I am getting back into the hobby after a 20+ year hiatus. I am currently building the fuselage of my LT Kadet 40 and had a question about fuel proofing.

The instructions call for painting the engine compartment with dope to serve as fuel proofing. I have read in this forum that it is best to epoxy the engine compartment. In addition to providing fuel proofing, it adds to the structural stability of the area. However, I would like the engine compartment to match the color scheme of the aircraft, so can I epoxy over the dope or dope over the epoxy?

vkernus,
my personal preference is to epoxy over the dope. The epoxy affords protection for the paint as well as the structure. Any added strength benefit is minimal either way. You can thin the brush-coat of epoxy with a bit of alcohol for easier application.

I agree with vinnie, go with epoxy over the dope. The thinned epoxy will be great. Great Planes makes some finishing epoxy that is supposed to be perfect right out of the bottle. Have never tried it, but it's sitting on my bench just waiting there.

There's always someone who will disagree and I guess that's me on this one. What Vinnie and Jack are recommending will work fine, but let me point out a couple of my thoughts; then you decide.

To merely fuelproof you only need to dope the area. If you're looking to strengthen the structure, the finishing exopy works somewhat because it tends to soak into the balsa as it cures. If the dope were applied first, the epoxy would have less tendency to soak into the grain.

I recommend epoxy first, dope second, mount engine third, and fly for fun fourth. (had to get that alliteration in)

I really appreciate the input. Finding this board has been a great help.

It does seem to make sense to epoxy first, as Ed stated, the epoxy can leach into the joints adding structural strength to an area that is subject to extreme forces. While the instrcutions say that dope will help adhere the parts, I don't think dope has the strength of epoxy. I really wasn't sure whether the dope would adhere to the epoxy or flake off over a short period.

Again, I do appreciate the input

you can also add paint to the poxy and have the best of both

Sounds like overkill to me. The extra strength of a thin film of epoxy is minimal at best. If you're using dope for sake of the color, I wouldn't bother using epoxy over OR under it.

I agree with MinnFlyer 100%. I doubt if the additional strength would even be measurable. Think about the effort and the benefit.

Having said that, I alway paint the inside and outside of my firewall, landing gear mounts, and wing saddle with 30 min epoxy thinned with lacquer thinner. I also cover the outside of the firewall (after epoxy) with covering. It looks good and is very fuel resistant.

I asked a similar question a short while ago.

I ended up using thinned epoxy and then I sprayed over the area with Lustrekote....

Thanks for all the input. Gives me alot to think about. There is so much that goes into kit building, and I have been out of the hobby for so long it is nice to know there is someplace to get advice.