Home Main Truth Page Myth: R Value Myth: In Promotions Myth: Foam Beads Myth: Overlapping Rebar Myth: Drywall Screw Pulling Myth: Basement Additions Myth: Waterproofing for Insect Repellant Myth Q & A
"Does anyone have any information on how much force is required to pull a drywall screw out of a plastic strut in an ICF form? I have a local building inspector who has nothing better to do than ask dumb questions!”
Here are some common answers to this question:
1.) The strength may vary from manufacturer to manufacturer, but I have the actual test data from AMVIC Forms. A coarse thread drywall screw will withstand an average of 142.7 pound "pull out" load. The company doesn't rate their webs at this, because they have a significant safety factor, but this gives you an idea anyway.
2.) The answer for this is going to generate a couple of new questions. The key factor here is the type of screw. I have seen results as high as 179 lbs with a high/low thread "grabber" type drywall screw in an integraspec web. Standard screws do not have the holding power that the high/low does. With the same integraspec, they often failed at or below 100#. Mind you, the other problem was that they stripped easily, which is why we were having problems with accuracy.
If the building official is concerned, take a hanging scale capable of 200 #, connect it via a washer with tie wire to the screw, screw it into the wall and pull. I think that the building official should get enough information from this simple method to satisfy his/her needs. A more precise method, still simple, would be to take some weights and hang them off the screw/wire assembly until failure. This is how we tested them internally with calibrated weights from a local college.
3.) As mentioned, the pull-out capacity will vary from manufacturer to manufacturer. Most ICF systems utilize a plastic tie system imbedded in the foam. These are manufactured out of either a "regrind" (recycled) plastic, or a "virgin", 100 % new plastic granule. The regrind system will not have the same pull out capacity as a system manufactured out of new material.
Here are some capacities attributed to the FORMTECH ICF system with various fasteners being used:
"S" Fine Thread Drywall Screw: Maximum load 268.1 Lbs
Type "W" Coarse Thread Drywall Screw: Maximum load 287.3 lbs
This system uses a "virgin" plastic granule. If you want anymore information, visit their website. I hope this helps.
The first answer is probably the best answer. But what do those values mean to you as the builder or potential homeowner? Are these pull-out values enough to hold your kitchen cabinets to the wall after they are fully loaded with dishes etc.?
The first part of the second answer was pretty realistic of what happens in the field. The reason the ties get stripped out by installers is because they are rarely informed on how to install the screws into the plastic ties. So, just how strong is the connection to the wall when you are relying on the installer to know what to do?
The idea that you ought to build your own demonstration device for testing the screw pull-out values is beyond belief! First off, the building official is not qualified to accept a crude test such as a homemade mock up like this. All testing of building materials and processes are to be carried out by code-recognized testing labs that have accreditation and the ability to carry out such testing without bias or other concern. Don’t waste your time developing a testing program. The building official is just doing the job they were tasked with, which is to preserve life, health and safety. Most of all, if the building official accepts a test procedure like this, what else would he/she accept that may not be accurate? Ask the form system manufacturer for the data.
The third answer was going good, but once again, the focus was lost. The fact that the material is virgin or regrind plays a very limited role when it comes to screw pull-out values. The main detail that leads to higher pull-out values is the overall thickness of the tie material, and the type of “plastic” that is being used. Most all of the systems with plastic ties use mixtures of different types of plastic polymers, some polymers are stronger than others, some are brittle when cold, some are “rubbery” when hot.Ultimately, whatever material or brand of ICF that is used, the important issue to consider is whether or not it will perform for the particular application you are intending to use it in. Nearly every system on the market today has a tie that accepts a course thread screw with a pull-out value that is acceptable for hanging sheetrock. In most cases, we would suggest the use of embedded plates for hanging items such as kitchen cabinets. Ask the manufacturers for the numbers and while you are at it, ask them for comparisons of their product to wood and metal frame.