Thursday, January 28, 2010

Restoring Metal Carport Posts

I recently was tasked with replacing two metal carport posts and thought I'd share the experience. While at first this might seem a bit daunting, I think you'll find as you read that it's not as bad as it sounds. Most of the homes in our Northcrest neighborhood have metal posts supporting the 4" x 8" douglas fir support beams that are exposed in the carport and the front patio (if the home has one). This was a very common building practice by P&H Home Builders and is the norm for all the tri-level modern homes in this neighborhood, and those homes built by P&H in Northwoods and other local communities. Howard Hardrath's brother, Buddy, continued with this practice in his version of the P&H Split in Lilburn, Stone Mountain and other areas. It was also used by very many other modern builders in the area, although the pipe diameter may vary a bit.

Let's talk a bit about the construction. These posts are mostly made of 2 1/2" diameter steel pipe welded to a 1/4" thick metal plate with dimensions of about 3" x 6", offset (meaning the pipe is welded to one end of a rectangle). I've found the plate to vary a bit in length, with a minimum of about 5" and getting up to about 5 1/2" at a maximum - the plate always has four holes drilled at the corners where nails were pounded into the beam above for stability. The pipe used provided almost 1/2" of additional diameter provided a total diameter of around 3" (metal pipe is measured by the inside diameter so in order to get 3" on the outside, you buy 2 1/2" pipe, which has a wall thickness of slightly less than 1/4" providing the total diameter). What I find interesting is that almost all of the original posts in the neighborhood only have a plate and are attached at the top - the bottom is the open pipe, usually sitting flat on the concrete pad or brick wall below. I'm not sure if you can get away with this method in modern construction - seems non-code to me. I think this method was used for a practical reason, rather than as a cost-savings one - as the home expands and contracts with weather, there's some movement in the wood - by "floating" the bottom post it's possible to allow for this movement - however this is conjecture on my part. Some of the posts I've seen also have a bottom plate, but strangely they aren't attached either (no nails, lags, etc) so that's not really a clue.

In any case, as with any metal and especially metal that touches concrete, over time and with repeated exposure to weather produced rain water, the bottoms frequently "rot out" - usually it's the posts closest to one end of the building's side or front. With this home it was the two to the outside of the carport, which would have the most access to rain. Normally a little pitting or rust can just be treated - but these posts each had quite a bit of rotting - one was actually hanging from the beam above and both could easily be moved around by kicking around the bottom. (as an aside, if you want to just treat the posts a bit of sanding or grinding of any rust, body filler if there's only some slight pitting, and a bit of good metal primer and paint will go a long way to preserving what's there).

My first task was to determine the width - I initially did this with a good tri-square ruler to determine the general diameter - I later confirmed using an outside-caliper - these posts were just slightly under 3." The next task was to source the goods - there are many good steel fabricators around the area - I got a list of three that were north of here from a friend who used to build homes in Forsyth and Cherokee County. I decided to go with a local shop near Tucker, Dekalb Steel.

You'll need to determine the actual length of the post (make sure you include the plate thickness) by measuring the actual distance from the beam to the floor (concrete or brick) - this can be off by a bit if you think the beam has sagged with the deterioration of the post - just make sure you go over-sized and not under-sized! It's also good to provide a small sketch of the construction for the plate - I did this by going into SketchUp and producing a nice 3-D rendering, and then making a jpg image to fax to Dekalb Steel. By doing this and showing the location of the drill holes, you'll get something closer to what you're asking for - welders produce good results when giving good images and instructions.

