Cabosil strength?

[mrdebian]

Hi all,

I made a test with isophtalic polyester resin mixed with aerosil to make a putty in order to glue and fill the gap of a bulkhead to a kayak.
That was a much easier and faster job than appying cloth/resin to put in place the bulkhead and I was wondering if it is a decent way in terms of strength to use instead of applying cloth/resin?

Is it acceptable to bond the bulkhead (made from 2 layers of mat plus foam core) and general filling small gaps with cabosil?

 

[gonzo]

I think that adding fibers would be better. Cabosil/polyester is hard but also very brittle.

 

[mrdebian]

What about if I make filler with resin and small pieces of mat or a filler that has already cloth in it? I guess that is more or less the same.

 

[ondarvr]

You can buy milled fibers for this purpose, glass strands (shredded CSM) will make it a bit stronger, but the longer the strand, the more difficult it is to work with.

Bonding putties, which is what you would be making, can work in some applications, but as mentioned, they tend to be less flexible, so may crack.

Bond something together and do some destructive testing to see if it works in the way you want it to.

 

[powerabout]

Once you have used rubberised epoxy like spabond you will never go back to making glue

 

[fallguy]

It all comes down to the demands on the joint and the risks of failure.

For a kayak, risk of failure may simply be access is impossible once the deck is on, etc.

To build ultralight, you can skip a tape, but a tape of 4" wide 6oz can be cut in half to 2". A 2" tape with resin weighs 12 ounces per 54 feet or about 1 ounce per 4 feet with resin or both sides taped about 1 ounce per 2 feet, so for a bulkhead; you are saving maybe 2 ounces not taping.

It can get to be hair splitting with a downside risk of poor access.

 

[rxcomposite]

Don't use cab-o-sil as a bonding agent. Its shear properties is very low, in the order of 1.6 MPa. Comparatively, even Sikaflex adhesive is still low at circa 4 MPa. Others claim they have used it. Cab o sil is used only as a compliant fillet to enable the fiber cloth tabbing to bend at corners.

CSM is the lowest I will go at 62 MPa. WR is around 82, biax is around 95 MPa and this I always use for tabbing bulkheads or stiffeners.

Bulkhead is classified as a primary structure. Use the strongest material possible.

 

[fallguy]

Don't use cab-o-sil as a bonding agent. Its shear properties is very low, in the order of 1.6 MPa. Comparatively, even Sikaflex adhesive is still low at circa 4 MPa. Others claim they have used it. Cab o sil is used only as a compliant fillet to enable the fiber cloth tabbing to bend at corners.

CSM is the lowest I will go at 62 MPa. WR is around 82, biax is around 95 MPa and this I always use for tabbing bulkheads or stiffeners.

Bulkhead is classified as a primary structure. Use the strongest material possible.

can you expound on this?

For example, would you bond a bulkhead with something other than cabosil amd epoxy?

I bonded with same as fillet material which was cab n epoxy..

 

[KD8NPB]

can you expound on this?

For example, would you bond a bulkhead with something other than cabosil amd epoxy?

I bonded with same as fillet material which was cab n epoxy..

the bonding is only supported by the resin itself.

the cabosil does not improve the physical properties.

 

[fallguy]

the bonding is only supported by the resin itself.

the cabosil does not improve the physical properties.

I did not expect it would.

 

[gonzo]

There are plenty of adhesive/caulks that can be bought in a tube and will be adequate for a kayak bulkhead. For example, 5200 and Sika 291.