor, which is dense foam glassed both sides, at a 45* bevel so that it locks back in without having to add a lip to support it. The goop will also be vinylester with cabosil, hopefully it won’t squeeze out on the inside leaving debris in the tank.
I should probably add an access port anyway.

 

After cutting the floor 45* which is a good idea, you can make an access port in this cut out part of the floor before gluing it in. Unless the access port has to be somewhere else.