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Glueing cellular PVC board to fiberglass

Old 07-13-2020, 10:45 PM
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Default Glueing cellular PVC board to fiberglass

Specifics: I want to glue a couple of 1/2" thick pvc panels to the inside on the vertical surfaces (back and sides) of a very thin walled fiberglass, T-top electronics box.

This will serve to mount items including terminal blocks, maybe a mic clip, switch panel and to have something to neatly affix wiring to. Nothing too heavy or critical will be attached but I also don't want it delaminating in the rough service that it will see and would hate to have to take everything back apart to clean and re-bond it.

If the pvc panel is going to be a marginal solution then I may have enough marine plywood to get me by. I'm plenty experienced with that and epoxy but really wanted to try the Cellular PVC of which I now have plenty laying around but have absolutely no experience with.

This material is cellular PVC and comes in a variety of names, including Celtec, Veranda, etc.

Will plain old west system epoxy with a little cabosil, work? I have plenty of that on hand and that is my preference. I don't plan on using any fasteners from the outside or a fiberglass skin over it from the inside, just a bedded bond with whichever adhesive.

I plan on hitting it with 40 grit prior, maybe even scoring it with shallow circular saw kerfs, but wondering also if it would be advisable to flame treat it like I would starboard?

I am seeing recommendation that are all over the place that include bondo resin jelly, various epoxy formulations, west g-flex, even PVC or ABS cement.

Any help before I dive in?


Old 07-14-2020, 08:26 AM
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I did a similar project, roughed up the pvc and used thickened epoxy. Has held up for 4 years so far.
Old 07-14-2020, 08:56 AM
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Originally Posted by CR295 View Post
Specifics: I want to glue a couple of 1/2" thick pvc panels to the inside on the vertical surfaces (back and sides) of a very thin walled fiberglass, T-top electronics box...

...I am seeing recommendation that are all over the place that include bondo resin jelly...

I haven't used it myself but I have noted
Bondo Fiberglass Resin Jelly Bondo Fiberglass Resin Jelly
has been recommend in the past, as you've suggested.
Old 07-14-2020, 09:14 AM
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I used a PVC block on my transom for a transducer mount. First rough it up then apply PVC glue to the block and let it cure. I then used 5200 to stick to the hull and it has held up just fine. The 5200 sticks to the PVC glue and not the actual PVC. Read it somewhere and it works and it simple. For your application you could use 4200 and be less permanent.
Old 07-14-2020, 11:49 AM
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40 grit + flame + thickened epoxy will work great and last forever.
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Old 07-14-2020, 01:06 PM
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Thanks for all the responses. Excellent info and I'm learning some good stuff on a material that I havent worked much with.

I did some experimental test bonds with scrap PVC board that I had laying around (to each other) not to fiberglass. I used abs cement and holy cow when it was clamped there was no seperating it without breaking it. This in my opinion might be a great way to make a custom switch panel box in the t-top so I'm gonna give that a whirl.

For the project at hand, I'm prob gonna go with the thickened epoxy, 40 grit and flame treatment route because I have plenty of west system around.
Old 07-14-2020, 01:54 PM
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did both sides of the interior of my console using 5200. Have a 6 channel amp mounted on one, an inverter on the other, plus my N2K Ts on both sides. Has held up perfectly for four years so far.



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Old 07-14-2020, 01:56 PM
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also, there's really no need to flame treat the pvc board. With Starboard, yes, but not with PVC.
I'm sure it doesn't hurt, but I've used pvc board attached via 5200 or epoxy plenty of times.
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Old 07-14-2020, 02:59 PM
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For your use, rough it up and glue with thickened epoxy.

There are two articles addressing glueing. The first using West systems looked at peel strength, and either flame or pvc primer and cement yielded the best results, but most composite foams offer poor peel strength because the resin doesn’t penetrate deeply into the surface.

The second article used Gflex epoxy for structural repairs. The results were impressive, but overkill for bonding glass to pvc for backing blocks or even for low stress laminates.
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Old 07-14-2020, 03:42 PM
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You are right that flame oxidizing probably isn't necessary, but it does improve the bond and I do like fire....
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Old 07-14-2020, 03:47 PM
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Originally Posted by croakerpoker View Post
I used a PVC block on my transom for a transducer mount. First rough it up then apply PVC glue to the block and let it cure. I then used 5200 to stick to the hull and it has held up just fine. The 5200 sticks to the PVC glue and not the actual PVC. Read it somewhere and it works and it simple. For your application you could use 4200 and be less permanent.
Interesting concept. I found some articles on this (once I was educated enough to use the proper search terms).
Thx man.
Old 07-14-2020, 04:15 PM
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Good education for me.

On another note, if someone is considering using cellular PVC sheet as a top material on a small T-top, I provisionally recommend it.

