Here's the letter we sent to the vendor for Corning LiteForms, the insulated concrete forming system we used.
We recently purchased Owens-Corning LiteForms components
from you for the foundations of the rammed house we’re building. Now that the
foundation pour is complete, I thought I would relate to you our experience with
the this system.
The remoteness of our project, the need to keep the forms
in place after pouring to provide support for the rammed earth forms, and the
need to insulate the stem walls led us to investigate insulated concrete form (ICF)
systems. The LiteForms system was selected after reviewing a number of competing
insulated concrete form systems in large part because it claimed to be capable
of forming the 24” stem walls called for in our plans. We reviewed the product
literature including the instruction manual. The product appeared to be fairly
straightforward to use and was price competitive with the alternatives. Local
support was also an attractive feature. Upland’s quote, based upon
construction documents, included
the option of delivery of assembled components which we found attractive since
it appeared it would save us time.
Our experience in using the LiteForms systems has left a
very sour taste. The use of pre-assembled forms was nothing short of a disaster.
The drawings clearly show two rows of rebar dowels set in the spread
footing. Maneuvering 30’ sections of 24” wide forms over the dowels was
extremely trying. Because the dowels had to align correctly with both the
plastic ties and the wire mesh, each form had to be lifted and lowered multiple
times to get most of the dowels in the right place. Even after that, numerous
ties had to be removed (often with great difficulty) and reinserted on the other
side of a dowel. Other dowels were bent to allow the form to sit right.
The subsequent installation of the balance of the rebar was made very
difficult, since it had to be threaded through the forms. Installation of the
assembled forms in the grade beams was simply impossible. If the forms were
installed first, it would be impossible to later install the rebar. If the rebar
was installed first (as we ended up doing), it was literally impossible to
install the assembled forms. This situation should have been clear from the
drawings to someone familiar with the LiteForms system. In the end, we had to
completely disassemble the forms and rebuild them around the rebar in the grade
beams. So, not only did we pay for unnecessary assembly, we actually had to
expend the effort to take it apart just so we could reassemble it!
The installation of the forms was made all the more
difficult because our trenches were often little more than 8-10” wider than
the forms on each side. Afterwards I re-read the instructions and there is no
mention that installation (even of pre-assembled forms) requires an absolute
minimum of 12” and preferably 18” on each side of the formwork to provide
the required access.
It is not clear to me that the 24” tie system is
appropriately engineered for use in the same manner as the shorter ties. The
instructions call for nailing cleats on the outer side of the forms. This works
fine with the 6” wide form, which
is quite stiff. The 24” ties have the same cross-section as the 6” ties,
however, and therefore have none of
the stiffness of the 6” ties. The ties are inadequate to hold the forms apart
until filled with concrete. As a consequence, the flexibility of the assembled
form using 24” ties combined with the interference with rebar dowels makes it
almost impossible to get the forms properly aligned. We also couldn’t help but
notice that unlike the 6” wall which also contained half ties, all the ties in
the 24” walls were full ties, which required cutting the slots deeper.
The manner in which the forms were constructed led to
additional problems. One glaring error was the manner in which the “stubs”
for the grade beams were assembled. These should have been a trivial exercise
– assemble four tiers of 8” material. Instead, a decision was made to
assemble a longer section using the standard brickwork pattern, then cut the
stubs from this longer piece. As a consequence, the stubs almost always
contained pieces as short as 8” at the ends, making the parts far more fragile
than they had any reason to be. The
same problem occurred in the stem wall forms where the grade beams intersected
the stem wall. Since no consideration of this intersection was taken in the
pre-assembled components, cutting the opening left small pieces. In the worst
cases, the single level of LiteForms which was left over the opening had a break
in mid-span, which necessitated rebuilding the top layer to shift this break.
The instructions fail to describe the bracing required for
inside corners, such as those at our grade beams. Bracing at the joints between
straight sections is also not covered, presumably because it is not anticipated
since most people would not knowingly create such breaks. In fact, even with
pre-assembled units this wouldn’t have been necessary if the forms had
been partially disassembled at the breaks rather than cut, though admittedly it
would have been nearly impossible to place the parts in the trench such that
they could be successfully aligned. Except for the excellent on-site guidance
provided by Lars, this phase of the assembly would have been an unmitigated
The concrete pour revealed one last problem with the
system. The drawings called for two 2”x 6” keyways in the top of the
stemwalls. The ties make it impossible to form these to full depth in any
reasonable manner. Were it not for the fact that we were provided only with full
ties rather than the half ties called for at the top and bottom course, even the
undersized keyway would have impossible.
After the project was complete, we were left with almost
100 extra ties, a small mountain of excess XPS, even after using some of the
excess to form one of the grade beams. I don’t know if this is a consequence
of using pre-assembled forms, errors in estimating, or normal practice.
All told, we devoted over 100 man-hours to installing the
pre-assembled forms. Part of this was spent disassembling already assembled
forms, a very tedious task considering that the mesh was tied to the ties. While
we did not have previous experience with LiteForms, we had enough prior
experience in other construction tasks that this time would be only marginally
reduced with experience. The fundamental problem was the unsuitability of the
material to the project, especially in a pre-assembled form.
We believe there are several key lessons to draw from this experience:
ICFs are clearly an important new asset in the builder’s toolbox. However, experiences like ours will slow the penetration of this technology. More thought in the sales process, especially around the appropriateness of pre-assembled forms, and better documentation of the use of the forms could have prevented this negative lesson.