Mystery of frame rust revealed by "boatdoc"

[boatdoc]

Mystery of frame rust revealed.
First, I need to assure everyone that I am not connected to AS manufacture in any way. Therefore, no favoritism will play a role in this article. First of all I am tired of hearing all this belly aching about AS, without a proper understanding how complicated moisture control can be. For those who do not believe this statement, they should buy a better product and not AS. Since this is a subject that affects all, I may get the “most crap” award contained in one article, but for your benefit just bear with me. Today in the field of global economy all manufacturers are facing number of economical issues, not to mention [why should I care] attitude in regards to workmanship. Since further discussion on this subject is not the goal of this article, let’s address the causes to which some remedies may not be economically possible to institute by the manufacturer.
Causes;
 #1 is Condensation [most difficult to control] and not easily avoidable unless complicated measures are instituted.
 #2 is Road salt.
 #3 is exposure to adverse effects of towing on wet roads.
 ]#4 is placement of the trailer [your parking spot.
Since the condensation is the biggest and most difficult subject, I like to save it for last.
Unavoidable road salt is avoidable if you do not tow your AS in the snow. Let’s look at this realistically. YES, you should rise off the salt Tom, after towing on salted road. This is not the Factory’s responsibility, it is yours. You take a shower daily or when you get dirty? You cannot compare automobile to AS. AS does not expel lot of engine heat which can dry up quickly open and exposed to heat metal, thus minimizing the salt effect on metals while it is in a dry state. Just wash and blow dry the AS and it will be fine too.

Exposure to adverse effects while towing, is to some degree avoidable if you maintain the integrity of the belly skins. While towing your AS at 65 miles per hour, fighting a strong head wind, the water will be forced in to the low pressure area inside the belly skin through most minute gaps. Unless your belly skin is maintained and totally sealed [which is just about impossible] water will enter it. Solution for that is to provide a clam shell effect drains, in back of each compartment within the frame. The exit end must face rear or you will create a ram effect for water to enter.

Where, your AS spends its life is equally important. We all park our cars in a driveway don’t we? Does your AS sit in the grass or unpaved lot where the condensation process occurs twice a day? Have you ever noticed a dew on the grass on days when the temperature changes drastically once at the evening and then on the morning? Where do you suppose that moisture goes on the morning? Pavement acts as barrier, preventing the moisture from being raised up at night by the warm air from warmer than air and moist ground.

Instead of parking your AS in the weeds, park it on large tarp if you cannot park it in the driveway. Tarp will provide a moisture barrier.

Now let’s get into the meat and potatoes of CONDENSATION mystery.
Whenever you enclose airspace, condensation becomes very hard to eliminate or to control. Condensation occurs when two opposing temperatures collide against, on a temperature transferring barrier such as the belly pan. This process was very helpful in the prohibition time to those who had homemade stills, it is however detrimental to AS. To be able to remedy this condition one must understand what takes place between the belly pan and the floor. If there were no temperature changes such as in a controlled environment, rust would not take place. Since the reason for having RV is to be in elements we must try to some extend control causes of condensation. While manufacturer can take additional steps to limit it, this can be very expensive to implement, and that can place them out of competitive pricing in today’s market.

There are some relatively inexpensive measures which can be implemented at rather low cost to the consumer wanting the best. However this is where custom options come in.

In order to minimize effects of condensation [which cannot be eliminated] in the belly pan, a temperature barrier of good “R” value must be in place. Ideally this barrier must provide a solid moisture barrier on both sides of it. On one side of this barrier, we must provide a dead air space for it to have a full effect. This means that we must prevent the cold and the hot air from coming in contact with each other. Let’s take a look at fiberglass insulation used in a house. Inside and outside walls form a sort of a temp barrier along with dead air space between them. One side of the insulation has treated paper which is your moisture barrier. The double thick edges of paper are stacked on top of the studs pinched by the sheetrock thus creating a good seal. In AS frame a good seal is almost impossible to create or maintain. Once the moisture barrier is compromised, plywood floor will get wet and eventually rot. Let us look at places where rot starts. It is always in the edges where the barrier seal is compromised and hard to maintain. Sealing the moisture barrier to the frame is a very difficult task, with the weak paper barrier used in fiberglass insulation. There is no easy way to seal the joints, and after time it may get torn up for number of reasons. When it does, it stops to function as what it was meant to do. While the frame coating can be improved at the factory, stopping the condensation is another story.

