Voids found after new transom install

[KesselRunner]

Been working on restoring an old powerboat with a 2 stroke 115 hp outboard.
Recently installed the new plywood core in the transom. Did it from the inside using thickened epoxy.

My problem:
After the install it feels rock solid. But, I have found some voids where it seems I did not get enough clamping pressure. The location where I got a good bond and where there are voids between the plywood and outer skin can be seen in the attached figure.

Since the larger center regions of the transom got a good bond I do not feel like ripping it out again which I could only do by completely destroying both plywood and skin given that there is proper adhesion on the greater part of the surface.


As I see it I could either remove the skin in the regions where I have found voids from the outside which would allow me to do a real surface prepp, fill with thickened epoxy and then re-install the skin with bevelled edges and new glass.

Or I could just inject slightly thickened epoxy in these areas but I'd really like to hear some thoughts on how good that adhesion can be expected to be as I cannot sand the surfaces and the plywood has been covered in a layer of epoxy so it's actually a cured epoxy to cured epoxy bond that would be happening without any surface preparation.

Filling the voids to stop moisture from accumulating in these areas are of course something I will prevent by just filling these pockets with a syringe but what I want to make sure is that it is structurally sound. Advice and thoughts are much appreciated.

 

[sphelps]

I think your on the right track with injecting epoxy .. You may want to drill a few weep holes to let the air out of the void and ensure coverage of the injection . Then clamp it down somehow till it cured .
Maybe pop a few short screws through the skin to help pull it tight ..

 

[KesselRunner]

I think your on the right track with injecting epoxy .. You may want to drill a few weep holes to let the air out of the void and ensure coverage of the injection . Then clamp it down somehow till it cured .
Maybe pop a few short screws through the skin to help pull it tight ..

Would this do more than just fill these voids? I mean, would it add something for the structural integrity?

Since these are regions where I would be putting epoxy on unsanded epoxy trying to glue it to another unsanded epoxy surface.

 

[KJM]

How do you know there are voids there? I would do as you suggest and inject slightly thickened epoxy. Not sure clamping or screws are necessary as the 2 pieces are already bonded together and cant move. Weep holes for air to escape are a good idea, also you will know you have it filled when epoxy comes out of the other hole.

 

[KesselRunner]

How do you know there are voids there? I would do as you suggest and inject slightly thickened epoxy. Not sure clamping or screws are necessary as the 2 pieces are already bonded together and cant move. Weep holes for air to escape are a good idea, also you will know you have it filled when epoxy comes out of the other hole.

First knocking and then drilling some small holes to confirm.

Any thoughts on how this affects structural integrity?

 

[KJM]

First knocking and then drilling some small holes to confirm.

Any thoughts on how this affects structural integrity?

I would think if you filled the voids with epoxy it should be fine. Did you put much fiberglass on the inside after replacing the plywood? If the inside is good and thick and is tied into the sides securely then I would think you are good. Did you have lots of thickened epoxy around the edges of the plywood core? Having said all that, I'm no engineer and others might have a different opinion. I replaced my transom last winter, gluing it in with thickened resin over CSM and i'm sure there must be some small voids in there but the boat has been perfect all summer and is solid as a rock.

 

[KesselRunner]

I would think if you filled the voids with epoxy it should be fine. Did you put much fiberglass on the inside after replacing the plywood? If the inside is good and thick and is tied into the sides securely then I would think you are good. Did you have lots of thickened epoxy around the edges of the plywood core? Having said all that, I'm no engineer and others might have a different opinion. I replaced my transom last winter, gluing it in with thickened resin over CSM and i'm sure there must be some small voids in there but the boat has been perfect all summer and is solid as a rock.

Yes I added some thick cloth to the inside skin after I had removed the old plywood so there are no problems there. I slabbed on what I thought was a good amount of thickened resin and it oozed out at some locations but not all which was the reason I started to worry in the first place.

Having drilled here and there now I know that for the major part there was good plywood-skin compression. Still worry about the size of the voids and wish I had been more generous with thickened resin.

 

[kcassells]

That's a lot of voids. Resin alone won't do much. Its brittle and would probably crack on stress. Needs chop strand. I would open all the voids from inside as large as the void, fill with PB/chop strand the finish with glass.
Slow tough repair. Bummer.

