Pouring SLC over an electric heat system is an alternative to setting the mat or wire in thinset. Some people find it quicker and easier than troweling thinset over the heating system. It is also more expensive.
When installing electric radiant heat flooring you will find that every manufacturer has slightly differing recommendations to their installation guidelines.
The following method is for use over plywood subfloors or cement slabs.For cement slabs there is no need for any metal or plastic lathe as is used for a plywood installation.
Following the manufacturers recommendations for installing the wires or mats is important, following their guidelines for installing tile directly over these mats generally leads to frustration and in many cases an installation that has an inferior finish due to trying to set over a surface that is not flat and sometimes one that has sensors that are thicker than the thinset bed you are trying to set tile into.
As a professional installer we have found that installing the electric heat and following this with a Pour of Self Leveling Cement to a thickness of 3/8-1/2”(depending on heat system) provides an excellent flat surface for tile installation and additional mass to retain heat. Once poured it also protects the Heating System from damage while setting tile.
A Word of Advice: Some manufacturers include an alarm (others have it as an option)to hook up during installation that are designed to indicate a problem should one occur. Using these is fine, and we recommend them as they will tell you immediately if a break has occurred and be assured it will be right where you are working. There is no substitute however for using a proper Ohms meter before pouring a Self Leveling product over the installation and at the points mentioned in the instructions that follow. Write down your readings as you take them, date and time of reading also. When finished, keep this note with your warranty papers.
The following method is what we used professionally.
1 - Prime floor 1 coat with Self-leveling Cement primer.(seal or cover any cracks seams or holes with caulking) Some substrates such as CBU, plywood or very porous concrete will require two coats.
2 - Install radiant heat system as per manufacturers instructions.
(note #4 plastic lathe can be installed first but we have found that on some models sensors can rise in the mix, putting lathe above which requires caution in stapling, eliminates this problem with some models)
3 - Test heat system with ohms meter and note numbers
4 - With bare wire system install plastic lath carefully. Fasten with staples every 3" minimum, more staples may be required to get plastic lathe flat. Use lath such as Duralath from Custom or similar.This step is only required when goingover a wood substrate.(this is not necessary with wire Mat systems where the mat material acts as reinforcing for SLC)
5 - Install self-sticking foam strip insulation around perimeter of room. Frost King ¼”wide x ¾”high was our standard.
6 - Cut 1x2 into dam material for use at doorways or anywhere Tile will end and meet with another flooring type. Leading edge should have layer of duct tape run lengthwise and wrapped underneath. This helps to insure a clean break when Dam is removed. Stuff ducts with old towels , rags etc and Staple Heavy cardboard strips that are faced with duct tape inside floor heat ducts. Caulk around edges to seal and add duct tape inside for added protection. Seal any potential leak areas with either caulk or larger areas with expanding foam.
7 - Test wire leads with Ohms meter and note numbers.
8 - After all material used to seal potential leak areas has dried, coat area with SLC Primer using a pump type garden sprayer for insecticides. These type sprayers are generally available for around 10.00 at garden shops, fleet farm etc. While this dries we prepare our water, bags are opened etc
NOTE:
Spraying of primer is not a duplication of step #1. It provides a primed surface on the new components, heating mat/wire and plastic lath, that have been added since the initial priming.
9 - Wait approximately 1 hour for primer to dry. While this is drying prepare your bags, buckets mixing equipment etcetera.
10 - Test all leads with ohms meter again making certain no damage has occurred. This is your last chance before wires are covered.
11 - Pour Self Leveling Cement following Directions already in library as provided by Flatfloor.
12 - Allow this to dry overnight.
13 - Remove all Dam material from Doors, ducts etcetera. Carefully scrape down level any high spots. DO NOT remove extra perimeter insulation material. Leaving it in place will insure proper expansion is achieved for next steps.
14 - Using a straightedge that is a minimum of 8’ long, check all areas for flat. If you do find any area’s that are not flat you will want to repair or fill before proceeding to the next step.
15 - Install a membrane from Schluter, Noble, Custom etcetera that is designed for use over a radiant floor heat system.
16 - You are now ready to layout and install your tile following recommended guidelines and being certain to include field expansion joints as Per TCA recommendations
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