Being kind in the use here, as 'shim' implies thin. The shim being used for the Sealy consists of 4 folded bath towels, two folded sheets, and then two layers of mattress pad. That, foks, is not a slim shim.
Too, remember, in some engineering circles, the use of shims points to poor design or workmanship. Of course, it could be related to material, to boot.
What does this problem imply in the case of Sealy? As we saw before, their quality assessment filters out, very successfully, this type of problem. That is, they seem to have consciously applied techniques that do not 'see' the problem. Not only is their assessment targeted to looks (as in, a 1 1/2" permanent depression considered okay), the whole approach averages across an eight-inch span.
I was given the challenge of finding a 'functional' test that would be fair. Hence, these posts. The challenge did not come directly from Sealy, yet one has to think that they know about the issue.
Imagine trying to sleep on a 'firm' mattress that has differences in how much the mattress sinks when a small amount of weight is placed on the surface. And, consider that the difference in the 'give' amounts to several inches at one point.
10 lbs test (actually, a mere 2 lbs)
head of mattress
middle of mattress
foot of mattress
This table show the amount of 'give' at nine points on the mattress, using two five-pound weights placed together. The measurement was to the lowest point of the mattress from a string that was stretched across the mattress and that was weighted on both ends. The string was similar to the one in the 'jig' set that was used by the Sealy representative when he did the static (averaged) test.
One could characterize the experience as sinking into a hole out of which one has to climb in order to get out of the bed. The 'hole' appears only on one side, as if the mattress is firm on one side and the most plush of the plush on the other.
A mere three and one-half inches (3 1/2", 8.89 cm)? (See Remarks, 04/29/2011) Probably, the psychological impact ought to use a logarithmic scale for any depression beyond the 1/2" expectation.
But, what is 'firm' in this context? We'll look at that and more.
There will be a re-measure (see Remarks, 04/29/2011 -- the new measure doubled the weight in a couple of areas), using a smaller basis for the 10 lbs. The above numbers actually applied only about a 2-lbs test, due to the fact that the 'jig' had too broad of a span.
11/24/2011 -- The finale.
04/29/2011 -- The store is honoring its guarantee and replacing the mattress. Before it left the premises, I thought that there ought to be one more measurement. Remember, from the above table, that a 10-lb pressure test was used. Between the highest and lowest depression, there was a difference of three inches. So, what would it look like if, at those two areas, we added 10-lbs to the weight (broad base, that is, this was not a point test)?
In the more firm area, the additional ten pounds (20-lb test) increased the depression a little over an inch. In the softer area (reminder: ultra-firm mattress), the additional weight caused a depression, in that area of the mattress, that measured almost SIX inches. That is, the additional ten pounds pushed the mattress down a further 2 1/2 inches.
And, the difference between firm and soft increased from three inches to four and one-half inches. Would that not be considered significant?
Reminder: we're talking a functional, pressure test that ought to be within the capability of Sealy. Their representative mentioned that he thought such a test (see Sealy Snafu) would be an improvement (and said that he had asked an engineer customer, to no effect). In their static test, which was cosmetic, there was no way to test how a mattress performs while in use. Too, their current jig is seriously biased in their favor. The outer cover may spring back, yet yield like soft butter to a reclining body.
Given their current scheme, how the heck can Sealy learn anything to make improvements that are functionally sound?
03/15/2011 -- Status, the store will replace the mattress. They, essentially, were waiting for Sealy to step up to its responsibility which never happened. Further measurements coming.