Flooring and Carpeting/9 x 9 asbestos tiles


QUESTION: hello Chris,

I am currently in the process if rerenovating the den at my parents house. While removing the carpet I noticed  that carpet was installed on top of carpet. After removing the first carpet and attempting to pull out the 2nd carpet I noticed that the bottom layer carpet was glued onto 9 x 9 floor tiles which I read were most likely asbestos containing. The bottom layer carper smells if mildew so I ripped it up. In the process a number of tiles came up with it. while soaking the floor with water, sealing the room, and wearing a hepa respirator, I began to see if I can pop out some tiles in the area. Most of the tiles are coming up pretty easy and only some have the black mastic residue left behind. while "flooding" the floor I noticed puddles forming on the low spots in which I want to level out. we are looking to install a floating engineered wood floor. My question is... do I continue to pop off all the tiles and leave the mastic?  or do I leave what's there and flash patch th
e missing tiles I pulled out? then I also have problem with the low spots.... can I use leveling cement over tiles or should I removed tiles and pour leveling cement over mastic?

what are my options as I may be creating much more work by popping off tiles and not cleaning mastic off of concrete.


ANSWER: Hi John,

Ok , first off if the den is not to large I would demo all the tiles, especially if they pop right off. The only time they release asbestos fibers is when they are pulverized or sanded. Otherwise I would be dead by now. Studies show that they contain very small amounts of asbestos as compared to ceiling tiles or air ducts.

With that out of the way you can skim coat the floor manually with any of these products and save lots of money compared to self leveling products.

Lowes carries MAPEI (I use this a lot)


Home Depot carries HENRY products

WEBCRETE 95..a great product !! always my "go to" if available

These allow you to cover the black mastic...and fill in low spots easily using common trowels and screeds for larger areas. Multiple coats allow you to build up and fill larger areas in a matter of hours...dries rapidly too and a fan speeds things up as well. All manually hand troweled floor patches should be a POLYMER MODIFIED CEMENT of a gray color that you mix with water. The goal is to get the floor flat...not level.the tolerance for the wood floor is 3/16" deviation in 8-10' However it is not super critical as you have the underlayment to cushion minor differences.

Here is a video on you tube in regards to skimming a floor.
After the skim coat dries you can add more to low areas and blend in the edges with a damp towel ...or knock down ridges that have dried. For a super smooth glass coat on the last application you can add a bit more water.

Let me know if you have further questions


---------- FOLLOW-UP ----------

Thanks for all the great info.  The den is about 300 square feet.  I will look into using Home Depotís Unipro universal patch and skimcoat.  I was only thinking about using the leveling cement because I thought that might be easier.  
Should I scrape up the heavy mastic spots or leave it alone?  I was told by a floor guy that the black mastic is more toxic than the tiles and Iím just better off popping out the tiles, leaving the mastic alone, and skim coating over everything.  I am just worried about the high spots as I do not want to keep coating and building up the entire floor to cover everything.
Thanks again

ANSWER: Hello John,

The flooring guy you spoke with is correct. The adhesive contains more asbestos than the tile, and when you scrape or sand the dry adhesive it is possible that you are releasing asbestos particulates into the air. To avoid that "FRIABLE" asbestos we emulsify it with a dash of liquid detergent in a 5 gallon bucket of water and wet scrape the floor. Basically everything is wet and no dust flies.

The WEBCRETE 95 specifically states that it is made to skim over the mastic residue,on the back of the bag. Although I have used the Mapei as well for this I am not sure of the Henry product. I just had access to the other products wholesale and never had to purchase at the retail level. Look in the yellow pages under CARPET SUPPLIES...usually after the CARPET RETAIL section. If you can find a company that sells supplies to the trade you will save $$$ on all the products you are considering. Including tools in some cases. They are always open to the public.

The big question at hand is how high and how low are the differences of your floor. They way I determine this is to have a straight edge or feather edge screed tool and stand it on edge somewhere on the floor. Then I start to swing an arc (circle) with the tool and notice the light shining underneath it. I will measure and mark the floor with a marker sometimes a simple - mark for the low...or a + for the high. I try to find the highest spot usually indicated by a severe rocking of the tool.

In the end I myself (you in this case) have to determine if the floor is so bad that it requires the added expense of SELF LEVELING or can it just manually be skimmed / floated.

I will admit that sometimes for a DIY'er the idea of self leveling might be easier than the art of manually troweling. But I will be happy to help dispel any mystery about floating a floor.

In all honesty I can say that I cheated many times over when it came to laminate flooring in regards to high and low spots. I would notify the customer of the added expense and they would waive the floor prep. Sometimes I would just do a minimum to satisfy myself , so I could sleep at night.

It is my opinion that laminate flooring with the underlayment is very forgiving up to 1/4" and possibly 3/8" ...to rapidly repair an area we would install 1/8" VCT tile as needed and feather / skim off the edges to blend with the concrete. You have to remember that the specs of the wood floor / laminate floor, allow a deviance of 3/16" in 8-10 feet. So 1/4" would only need the slightest amount of prep...1/2" would require some more work / expense. If the floor dropped an 1" or rose an inch in a 10' radius I would BUSH / Grind with a demo hammer and skim it smooth ...instead of trying to raise the low areas to the high. You literally will need to mark and map the floor out by measuring with a screed/ straight edge tool.

