Over the years, I've set lots and lots of aluminum caps on 5/8 in. iron rods and have been well satisfied by how permanent they've been. I expect caps set more than twenty years ago to be still tight and perfectly legible as long as fence builders and drivers of heavy machinery have kept a respectful distance.
However, apparently not all aluminum caps are created equal. A recent project involved resurveying various tracts whose boundaries had been marked in 2004 by someone else with aluminum capped 1/2 in. iron rods that had failed in that the plastic inserts in the aluminum caps, the essential ingredient holding the caps on the rods, had degraded to bits and pieces. I don't know who the manufacturer was, but the caps had a hexagonal cavity in their stems that slipped over the rods. The plastic was some inferior sort that had degraded without any UV exposure. It was in a rural setting miles away from civilized life. I saw no evidence of fire.
I've had very good success with the aluminum caps (with plastic inserts) made by Surv-Kap and was shocked by how these were falling apart for lack of a five-cent plastic insert of sufficiently good plastic.
How do those caps fair in fires? Grass fires would I imagine be common.
Plastic would melt quickly. Do they fall off?
I imagine a hot fire would melt the Aluminium anyway.
Do they make the caps from 'superior' quality Aluminium?
Some aluminium here degrades fairly quickly in harsh environments.
Wondering why a plastic inset not a barbed hole /recess under the cap that grabs onto the reo?
> How do those caps fair in fires? Grass fires would I imagine be common.
> Plastic would melt quickly. Do they fall off?
> I imagine a hot fire would melt the Aluminium anyway.
> Do they make the caps from 'superior' quality Aluminium?
> Some aluminium here degrades fairly quickly in harsh environments.
>
> Wondering why a plastic inset not a barbed hole /recess under the cap that grabs onto the reo?
Richard,
From what I've observed a "plain old" grass fire moves relatively quickly and the temperatures aren't really that high. While they will deform the plastic caps on rebar (if they're prominently above the ground) and make them droop, I've never seen a grass fire hot enough to affect "aluminium". (we call it aluminum around here)...;-)
Aluminum melts at around 1200 degrees F. and the temperature at ground level for a grass fire is usually only 600 to 800 degrees briefly. A grass fire is actually a moving occurrence. Once the fuel is oxidized, it cools quickly because the flames move on. They can at times move as quick as a man can walk...and even a lot faster if driven by high winds.
Woodland fires of course are a different story. If there's a good amount of deadfall on the floor of the woods, the temps can (and do) get hot enough to melt some metals. I've seen cans and sheet iron in a woodlands blaze that has approached melting.
Aluminum oxidizes 'quickly' in some environments. An extremely alkaline (clay) soil in the presence of a bi-metal (where the aluminum is actually in contact with the steel rebar) connection can provide an anode/cathode electrical charge and breakdown the aluminum in just a few years. The plastic insert in today's monument design insulates the metals and keeps the bi-metal corrosion at bay.
From my experience some manufacturer's plastic inserts work a lot better than others. Berntsen's are of a good quality I've found.
> How do those caps fair in fires? Grass fires would I imagine be common.
I'd agree with paden that low-intensity grass fires are not much of a problem. Typically, in rural settings I'd set aluminum caps no more than a few inches above ground level.
> Plastic would melt quickly. Do they fall off?
I've never seen a plastic insert that had melted. The environment seems to deteriorate poorly chosen plastic so reliably that no fire is ever needed. :>
> I imagine a hot fire would melt the Aluminium anyway.
Actually, there aren't many rural settings where there is enough fuel to make a really hot fire in Central or West Texas, particularly right at ground level.
> Do they make the caps from 'superior' quality Aluminium?
It is a relatively pure, ductile aluminum.
These are the rebar caps I've used for about 25 years now:
Richard
The plastic insert is to prevent a galvanic reaction between the iron rod and the aluminum. With a free flow of electrons from metal to metal deterioration of the metals comes very quickly.
Paul in PA
Berntsen caps once had very thin flimsy red plastic inerts, easily crushed during installation. I hated those inserts. Their inserts now appear to be very good, thick plastic that I believe is yellow for 1/2" and magenta for 5/8", and seems virtually crush proof. It's a good point. You expect the aluminum to have a long life span. It's a shame that the insert would be the point of failure.
Eliminate galvanic reaction
> The plastic insert is to prevent a galvanic reaction between the iron rod and the aluminum. With a free flow of electrons from metal to metal deterioration of the metals comes very quickly.
>
> Paul in PA
Cor-Ten caps?:-)
Looks like I lost that round soundly too:-)
Hadn't thought about iron eating Aluminium er Aluminum.
Grass fires. That's a hot topic here in planning that cannot be evaded.
I won't go down that track.
Best keep to topic.
I reckon slashers as we call them here would be their worst enemy, as well as whipper snippers/ brushcutters
One of the issues we have, particularly in the northern part of the county, is the salinity of the soil. I have seen 2" aluminum caps that were buried reduced to a mushy powder leaving the plastic insert attached to the top of the rebar.
