Frequently Asked Questions

Click on any topic below for more information.

 

Q.
How thick does the waterproof membrane need to be?
A.
Many products on the market can create a waterproof environment with minimal thickness coverage. However, applying too thin or too thick of a coat can create unfavorable conditions. The goal is to stay within the thickness guidelines to maintain the manufacturer's warranty. One of the most common ways to ensure you are obtaining a proper thickness is with the use of a cloth fabric that is sandwiched between two coats of membrane. The fabric works as a precise gauge to insure the proper application thickness of the liquid membranes. Typically liquid applied membranes should be checked using a wet film thickness gauge, the thickness should be between 13 mils to 22mils when dry; about the thickness of a credit card.

 

Q.
Why do some waterproofing membranes use fabric and not others?
A.
Although some liquid membranes tell you that fabric reinforcement is not required; it is our recommendation that all Merkrete liquid applied membranes should use fabric reinforcement in transition areas such as floor to wall or around drains. The fabric works as a precise gauge to insure that the proper application thickness of the liquid membranes is correct in the most critical areas.

 

Q.
How soon can you install tile over the membrane?
A.
Typically 4 to 24 hours depending on the liquid membrane you are using, more important is the job conditions (temperature and humidity). Almost all liquid applied membranes are water based and require evaporation in order to dry. Check the inside corner by pushing lightly with your finger to see if the liquid transfers. If so, it still is not dry for water "flood" testing. Leaks in liquid waterproof membrane are more often because the product was applied either too thick or was not allowed to dry properly. See Merkrete Technical Bulletin #125; Curing and Dry Times on Liquid Applied Membranes.

 

Q.
What is the purpose of a crack isolation membrane?
A.
The application of the Crack isolation membrane is designed to isolate the finished tile from the substrate by acting as a buffer or movement cushion. As substrates expand and contract through normal cycles the crack Isolation membrane will guard against crack transfer to the tile. Often, the concrete substrate has cracking caused by shrinkage of the concrete while curing. The crack isolation membrane like the Merkrete Fracture Guard products, assist in preventing that cracking from transferring to the tile installation.

 

Q.
What is the difference between the liquid membrane and the peel and stick crack isolation membrane?
A.
Liquid Membranes control up to 1/8" of a crack expansion. Whereas, the peel and stick sheet membranes, like Merkrete's Sound Shield PNS 40 and PNS 90, control cracks from 1/8" up to 3/8".

Note: Peel and Stick membranes are generally thicker than liquid applied membranes, so a height change should be noted.

 

Q.
How soon can I install tile over the membrane?
A.
Liquid applied membranes: Dry time is generally 2 to 8 hours depending on temperature and humidity, dry to the touch.

Peel and Stick products: Tile installation can begin immediately after the membrane is in place.

 

Q.
Can I use thin set to patch holes and voids on a floor surface?
A.
There are some installers that repair minor shallow imperfections with thin set. However, caution should be used: holes and/or voids should be prepared with either a patching compound (Pro Patch) or a surface preparation underlayment (Underlay C — RS - SLU) in order to insure a sound substrate.

 

Q.
Why do you need to use a self-leveling underlayment?
A.
Self-leveling underlayments provide a true or level substrate prior to the installation of tile or other floor coverings. As tile become larger, it is important to have the substrate as flat as possible, the industry standard is no less then 1/4" surface deviation in 10', to insure a proper tile installation.

 

Q.
What product do I need if I have old black adhesive on the floor?
A.
: The industry term for this residue is "cut-back adhesive", and bonding to it can be difficult. The removal of resilient tiles and adhesive should be done cautiously. Please before considering, review the Resilient Floor Covering Institute Bulletin "Recommended Work Practices for Removal of Resilient Flooring".

Merkrete 735 Premium Flex can be used to install tile directly to the substrate provided that the majority of the black adhesive is removed and the surface cleaned. For more difficult or questionable substrates; Merkrete 626 Primer can be applied prior to normal tile installation with a polymer modified thin set.

 

Q.
Why are there different thin sets… aren't they really all the same?
A.
Simple answer: No, they are not the same. And there is a good reason why there are many types of thin sets in the market today. The proper thin set type is influenced by the type of substrate, the tile type, the size of tile, area of installation, interior or exterior, wet or dry, etc. New tile designs, and larger formats, are an ever-changing process: Tile is one of the most versatile and cost effective finishes available today and the areas of application continue to grow. Thin set adhesives: They too are changing and improving to meet these new demands. Your tile distributor can assist you in obtaining the proper thin set type that is right for your project.

 

Q.
What does it mean when it says Medium Bed?
A.
Medium Bed mortars can be troweled thicker than traditional thinset mortars, thus allowing thick-set attributes to be used for thinset applications. Can be applied 3/16" — 3/ 4" thick after beat in. Used for large format tiles, inconsistent thickness dimensional stone, slight substrate irregularity.

 

Q.
What do the numbers ANSI A118.4 and A118.11 mean?
A.
ANSI A118.4 = Testing specification and validation criteria for polymer modified portland cement thin set mortars.

ASNI A118.11 = Testing specification and validation criteria for polymer modified portland cement thin set mortar when bonding on Exterior Glue Plywood (EGP).

 

Q.
When should you use a sanded verses a non sanded grout?
A.
Sanded grout is most commonly used when grout joints are between 1/8" and 1/2". Non sanded grout is used when grout joints are 1/8" or less. Merkrete Versatile Color Grout was developed to take the guess work out of the grout selection. Versatile can be used on all grout joints from less than 1/16" to 1/2" for walls and floors.

 

Q.
After installing the grout... How much time should you wait before you start to clean?
A.
Cleaning can begin when the newly applied grout becomes firm enough to touchlightly and will no longer dent or transfer. The time in which this occurs is dependent on the type of tile and substrate the tile was applied over. It is important to use as little water as possible when cleaning the surface of the tile and fresh grout joint. Too much water or cleaning the surface too early can result in grout removal and discoloration.

 

Q.
: What is efflorescence?
A.
Efflorescence is a common occurrence that typically occurs during the initial cure of a cementitious product. As water evaporates, it leaves a salt behind which forms a white deposit, or in colored cements the appearance of missing color or color variations. Should you experience efflorescence on your grout, follow the steps below or contact our technical Department at 800-226-2424; 1) Pro Clean SA is a crystalline sulfamic acid that is added to water and use to clean the grout surface.

If needed, consider Merkrete's Revive stain and sealer for grout.