Sealing the Gaps

Finished gaps between containers

This is a task that has spanned more than a year and a half.  It’s not that it had to, it’s just that there always seemed to be something more pressing to do.  I did finish the interior portion of this in April of 2010 right after I had the interior container walls removed.  That worked OK for the first winter, but I really needed to finish it before this winter to avoid any cold spots on the few metal wall remnants that are just behind the drywall.  There was a small amount of condensation on them last winter, and I’m sure it was due to the cold air reaching deep into the gaps.

The most common method I have seen to seal the gaps between containers has been to weld steel plate on the outside.  Not being a welder, I wanted to figure out something that I could do myself.  I also had new containers in a decent color that I wanted to keep as original and attractive as possible.  My plan was to use a combination of backer rod, spray foam, and caulk to seal everything up.  The picture above shows the finished product on the back side of the cabin, and I must admit it looks better than any welding job I could have done.

The first thing I did when the walls were removed was to install some foam backer rod between the containers.  I recommend getting a variety of sizes since the gaps can vary.  I tried to place the rod at a consistent depth using a marked plastic drywall knife.  This was in place by itself for a couple of months in the spring, and it did at least keep the bugs out of the containers.

The next step was to seal the inside gaps with some Great Stuff foam in a can.  As you can see in the picture below I didn’t have to be too careful since it was going to be covered with more spray foam in addition to the drywall.  You can see the metal wall remnants here that come right up to the back of the drywall.

A few weeks ago I was able to finish the outside gaps.  After some research on foam insulation and mice, I felt it would be prudent to include some sort of barrier in the gaps just in case.  I decided on a layer of coarse steel wool over the original backer rod I had installed from the inside.  I don’t think mice would have made their way through the foam, but it was only a few dollars for the steel wool and 30 minutes more time.  Better to err on the side of caution when it comes to mice.

After the steel wool was in, I added another layer of Great Stuff foam.  This was the hardest part of the project since I had to keep the foam at a consistent depth for the final layer of backer rod and caulk – I had to continually scrape away the foam as it expanded and dried.

I then placed another layer of backer rod on top of the foam as a base for the caulk.  The rod was probably unnecessary, but I thought it might help me create a more consistent base.

The final finish was a layer of OSI Quad caulk.  While this is great caulk, I found it a bit harder to get a smooth finish than others.  It’s also a pain to get off your skin.  Here’s a closeup of the finished gap on the backside of the cabin.  I could have gotten a better color match with the caulk, as Quad is available in hundreds of colors, but I would have had to special order an entire case.  Since I only needed four tubes, I used a stock beige color which actually looks OK.

13 thoughts on “Sealing the Gaps

  1. Dave

    I can sympathize with doing it this way, as I too know nothing about welding, and welding is complicated. How did you decide that this method would work long term? Or are you ‘experimenting?’

    Reply
    1. Steve Post author

      Hi Dave:

      It sometimes seems that everything I’m doing is an experiment. 😉 There are several things I would do differently knowing what I know now. The good news is that none of them were critical mistakes.

      I consider this a low risk experiment as I can always hire a welder to come out and weld some sheet steel to the gaps. I would have needed spray foam in the gaps anyways, so the most I would be out is a few tubes of caulk. I’m fairly confident that the OSI Quad caulk will hold up well, and be easy to maintain and repair over time.

      Steve

      Reply
  2. cheryl

    Have you made a post of the things you would do differant? Or a ‘lessons learned’. The beige is a good color compromise and I like the steel wool for the mice. Nice job.

    Reply
    1. Steve Post author

      Cheryl:

      I have thought of a “lessons learned” post, but I’m afraid I still have a lot more lessons to learn. When everything is finished (next summer?), I will try to add a few posts that wrap up the entire project.

      Steve

      Reply
  3. Tom

    Could have used the caulk for pre-cast concrete panels used in tilt up buildings. I don’t know the exact name of the stuff but I do know that it would be probably perfect for your application. You would still need to use the backer which the make for this application. I can weld but that would be a lot of welding, time, and expense. I think the mentioned caulk would be my personal choice for many reasons.

    Reply
  4. troutdog1959

    I like this idea for building a cabin. I have a 30 plus year in wholesale building materials. On the caulk your discussing. I have been involved in Quad caulking for over 20 years. Good product,but for this application there is a better one. TiteBond makes a product called WeatherMaster. The product is the sealant used between fenders and firewalls in your cars and trucks. It has a much higher temperature range than Quad and is there for used on metal roofing applications. Weathermaster contains no solvents or water,so no vapor problems and less than 2% shrinkage.What you put down is what you will have. WeatherMaster was originally designed for the metal parts in the auto industry,so it is by far a better choice. In a warm southern climate,you might find Quad get hard and brittle down the road. Cost is about the same,and just as many colors available.

    Reply
  5. Jim C.

    So how is the cabin fairing after the past year+?
    Really interested to know how the caulking and rod idea held up or if you had to replace or refill any spots.
    We live in the arctic and want to take a shot at this idea for fun.

    Thank you in advance for your advice,

    Jim

    Reply
    1. Steve Post author

      Jim:

      The cabin is holding up very well overall. The only recent problem was last spring when my deck piers had heaved a couple of inches from the winter. I removed the piers and floated the deck with some short posts on top of patio pavers and didn’t have any problems from this winter.

      In regards to the caulk, I haven’t specifically looked at it yet this year. Next time I’m at the cabin I’ll take a look and post what I find here.

      Steve

      Reply
    2. Steve Post author

      Jim:

      I checked on the caulk this weekend and it looks to be holding up very well. The only issue I found was a small hole (~1/16″) that was present in one of the seams. I don’t know if this was a flaw in my original application, but in any case it will be easy to fix with the OSI Quad caulk. The caulk itself is still flexible and adhering well to the container metal. Based on what I have seen, I would do it the same way again.

      Steve

      Reply
      1. Tim

        Steve,

        I have a metal guy that tells me to provide room between containers for movement due to metal temperature change. Your Seal Gaps posts make no mention of welded containers (shrinking/expanding) due to temperature. Have you noticed any movement due to hot or cold?

        Reply
        1. Steve Post author

          Tim:

          Since my containers are all welded together at the adjoining corner blocks, they should be acting as a single monolithic structure. As such, there should be very little thermal expansion or contraction in the gap between the containers. For example, imagine a 20′ length of sheet metal with a 1/2″ hole drilled through. While the metal panel itself will expand/shrink about 1/2″ along the 20′ length over a 100 °F temperature range, the 1/2″ drilled hole will only vary by about 1/1000 of an inch.

          And to answer your original question, no I have not seen any movement due to heat or cold.

          Steve

          Reply
  6. Jim

    Hi Steve,
    Thanks for your update!
    I will keep this in mind, as we do get a significant amount of frost heaving/settling up here.
    Jim

    Reply
  7. Muchiri

    This is very great stuff here and I am enjoying reading it so much. I am contemplating a journey of my own of making a permanent residence using shipping containers. I live in Africa where the cost of material is usually higher that all the other continents. However, I think shipping container housing could be the next big thing this side of the globe where scarcity of everything including living space is eternal.

    Reply

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