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Pele2048 02-06-2013 08:36 PM

Dirty HardiBacker? Screw heads?
There's a backstory to this which I can get into later, but I'm going to hit up the key points...

Long story short, I put HardiBacker in my kitchen a year ago.
I've been walking on it for the past year... Just raw HardiBacker.
It's a Kitchen... It's had stuff spilled on it. My dogs come in and out of the sliding glass door and track mud on it...

Is there a way to clean it? I've scrubbed and scrubbed with a stiff bristle brush and it won't come as clean as new.

Do I have to worry about this? Will Thinset bond to the dirty HardiBacker?

Also, when I was originally putting it down, I used the HardiBacker screws to attach it to my old wood subfloor. (Same section as HardiBacker at Home Depot... "Backer-On" is the brand name.)

When I put the first few in, they did not completely counter sink into the HardiBacker... They ended up flush at best. Most have the conical section of the head sunk into the HardiBacker, but the surface of the head is still slightly over the surface of the HardiBacker.
If I leaned my weight on the drill and pulled the trigger, the tip of the Square or Phillips drive bit would break off... So I left them at that. I did put them in while the Thinset under them (between the subfloor and the HardiBacker) was still wet.

JazMan 02-06-2013 09:45 PM


Don't ever do that again? What were you thinking?:eek:

That stuff is dangerous, it contains silica and other bad things. You can not use it as a floor surface to walk on.

Will it take good quality thinset? Maybe, probably, I don't know.

I'd want the screw heads flush. Phillips heads are useless. Square-drive work well. Your tip must have been worn. I found that if you drive the screw till it makes contact, then back it out a bit, then drive it home, it'll work better. Either that or use roofing nails as I always used to do until I switched to Ditra.


Pele2048 02-07-2013 03:00 PM

What I was thinking was, I can only eat microwaved meals for so long... And running a hot plate on a 15 Amp Aluminum wired circuit is not advisable. It takes 20 minutes to get a pot of water boiling and the connection in the Federal Pacific breaker panel is usually smoking at that point as well.

Like I said, there's a backstory.

I bought this house that for all intents and purposes should've been a foreclosure or short sale. The previous owners concealed a rodent infestation such that the FHA appraiser, home inspector, and termite/wood destroying insect inspector didn't notice a problem. Only because of a misunderstanding in the contract did I find out about it at the closing table.
VA law states that the buyer pays for a wood destroying insect inspection, but the seller got one also. I got a call from one of them indicating "signs of mice"...

No legal recourse because my only contingency on the contract were any items that showed up on the home inspection. Home inspector didn't find rodents because he's not allowed to move property in an occupied house.

Upon hiring an exterminator, I found that the rats in the back yard were well fed enough that they weren't eating the mice on the inside of the house... Just killing them and leaving the bodies. The mice inside the house had taken completely over the kitchen and had nested in the insulation in the walls.

To get rid of the rats, I'd have to get rid of the mice...
To get rid of the mice, I'd have to eliminate their food stores in the walls...

I went into the kitchen swinging a crowbar. Getting to the nests in the insulation meant taking down the drywall... But there were cabinets in my way.

Once the drywall was down, I found all sorts of hackjob electrical and plumbing work. Junction boxes hidden in the wall, joining copper wire to aluminum wire without anti-oxidant compound, 14 gauge wire on 20 Amp circuits, and somehow either the ice maker in the fridge was running on hot water or the dishwasher was running on cold water because they were both Teed into the same line.

So basically, a new kitchen from the ground up including refeeding wire across the house.
Then I found out about the bat problem when I was running wiring through there. Apparently my pest control solution didn't take them into consideration.

I've also had to deal with the fun of becoming a new parent through all this.

I figured tile would be a cosmetic issue. I didn't realize the cement board was dangerous. There were no warning labels on it.
I figured it was fiberglass cloth in cement... All cutting of it was done outside.

funfool 02-07-2013 03:21 PM

I congratulate you on taking the time to do it right.
Although I would not have put down the hardibacker until ready for tile. Is no changing that now.
Just clean it good as you did, I see no reason for special thinset, would think the product recommended from the tile manufacturer will be fine.

