Polyurethane foam water absorption

Yeah, well unanimity is not quite there, but there is a fair body of contra-PU stories here. Obviously the convenience factor is high as regards installation and complete filling of voids. I assumed PU foam was ( in its rigid form ) 100% closed cell, which on further research is found not to be so. I guess the proof of what happens in practical use is what matters. I would be happy to go up in density if I thought that would help, any thoughts on that ?

 

So,what application are you looking at? can you hot wire cut polystyrene to fit the spaces.
Steve.

 

Unfortunately only pour-in is practicable, into an existing hull with a glassed in foam-sandwich floor. Have to cut in some ports in the floor, and obviously leave open while expanding, and then fit screw on "lids". There is not a lot of potential for water contact here, I just wondered whether 4lb foam might stack up better.

 

Ok, i have used pour in foam for this application in my sons boat 23yrs ago and it is fine today.The hull is faom cored and i filled the areas under the full width afterberth and the vee berth. The berth tops were 1" pink polystyrene with a layer of glass cloth each side, i drilled a bunch of 2" holes in the berth tops with a hole saw to pour the foam in and for it to expand out of,it foamed out like cupcakes and then were sliced off with a hand saw and then sealed with a circle of glass/epoxy.It has not absorbed water so far as it is surrounded by cored structure, acrylic modifed epoxy hull,west epoxy berth tops. I do like that a large area of the hull is stiffened a lot by solid foam. You could us more dense foam but im not sure how much better it would be.
Steve.

 

Thanks Steve, this is a cored hull too, and I am familiar with the underfloor layout and dimensions, so quantity estimation should be reasonably accurate. I will be careful to ensure it is dry to start with, and will stay that way after foam goes in. Glassing with epoxy sounds a good idea.

 

This is part of a post I made on this subject on another forum. Why re-invent the wheel.

http://forums.iboats.com/showthread.php?t=452209

My first encounter with this was in 1984 when I was made the project officer on a research project to test machine made 2 lb density closed cell foam by submerging it in clean fresh water (actually we used distilled water) under laboratory environment. Yes I know this does not reflect reality but when conducting experiments you have to have control over the variables. We submerged coupons of foam for two years. each coupon was weighed at the beginning and weighed again monthly. There was virtually no water absorbed over the two years ( see quote above)

My next encounter was over twenty years testing boats for flotation, mostly brand new boats, but an occasional used boat. Most had no problem with water in the foam, but some, a significant percentage, did. If a boat failed flotation testing we would keep it until the builder fixed it then test it again. On a few occasions the boat would have increased in weight several hundred pounds. This was foam soaked with water.

We collected foam samples from boat manufacturers as a matter of routine and had them tested. All of them test fine. Why? a huge flaw in the procedure. These were almost entirely taken as test shots by the boat manufacturer at the beginning of the day, when everything was clean and calibrated. But we also collected samples from existing boats and boats that had water problems. But none of this told us why it was happening.

So in 2004 the USCG started a research project with a lab, and done in a more rigorous way to find the problem. Without going into in detail not much came of it. We really did not learn what the origin of the problem is.

So what have I learned over the years and why I believe it happens.

Block, machine made foam does not have these problems. Why? because it is made in a factory under near perfect, almost laboratory, conditions. Everything is clean, the chemicals are at the right temperature, they are new and have not been sitting in storage for a years, the humidity is right, and conditions are tightly controlled.

So what happens in the boat factory?

In most large volume manufacturers they use two part foam that is sprayed into the boat using a gun similar to a paint spray gun. Two chemicals from separate tanks are mixed in the output of the gun sprayed into a compartment. It is allowed to foam and then any overage is cut off and the compartment sealed.

So what's the problem? Any manufacturer of foam will show you a long list of instructions on how to use this stuff. The guns have to be clean and calibrated for the right ratio. The factory has to be between 50 and 70 deg ( that also depends on the brand) and the the humidity has to be right ( can't remember what the spec is. brain fart!) The chemicals also have to be at the right temp. Unfortunately they are usually stored in unheated store rooms and even sometimes outside during all seasons.

All these conditions affect the exotherm. Exotherm means heat output. When you mix these two chemicals they start a reaction which generates heat. If it's too hot during exotherm the cell walls are too thin and easily break. In fact they look a lot like broken glass. Not enough exotherm and you get something that looks like bread dough or a cowpie. Neither comes out as closed celled two pound density foam, and both will absorb water.

So at the beginning of a shift they clean and calibrate the guns and do a test shot into a paper bag or a box. If everything looks ok they start foaming boats. So what happens when they take a break, or lunch? All this stuff gums up in the gun. By the end of the day what they are spraying is not very good. The good ones clean the guns and adjust the ratios several times a day.

In small volume manufacturers they can't afford this fancy equipment so they mix the two in a bucket and pour it into the boat, How controlled is that?

To add to all of these problems, foam in boats is exposed to all kinds of environmental conditions. In northern climes they sit out in all kinds of weather, go through extreme freeze thaw cycles and in the summer extreme heat. People let their boats sit on the trailer full of water mixed with gas and oil and cleaners, and God Knows what else.

