Best filler to replace balsa core

J

John S

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C Dory Year
2021
C Dory Model
255 Tomcat
Vessel Name
TomCat
Hello all looking for some advice.
Noticed my Bomar hatch was leaking so decided to pull it and reseal. All the wood in the core surrounding the window was saturated with water. I dug out all the wet Core and now I need to fill the void. It measures approximately 1/2 inch thick and goes back 2 - 3 inches all the way around the hatch.
Any suggestions on the best way to fill this void?
Thanks!
 
Probably the best way to go is a couple of tubes of West Systems, Six 10 thickened epoxy adhesive. It is nor worth putting in core such as balsa or trying to cut a material such as foam. The Six 10 is self mixing as you squeeze it out. Be sure that the core left is dry.

I have used epoxy with micro light and cabosil filler mixed together in a peanut butter consistency. This is a little cheaper if you already have all of the epoxy and fixings laying around. No reason to add glass for any structural effect.

Use 4000 for bedding the hatch frame after cleaning it off.

I have had to redo the fore deck hatches on all of the C Dories I have owned, except the first 22. Usually they are not well sealed, some the cutouts for the hatch are too big.

This goes back to every hole in the deck should be sealed with epoxy--some will never develope moisture or rot--but to be sure, since the boats keep their value and last a long time, it is worth it to do the potting properly.
 
X2 on giving the core time to dry. Bog i.e. thickened epoxy to replace the core doesn't need to stronger than the old balsa. Micro spheres or balloons usually used in fairing compounds ought to be adequate as thickener. Some fumed silica (cabosil etc.) may improve the handling characteristics of the bog.
On this big of a pour there will be a lot of heat generated. Consider doing it in stages.
System Three and West Epoxy have good on line booklets that will be very helpful.
 
Thanks guys! I have the epoxy, cabosil and silica on hand (hopefully in sufficient quantity)
Any advice for getting it filled all the way into the back side of the void?
 
At that thickness and depth, could be pieces of any lightweight wood, precut to fit with about a half inch gap at the inside, maybe three eighths thick will work better. Paint the wood with resin and lard the cavity with thickened resin, slid in using a spatula first, so you get plenty of squeeze out. Problem with just using resin/ filler mixes is anything thick enough to build a half inch thickness will be darn hard to squeeze in there using a syringe/tube combo. If you elect to stick with resin, get slow hardener, so you have plenty of time to mix and inject.

It might be you can mix the resin in the syringe (50 cc or larger), add fill and mix again, then insert plunger while turning syringe tip up to expell air, then go for it. Probably take several loads of 50 cc batches. Filling a syringe with thickened epoxy is difficult. The thickened stuff does not pour, so you have to spoon it in there. And if it is really thick, very hard to suck it into the syringe.
 
You might try a pastry bag to insert the mix.

Jerry C Nile
 
No to hi-jack this, but I need to do the same to my deck where our anchor rode enters the locker. The deck hole, at the windlass, is only sealed w/ what appears to be 4200/5200 or similar. I want to cut off any problems before they occur. Should I use the same products?
 
I would like to add a word of caution when using epoxy in confined areas such as this. It will build up some heat during the exothermic chemical reaction as it kicks off. This heat can cause the fiberglass laminates to warp and will make bedding the hatch covers more difficult to get a water tight seal.
When filling a 2 to 3 inch void, its best to layer it up a 1/2 inch of thickened epoxy at a time. Allow layers to begin to gel, to ensure the heat will dissipate before adding the next layer to maintain the chemical bonds. Also, when I filled the void around my larazette hatch covers I used a West System fillable caulking tube which was good at getting the thickened epoxy mixture back (3 inches) into the void. Good luck with your project.

Grazer
 
Hadn't read the last post until now.
Mixed up too much at one time and it ran away in my mixing bowl and now I'm out of epoxy.
I don't mix peanut butter mixture enough to know how much filler it will take before hand. I had too much epoxy and was too slow adding filler to bring the thickness up.
Started expanding in the bowl I took it outside and then it smoked. Nearest epoxy supplies are over two hours away.
 
Grazer":f0p085hw said:
I would like to add a word of caution when using epoxy in confined areas such as this. It will build up some heat during the exothermic chemical reaction as it kicks off. This heat can cause the fiberglass laminates to warp and will make bedding the hatch covers more difficult to get a water tight seal.
When filling a 2 to 3 inch void, its best to layer it up a 1/2 inch of thickened epoxy at a time. Allow layers to begin to gel, to ensure the heat will dissipate before adding the next layer to maintain the chemical bonds. Also, when I filled the void around my larazette hatch covers I used a West System fillable caulking tube which was good at getting the thickened epoxy mixture back (3 inches) into the void. Good luck with your project.

Grazer
Click to expand...

THIS!!!! That much epoxy all at once is going to smoke and end up burning stuff. "Some heat" is putting it mildly. Sometime, over a beer, ask me how I know this.
 
Sorry that your resin kicked off too fast. I should made some cautions--including what I have done before--you have to have the proper hardener for the temperature and size of the job. When in larger batches or warmer weather you want a slower hardener I happen to have been using West Systems for over 40 years--so I keep an assortment of hardeners.

