Foam fill material

[scot]

I have a small area in the upper/forward cap wrap that is void and I am going to fill with foam between the outboard and inboard panels (to make it solid and better resist impacts without adding weight via more glass). I am looking at Liquid Urethane foam. Is this a good choice for filling an above the water line void?

[CaptPatrick]

Scot,

Better explain the void you're filling... 2 part expanding foam can be like lighting the fuse to a bomb.

[scot]

I am fabricating a forward structure above the gunnels that replicqates the Bahia Mar lines and functionality. The forward structure that makes a Bahia Mar... a Bahia Mar. The structure has 1/8" FRP exterior panel and 1/8" FRP interior panel approx 2" wide x `15" tall x 6' long (each side) of the forward section of the cockpit. I need to fill these voids with foam to stiffen the structure. With the panels installed, I plan to fill from the top, trim the foam once cured and cap with glass.

As a rule, I hate foam in a boat. But in this location (3ft above the waterline) and in this small amount it appears to be a good (light) solution.

[scot]

BTW the top of the 2 panels will be completely open to allow the foam to expand "up & out" of the panels...to be trimmed after cure

[CaptPatrick]

You should be OK then, but plan to mix and pour only 1/2 gallon per pour, (qt each part a & b), and allow 20 minutes between pours. Once the two parts are mixed with using a drill mounted mixing paddle, (20 seconds), you'll only have about 5 - 10 seconds to empty the bucket. For best structural use and reduced expansion, use 4 LB Density Urethane Foam. This stuff can get real messy if you don't have all your ducks in a row...

[scot]

Thanks Patrick, as usual good advice and trusted sources.

[PaulJ]

What about foam insulation for a small built in cooler? I've been looking into Dow's Great Stuff product as 2 or 3 cans would easily do my project.

Http://great stuff.dow.com/

Thanks,
Paul J
1973 B28 - PALADIN

[CaptPatrick]

Paul,

That Great Stuff is Crappy Stuff in disguise... It skins over quickly and then continues to expand, and expand, and expand for over 48 hours. The two part is a chemical reaction, independant of humidity or air contact. The reaction is done, finished, ended in less than 15 minutes, if mixed correctly. Save the Great Stuff for shoring up holes and small voids around walls and foundations. For thermal insulation, use the 2 lb density.

[PaulJ]

Thanks for the advice.

Paul J
1973 B28 - PALADIN

[Bob H.]

Scott, to stiffen up the Bahia Mar wind screen I laminated 3/4 foam sheets then glassed them in place. Really made a big difference when I glassed the cabin/hardtop in place. That expandable foam is tricky stuff, have gloves and plenty of trash buckets to throw all that extra foam that "will" keep growing...lol..BH

[CaptPatrick]

I've poured probably around 50 or 60 gallons of 2 part urethane foam over the last 20 years and have gotten it down to a set routine...

What you need to have on hand:

Nitrile or latex gloves -- one pair per pour + extras (I usually have 100 pair on hand at any time)
Large paper paint pot
Mixing paddle for electric drill & large cardboard box
Paint mixing stick (not to be used for mixing components)
2 paper cups for measuring the 2 components
Masking paper -- butcher paper, waxed paper, or similar
Masking tape
Rolls of cheap paper towels
Large trash bag fitted into a box
Clear work surface close to project
1 gallon of acetone
Propane torch

The layout:

Cover the work area, including floor, with masking paper.
Work from a table top if possible. Place the part A container on the left side of the table top, part B on the right.
Acetone and paper towels in the middle.
Mark 2 equal sized cups, one A & one B. Set in front of respective chemical containers.
Chuck up the mixing paddle in the drill and place it in the box next to the table.
Mask off any part of the project that shouldn't get the foam mix.
Make sure that the area within the project has a fully open top and sealed below to prevent leakage.
Stop and think out the steps, how you're going to proceed, and if all is ready to proceed. Once the mixing starts, there's no time for second guessing.

The procedure:

Measure an equal amount of each component into the respective cups. (Generally not more than 3/4 full and total mix less than 1/2 gallon)
Pour both parts, simultaneously, into the large mixing pot. Don't stop to get every last drop, just dump the component cups and grab the drill.
From the moment you pour the two parts together, start a slow count. You have 20 seconds to finish the mixing before the pour.
Don't waste time wiping the mixing paddle, just drop it and the drill into the box.
Pour the mix into the form evenly across the bottom. Use the mixing stick to assist, but stop before the 30 second count. Scrape the remainder into the garbage bag.
Immediately wipe clean the mixing pot & stick. Wipe down the mixing paddle, and re-setup your work area.

Allow 15 minutes between pours. Depending on the density of foam you're working with, the expansion from just mixed liquid to fully set foam is as much as 10 - 12 times it's volume. Repeat until the project is slightly over filled. Cut off excess after 1 hour.

The propane torch will come in handy for the final clean up of your mixing paddle. Just burn and scrape off the layer of cured foam.

While still un-cured, acetone will remove the foam. After it cures, only sanding will remove it. If it gets on gelcoat it'll leave a brown stain, so mask your project well. If you're trying this for the first time, use a cardboard box as your test project and make sure you have the dance down before asking your prom queen onto the floor...

[Pete Fallon]

Scott,
Why don't you get a couple of sheets of Airex, Corecell or Divinycell material, easy to work, with no mess as with expandable foam, you can shape it and if it's thin enough you can bend it easily.
Pete Fallon