Can I use pour foam to fill in a concave and if so, US Comp. or who?

General Discussion
1

 

I would like to take most or all of the concave out of one of my surfboards.  Finding foam to fill the void and then shaving it sounds a bit too

involved and I think it might not work until I have more experience with foam, planers, etc…

 

So I think pour foam might do it - similar to what a boat-builder sometimes does to fill in voids and surfaces before glassing with resin.

 

Just curious if anyone has ever tried this and will it work?

 

I want to just buy some pour foam (probably 16lb. density), then pour it in (I guess followed by the activator).  Then just toss a piece of plywood over it to

keep it weighted down and to make it come out nice.  Then I can either go flat or put a slight concave back into it, less than the original.  I just want to know - will this basic approach work?  Will the plywood lift up - should I weight the plywood down?  Should I put a little vegetable/olive oil/surfboard wax on the plywood to help it pull up more easily so it doesn’t cause voids in the foam?  How long will it be before I can put the sheet of glass/resin over it to finish the job?

 

So questions are:

  1. Good idea?

  2. Which vendor - Fiberglass Supply Co. (8lbs) or US Composites (16 lbs - and do they have only a pint size?).  I don’t want a quart or gallon of this stuff.

As for an exact product - I will need something that is marine-grade (water contact won’t harm it).  For example, Fiberglass supply has 8lb density pint:

8 lb. Density Pour Foam Kit, a two component, 8lb/cu.ft. density rigid  hard-skinning polyurethane pour foam.  Use for filling voids,  tooling, molding and taxidermy.  Mixing Ratio A/B by weight  50/50.

K08-8321 2 Pint Kit, 8 lb. Density Pour  Foam (A + B) 2.3 lbs. = Approx: .27 cu.  ft. It costs $35.19

3) How much liquid will I need? Expanded, very roughly I will need about 1/4 in. x 2 ft. x 6 ft./2, /2 since it's less at the sides = 1/48 ft. x 2 ft. x 6 ft. /2 = 6/48 cu. ft.  This is a very rough estimate based on the volume of the concave that I want to fill.

So does anyone know how much of my 35.19 I will use up?  If it's not too much, then I'm not worried.  How much will the liquid expand?

4) Should I protect the surfboard's bottom or coat the bottom with anything first?

5) I realize that Jamestown Distributors has little 1" thick sheets of foam that are 1' square for like 9.95 a block.  So is there foam hard enough?  I thought of the pour foam idea because I am so worried that I'm going to order from Jamestown or some distributor and wind up with foam that came off of a roll and it's

not stiff and it's for seat cushions or something.  I NEED closed-cell, stiff, marine-grade polyurethane foam and it must be good stuff.  I don't want something

that's junk.

 

Well anyway, if anyone can guide me a bit, I've never used pour foam.  And if I were to buy the foam from Jamestown, I would need to get a bench grinder and sharpen my hand-planers.  I have not yet bought a power-planer.

 

I really don't want to spend a whole lot of money.

I guess there are other void-fill methods I could use, but I like the idea of putting foam in there and glassing over.  But perhaps there are other void-fill

materials other than foam.  I could use cabosil/resin but it's an awful lot of weight and perhaps cost.  But at least it would work fine.

 

So my last question is:

6) Should I not use pour foam, and just add a little too much weight with the cabosil?  It's a lot of cabosil though - it was perhaps a reject surfboard - the concave is WAY too deep - like 1/4" or more.

 

Anyway, any comments appreciated - no hurry.

Thanks.

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2

Thanks for your comments, yeah, the weight is much better with foam, than cabosil, the only reason I mentioned cabosil, is that it’s cheap and it’s a technology I already understand - two pretty good reasons to use it.  A third reason is that it’s so simple, just spread it on, wait until it’s dry, then sand and glass, and sand again.

 

Yes, the board is already glassed.

 

But Home Depot sells 20 oz. cans of expanding foam - I’ll have to take a look.

 

I’ll make my decision by the end of tomorrow and I will post pics of the process.  If the cost of cabosil is like 5 times less than the other method, I might go with it since the extra weight is not enough to worry too much about - I am already 196 lbs…  Notice my weight calculations below: the 7’2" board is roughly 7/200 = 3.5% of the weight of me + the board.  Yeah, I will sink a little deeper into the water = slightly more

drag.  I haven’t actually weighed the board - but I promise I will keep track of that (and some pics) so people can learn from this.

 

Method 1. Cabosil

Me + cabosil/resin + fiberglass + resin + board = 196 + 13oz. + 4oz. + 9oz. + 7lbs. = 204 lbs. 10 ounces

 

Method 2.  Foam

Me + foam/microballoons + fiberglass + resin + board = 196 + 3oz. + 4oz. + 9oz. + 7lbs. = 204 lbs.

 

Extra sink with cabosil/resin mixture in there = 10/16lb over 204 = .3%.  Extra drag due to immersion increase = probably about .7 or .8%.

Hah-hah!

I’ll wait a day or two to decide but I think most professionals would use the foam approach either from a can or from sheets.

Thanks again.

3

My calculations of volume DO seem to imply that I would use a whole can of pour foam so perhaps it wouldn’t be cheap, this is my main fear.

4

i use the pour foam from us composites all the time and that stuff works great for me in certain applications, i dont think you will need 16 lb density i would go with the 4 lb, even at 4 lb density te stuff is still way stronger than normal pu foam, the main down side to using this stuff is that it is a brownish sostada color when cured and when ever i use it i always sand it bellow level then fill with microballons to cover it all up, i think getting a quart of this stuff would be more than enough, and i think using wax on the plywood should work decently enough and wiegh it down good because the stuff expands like no other

i would not go with using any other filler other than foam for this project, it would add way too much wieght

i do remember some one else around hear that uses a expanding foam( i dont remember the name of this stuff ) that does cure nice and white, i think he said he gets it from home depot but not sure, the only down side to that stuff is he said it takes around 4 hour to cure, the i use take around 10 min.

but a question for you, is the board all ready glassed, if it is i would say go with the pour foam , if not then i would go with buying that sheet of foam and using that stuff

hope this helps and good luck, oh ya you should post some pics of the proses if possible

5

Pretty much what sdrepairman said. I used the 4lb. A-B stuff from Fiberglass Supply for floatation foam under the deck of a boat that I built. Pretty dense stuff. A little goes a looooong way! Do a little practice with it if you can spare some. This stuff expands like crazy and it will move and push things around thats on top of it. 

It’s very messy and make sure you are all set with everything before you pour because once the two components mix the expansion is instant. The stuff sands pretty easy, I used a breadknife to cut off big slabs that weren’t needed. I’m sure you can use a surform too, not sure if a planer will tear it out though.

 

6

IMO you're going to add a lot of weight and a lot of stiffness to the structure with foam and another layer of glass. If this is just an experiment to see how it rides with a different bottom use superlight body filler (bondo), you can sand it off later, or sand in a slight concave to test, etc. This has been done before with reasonable success.

7

Cool idea to use bondo so it can be sanded off in case I don’t like it.  By the way, here’s an article on the chemistry of body filler:

http://www.secondchancegarage.com/public/555.cfm

Thanks.