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Recommendations for Hull sealing and Fiberglass insulation

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Hi All,

currently building the Dumas R/C “Carol Moran” Tug ( 1/24 ) and need two recommendations:

1. I just finished planking the hull and need to fill gaps. I bought Bondo and was wondering if there are other products that are easier to apply and sand?

2. The instructions highly recommended applying fiberglass fabric and resin to the outside hull and applying resin to the inside hull to ensure the tug is watertight. I work out of my garage and have never worked with fiberglass nor the resin, is it wise to farm the fiberglassing to a professional?

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I have never done it myself, but Amazon has this:

3M 420 Fiberglass Resin & Repair Kit, .45 Pint   < $ 20


Take a look and see if you can tackle it.

I am not sure how fierce the epoxy resin solvent fumes are or what your ventilation safety is but factor that in.

A thought =  you are covering a wooden surface?  Resin strength needing re-enforcement is not a factor.  Could

you not use actual cotton or linen cloth or even bond paper with the resin, instead of glass fiber or carbon fiber on the


Another thought + Use a solvent based varnish and paper or cloth instead of epoy.  You have your strength already.

All you want is a seamless water proof layer. 

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I helped my grandson build a Dumas vessel with wood and PVC hull. We had to fair in the chine against the side planking and we used both Rage and 3M 2 part mix that sands easily and gives an incredibly smooth finish. I (we) found it worked better than Nitro Stan putty as it does not shrink when dry and it is a dry sand process rather than a wet sand which can be tricky near, for example, the wooden planked sides.


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Hi - Here's a link that will explain how to use cloth and resin successfully.  I use the roller method and although the instructions are a bit wordy, once you get going its actually very easy to do.  I always use isopropyl alcohol between coats to take the "fat" off of the set resin.  It works well for me and gives a glass like finish ready for painting.  The instructions are for an aircraft but the process is identical for hulls.




I hope this helps and good luck


Edit - I should have said; use epoxy resin not fibreglass resin as the fumes are a lot less and its far easier and less messy to work with.

Edited by No Idea
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  • 2 weeks later...

The polyester also uses the heat of the reaction to set, and in thin sections may not harden well. One one of my Combat Warship models, I had to put the hull in the hatch of my car and park it at work so that the sun shone in all day. It took several days to finally set fully. The car stunk to high heaven for a week, but my hull was ready.

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  • 4 weeks later...

After building a couple of plank on bulkhead models and later seeing gaps appear between some of the planks I decided to try something else.


I used a two-part liquid epoxy "paint" to coat the inside of the hull planking (single layer planking). Airplane modelers use this paint (actually it is a bit thicker than ordinary paints) to seal balsa engine supports and firewalls so fuel doesn't soak into the wood. It is thin enough to just paint on with a disposable brush - I applied a couple of coats to build up a thick layer.


Because it is thin and runny at first it oozes between neighboring planks and fills cracks, and it flows between the planks and the bulkheads. It also soaks into the wood a bit. After it hardens the hull is very strong.  You can sand down any glue beads that flow to the outside.


I think I also painted a very thin layer on the outside of the planks. It is colorless after it hardens and after it is sanded you can use 0000 steel wool to polish the planking to a nice satin sheen. There was no noticeable discoloration of the wood (and still isn't).


As I recall it set in 30 minutes and has almost no odor.


After about 20 years now there still are no cracks between planks in the hull.




I know some people apply fiberglass to the inside of planking, but I think this is overkill, except possibly for hulls that are two or three yards/meters long. A heavy coat of epoxy makes a good seal and holds things together nicely.



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