Degredation and complete destruction of aluminum caps in some areas in my state is common due to the chemical characteristics of the soil. Its not a galvanic issue, as it happens whether the cap has a plastic insert or not. We have seen an aluminum cap completely destroyed in 12 years. The large plastic Morasse brand caps are in perfect condition after 35 years of UV exposure at 7000' elelvations. In spite of this, our state professional society has recently completed new minimum standards eliminating the use of plastic caps. Most disheartening...
> The large plastic Morasse brand caps are in perfect condition after 35 years of UV exposure at 7000' elelvations.
Yes, in Central and West Texas the Morasse caps perform much, much better than all the other plastic caps I find, some of which have basically completely disintegrated just from UV exposure in under ten years. If someone can devise a system for adding custom stamping in the field to a Morasse cap, that would be a worthwhile improvement.
> Berntsen caps once had very thin flimsy red plastic inerts, easily crushed during installation.
These may have been Berntsen caps. The distinctive thing about them was the hexagonal hole in the stem that fit over the rebar and the aluminum alloy seemed a bit on the brittle side.
If Berntsen has kept their aluminum caps the same dimensions and only changed the insert design, it might be worth trying to order a bag of inserts to replace the faulty ones with. Otherwise, pretty much all of the rod and cap markers with the faulty inserts will come apart and stay apart until the cap disappears.
We've been using Morasse caps since '97. We've been very pleased with them. The only issue I've seen with them is that occasionally animals like to chew on them (not sure what kind of animal it is yet).
I've been told that the Morasse caps are impressionable, but I've never attempted to do so. We really don't have any room on our caps for stamping.
I've found some of the plastic permamark style caps do okay in UV. Dad used them before going to Morasse from about '87-'97. We still find them, legible, today. Some are even in full sun. He used yellow. Recently I've found red permamark style caps that are about 20 years old that look like they simply shattered. I find shards of plastic around the rebar. I don't know if the color makes a difference or if it was in the plastic blend used.
We have seen an aluminum cap completely destroyed in 12 years.
There are some caps I've come across here that have lost the stenciling, I'm pretty sure because of who did them that they stamped them when they were set. I haven't seen any brass caps that have had any issues only the aluminum ones. The plastic ones are intact about 1 out of 10 times, usually unreadable or in shards around the rebar.
> If Berntsen has kept their aluminum caps the same dimensions and only changed the insert design, it might be worth trying to order a bag of inserts to replace the faulty ones with. Otherwise, pretty much all of the rod and cap markers with the faulty inserts will come apart and stay apart until the cap disappears.
I had a batch of Berntsen caps with the bad inserts. I contacted Berntsen and they sent me replacement inserts. It was easy to remove the old inserts and insert the new. No problems since then.
Ken
> I had a batch of Berntsen caps with the bad inserts. I contacted Berntsen and they sent me replacement inserts. It was easy to remove the old inserts and insert the new. No problems since then.
I was thinking about carrying replacement inserts to rehab these monuments whose original inserts have disintegrated. The rods are still in place and the caps are in good shape, but just sitting loose on the rods. I thought about kneadable epoxy as a substitute, but just popping another insert on and reseating the cap would be much easier.
Kent, not to change the subject
totally, but I had an occasion to set some rods in Sargent, Texas fairly near the beach. I noticed that almost all of the rods I found were encased inside PVC. The rods that were not encased inside the PVC were almost totally destroyed by oxidation (salt-laden air). The "rods" inside the PVC were in bad shape, too, but the value of the PVC was that all of the flakes of ferrous material were contained inside the PVC, which still retained its magnetic signature. The sun's emissions had quickly caused the deterioration of the PVC where exposed to open air and sunlight, but the PVC was intact just a few inches below ground surface.
I thought the solution (PVC pipe) was a very handy one.
Kent, not to change the subject
> totally, but I had an occasion to set some rods in Sargent, Texas fairly near the beach. I noticed that almost all of the rods I found were encased inside PVC. The rods that were not encased inside the PVC were almost totally destroyed by oxidation (salt-laden air). The "rods" inside the PVC were in bad shape, too, but the value of the PVC was that all of the flakes of ferrous material were contained inside the PVC, which still retained its magnetic signature. The sun's emissions had quickly caused the deterioration of the PVC where exposed to open air and sunlight, but the PVC was intact just a few inches below ground surface.
>
> I thought the solution (PVC pipe) was a very handy one.
I'd think that a galvanized rod with a closely-fitting PVC pipe around it would be an interesting experiment for corrosive environments. Thin-wall 1/2 in. irrigation pipe is a close slip fit over 5/8 in. rebar, paradoxically enough.
Kent,
Just call Bernsten up. We lost a ziplock full of inserts for our caps one time. I called them up and they shipped just the inserts right out. It was cheap.
There was one outfit here in the PDX area that used aluminum caps as far back as the late 60's. There was no plastic liner on these caps, they simply hammered them on to the top of the iron rod. When you find them today the cap is usually pretty loose on the rod and the act of digging them up often separates the cap from the rod. But, when found, both the cap and the iron are always in good shape.