To minimize its effects we must provide a temp barrier, ventilation and drainage of the belly pan. This must include moisture barrier insulation such as Prodex, which provides an excellent double moisture barrier. This should be attached to the frame and cross members with dead airspace between it and the plywood floor. This dead air space can be obtained by cutting a closed cell urethane foam ¾” thick to 2” strips glued to the floor at about 18” apart to which you can glue the Prodex. The second area of dead air space will be below Prodex and the belly skin. This area however will require drainage and nominal ventilation. Each section between cross members should have a drain. The cross members at the bottom edge are bent up providing perfect spot for pooling of water. Factory should provide a small horizontal drainage at the belly pan level to eliminate this condition. Drainage from the belly pan can be achieved by making a ¼ “ cuts in the center of belly pan facing across, just in the front of each cross member which may stop the water from draining into next section. By placing a small flat screwdriver pull the front side of the cut, thus creating a small clamshell drain. Be sure that the opening is less than 1/8” in height to keep yellow jackets from entering. My AS will also include a small screen protected computer fan in the belly skin in the rear of underbelly. They operate on 12 or 24 Volt DC and draw only about 0.17 Amp which is no threat to any battery. In the front in the underbelly I will cut a 2”x 8”opening for intake air, sealed with SS screen.

To keep water from entering, a small clam shell with the opening facing rear will prevent water entry when towing. This will create air exchange, preventing the dead air from condensing and speed up the drying process in the underbelly below the insulation. Instead of complaining, there are things you can do to considerably slow down the decay process. Nothing made by us lasts forever. We are the throw away society and are used to it. While all the complaints are valid they do not resolve any issues unless someone does something about it. I did not wanted any rust in my frame I have made new one from Stainless Steel without complaining, because it would accomplish nothing. This article does not represent views other than my personal research in the boating industry for past forty years, where cold water and hot sun create ideal climate for condensation. We to had to come up with a solution to the problem, you can to.

Thanks, “Boatdoc”

[TomR]

Boatdoc...Thanks for the interesting discussion. I wish I too had the ability and desire to create my own new frame and restore 30+ year old ASs ...but I concluded awhile ago that I do not have the time, skill or desire to go to such lengths...thus my change in focus to the new or "near" new ASs.

I don't think Airstream wants to sell their trailers with a limitation of not using in the snowbelt...or near either coasts...to prevent frame rust. I doubt many owners have facilities to wash off the belly and dry off if/when they use their AS during or after a snow...or after every trip to the beach...and I assume some will park on grass. Yes, moisture, salt and the elements are going to impact your trailer and should be considered by the manufacturer when designing their product..

Your insulation/drainage and airflow ideas may indeed be a great start...but why doesn't AS take these steps to protect their $100K trailers? I am sure some who read your ideas will be appalled that they, as new purchasers of an expensive AS, are expected to be able to make the modifications you have suggested. One thing as you restore a 33 year old AS...another if you spend $100K to buy a NEW one.

Auto makers have worked hard to make there products much more rust resistant than say 20-30 years ago and have been quite successful. I am sure they are still trying to do better...never had an auto company tell me to spray off the salt each day and dry off the underside...gets pretty cold up here when the salt is on the road!

Boatdoc...I am envious of the skills you have to perform such "deep" level restoration and fixes...but I don't think most/many new AS buyers feel they should NEED to make such modifications on such an expensive new product.

I hope others have some further insite regarding new(er) AS moisture/rust prevention factory fixes. Thanks...Tom R in cold and "salty" Two Harbors, MN.

P.S. Please don't resort to the "just buy SOB if you don't like it"...meant to be a positive discussion. BTW...maybe the lack of a belly pan on the SOBs is actually an advantage?...the frame and underneath can "air dry"?...TomR

[LI Pets]

So what do you think about my idea of no insulation in the belly at all let it air dry and drain as you suggest (i like the slit idea).