Foam is subject to vibration and pounding and slamming while underway. Foam is usually not out in the sun, but it is subject to UV degradation when it is.

So. if you have a well made boat with foam flotation that was made correctly it will last the life of the boat, if treated well. If you have a boat where the foam was made under not so good conditions, it will more than likely absorb water. Add into the mix where your boat is, northern cold climates or hot sticky humid climates. Also how is the boat stored? Is it under cover or left exposed to the elements? All these affect the outcome.

 

The Good



The BAD (The boat was cold when they shot the foam in)


The Ugly ( Way too much exotherm. Hot hot hot!

 

Ike, thanks for the info on your testing. Just a couple of things,when you refer to "block foam" are you talking about polystyrene or polyurethane (i have not seen polyurethane block foam) or both? Did you test any 2 part PU foam that was ACCURATLY MEASURED AND MIXED in a bucket the way any amature or small production shop would do it? i ask this because you infer that this CANT be accurate wereas i would contend that you may have better results this way than with poorly calibrated more sophisticated equipment. All the pour foams i have used are 1:1 mix ratio, hardly rocket science. Oh,btw,you can glass over the polystyrene blocks with polyester, it just needs to be one of the ones made for that purpose, such as styro safe, there are other brands.
Steve.

 

Accurate measurement and mixing ( using an electric drill and paint mixing attachment, not a hand-held paddle ) should not be a problem, the stuff I have used in the past all had consistent appearance when cut.

 

In our initial submersion tests we used both PU and styrene foams. In fact I think we also had some Polyethylene in there

I am not saying it can't be done in a bucket. If you are careful it can come out all right, but I have been in hundreds of boat factories and some are not so careful or clean. In some the bucket looked like it had been used to slop the hogs. At the boat testing lab they have used block, 2 part with the bucket, and foam in a can successfully. The point to stress here, and reading through my own post I didn't stress it enough, is to follow the foam manufacturers instructions to the letter. I have talked with most of them and they all say the same thing, follow the instructions.

Of course being an engineer I always read the instructions last.

Yes we did get samples from the bucket method and some were just fine. And yes you are right, a poorly calibrated or dirty gun turns out crap.

I wasn't aware of styro safe. I'll have to check it out.

You can buy block PU, but for amateurs or back yard builders it is hard to get. A quick Google search for polyurethane block foam came up with a number of suppliers. But I have never seen it at IBEX or other trade shows.

I have always recommended to back yard boatbuilders and low volume builders that they go buy insulation foam at Home Depot or Lowes and bag it or glass it. It comes in 8 foot by two foot by 2 in. sheets and is easy to cut to size with a knife.

I think for the foam manufacturers there is more money in the equipment used for 2 part. Correct me if I'm wrong. I don't want to paint a negative picture of them. They have been very helpful with info and samples for testing over the years. In fact the second pic above was foam supplied by PolyFoam. If I had included more of the cup in the pic you could see their logo. And they are just as interested in why some fails as we are.

 

Other options if you can't get access to place large blocks includes plastic drink bottles, or maybe flexible foam like polyethylene as used in " Pool Noodles ". All better than no flotation.

 

Ike thanks for the information. I have always wondered about why a substance that chemically should be immune to water damage seems to show up damaged so often. What I take away from this is that if the foam is layed up perfectly it is fine. But any deviation from correct procedures can result in something that is almost worse than nothing.

So while I will accept that those manufacturers that do quality work can reasonably use two part foam, I will continue to recomend against anyone else using it.

 

A poorly mixed batch of anything yields poor results, a bad batch of concrete, poorly mixed resin etc. It is very easy to get an accurate 1:1 mix but as you observed Ike, mixing has to be done carefully, i personally prefer to use a stick rather than a mixer in a drill so i can be continuously scraping down from the sides, but thats just me,(i also prefer white hardner with bondo because i dont need colored stuff to thoroughly mix it) I think that due to the rather quick reaction time with the foam people probably rush the mixing. Not much has been said about the hard skin that forms at the surface of the foam, i have found this to be quite impervious to moisture so when manufacturers of, say, small powerboats where they pour the foam between the structural floors under the sole, then slice it off level with the top of the floors and the instal the sole,unless they properly seal where they cut the foam,which they dont,they are inviting problems since these areas are not generally sealed.
Steve.

 

Mr Efficiency,another option may be to drill some srategically placed holes and use a powerfull shop vac with a screen over the hose end,to fill the compartment with styrofoam packaging peanuts,(make sure that the peanuts you get are not the ones that look the same but are made from corn or something and are made to disolve in water) I have not tried sucking them in like this but it should work. I have used the peanuts to fill between blocks of foam.
Steve.

 

PU foam adsorption properties

Perhaps a source of differences in observations regarding absorption properties is in the density of foam used.

I was told by a boat manufacturer that two part urethanes must be at least 2.5 lb/cu.ft. to achieve a closed cell structure. They were very cost conscious but still used 2.8 to 3.0 lb density two part urethane foam. They had the commercial equipment to spray the foam into the boats. He also said the 2.5 lb min was required by the coat guard.