JOINT FILLING IN SEALED,
COATED OR COVERED FLOORS

MM-80 is frequently installed in floors that have received or will receive chemical surface treatments such as curing compounds, cure-and-seals, liquid hardeners, coatings, etc. Occasionally MM-80 may be used where the entire floor will be covered with vinyl composition tile (VCT), ceramic tile, high-build coatings, terrazzo, epoxy toppings, carpet, etc.

This technical sheet is meant to be a basic guide to the recommended installation process for these conditions.

MEMBRANE FORMING CURES, CURE-AND-SEALS
The function of a curing compound is to keep the moisture in the slab until the maximum amount of cement is hydrated. In a vast majority of cases, the curing compound is applied to the surface before the joints are cut. But if the compound is applied to the face of the construction joints, or re-applied after the cuts are made, it can act as a release agent and interfere with the adhesion of the MM-80.

Prevention
Before applying the compound, fill the joint with wet sand or insert a temporary compressible backer rod at the top of the joint to prevent compound penetration.

Correction
If the compound has gone into the joint, it must be removed prior to the joint filling. Re-sawing the joint is the surest means of removal. Sand-blasting may also be acceptable, if it removes the film.

LIQUID HARDENERS (WATER-BASED SILICATES, ETC.)

MM-80 has been used on thousands of floors treated with Ashford Formula and Lapidolith. MM-80 adheres well to previously treated surfaces that have left no film residue and are properly rinsed. Both products can be safely applied when the MM-80 is already in place and has cured for 24-48 hours. Please contact our office if other brands of liquid hardeners are to be used.

Note: It is a common practice to overfill the MM-80, then shave off the excess at a later time. With this filling process the MM-80 may leave a stain on the adjacent concrete. This stain film may prevent the penetration of the hardener. If the MM-80 is to be installed first, joint edges should be taped prior to installation to prevent stains that could affect the adhesion of the hardener. We recommend applying the hardener first. This ensures hardener penetration and usually reduces the darkness of the MM-80 stain.

COATINGS AND SEALERS, FILM FORMING
It is our general recommendation that final, film-forming high build coatings be applied after the MM-80 is installed and allowed to cure for seven days. The coating can stop at the joint edge or be applied over the MM-80 to create a seamless floor.

Joint edges should be taped prior to the MM-80 installation to prevent stains that could affect the adhesion of the coating. Shave off the MM-80 overfill as usual and remove tape residue. If applying the coating over the joint, the MM-80 surface should be mechanically scrubbed/abraded to ensure coating adhesion. Contact the coating provider if adhesion testing is needed.

Note: Concrete shrinks for a period of one year or more. Shrinkage will result in a widening of the joint, and thus touch-up of the coating over the MM-80 may be required. See technical sheet T5 for the detailed information on shrinkage-related joint opening.

VCT, CERAMIC TILE, TERRAZZO, TOPPINGS
In general, these floor coverings are used primarily in pedestrian traffic areas. This raises the question as to whether the heavy-duty MM-80 is actually necessary.

Unless unusual traffic applications are present, we suggest that our less expensive EDGE-PRO XL be used under floor coverings. "XL" should prove more than adequate to support the covering and prevent its deflection under most loads imposed. In the case of toppings/overlays (1/4" epoxy, etc.), the joint filler selection should be determined by the topping manufacturer to ensure singular responsibility.

Caution: Potential Problem Filler Humping

A new concrete floor is a living, breathing entity that contains an excessive amount of moisture which normally evaporates over time, if subjected to the air. Most of the moisture is at the bottom of the slab. If the slab is placed over a vapor barrier and the surface is later coated/covered with a non-breathing media, the excess moisture is in effect trapped within an air tight envelope. This can create a phenomenon called "joint filler humping."

Eventually the trapped moisture will re-distribute itself (swell) evenly throughout the slab. As the moisture rises, the top of the slab may grow in dimension, causing the joints to narrow and compress the joint filler. Since the filler is restrained on three sides by concrete, it may extrude upward, causing a hump in the coating or covering. The humping phenomenon is unpredictable from project to project and can occur with MM-80, EDGE-PRO XL or any joint filler that is used, including flexible polyurethane sealants.

There is no sure method of avoiding humping since it is solely a function of the concrete and occurs in only about 5% of all projects. Look first to minimizing the chance of joint compression by using shorter joint spacing and placing concrete with a lower water content. Another option is to install the filler earlier, for example after ten-fifteen days of concrete cure. The joints will open and a void will occur between the filler and the concrete. The filler will still provide support for wheel traffic and the voids will allow for some joint compression before extrusion occurs.

Please contact our technical department should you have any questions concerning joint filler humping or any of the other subjects covered in this technical sheet.