I am putting the Prodex inside on top of my fiberglassed floor, then installing pergo on top. Instead of using the Pergo blue foam, the Prodex will take its place.

The only other option I'm considering is coating the floor underneath with West resin, no glass

[boatdoc]

Hi Tom R; Thanks for your reply, and I am happy to find out that my last post is working. My point was taken but something is still missing. What is missing is a suggestion not to give someone $100K for something that is not right. You have an idea what the problems are, expect them to correct those problems before handing them the money! If everyone demands it, guess what will happen? They will change, or be out of business. There is no grounds for dispute that frames rust much too prematurely. I am glad I got you fired up, it may make you think differently. And you are right about SOB's they dry up lot faster because they are open on the underside. My aim was to point out that no one has to accept what what is being offered. Second point was to make everyone who owns AS aware that there are some remedies if you willing to correct the problem. Thanks again, "Boatdoc"

[boatdoc]

Hi Lipets; Placing the Prodex on top of the floor will definitely help but for how long. This can present a two fold problem, one - your floor plywood will have no vapor barrier on the underside. It will rot as quickly unless is kept totally dry at all times. Plywood gets soaked in five minutes, but it takes weeks to dry. Second concern is the Prodex resilience when placed under the floor. I would ask Prodex representative if it will withstand that kind of application. Your idea of applying resin would work but not for long. Plywood would still get wet where it sits on the frame if you cannot coat those areas.
Moisture lays in those spots where it is hard to dry up. Do some thinking before you go on with your project, so that you do it only once.
Thanks, "Boatdoc"

[TomW]

Originally Posted by boatdoc

...YES, you should rinse off the salt Tom, after towing on salted road...

But I would always rinse off the salt if they ever used it around here in AL.

On a serious note, I appreciate the information you posted and the time it took to formulate your viewpoint. The problem is that I don't think the Mother Ship really wanted their products to last forever or they would have incorporated many of your suggested improvements.

Karma, though, for good advice to the masses.

Tom

[LI Pets]

I did check with Prodex on using it under the wood floor, that's not an issue.

If I coat the woods under side with resin, I can't get the resin where the wood is sitting on the frames

At least it won't wick up and on top of the frames as it does with the pink insulation.

The floor right now is bone dry (other than the moisture % in the air) it has been sitting about a month with the belly pans and banana skins down.

The wood is clean and in very nice condition.

There must be a solution, this isn't rocket science

[TomR]

Boatdoc...why don't you invent a pre fabricated insert that would allow us less skilled to simply cut a hole/slot in the belly pan and then install a one piece aluminum "vent" with the water "shield" built right in? You could have a design plan showing how many were needed to provide both a drain and an air vacuum to create a movement of any moisture and pull air out of the belly pan cavity as you travle down the road...all with protection against water coming in your "vent".

I actually think 1) it is a very constructive idea (since the company seems to not have a solution) and 2) if it were pre fabed and all us less talented had to do was cut a hole according to a template and instal with the supplied screws...that might help a lot of AS owners.

Let me know if you need to raise financing to start a business...that IS what I am good at! Tom R in Two Harbors, MN

[LI Pets]

I read that introducing air via a vent has shown to increase moisture in basements and it is now recommended in most cases to shut the basement ventilators off.

So the boatdoc’s idea is great but they need to be small, not seeking to ventilate.

Or…………..

Maybe all that's needed is some strategically placed weep holes to allow any excess water out. Thereby prevent pooling of any water either though condensation or rain water.

[wahoonc]

Originally Posted by Lipets

Maybe all that's needed is some strategically placed weep holes to allow any excess water out. Thereby prevent pooling of any water either though condensation or rain water.

I don't think that the pooling water is the whole problem, I think the problem is the water being absorbed by the insulation...repeatedly. The belly pan on mine wouldn't hold water, but the insulation will sure absorb it. On my unit the laps were never caulked (aren't supposed to be from what I know) so there are plenty of places for water to get out. However it being a perfect world and all, I am sure the water ran down along the frames and found a low spot to settle, it also ran down the inside of the frames, and around the outriggers and....