BigJim 02-07-2013 04:12 PM

Good gravy Pele, that is unreal, that is a bunch of work and money. I wish you all the best in your rebuild.

JazMan 02-07-2013 04:16 PM

Holy crap Pele, what a mess. Congrats for staying with it and trying to correct everything.

I agree to just use a good quality modified thinset. Be sure to dampen it or mist it just before you spread thinset to every area. Hardie is porous. Did you tape the seams? Have you checked that the floor is very flat?


Pele2048 02-07-2013 05:05 PM

I put down the HardiBacker because it covers ALL of the subfloor in the kitchen. It's under the cabinets.

When demoing the kitchen, I found that it appears that this kitchen went through several different flavors of flooring in the mid 1970's... Which is interesting because it was built in 1973.

There was a top layer of Avocado Green Linoleum, Below that were brown faux Parquet lick-n-stick 12 inch vinyls, Below that were thick (approx 1/8th inch) 9 inch square tiles. I assume those were Asbestos. Under all of that was 3/4 inch Particle board that was glued AND stapled to the plywood subfloor.

I decided to remove it all as an assembly to reduce dust. I was fairly successful in getting a prybar under the particle board and getting it up in almost complete sheets.

After getting it all up, I measured the plywood. It came out to be a hair under 5/8ths. 19/32nds... I'm now finding out 19/32nds is 5/8ths in carpenter math, kinda like a 2x4 is really 1.5x3.5
Since the HardiBacker recommends a 5/8ths minimum plywood subfloor, I thought my subfloor was subpar and I decided to use 1/2 inch HardiBacker rather than the 1/4 inch stuff. It's also the Mold/Mildew/Moisture resistant stuff.

Under the cabinets and on top of the HardiBacker is 1/2 inch pressure treated plywood to make up for the Height difference that the tile would make.

Other than that, the install of the HardiBacker is pretty typical to the install guide. Screws every 8 inches, 1/4 inch trowel for the thinset under the Hardi, The plywood and Hardi joint lines are not in the same places, No four corners touching...

I'm pretty much looking at the only imperfection being the dirt and the screw heads sticking up just slightly.
I'm not sure it was the bit being worn out, I got a whole box of new bits and brand new ones were snapping off too.
I could go out and swap out the Phillips screws with square head ones, but the thinset under the Hardi has dried. I'm not sure if that's a good idea... Thoughts?

Also, point of note, I did call in a tile contractor for an estimate on completing the job... They were saying that they'd run a belt sander over the dirty HardiBacker to clean it up for the thinset to adhere better.
If this stuff is really that dangerous, then I'm glad I didn't go with them.

Anyhow... I've got bags of Maipei Thinset, boxes of Ceramic tile, spacers, grout, and all the stuff I need sitting here in my living room. I'm just trying to make sure that this tile job is going to last.

JazMan 02-07-2013 07:33 PM

Well, 5/8" ply as the subfloor huh? Hardie says 5/8" t&g if in perfect condition and installed correctly is good enough as the base for their backer for ceramic/porcelain. I don't know how your '70's subfloor can meet those specs. Plus they always note with *'s that it has to meet L360 max deflection, the subfloor and the joists I mean. That floor sounds a bit shaky to me.

Talking of the joists, you should tell us their size, species and grade, on center spacing, and unsupported span. This will tell us about the joists' deflection.

It didn't make the floor stiffer when you decided on 1/2" instead of 1/4". Neither adds structural strength, just a tile-friendly surface for tiles. Actually, 1/4" has a higher compression strength, but it's not really relevant anyway.

It may not matter in your case, but you should not use pressure treated indoors. It starts out too wet, and tends to deform as it dries.

I guess there's no changing what you've got now, so go ahead and install the tiles. Do check and get back with the joist info though.


Pele2048 02-08-2013 08:28 AM

Great... maybe this was a bad idea and I should have gotten a pro in the beginning.

