Hi All,

Our team of the Alexander Chapter-NRHS is making great strides in the restoration of our narrow gauge Lawndale boxcar. We have repaired one intermediate sill, repaired one body bolster a la' the Abatron product, replaced one side sill, and have started now on all the interior bracing- all with tendons & mortices.

Thanks to many of you on this board who have offered previous suggestions- and thanks to RYPN for merely existing.

Anyway, we have enough volunteer help that we also want to go ahead and start a crew on the roof, which is a double-layered tin roof that certainly has not leaked a drop of water in at least 60+ years.

The roof is really in outstanding shape, so much so that we have gone to great pains to leave it alone as we rebuild walls/etc. There are a few patches on the edges that will deserve the wire brush treatment, but overall, surface rust is the worst demon. Some of our members are for wire-brushing or using naval jelly on roof from end to end and priming it, some say this surface rust is actually a protector and should be merely primed over and then painted. Looking at the RYPN archives, there also seems to be something called RustExtend, which converts the rust to a protective coating.

What say you?

Thanks in advance,

Matt Bumgarner

You are looking for a rust converter product that will chemically convert the surface rust into an inert paintable coating. The best I have used is OSPHO, which is probably available from a good industrial paint supplier. I have not had good fortune with the home grade products available from your local big box store - it doesn't penetrate and is a bit too innocous itself to go after the stuff in my experience - you can even get it on you without noticing.

Whatever you use, removing dirt and flaky loose stuff will be required first. Then treat the surface rust to kill it, and prime and cover with high quality metal paints or roof paint, depending.

I think ABATRON makes a metal filler epoxy product that can be used to fill holes in the tin, and a good caulk will do wonders on the cracks.

dave

Agreed, I would shy away form any hardware store grade of rust converter. Understand they are not inexpensive and I would consider it a must that any surface rust be removed, loose dirt, loose paint, etc. To see if it qualifies as loose rust, go after it with a knotted wire cup on a grinder and if that blows it away, you know what you have to do. I would also wipe down the 'cleaned steel' panels with xylol, naptha, or mineral spirits, - the rags will certainly come away black.

Then use the rust convertor or proceed with priming and painting. I have had good luck with QUALITY oil based alkyd and urethane fortified alkyd enamels. I have not found it necessary to go to two part epoxy products.

One question - you described these as a 'tin' roof. If that means they are galvanized, then the zinc coating may require use of an 'etching primer' as most paints will not adhere to that. Some may tell you to prime galvanized steel with a zinc chromate primer, but my experience with that has been hit or miss, and I think you should consider today's technology of an etching primer.

Bob Kutella

This is only a suggestion. I have used crushed crushed walnut shells to great success in removing surface stuff without abrading the material underneath. You use as if you are sand blasting, but it is the media rather than sand. It is great to clean things up where you may use a different conversion process but don't want to be overly aggressive on the raw surface. I have even used it to blast away tary type roof coating on stainless car roofs to return the car to orininal appearance. Its a great time saver if you have access to the equipment.

I would suggest caution…

We had (still have but no longer functioning as a water tight surface) a terne metal roof (a variety of lead washed sheet iron with soldered joints) on our 1882 narrow gauge passenger car.

When received the roof was mostly tight, but rusty.

We tried several techniques on small areas as we restored the car… We wire brushed loose material (this was too aggressive, and could result in damage to the remaining metal) we cleaned seams with various acids and tried to re-solder them with limited success. We used walnut shell in our “sand” blaster to clean rust. We tried various rust converting primers (industrial types, not local hardware store formulas) then we painted the roof with a compound, purchased at an industrial roof supply house meant for old iron roofs…. It looked good for about 3 years, then, the underlying iron just exploded in rust, apparently from within…

We are now planning a complete replacement of the old iron. The material is still available (www.follansbeeroofing.com) We are hoping to offer a weekend seminar lead by restoration professional Glenn Guerra (http://www.midcontinent.org/collectn/wo ... age01.html)
We are still trying to understand what went wrong… It never was really clean before applying coatings, it appears that the high tech coating sealed moisture into the metal… In retrospect, the roof was nearly gone when we started our efforts, and If we had put the car indoors it might have worked…

Preservation is a tough business. We are trying to preserve old material choices and old methods. Many times these were not good choices to begin with. Metal and wood do not expand and contract at the same rates, and in many cases would never work well together.

One hundred years ago much of the science may have been imperfectly understood, if at all.

So the challenge is to keep any material dry by using a coating. For that the base material must generally be REALLY clean. Often that is nearly impossible without dismantling and removing the material and then resorting to chemicals.

Putting something back together is tough also. Maybe instead of trying to make a watertight sealed roof, we should instead think of preserving the roofing material and systems, and trying to assure that water and moisture can be channeled away.

It is almost impossible to devise a totally impervious roof covering.

Bob Kutella

100 years ago they would have been thrilled to get 20 useful years out of a car roof, and 40 useful years out of the car. They aren't designed to last this long. Only us unreasonable preservationists believe we can make them do better, and devote huge amounts of resources to doing so - and I am amazed as to the extent of it we actually manage to pull off......

Terne is actually copper coated with lead - Jefferson used it on Monticello, but I have seen the term used to refer to sheet iron coated with lead as well - sort of an early galvanized. I'd wonder if the rust converter might have actually reacted with the lead and created a disconsolidation problem between the lead coating and the underlying iron?

CRRB 2 had a roof made of small squares of this stuff joined with folded soldered seams as well. Given the indoors of the Savannah roundhouse was about as tight as the outdoors, we chose to use elastomeric roofing products to repair the cracks, rust holes, etc. This system uses a tape to cover cracks and holes, impregnated with a coating of a pasty rubbery filler. this stuff moves and flexes nicely. Once the patches cured, the whole roof was painted with an elastomeric roof paint, then cover coated with latex paint in its final color when cured. I don't know how long it will last, but kept out of direct sunlight probably for some time. Any moisture present in the wood beneath will migrate downwards through the ceiling, but after siting outside in the south for decades in the sun the roof decking is really dry.

If the whole roof is gone and needs replacing, seamless rubber is not historically correct, but very practical and long lasting.

dave