Aaron

[Jim & Susan]

Aaron, is this the definitive word on sealing the belly pan? Not to question you at all, but here is why I ask.

As many of us have discussed before, the design of the banana wraps/belly skins of the early ‘70’s trailers is meant to leak. (A couple of pictures below). Water simply pours into the belly pan. This was the biggest problem with my camper. The constant moisture (as everybody described above) caused the floor to rot and the frame to rust. But here’s the weird part. The very bottom of the trailer, the flat part of the belly pan closest to the ground, were sealed with Vulkem. Result? Water poured in during even a light rain, then was trapped in the belly because of the Vulkem. ARRGGG!!! Is it possible that it was designed that way?

I would like to have an outlet for the water to drain. I’ve sealed the skins in the pics to stop/slow down the water ingress into the pan. But I would like to allow for some type of air to circulate/real drain out of the pan (nice ideas above, BTW).

So, I guess in the case of my trailer, the steps are:

1) Seal the tops of the banana skins (as pictured) to keep rain water out.
2) Create drains of some sort to allow any rain water/water vapor to drain/dissipate.
3) DO NOT seal the belly skins against the banana wrap to allow for air flow in the belly pan.

Anybody agree? Disagree?

Jim

[wahoonc]

Jim,
I agree that the banana skins need to be sealed at the upper edge. Just the joints underneath need not to be sealed so what moisture does get in has a place to escape. I have been removing my moulding, cleaning ungodly amounts of silicone off of it, and resealing with Vulkem behind it and along the top edge. What is interesting is that "THE BOOK" shows the wraps behind the main skins, but I can't see how they could have done that based on the pictures of how the trailers are built. Once again Production trumps Engineering The older vintages ie; 60's and IIRC 50's the side skins actually wrap down and become the banana wrap

Aaron

[boatdoc]

Hi TomW; Boy you sure got the hint in reference to the throw away society. And you are right, it seems as job security by replacement may be a motto. All of you are correct, there are much better frame coatings. On the other hand how many buyers of new AS see this as a issue? They properly do not even think about it because it is new. On the third hand, negative publicity does get attention if it is spread among buying public. Perhaps a new buyer not knowing about these problems will not point it out at time of purchase but for all of you that are aware of the problem, articles written to appropriate magazines will draw amazing level of attention by the manufacture. I have done it very successfully in Marine Industry. Thanks for your reply to my post, "Boatdoc"

[boatdoc]

Hi TomR; While your suggestion is excellent, there are some cases where the fiberglass insulation may lay on top of the belly pan. The insulation along with the paper vapor barrier will considerably slow down the air movement throughout the underbelly. This condition would make the idea useless. Wet fiberglass insulation is very difficult to dry for that reason. Try to understand that reversed clam shell is not going to force the air in. Something like a small exhaust fan mounted in the rear must pull the air from the front of the air intake. Some water ingestion in front intake pending location may be unavoidable during towing, but it can be drained easily. Than again the drying process with the help of the fan while trailer is parked would be shortened considerably. So as you can see that idea will work for some and others will see no benefit if the air is not free to move in the underbelly. As for the idea of the clam shell production we are speaking only about cents for the material. There is a solution to every problem but every problem is not the same, and must be considered individually in order to resolve it. The one more thing I need you to understand that the enclosed bellypan traps the hot or cold air [pending time of the day] and encapsulates it, then when temperatures change drastically it acts as a condensing chamber by allowing the varying temperatures to collide at the skin. Unless provision is made to balance the temperature inside the bellypan with the falling or rising temperature outside as quickly as possible while providing a good vapor barrier to the floor, nothing will change. Thanks for your reply TomR. "Boatdoc"

[boatdoc]

Hi Lipets: While you are correct in your statement you have missed my point. The reason for that is that the basement usually stays much cooler or much warmer than outside air. Venting the basement, brings in air of different temperature to collide with opposing temperatures inside to condensate. As you can see that statement reinforces my theory. In the basement you can control the temp's, in the bellypan you cannot. Air will warm up or cool down and will stay trapped. For as long as it takes for the temperature inside the bellypan to equalize with the temperature outside of the bellypan, condensation will occur. Thanks for your input Lipets, "Boatdoc"