Now, the tools aspect. Feather edges and screeds aren't cheap so I offer this ...go to the Box store and purchase a metal framing stud for about 3-4 dollars. They range from 8-10 ft. get a couple of the 10' units and you can actually use them as a measuring tool and as a screed later. They are easily cut to size with a pair of tin snips so you can have a nice combination of lengths. They usually come in 2 different gauges ..25 being the lighter...20 being the heavier. The heavier gauge will be the one to have if possible.

No matter which method of floor repair you use you need to contact the manufacture and ask if the material can cover the mastic and what procedures are needed for proper bonding. Always call the 800# on the back of the product and ask for customer service or TECHNICAL SUPPORT to make sure that the product will do what you need it to.

Things you might consider:
razor blades
knee pads
sponges / rags
crayon / wax marker
Craft paper / painters paper
painters tape 1.5" for masking off special items
wood glue for the laminate floor (TITEBOND II)
5 gallon buckets
1/2" heavy duty drill and mixing egg beater
common dust mask  (cheap)
Mop for clean up and throw away

As I sit here thinking "what else" I'm sure I could expand but for now I will let it be...

Most importantly I want to convey the idea that it is easier than you imagine. It is not rocket science. You can do this and there really is no way to fail if you follow the directions from the manufactures and other trusted sources you come across. The worst case scenario is you will have to scrape off some areas and re coat manually to make smooth.

I invite you to contact me via my cell phone should you have an urgent question. Text is fine as well if you prefer.

Best regards,

Chris Phillips
(626) 222-6868

---------- FOLLOW-UP ----------

Room entrance
Room entrance  

I would like to thank you once again for all your help and even giving me your phone # for emergency help.  So this is the latest.  I used the Henry Unipro patch and skimcoat to skim over most of the mastic but it was hard to spread and each bag only covered a small area.  I also used it to fill in low spots.  One of the major low spots was at the entrance to the room.  I was spreading layer after layer letting it dry each time but it was taking forever so I went a bit heavier.  When it driedÖ.it sounded hollow and began to hairline crack.  

The floor was still a mess from the mastic and all the low spots so I went out and bought Henryís leveling cement to save time regardless of the price.  I got 6 bags to do the 300 square feet.  I left the hollow sounding hairline crack area at the entrance figuring ill cover it up with the leveling cement. So I primed the whole floor very well and went back the next day to pour the leveling cement with my sisterís help.  I tried to do it as fast as possible because it only has a 10 min flow time and I think in some areas I spread it too thin because I thought I was not going to have enough to do the whole room.
So here is the outcome:       

The floor looks nice and flat and all the low spots that I had marked originally are nice and flat and level.  

Problem # 1: I did see a few low spots today in the areas that I went thin on when I thought I was going to run out (it looked level while poring it).  

Problem # 2:  When I went to enter the room todayÖ it instantly hairline cracked again when I first set foot in the room and you can tell it is still hollow sounding underneath.

I have Ĺ bag leveling cement still left.  Should I use it to fill the low spots that I missed and use a straight edge to push it evenly?  Also, what do I do about the hollow sounding hairline cracked area.  Do I break it up in pieces, clean it all out, and pour again?  I guess I can use the remaining leveling cement or get the patch stuff again.  Itís got hairline cracks, its sounds hollow, but itís flat and level.  I just donít want that spot to deteriorate over time and crumble when people walk on the floating floor.  What do I need to do?

Thanks so much!

Hi John,

Sorry to hear that the patch did not bond to the floor. I recall saying to you, "call the manufacture" of the patch to make sure they could say that it would or would not stick to the mastic. Sometimes they recommend a primer.

So with the cracking and hollow spots I would have removed that first , then investigated (call the manufacture) , then primed, floated with the self leveling. The problem will not go away by just covering it up with more products.

I am surprised that the Henry patch was difficult to work with ...usually we add a bit more water or latex  so that it is easily manipulated to do as we desire. I have always mixed it a bit loose as it starts to go off sooner than later.

Call Henry , on the back of the bag there will be an 800# and ask what they recommend. Make sure you let them know you are attempting to cover the CUT BACK adhesive.

Feel free to ask anymore questions

All the best to you,


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20+ years flooring installation ...carpet,wood,tile and vinyl. Residential and commercial. I do not sell the products , just install what ever the shop / customer has purchased. I actually love seeing the finished project completed and it gives me great satisfaction to help others acheive that goal. If I don't know the answer I will say so, and then I will recommend another expert for you. I may even research the subject and answer to the best of my ability ...including links to my sources. I wish you all success Chris


20 years as an independant contractor

H.S. diploma A.S. agriculture Mt San Antonio JR. College

Past/Present Clients
Gene Bonas and Kevin Churnock Inc. Sheward&Son&Sons Century 21 Forte Const. Famous Footwear BOSE Corporation Homebodies General Contractor Perry Floors, Tri Cord Flooring T.J.'S Supplies

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