I don't have the equipment to test the deflection of the floor or joists. Nor can I determine the species or grade of the joists unless it's printed on them. (Which I'll find out when I start gutting the basement ceiling.)

The best I can tell you is that the joists are 2x10 on 16 inch centers. Longest unsupported span is about 12 ft between the center I-beam of the house and the back cinder block wall of the basement.

JazMan 02-08-2013 09:00 AM

We use span-charts to confirm deflection. Lumber is stamped, but often can't be found. Most joists are SYP or Doug Fir, grade #2. If they span about 12', you'll be fine. As I said before min. spec is L360 deflection and you're probably better that that.

The subfloor is your weakest link. Can't get any worse than that. How does it feel?


Pele2048 02-08-2013 03:45 PM

I figured the deflection test involves some sort or computer measurement device that puts out a specified force and measures how much the floor moves...
I didn't realize it was a calculation that's on a table...

Subfloor is fairly solid. Only squeaked in a few spots and that quit when I started driving screws for the HardiBacker into it.

Would it be a bad idea to pull out all my Phillips screws and install the square drive screws since they tend to go in a bit better?

There were two boxes of screws next to each other at Home Depot... The Phillips ones were the "Backer-On" official HardiBacker endorsed ones... The Square drive ones were generic "Rock On" and mentioned Wonderboard and other Cement type boards on the label, it said on the label to specifically use "Backer-On" screws for HardiBacker.

My other thought was to put down a very thin layer of Self-Leveling cement that'd cover any imperfections in the surface.

Good news is that the dirt is coming up with nothing more than water. After a couple rinses, it looks almost new. I'm going to start taping up my joints this weekend.

JazMan 02-08-2013 04:11 PM

Yes, the span charts guide us on what to choose and to tell us roughly how your floor rates. There's ways to do field calculations, but usually not done for obvious reasons.

Replacing the screws is probably not necessary, but I've never done it or thought I needed to. Next time try roofing nails.

It would be smart to check the floor for flatness, get a long straight-edge 6, 8 0r 10 ft. long. Record the results. Be sure to prime if you use SLC.


Pele2048 02-09-2013 09:03 AM

I have a 4 foot level and a 4 foot square. Both show the floor as pretty flat across...
Since you recommend something bigger, I went and got a piece of drywall that I had cut lengthwise and used the clean edge as a straight.
I suppose I could use a credit card as a feeler gauge, kinda like checking the warpage on a cylinder head or engine block.
Could also have been the screw heads... Seeing as how with screws every six to eight inches, I'm bound to set the straight edge on at least a few of them.

Everything I'm seeing shows a similar process as making a drywall joint; tape the joint and spread on joint compound, then feather the compound out to make the transition between the two pieces of drywall smooth.
I taped the joints with the approved alkali resistant fiberglass tape, looks just like drywall tape except grey. Then I mixed up half a bag of thinset mortar...

I have never felt more in over my head...
I just can't get a smooth joint because the thinset is so gritty. Even when it's watered down, it's much thicker than drywall mud.
It's like trying to perform brain surgery with a sledgehammer.

JazMan 02-09-2013 09:30 AM

Four feet distance is not enough. The spec is less than 1/4" in 10 ft. and 1/16" in 12". If you use 4' and guess at 1/8" i.e. it could really be 1/2" in 10 ft. Way bad. Get something straight and longer.

What size and type are the tiles and which specific mortar?


Pele2048 02-09-2013 09:48 AM


Originally Posted by JazMan (Post 1113012)
Four feet distance is not enough. The spec is less than 1/4" in 10 ft. and 1/16" in 12". If you use 4' and guess at 1/8" i.e. it could really be 1/2" in 10 ft. Way bad. Get something straight and longer.

What size and type are the tiles and which specific mortar?


Mapei Grey Ceramic Tile Mortar - Polymer Enriched
Lowes receipt says it's Model #29325 / Item #37682

Tiles are 12 inch square Ceramic, PEI grade 4.

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