[boatdoc]

Hi Aaron: You are right, lapped joint are not sealed. However, the cross members on older units have a bend up wards which creates a pool with no provision to drain it. Collected water is there to evaporate again when temp's change. And yes, the insulation sponges that that water as it evaporates. The second issue is the small amounts of water trapped between the bellypan skins and the frame which is hard to dry. This is where the rust starts. The lapped joints can be plugged with road dust and may contribute to collection of water the sooner you drain it the better you off. Thanks for your input Aaron. "Boatdoc"

[boatdoc]

Hi Jim & Susan; Your thinking is on the right track. It is important to seal the banana wrap behind the molding. I have found out that a silicone sealers often separate with time allowing the rainwater to enter the bellypan. For that I recommend small but uniform bead of 3M #4200. As for the small drains pick the lowest spot in the belly skin near the back, which most likely be in the center of the frame. Thanks. "Boatdoc"

[LI Pets]

Boatdoc, only a sailor would recommend 3M #4200

[TomR]

Originally Posted by boatdoc

Hi TomR; While your suggestion is excellent, there are some cases where the fiberglass insulation may lay on top of the belly pan. The insulation along with the paper vapor barrier will considerably slow down the air movement throughout the underbelly. This condition would make the idea useless. Wet fiberglass insulation is very difficult to dry for that reason. Try to understand that reversed clam shell is not going to force the air in. Something like a small exhaust fan mounted in the rear must pull the air from the front of the air intake. Some water ingestion in front intake pending location may be unavoidable during towing, but it can be drained easily. Than again the drying process with the help of the fan while trailer is parked would be shortened considerably. So as you can see that idea will work for some and others will see no benefit if the air is not free to move in the underbelly. As for the idea of the clam shell production we are speaking only about cents for the material. There is a solution to every problem but every problem is not the same, and must be considered individually in order to resolve it. The one more thing I need you to understand that the enclosed bellypan traps the hot or cold air [pending time of the day] and encapsulates it, then when temperatures change drastically it acts as a condensing chamber by allowing the varying temperatures to collide at the skin. Unless provision is made to balance the temperature inside the bellypan with the falling or rising temperature outside as quickly as possible while providing a good vapor barrier to the floor, nothing will change. Thanks for your reply TomR. "Boatdoc"

Boatdoc...I think we need to divide our discussion into "new or newer" vs "older"...I am not sure where the break point between the two is. The reason I say that is that it "appears" that the factory is no longer using the "bat" type insulation that is so likely to absorb water and drop to the bottom of the belly plan...as you discuss. See quote below:

"found a recent Jackson Center visit report that may be good news for you, confirming that the fiberglass under-floor insulation is now replaced with bubble foil insulation."

1) Question for Boatdoc and all??? If you installed Boatdocs "reverse clamshell" drains (say three or four?) and a very small exhaust fan (with appropriate protection from incoming moisture and bugs, etc) in a new AS with a clean belly pan...might that allow any water that gets in to drain...AND to allow the exhaust fan to pull air through the belly pan to cpmpletely dry it out...maybe after you return from a trip...or while camped????? Seems like this could? work with some type of pre-designed and fabricated parts and "fix" kit. Many products have aftermarket "fixes" that work and often are adopted by the manufacturer at some point. Maybe Andy will join the discussion.

2) My other thread on this topic drew the following response:

"You could import an Airstream from Europe. There they have galvanised frames . And aluminum sheathed foam floors . It appears they are having the entire chassis built by BPW in Germany."

Does anyone know that this is true??? If so...there is NO! reason Airstrem should not do this here. Maybe someone can confirm the above claim. BTW...I am NOT planning on importing one from, Europe.

Seems like Boatdoc has got something good going here...but I think we need to label our comments as "new or newer" vs "vintage" or pre-bubble insulation...assuming the factory is now using a non (or less) water absorbing under floor insulation.

Thanks All...Tom R in Two Harbors, Minnesota

[LI Pets]

Here's another issue, we're all talking about draining and ventilating the belly pan. What about draining and ventilating the bannana skin areas?