I am fixing the busted nose on my JP which means I will have to cut away a section of the old foam core which is wet and fractured.

What product is suitable to build up the core shape again before applying a new layer of Divinycel and fibreglass?

The Board Lady says: To reinforce fractured EPS foam, I use a Marine Urethane foam by Evercoat. As opposed to the stuff from the hardware store that comes in a spray can, this foam does set up hard.

What is 'Marine Urethane foam' sold as in Australia? Is there a better product to use?

PS. Thanks to Nebbie the ledgend for donating his left over Divinycel for this project even though we have never met. Gotta love the seabreeze community !!!

Marine grade polyurethane

We would suggest going to a local shipwright or Chandelery and ask if you can buy some.
It comes in two parts (both liquids) which need to be mixed in equal parts.
You should also see if you can track down a big syringe (plastic end no needle)
You can use this to measure the amounts and insert it into a container to mix.
In our experince 20 - 30ml of each part will create enough foam to fill a beer can.
The stuff only needs to be mixed for around 10 - 15 seconds (we used an old splade drill bit attached to a cordless)
Mess around with some first to work out how much it will make and how much time you have once it starts to go off.

Depending on the size of your job 250ml of each component should be heaps.

You simply pour it onto the old foam (after you have cut away any bad or wet stuff) and it bonds to it like the proverbial sh_t to a blanket

Good luck with it and keep us posted how you go

Thanks WW, I will try the Chandelery at Hervey Bay.
Can you also tell me how to bond Divinycel to the foam?

Use the epoxy that's holding the internal glass. So put a bit more of a coat on than you normally would for the internal glass, because the divinycell soaks up a bit of epoxy.

Before you do this, however, spend twice as long as you think you should on making the divinycell mold properly over the EPS core. This is where I messed up my nose job, had to spend another three days just fixing this up, whereas I could have spent an extra two hours on the fit and saved myself lots of time.
Lots of separate bits of divinycell that mold properly is better than a couple of bits that don't fit very well, providing you can hold them down as the glue cures. Be very prepared on how you are going to apply pressure to the divinycell as the epoxy cures. This is the hardest part, everything else is quite straightforward. Don't think that you will make it up as you go, you need to have done a test run with the divinycell first to make sure that you can apply pressure evenly all around where it's going to go.
You can also heat the stuff up in an oven apparently, this makes it easier to bend to shape.

If you've got access to a vacuum bag then it's easy, but otherwise you have to do some serious backyard inventing!

If you're cutting away the whole nose, why not replace the trashed foam with a piece of new foam? The Urethane foam is good for reinforcing as it works its way into all the fractures and compressed bits of foam - but you're not reinforcing from the sounds, more like replacing.

Visit an insulation place, or polystyrene factory and see if you can get a free bit of foam of a similar density to the stuff you've cut away (there are a variety of densities available).

Use a proper polystyrene glue to attach the new foam to the old - epoxy sets hard, and introduces a stress line. The proper glue is similar in density and flexibilty to the polystyrene, so will transmit any impact right through so it can be absorbed over a greater area. A proper glue will also not 'eat' the polystyrene, which would result in an even bigger job for you to do!

Sand the new foam to shape with some fine paper, and then glue the divinycell on with epoxy (that's what the manufacturers use).. If you have access to a vacuum pump (or a stuffed fridge that you can steal the pump out of and modify) that will help the divinycell conform and ensure that it is stuck down well with no voids.

Make sure that you stagger any joins in the different layers - so taper the existing divinycell back past where you've joined on the new polystyrene, and overlap the new divinycell onto the new. The boardlady shows this nicely on her site.

Whatever you do, clear out the smashed bits and leave it to dry for ages in a breezy spot before sticking anything back together! Oh, and take plenty of photos before ripping anything to bits so that you can later remember what shape it was meant to be when you're sanding it up!

If there's enough interest in DIY vacuum pumps I'm happy to write up an article on how to modify a fridge compressor to do the job of a $600 vacuum pump for around $30..

