The NOFMA "Installing Hardwood Flooring Guide" recommends asphalt mastic for the vaport barrier. I just picked up some "Karnak 112AF Foundation & Roof Coating" and noticed that it has a cancer warning on the container? Is it OK to have two coats of this stuff on my floor? Has anyone looked into this? I am wondering what the risk is?

Would it be so bad if I revised my plan as follows:

Old Plan:

1. Prime and apply cold-type asphalt cut-back mastic
2. Lay down 15 lb asphalt paper (overlapping edges 2 - 4")
3. Put down another layer of asphalt mastic.
4. Put down another layer of asphalt paper
5. Lay down 3/4" plywood as a subfloor
6. Powder nail the subfloor to the concrete (nailing through the layers of asphalt paper and asphalt mastic).
7. Put more asphalt mastic over the plywood.
8. Lay down another layer of asphalt paper.
9. Lay down the planks.

New Plan:

1. Lay down 15 lb asphalt paper (overlapping edges 2 - 4")
2. Put down another layer of asphalt paper
3. Lay down 3/4" plywood as a subfloor
4. Powder nail the subfloor to the concrete (nailing through the layers of asphalt paper and asphalt mastic).
5. Lay down another layer of asphalt paper or 6 mil polythylene.
6. Lay down the planks.

guru10cea you must live in California...everything causes cancer there...move.

Look. The mastic and felt are an integrated system. Use must use both IF you're going that route. I think you'll be disappointed though. I also do NOT trust nailing only for plywood to concrete. Seen many failures. Why not get the slab as flat as possible, install some 6 mil polyethylene and just float some 16" x 8' strips of CDX plywood. This is a NOFMA approved method. Way neater, cheaper and faster.
http://www.nofma.org/Portals/0/Publicat ... 010_04.pdf

Thanks for the replies!

I live in New Jersey, but it did state that California recognizes it a cancer causing agent.

I'm wondering if the stuff I have is correct. This is what I bought (scroll down to 112AF)--> http://www.karnakcorp.com/pro_dp.html

This stuff is black and sticky and has a strong chemical smell. The container says to apply it with a roller or brush. The NOFMA guide says to apply the "cutback adhesive" with a trowel. I can't see how this can be applied with a trowel.

Since time is running out and I need to get this done ASAP, I already started (last night) to lay the felt without the mastic (I reasoned that it is not worth the risk of exposing my one year old daughter to these chemicals). I am installing at grade (bottom floor of bi-level home) and am thinking the two layers of roofing felt (taped at the seems and under the plywood) and the layer of polythylene above the plywood would be enough to protect against any moisture. I hope I am not creating a disaster for myself. Has anyone ever seen the following approach done with success?

1. lay roofing felt (overlapping 4" - 6"). Have it go under the walls and tape it to the baseboard area. Tape all seams down the middle.
2. lay another layer of roofing felt. This time just tape the seams and not tape all of the baseboard areas.
3. lay the plywood (I already bought the plywood - I agree that powder nails may not be the best way to go. I'll use a combination of tapcons and powder nails or maybe all tapcons).
4. lay 6 mil polythylene over the plywood.
5. nail the planks into the plywood.

Basically, it is a mastic-free procedure (mainly because I have some concerns about the chemical, but more because I already started to lay the felt without it). I'll be doing this today and hope someone will stop me if I am truly making a serious mistake. If I picked up the wrong mastic, I'll consider pulling up the felt and laying the right stuff. If someone can assure me that I will be OK with the procedure above, that would give me peace of mind as I continue with the job.

Thanks to all who responded. Any other quick responses would be greatly appreciated.

PS - Yes, I am doing this on christmas eve and christmas day!!

Don't put the plastic over the plywood. It goes underneath the plywood.

It will cause the plywood to dryrot by going over it with the plastic. Or so I'm told, in the NWFA classes.

Thanks AustinFloorGuy!

I'm currently half way finished with the first layer of black felt. Should I lay the 6 mil plastic over the black felt and then put another layer of black felt over the plywood. The steps would then look the following:

1. lay roofing felt (overlapping 4" - 6")(no mastic). Have it go under the walls and tape it to the baseboard area. Tape all seams down the middle.
2. lay 6 mil polythylene (plastic). This time just tape the seams and not tape all of the baseboard areas.
3. lay the plywood
4. lay roofing felt (overlap edges / no mastic).
5. nail the planks into the plywood.

Using the felt without any mastic is setting your floor up to fail. The mastic will be under the plywood and under the flooring and shouldn't be a carcinogenic concern.

I thought I had read this post earlier and recommended not using the felt paper and mastic. Instead use a moisture barrier/anti-frature membrane. This method will protect better as well as being less messy.

Don't be stubborn and take our advice.

Good Luck and Merry Christmas