Installing Heater with RTV
In some cases the bed heater may need / want to be installed with something other than the normally provided 468MP adhesive sheet. This can be a heter ordered without the adhesive, a heater being reinstalled, or a desire to have the heater glued on above the rated temperature of the 468MP adhesive.
Note: This guide is NOT intended for installing a heater that already came with a 468MP adhesive sheet installed.
In my experience 468MP starts to degrade when going over 115C, not that there is a risk of adhesive failure but that it starts to smell really bad, and that smell only gets worse with time. It is permanent. Not everyone is affected though so the exact cause is still unknown. 468MP has a shelf life, it is possible it is related to that (maybe I had old stock, maybe it depends on environmental factors…).
If you install your pad with RTV instead of 468MP, then you don’t have to worry about potential failure of the adhesive (either from death smell or actual adhesive failure causing the pad to detach), even if your bed is somehow stuck at full power for extended periods of time. You should still use a thermal fuse to disconnect the power, just like stock builds, as a final safety against a runaway heater.
I used RTV106 because I found that it was specifically called out for by an industrial silicone heater pad manufacturer, but for our use case I believe any high-temp RTV will do. Read the instructions for the specific RTV you are using to know how long to cure at room temp (mine was three days). I just let it sit there with some weights until the curing time was up. If you have a magnet to install on the other side, do that before.
If you use spring steel, don’t forget that the magnet over the bed also has special adhesive, and that the usual China sources generally don’t use adhesive that is rated for more than 70C. I know SubtleDesign uses 300SLE (which is rated for 148C) for their StayMag sheets so they are a known good source, there may be others depending on where you live.
- Lots of paper towels
- Masking tape
- Nitrile/Latex gloves
- Trash bag (to keep those used towels & gloves in!)
- Spatula (I used a plastic spatula meants for wall plaster)
- Face mask (the smell is surprisingly strong!)
- Outline the edges of the plate where the RTV shouldn’t go with masking tape. Assume that anything not covered will get RTV on it.
- Spread the RTV all over the plate like a cake with the spatula.
- Go quickly but don’t rush. You have about 5 minutes to complete the whole process.
- Lay down heater, start on one edge and keep going slowly so you don’t trap air bubbles. The RTV will squish out onto the masking tape.
- Once you are happy with your application, remove the masking tape.
- Add weight (use a cardboard cutout so you don’t crush the silicone bulges in the heater).
- Let cure for the time specified by the RTV (between 24-72 hours).