Foaming the Spider

[Paul Proefrock]

I want to add foam to the spider's cavities on my RCR GT40. I have read the articles by Tom Schwab (Eglitom) where he outlines the use of specific epoxy foam, Secomin PB 175 or PB250, however it is not readily available here in the United States.

1) Has anyone used a similar expanding epoxy foam? I've exhausted my Google skills and haven't had any success finding a similar slow-cure epoxy foam available in the US. Seems our market leans towards Polyurethane, which has different characteristics. Has anyone found an acceptable/available alternate?

2) Some guys have used low-expanding insulation foam from Big Box stores. This will fill the cavities for sound suppression but they don't add much in structural strength. Searching the forum, I don't see any specific brands as being better (or worse) for this application. Has anyone done this? Did it turn out as you planned? Would you do it again? What brand did you use?

 

[Brian Kissel]

Paul. I don’t remember who, or when, but I thought someone on here posted that they used a marine foam, like what is sprayed for flotation under the seats of canoes and boats.
I could be wrong, but that is what I thought I read. I know at some point I researched it, but it’s on my old dead computer.
I have had a couple of computer guys try to retrieve the information. It is in my Outlook express ( which is no longer supported) files which they haven’t had good success retrieving all the information.

Maybe the 4# foam. Need closed cell for strength.

Marine-grade spray and pour foam (primarily closed-cell polyurethane) is essential for flotation, insulation, structural support, and sound deadening in boats, docks, and kayaks. It provides buoyancy, prevents condensation, reduces vibration, and fills gaps to strengthen hulls. Key types include 2# density for general flotation and 4#+ for structural support.
This video explains the pros and cons of using foam to fill a boat's hull:
Top Marine Foam Products & Types

• TotalBoat 2-Part Polyurethane Foam: Available in 2-pound density, popular for filling voids, providing buoyancy, and strengthening decks.
• AeroMarine Products 2# & 4# Foam: Closed-cell, rigid, and expanding; used for flotation in canoes, kayaks, and boat hulls.
• US Composites 2-Part Foam:Known for a slower, more manageable activation time for larger pours.
• Loctite Tite Foam: A commonly used expanding foam for sealing gaps.

Key Considerations for Marine Foam

• Flotation Requirements: US Coast Guard mandates foam flotation for boats under 21 feet.
• Closed-Cell vs. Open-Cell:Always use closed-cell foam for marine use to avoid water absorption, which leads to heavy, waterlogged, and rotting, or corroding, structures.
• Density: 2 lb/cu ft is standard for buoyancy, while 4 lb+ is used for structural support and high-density applications.
• Application: Generally, these are 2-part liquid kits that are mixed (1:1 ratio) and then poured, expanding to fill voids.
• Temperature Sensitivity: Pour foam expansion is affected by temperature; it requires careful preparation and mixing (30–45 seconds).

Common Applications

• Flotation: Filling hull cavities, under-deck spaces, kayaks, and docks.
• Insulation: Cabin walls, hull interiors to control condensation, and insulating ice boxes.
• Structural: Supporting fuel tanks and reinforcing flooring.

For the best results, ensure the application area is clean, dry, and properly prepared, as the foam may not bond well to vertical surfaces without proper application.


Regards Brian

 

[Paul Proefrock]

Brian,
The RCR spider has the inner liner bonded to the outer shell. There is about a 1 to 1-1/2" gap between the two, however it is only accessible from the rear bulkhead. The real issue is the A-Pillars. When the spidere is taken off and propped 'nose down', the pillar is not readily accessible. Most foams require mixing then pouring into the cavity. They foam and cure in less than 5 minutes. The beauty of the epoxy foams is they take about 30 minutes before they foam, allowing them to run into the areas that are not directly accessible. Then, after they foam, they cure to give them the structural strength.

I would prefer not to drill a bunch of holes in the liner or spider to introduce the foam. I am hoping someone will have a US source for the Epoxy foams.

Paul

 

[Brian Kissel]

Make sense to me. I was planning on putting holes in so I knew the foam went where I wanted it. I am anxiously awaiting your results.

Regards Brian