Agreed with others on not using expanding foam for this. I personally used balsa wood to replace the rotted core as it has the best strength to weight ratio and is pretty easy to work with. There are structural foams that can be used but most do not have quite as good mechanical properties as balsa wood. My other tip is that where you know you will be putting a hole through it can be good to go with solid laminate in that area instead so you don't have to carve out the balsa and fill with epoxy later. Especially at structural points (bulkhead bolts for example). When I did this on my C&C 34, I used 1/2" G10 plate. Roughen both sides and bond in place of the balsa. Complete the lamination and painting and then cut or drill for the fitting. Adds a little weight and a lot of strength.
Some photos showing what I did to repair the core in my deck in 2020 are here: https://photos.app.goo.gl/8W4AdgmKqKxARvsY7 These show the G10 plates used where penetrations are made later for the bulkhead attachments and the fan in the head. I didn't do that around the chain plate and instead just filled an area with thickened epoxy but on hindsight using G10 there too would have been better and will avoid the problem happening again in the future. Note, in some cases, I rebuilt the deck laminate from scratch and in others I laminated the original back in place and then created a tapered grove and laminated the two parts of the top deck back together for strength using narrow strips of fiberglass. I used weights to hold the G10 in place while bonding it with thickened epoxy to the lower skin but then used a vacuum system when doing the larger lamination areas after doing a wet layup. Nathan ~~~ Nathan Post +1 (781) 605-8671 On Wed, Aug 25, 2021 at 5:43 PM Andy Frame via CnC-List < cnc-list@cnc-list.com> wrote: > That pretty much settles this discussion! > > Thanks to everyone for their thoughts. > > > On 8/25/2021 2:26 PM, Della Barba, Joe via CnC-List wrote: > > Expanding foam has no structural strength at all and is easily > > compromised by water. I would not even think of it for this use. > > > > Joe > > > > Coquina > > > > *From:* SV Mary Me via CnC-List <cnc-list@cnc-list.com> > > *Sent:* Wednesday, August 25, 2021 12:19 PM > > *To:* cnc-list@cnc-list.com > > *Cc:* SV Mary Me <svmar...@pm.me> > > *Subject:* [EXTERNAL] Stus-List Replacing Cabin/Deck Balsa Core > > > > I've got some soft spots returning on the deck at the base of the mast, > > that a previous owner had made an attempt to shore up. According to the > > owners manual, the cabin-ceiling/deck sandwich is balsa cored, so I'm > > working with the assumption that this has rotted away. > > > > The local supply store has a plastic honeycomb panel to use as a base > > material for fibreglass work that could use to fill the space, once the > > rotted material is dug out. I also thought about using expanding, > > self-hardening construction foam that could be shaved and shaped, then > > 'glassed over. > > > > Has anyone used, or have any thoughts on using the expanding foam? > > > > s/v Mary Me > > > > 1975 C&C 24 > > > > Labelle, Florida USA > > > > -- > s/v MaryMe > 1975 C&C 24 > Labelle, FL USA > Thanks to all of the subscribers that contributed to the list to help with > the costs involved. If you want to show your support to the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray Thanks > - Stu >
Thanks to all of the subscribers that contributed to the list to help with the costs involved. If you want to show your support to the list - use PayPal to send contribution -- https://www.paypal.me/stumurray Thanks - Stu