I had a choice of going the Sunbrella laced fabric route ($250 to $350) or making my own top out of Starboard (expensive and heavy) or out of foam, coosa, marine ply (expensive and labor intensive). Once I looked at the big picture such as materials and labor involved, including waiting for all that crap to dry in between, the PVC sheet seemed like a no brainer.

I have a small 4x6 t-top that it worked perfectly for on a little skiff. A 4x8x.5 sheet was 68 bucks at the depot. Time will be the judge but so far its really nice and was super easy. On bigger tops, I'd like to know if scarfing, butt joints or other joinery methods would work out with joining 2 sheets? The bigger 5x10 foot sheet of the Celtec from a dedicated plastics supplier was about $200 bones.

Obviously not the right choice for every situation, particularly if it needs to bear any weight but for me it was perfect; half the weight and 1/4 the price of starboard and most other options.
Old 07-16-2020, 12:23 PM
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thats pvc board with some 1708 laminated to it with epoxy. 24 grit prep on the pvc board. Fiber will fail before the bond does.
Old 07-16-2020, 02:11 PM
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Originally Posted by CR295 View Post
Good education for me.

On another note, if someone is considering using cellular PVC sheet as a top material on a small T-top, I provisionally recommend it.

I had a choice of going the Sunbrella laced fabric route ($250 to $350) or making my own top out of Starboard (expensive and heavy) or out of foam, coosa, marine ply (expensive and labor intensive). Once I looked at the big picture such as materials and labor involved, including waiting for all that crap to dry in between, the PVC sheet seemed like a no brainer.

I have a small 4x6 t-top that it worked perfectly for on a little skiff. A 4x8x.5 sheet was 68 bucks at the depot. Time will be the judge but so far its really nice and was super easy. On bigger tops, I'd like to know if scarfing, butt joints or other joinery methods would work out with joining 2 sheets? The bigger 5x10 foot sheet of the Celtec from a dedicated plastics supplier was about $200 bones.

Obviously not the right choice for every situation, particularly if it needs to bear any weight but for me it was perfect; half the weight and 1/4 the price of starboard and most other options.
can you post some pictures of your PVC t-top, would love to see it.
Old 07-16-2020, 02:28 PM
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I know itís considered heresy but I have glued pvc boards to rough fiberglass on two boats with PL Premium construction adhesive. Less than $5 from Home Depot for a tube. Both have provided a mounting surface for a promariner battery charger with no issues. I think I read about it on here. Someone argued itís adhesion was just as good as 5200 albeit an ugly brown color. I was doubtful but it works and is great for areas out of sight. Itís a strong adhesive and bonds to the fiberglass and PVC well. First test was inside the console of a 1977 Mako 17 and have done the same inside transom of a 1993 Albemarle 24. Both have been worst case - pvc boards mounted vertically and the PL Premium is in 100% shear loading. No issues so far.

Last edited by 3.5_rings; 07-16-2020 at 02:35 PM.
Old 07-17-2020, 05:06 PM
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Originally Posted by leonreno View Post
can you post some pictures of your PVC t-top, would love to see it.



Old 07-17-2020, 05:16 PM
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Originally Posted by 3.5_rings View Post
I know itís considered heresy but I have glued pvc boards to rough fiberglass on two boats with PL Premium construction adhesive. Less than $5 from Home Depot for a tube. Both have provided a mounting surface for a promariner battery charger with no issues. I think I read about it on here. Someone argued itís adhesion was just as good as 5200 albeit an ugly brown color. I was doubtful but it works and is great for areas out of sight. Itís a strong adhesive and bonds to the fiberglass and PVC well. First test was inside the console of a 1977 Mako 17 and have done the same inside transom of a 1993 Albemarle 24. Both have been worst case - pvc boards mounted vertically and the PL Premium is in 100% shear loading. No issues so far.
Good info.

I made a bunch of test pieces with ABS glueing it to itself and to fiberglass only because I had a bunch of ABS cement PVC board and scraps of fiberglass laying around.

I havent been able to break the bond on any of it even with moderate pressure. No telling how long the bond with ABS cement will hold up though so I'll prob just use thickened epoxy as mentioned.

I've always been told it's very difficult to bond PVC to anything other than itself but Im beginning to see that's not or no longer the case.
Old 07-17-2020, 05:19 PM
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This is the PVC sheet I used. 68 bucks @ home depot.
Old 07-17-2020, 05:23 PM
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Originally Posted by SEABIRD254 View Post



thats pvc board with some 1708 laminated to it with epoxy. 24 grit prep on the pvc board. Fiber will fail before the bond does.
Damn that's pretty impressive, how much pressure to seperate the two pieces?
Old 07-18-2020, 06:21 AM
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Wasnít measured but I needed a flat shovel and a lot of leaverage to get off.

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