 

[KesselRunner]

That's a lot of voids. Resin alone won't do much. Its brittle and would probably crack on stress. Needs chop strand. I would open all the voids from inside as large as the void, fill with PB/chop strand the finish with glass.
Slow tough repair. Bummer.

Exactly what I thought about doing if syringes filling was no good.

I do not see the point in doing it from the inside?
I would have to remove odd bits of the plywood to access the inside of the outside skin.

From the outside I could cut out the full size voids, prep the surfaces for a thick layer of PB and chop-strand and then install the old glass that covered the void with bevelled edges.

Sucks with the added work sure, I'm just happy if I can get it good though.

 

[JASinIL2006]

I'd drill some large holes (and relief holes) and try to inject thickened resin using a turkey baster or something that would allow you to really squirt that stuff in and fill the voids. You maybe could even use PL Premium and a caulk gun to do the same. That sounds a lot easier than cutting the skin from the outside.

 

[KesselRunner]

I'd drill some large holes (and relief holes) and try to inject thickened resin using a turkey baster or something that would allow you to really squirt that stuff in and fill the voids. You maybe could even use PL Premium and a caulk gun to do the same. That sounds a lot easier than cutting the skin from the outside.

Yes, that's an idea, I'd use epoxy though.

The benefit with cutting the skin around the void is that I can do a surface preparation before filling it in.

 

[kcassells]

The ole' turkey baster method...yea, yea. That could work. Personally I would like to see the whole void so I can repair properly and never doubt myself. I was going for inside just to save the exterior transom skin repair, patch, paint.
Scott is usually 99.9% on the money.

 

[KJM]

Hate to be a downer, but have you considered that there might be smaller voids and empty channels all thru the contact area between the plywood and outer skin? You might be only detecting the big ones. Maybe for saftey sake and peace of mind you should just take out the plywood and do over? Sucks but at least you will KNOW its done right instead of hoping......

 

[KJM]

Another thought.....would a stud finder for walls in a house be any good finding voids in a transom?

 

[kcassells]

Personally I'd rip it out.

 

[KesselRunner]

Hate to be a downer, but have you considered that there might be smaller voids and empty channels all thru the contact area between the plywood and outer skin? You might be only detecting the big ones. Maybe for saftey sake and peace of mind you should just take out the plywood and do over? Sucks but at least you will KNOW its done right instead of hoping......

Thickened resin did ooze out from the perimeter around the whole central part during installation, otherwise i would have stopped right then and there. And like I've written I have done a series of drilling to confirm.

Knowing that it is properly done would be achieved by filling in the voids after exposing and prepping them, what would be the difference from starting from scratch except some more primary bonding? I really dont see it being that much better, just costing a lot more because nothing is going to separate without a lot of grinding..

 

[KesselRunner]

Personally I'd rip it out.

But if I have confirmed that it is limited to some areas and I do it the hard way by removing the glass it should be just as good as if it had been right from the start?

There really was good clamping and oozing out resin around the perimeter all around the center and bolt holes.

 

[KesselRunner]

Sorry dont mean to not be listening what is said but i have been lurking around the forums long enough to see "toss the hull" etc. a little too much.

I dont mind doing the work but ripping something out that people generally seem to agree on can be fixed seems extreme, especially since I'm considering not just doing it the syringe style.

Really, look again at the paint image in the first post before suggesting a total do-over. I did not guess what was red and what was blue. Should i find something completely different after removing some skin I'll obviously reconsider.

 

[KJM]

Like i said, I'm no expert, but if you're confident that the voids you have marked are the extent of the problem, then filling them thru drilled holes will probably work. I would think this will work, time will tell. With a good layer of glass on the inside, the sides embeded good and most of the outside secured, you are likely good to go. Others may disagree!

 

[flashback]

I'd drill some large holes (and relief holes) and try to inject thickened resin using a turkey baster or something that would allow you to really squirt that stuff in and fill the voids. You maybe could even use PL Premium and a caulk gun to do the same. That sounds a lot easier than cutting the skin from the outside.

Years ago I was able to get empty caulk tubes from west systems epoxy. They work well.