555

Yes please

I was jacking up the carport the other day trying to pull the poles out of the ground with a jack so that I can relocate it without dismantling. The bit of wood used as a prop flew out under a couple of tonnes of load and wacked me across the nose. Now I need some Rhinoplasty along with a couple of my boards.

leave as much foam as you can in there cracked or not, if it's wet leave it in the sun for a day to dry it out, any loose foam get rid of, i usually fill up the hole with epoxy with a sh-t load of Q-cell e.g 30ml of epoxy in a round continer, (the one's like your fried rice comes in a your local chinese take away, about 5 inches deep) fill half way with Q-cell, stir the epoxy through it so it's not powder, then put some more Q-cell in and mix again, i keep on doing this until the mixture is almost dry, you will know what i mean when you mix it, it will get hard to stir in.then just spatular it into the hole and push as much as you can get in there, once this goes off it's really eazy to sand into the original shape of the board, then glass over the top. the Q-cell is real light so your board won't gain any weight if you glass it right..

I would like to put my hand up for that fridge pump conversion Simon.

Corematt also works well after drying and injecting Q-cells.
Tapper the d'cell down to the glass, inject epoxy and q-cells into the EPS, 2x 4oz. down then 3 layers of corematt and tape 'n' weight if not bagging. Sands back well and is bullet proof then glass and fill, quick and easy.
I'm a big fan of the fridge pump, bagged 20 decks and 20 hulls with the same pump by recirculating the oil.
Good luck on your nose job.

I'd be very interested in the fridge vacuum pump too,
cheers
Jon

There already is a good write up on converting a fridges compressor.

ww25.dream-models.com/eco/vacuumpump.html

555 if your method is better/easier I'd like to see it as well.

I've used a pressure sensor from RS Components and a couple of relays instead of the old distributor, but I've had to add some hysteresis to slow switching time down a bit. I'm also using an old gas bottle as a Vacuum reservoir that also helps.

Hey Decrepit,

Was it something like this?

au.rs-online.com/web/

quote:

---

Originally posted by nebbian

Hey Decrepit,

Was it something like this?

---

Not quite, mine was only a sensor, didn't have the micro switch attached, that's why I had to add a couple of relays, it's switching current was very low.
That looks like it might almost do the job by itself, but it's going to blow out the $30 budget somewhat.

Very similar to that one Decrepit.. The principle is the same, but like all of these little projects, the specifics vary according to what is available at the time!

I've submitted a write up for publication, and will try to get some pictures of my 'hacked' fridge pump on there shortly after it is published.

The article has been published:
www.seabreeze.com.au/Members/Content/Articles/Windsurfing/How-to-build-your-own-vacuum-pump-for-under-50_1293413.aspx

Pictures still to come.

Yep, good job 555. I like the reservoir cause I'm not all that happy with the pump only being on .5sec, means a very high percentage of it's operating time is the initial "surge" current. This means the switch off spikes are bigger and the micro switch is more stressed and the motor may get hotter than it would if aloud to run a bit longer, (mine goes for 4-5sec). My other worry is vacuum going to high due to switching time, with a reservoir this doesn't happen. But this is only theory, if you've had no problems in practice that's all that matters.

quote:

---

Originally posted by decrepit

I like the reservoir cause I'm not all that happy with the pump only being on .5sec, means a very high percentage of it's operating time is the initial "surge" current.
...
My other worry is vacuum going to high due to switching time, with a reservoir this doesn't happen...

---

I've been lazy, and haven't bothered to add a reservoir to my system, BUT the same laziness has meant that instead of using 3m of vacuum line to connect the pump to the job, I've left the full length (~30m) so I get a bit of reservoir there. That said, my pump cycles in about 3 inches of mercury, so there's not really any vacuum spike worth mentioning.

I'm also not sure that % of time spent in that surge current is all that relevant - it's probably better to look at the number of surges. That should be decreased with a reservoir, but how many times per day does a fridge turn on and off in it's usual application? In it's new life as a vacuum pump, it's going to spend a fair amount of time sitting on the shelf turned completely off.. So I reckon the pump is actually less stressed over a year than it was in the fridge!

The guts of it is that as long as it does the job, and the end product is okay, I don't really care about the pump motor because I can get another one free at the drop of a hat. So far the first one has lasted me almost 6 years..

I took some pictures this morning, now just have to find a quiet moment at work to add them to the article.

I have no arguments to that logic, makes a lot of sense.

i'm sure that pressure gauges can be found quite readily on the goldcoast, particularly on the bonnets of little jap cars that go pitt-ssshhhh

quote:

---

Originally posted by Haircut

i'm sure that pressure gauges can be found quite readily on the goldcoast, particularly on the bonnets of little jap cars that go pitt-ssshhhh

---

You have those there too huh!

Unfortunately those gauges are the wrong way around - you need to be able to measure vacuum, not boost pressure.

Vacuum still goes pitt-ssshhhh though - it just doesn't make jap cars go any faster!