I would not use only cabosil--the microballons are OK--but I just prefer the micro light for large volumes. The Six10 comes in a cartridge--and it mixes the epoxy and hardener as it is squeezed out in what West Systems calls a "Static Mixer". As you work your way around, it will never build up enough epoxy to cause a heat problem. This is the reason I mentioned the six10 initially.

For epoxy on a job like this, I don't mix more than about 4 to 6 oz cup when it is all added up. Recently I have been using the "Greek" Yogart cups which hold 6 oz.

Certainly Dave's technique with wood, is an excellent way to do this, especially if you are skilled in this technique. You do have to put in enough thickened epoxy mixture in a bed first to reach to the old core, then the wood coated with epoxy--and make sure it fills all of it up at the same time. My concern with this is that in this case, the void was not a uniform depth. As long as you fill all of the voids up--this is a good technique. Scarfing wood in, with thickened epoxy can work very well in building up laminates of wood where it will not quite match up (rather than having a perfect glue line).
 
John S,

Been there, done that! Real glad that mix went off in the mixing bowl instead of in the void you are filling. Thataway's suggestion to exploit the reach of one of the mix as you inject two part cartridges is an excellent idea. If you can get one with slow hardener, all the better.

BTW, mixing smaller batches in the syringe, as I described earlier, helps prevent a batch going off, as there is no delay in transferring.

WEST does online ordering, I think. So does System Three, in case you want to avoid that 2 hour drive.

Good luck with the project. It is a challenging one ... but you already know that. :wink:
 
On the way home right now from the four hour round-trip to pick up more epoxy in Homer, AK.
No West system available only system three.
No problem finding a similar epoxy but the filler was a little different. System three had a silica that I bought. I couldn't find what I thought was an equivalent to the 410 Microlite fairing filler. I ended up buying a system three product called "Wood flour".??. It looks like 410.

It is worth noting that I had enough West system left, after my disaster, to mix up a 5 ounce batch of West system Peanut butter epoxy and it went very well. Used a plastic squeegee and a tongue depressor to get it back in the void. Completed about 10% of the job. According to an infrared thermometer the skin temperature never went above 80°F.

Interesting to note that the only hardener I can use is the fastest (206) because of the temperatures I am working in. It is 40 to 50° outside.
My mistake was mixing and storing my epoxy at room temperature.

On my successful batch I made my peanut butter first and then added the hardener.

Open to any thoughts on the system three fillers that I have bought, will start into this project again tomorrow morning.

Thanks again.
 
The wood flour is both a thickening and bulk former agent. It should work fine. If you use micro balloons you have to also use a thickening agent--and both Cabosil and wood flour are thickening agents. You should be fine. Again, I am far more familiar with West Systems--but I add the Cabosil until the material had thickened and then begin the add the thickening agent.

In Florida sometimes we cool the mixing container using an ice water bath, and then let it come up to temp after it is mixed. I can see having only the fast hardener in AK, especially when using out of doors. The environment throws all different types of tricks at us. Looks like your are on track now!
 
The System Three Silica is the same as Cabosil. Both will thicken the epoxy. I prefer those over wood flour as they mix in quicker, but the flour will get you there, also.

How are you measuring out your resin and hardener? Using the pumps? If so, may have to stick to room temp mixing to get the pumps to work well. If you stick to small batches, mix quickly and immediately apply the mix, you should be OK.

Sounds like you have a technique down that works.
 
Here's another idea, but I wonder if it would be strong/dense enough?

For hard to reach areas………..

Could you shoot foam insulation into the void?

I'm thinking of the kind that comes in a can like whipped cream.

After it hardens, you could pick out any that is near the edge, then replace it with the epoxy/microballoon mixture for strength.

Wouldn't work for something that had to be strong and load bearing, like a transom, but might be a way to fill it something that was otherwise difficult to get to, but not heavily stressed.


Joe. :teeth :thup
 
Joe,
I would want to test that--there is very little compression rigidity with the "Great stuff" foam, since it is mostly a crack sealer. Maybe if you painted or squirted in some epoxy to seal the core first and give a hard edge at the old core, and then put in at least 1/4" of thickened epoxy all of the way around the hatch inside.

The fiberglass in the deck is fairly thin. Much of the thickness is the gel coat in the non skid in the top layer. The bottom might be 2 layers of mat--or less...At least in my boats the bottom was not very thick.
 
This project is now complete.
Mixing small batches of 5 to 6 oz at a time seemed to help.
I also think it was helpful to leave the epoxy outside overnight at 40 degrees instead of starting at room temperature.

I didn't get a full cure until I stuck a 40,000 BTU propane heater in the open door of the boat and blasted it in. I monitored the fiberglass skin temperature near the epoxy with an infrared thermometer and it never exceeded 80 degrees.

I used a digital kitchen scale to mix my epoxy, with it set to grams.

Mixing the thickener and wood flour prior to adding the hardener also bought me some time. Just required VERY thorough mixing when adding the hardener.

I appreciate all the advice. If I would have had some 1/2" foam core, I would have liked to bed it in, but I didn't have any in the shop. I have made it a point to NEVER put wood core back in this boat anywhere it has been removed.

All the hatch hold down screws got pilot holes drilled into the mixture once it was cured and every screw was a excellent solid hold.

So....around this hatch it's all epoxy peanut butter filled. Glad to have some more wet balsa core eliminated!!

Just paid $2000 to have every bit of the wet balsa removed from my transom too. (All balsa got removed wet and dry)
 
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