It can take anywhere for a couple of days to about a week to turn around the fabrication. If you have access to a good metal shop you could do the task yourself - just make sure you can get a good 90 degree cut on the ends so they're "square" - this typically takes a metal bandsaw. Drill the end plate before welding so you can use a drill-press. Unless you specify otherwise, the post will come "raw" - complete with surface rust and any marks used by the handlers - you can have them paint it but it'll cost more and they usually just spray some paint on it, meaning that there's not much effort involved in doing the prep before painting so you may get mixed results (sometimes the rust and/or clay or wax scrawl on the metal bleeds through - other times the paint may flake off as there may be some oily or waxy residue on the metal). I chose to get the post bare and do the prep myself. The prep involved a light sanding followed by two coats of metal primer. It was about 16 degrees outside when I started the install so I spent a day doing the sanding and priming the posts on saw-horses, to give the primer a chance to set up. This was done in the sun so that helped harden up the paint. Usually it's too cold to do this type of work but I've found primer to be an exception to the "too cold" rule - later I'll relate how I got the black paint to dry in this type of cold.

The next step is to remove the old posts and replace with the primered new. To do so there are various methods, but as I had an extra screw-type jack-post I decided to use it. I nailed a short tubafor to the bean near the first post - with a bit of the nail-heads left proud of the surface for easy later removal. Next the post was adjusted so there was plenty of threading left to lift the head of the post (the head is a plate that can be screwed to the tubafor to help keep it from slipping off) - there's a flat threaded collar that can wrenched on, which drives the threaded part of the post up or down, lifting whatever weight is above it. I wrenched up until the old post easily cleared the concrete below - about a half inch. I then measured, cut and placed a forbafor post next to the jack - this was a little added insurance as I don't completely trust the post - probably not necessary but I wanted a bit extra for piece of mind.

Prying the old post off was relatively easy, as was attaching the new post. You'll want to use along level to make sure the post is plumb, holding it in place as you turn the jack screw the opposite direction to bring the beam/roof down. Before taking everything apart, check for plumb again and make any adjustments if you need to. I then repeated for the second post (this one involved the removal and later reattachment of a gutter).

The final steps were to float some concrete along the bottom (there was a depression in the existing concrete where the old posts had "drilled" into the substrate below) and paint the post. I waited until it was a bit warmer to do both of these, as concrete does not set up well in freezing temperatures. I used an oil-based enamel Rustoleum product in gloss black - being the closest color to the existing posts. Because of the cold I added a cap-full of Japan dryer to the paint in a paper cup. Japan dryer is a mix of chemicals (mostly naptha) that accelerates the evaporation of the paint's solvents - in this case the paint was dry to the touch in about an hour and completely hard in a day or two. The hazard of painting oil paints in cold weather is that they just wont harden - there isn't enough temperature for the solvents to evaporate so they remain tacky. Using the dryer is an old painter's trick - just make sure you mix enough to do the whole project and throw out any remaining in the mixing cup instead of pouring it back into the can. A little clean up and I was done.

-- John


Christiane Erwin said...

I can't tell you how much I appreciate this post! My hubby and I were just talking last night about replacing the wood posts under our deck with metal ones. Our remodeler didn't really get the whole mid-century thing, so little by little we are making changes that reflect the original character of the house. This was exactly what we needed! Thank you!!

TNT Crusader said...

What's tubafor and forbafor??
You mean 2 by 4 and 4 by 4??

Unknown said...

Thanks for this thorough walk through, John. We live on a block of 1955s and so many of us have this issue. We're also in coastal south Texas (Corpus Christi) and the weather is brutal on metal. I saw you have a DOCOMOMO link to blogs. I'm going to check it out. I'm a member as well.

Jesse Milton said...

We are facing an identical situation! We are budgeting for the project and curious as to how much the fabricators charged for the post and plate construction?

John Eaton said...

@Jesse Milton - it was fairly reasonable from the fabricator - I think less than $150 per post - of course that was 7 years ago. Have them fabricate (which amounts to cutting the pipe, plate and welding) and drill the holes - it will save you time. You can prime and paint yourself. Make sure you take an accurate height measurement for each post (if the post has worn into the slab measure from the bottom - alternatively you can jack the post first so you have the exact length. Keep in mind that some of these supports have rusted at the bottom or may have been altered.