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Author Topic: two part foam  (Read 2667 times)

Mikecotton

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two part foam
« on: May 16, 2016, 11:44:38 am »

Does anyone know a source of small quantities two part polyuretheane foam in the Bristol Area ?
I can find it on the web but delivery doubles the cost - and I only need a little. I tried builders expanding foam but it is not contollable enough
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Bob K

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Re: two part foam
« Reply #1 on: May 16, 2016, 12:00:11 pm »

I used this one
http://www.cfsnet.co.uk/acatalog/2-Part-Polyurethane-Foam-Liquid-2kg-pack-N2PSTD_002.html#SID=415

About the smallest quantity available, 2 x 1kg tins, one each of Part 'A' and Part 'B' liquid.
Expands at approx. 25 to 1 ratio, but you will need to run some tests according to your application.
Note this is genuine 'closed cell' buoyancy foam.  Regular builders foam is 'open cell' and may absorb water.
If using inside model boat hull voids suggest using a syringe to accurately control quantity.
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Chris57

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Re: two part foam
« Reply #2 on: May 17, 2016, 12:00:05 am »

Builders foam is open celled. Could you put builders foam in ,say, a small plastic bag in the compartment you want the buoyancy? If the bag is sealed, the foam should work?
Just thinking aloud here, not tried this.
Chris
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Bob K

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Re: two part foam
« Reply #3 on: May 17, 2016, 09:08:37 am »

If you just want to create a closed buoyancy volume inside your hull, rather than trying to fill a balloon inside it you may prefer to seal the chamber using regular f/glass resin around all the joins of the compartment. Just as effective.
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Mikecotton

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Re: two part foam
« Reply #4 on: May 17, 2016, 11:39:11 am »

Thanks Chaps. My problem is that I sanded through the skin on the chine at the bow of my 1/24 Airsea Rescue Launch built from MMI free  plan. Thought I had sealed it inside, but after maiden voyage, a lot of water dripped out. The front 1/3 of the boat consists of closed box sections and my first thought was to remove the anchor winch,cut through deck, run some resin into the cavities and "roll" the boat around until set - and hope ! Second thought was the foam. I made a mock-up of the bow sections and bought some Soudal gap filling foam from Range.(half the price of builders merchant)  A trial "blob" was weighed and stood(after curing overnight) in a saucer of water. I coud detect no increase in weight , again overnight. The first foam injection resulted in the 1/32 ply deck bulging -on the mock-up thankfully. Second try did not fill the cavity. Hence the search for 2 part foam that I can measure and mix to get the correct volume before risking it on my model.
I have found online a 500ml. pack LD40 from mblg. Trouble is it is 8 plus 7.99 p&p ! Hence enquiry for local supplier.
Guess I will just bite the bullet and pay the postage - but thanks anyway.
Mike
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Bob K

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Re: two part foam
« Reply #5 on: May 17, 2016, 12:28:10 pm »

As long as you realise that LD40 is a thermal insulation foam, not buoyancy foam as such, so can't guarantee it will not absorb water.

As to your requirement to local sources in/near Bristol, DIY superstores only do builders foam and it is unlikely that ironmongers will have anything that specialised.  I did look on Force 4 Chandlers, not too far from you, but could not see it listed.  Chandlers are full size boat specialists so more likely to stock buoyancy foam, which should not force out bulges.

If you have sanded through the hull skin you will need to repair and reinforce that first, not rely on pumping foam in the hole.
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Mikecotton

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Re: two part foam
« Reply #6 on: May 17, 2016, 01:11:51 pm »

I thought that I had reinforced the this bit - with plastic padding. Obviously not. The LD40 tech spec claims 90% closed cell structure
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rickles23

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Re: two part foam
« Reply #7 on: May 17, 2016, 04:32:20 pm »

Hi,

Try a Marine Center, they usually have a two part buoyancy foam.

Be warned however that if you use it in a confined space make sure you have a couple of open holes for the excess to escape!

Once mixed the stuff will expand with a vengance.

Regards
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Colin Bishop

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Re: two part foam
« Reply #8 on: May 17, 2016, 05:12:52 pm »

Just leaving holes won't necessarily stop the foam splitting the boat apart as it expands in all directions, not just where the holes are! A lot of people have discovered this the hard way!

Bubblewrap is another option, especially those strips with large air sacs on them. All you need to do is to enclose some air and foam is a messy and uncertain way of doing it.

Colin
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Netleyned

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Re: two part foam
« Reply #9 on: May 17, 2016, 05:21:29 pm »

Surely the main priority is to seal the leak.


Ned
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morley bill 1

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Re: two part foam
« Reply #10 on: May 17, 2016, 10:14:01 pm »

Beware of two pack foam it keeps on expanding long after you think it has stopped I once blew a deck joint with this foam Bill..
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Bob K

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Re: two part foam
« Reply #11 on: May 18, 2016, 08:10:59 am »

There is a technique in using 2 part PU foam.  First run some tests using carefully measured amounts into, say, a small cardboard box.  It does expand a lot (~25:1) but will stop in a short time.  Sounds like you put too much in and the resultant pressure did the damage, rather than continued expansion.

Suggest injecting the mixed PU with a small syringe, being very careful not to use too much, and leave a couple of safety holes for any excess to vent from. You can easily close those holes afterwards with f/glass & fine matting.   Works for me. 

1 cu ft will support around 27kg, so just filling a couple of small voids will not on its own save you from sinking.  As I said before, just sealing the joins in the compartment with f/glass is a lot easier.

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Onetenor

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Re: two part foam
« Reply #12 on: May 27, 2016, 01:56:33 am »

Personally I would lift the deck carefully rather than risk blowing it off .Seal and reinforce the break with glass tissue or cloth t  then replace the deck. Much safer in the long term. Expanding foam of any type can have a very powerful effect. When in the building trade I saw skirting boards and the like literally ripped off the screws they were secured  with. A sort of secondary expansion seems to have occurred over night The foam had become very dense too. the joiners were not happy with the brickies over this.They had to saw off the foam flush and replace the skirtings.I would play safe if I were you.If you still wish to fill the void with foam do it with the lid off then any excess can be trimmed off flush with the hull sides with a bread saw knife. O0
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