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Author Topic: sanding/grinding down unmodified thin-set mortar  (Read 10545 times)
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hessec

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« on: January 26, 2010, 09:53 PM »

Hi there, new member, love the board and obviously a festool junkie as well....  Long story short... I need to remove some thinset that was left over from the removal of a ditra tile membrane.  The thinset is in a waffle like honeycomb pattern about 1/16" raised off the floor.   I need to flatten this material so that I can re-lay the ditra membrane and re-tile.  I've used my RO150 with dust collector and some rubin paper and it works it to the point that it's manageable but i'm killing pads within a minute.  I have 400+ sq ft to do.   I have also used a belt sander and that works just fine but the dust is an absolute killer!!!    I need a delicate sand/grind because I have a heating element embedded below this thin-set.  All I need to do is remove the 1/16" raised edges on the 3/4" squares remaining.... and i don't care if it takes me 100 hrs and $500 in paper I NEED TO KEEP THE HEATING ELEMENT.....  Do you think that Saphir pad with the "hard pad" on my sander is up to the task?    I'm running out of options here because I just can't use the heavy duty diamond rental jobbers.  Please lend me your advice as I am in complete despair over this botched job.  Thank you so much. Chris Crying Crying
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WarnerConstCo.

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« Reply #1 on: January 26, 2010, 10:09 PM »

A multimaster may be your best bet, or the LS130 with the scraping attachment.
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quietguy

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« Reply #2 on: January 26, 2010, 10:14 PM »

Warner is right on with the Multimaster.  Use either the carbide cutter or rasp.  If there is any give to the thinset, you can probably use the scraper with good results.
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JohnDistai

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« Reply #3 on: January 26, 2010, 10:23 PM »

Have you asked this in the John Bridge Tile Forums? (Google it)  That forum is much like this one, except for tile.  You can probably do a search of old threads and find the answer right away.

JD
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Peter Halle
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« Reply #4 on: January 26, 2010, 10:28 PM »

Chris,

Pardon my manners, I didn't officially welcome you to the forum.

 Welcome! Welcome! Welcome! Welcome! Welcome! Welcome!

Sorry Your job went bad.  As a multimate owner I agree that if that is available, you should try it.

Peter
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hessec

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« Reply #5 on: January 26, 2010, 10:28 PM »

Yeah, I'm on John Bridge forums too.  They have suggested that I use the belt sander etc..   I have to live in this house and need a more precise/delicate sanding/hone.  thanks
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waho6o9

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« Reply #6 on: January 26, 2010, 10:35 PM »

 I'm using 24 grit Saphir on a Rotex 150 with the pad it came with and it's taking off tile adhesive off the wall.  It takes awhile , but it works.  Smile
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Brice Burrell

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« Reply #7 on: January 26, 2010, 10:37 PM »

I would try Saphir abrasive with the soft sanding pad and a carbide paint scrapper. The Saphir abrasive is made for tough jobs like this. Another option is a grinder with wire cup or wheel.

And welcome to the FOG!

(I see waho6o9 beat me to it.)
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WarnerConstCo.

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« Reply #8 on: January 26, 2010, 10:40 PM »

I have used my rotex and ras with 24 and 36 grit saphire to grind mastic and thinset before.
I always use a hard pad no matter what.  The multimaster will be quicker
and make minimal dust.  That is why I said to use a mm.
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hessec

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« Reply #9 on: January 26, 2010, 10:49 PM »

I can't figure out how to post a picture or i would... but don't think of it as a thinset with the trowel marks in it.... it is more of an embossment of a million 3/4" squares on the floor with the left over felt from the bottom of the ditra.   the raised edges are about 1/16" high around the perimeter about 1/16" thick.   I've ground down some of it with the abranet "heavy duty" 80 grit pads and it works but those were pretty dull from a previous attempt at grinding lippage off of the limestone tile that was once there.  I have a multmaster with the scraping attachment (non carbide) and that lasted about 20 seconds.......  I think i'll try the saphir in the 24 grit because at this point i'll try anything.  I can't live with the dust. 
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hessec

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« Reply #10 on: January 26, 2010, 10:54 PM »

www.northlandconstruction.com/.../ image/3692.jpg

don't know if i can do that or not but the picture is worth a thousand words.....

Thanks to all
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hessec

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« Reply #11 on: January 26, 2010, 11:03 PM »

that didn't work but here it is...


* P1000550.jpg (55.62 KB, 800x600 - viewed 369 times.)
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WarnerConstCo.

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« Reply #12 on: January 26, 2010, 11:13 PM »

I am familiar with ditra, and I know what it leaves behind.

the mm may be the best bet.
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counterfix

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« Reply #13 on: January 26, 2010, 11:27 PM »

400 sqft you  should try a floor sander 16' disk maybe 20grit i would do this in a area thats not heated if possible for testing the most affective grit there are many grits available also there is  carbide paper we use on limestone ,marble, travertine, soft stone this type of paper is 5" and works on a flex type grinder its  very affective as for a MM i think you will be there for weeks scraping  Crying  good luck
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JohnDistai

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« Reply #14 on: January 26, 2010, 11:30 PM »

How about a rotary hammer and a gentle touch?
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Dan Clark

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« Reply #15 on: January 26, 2010, 11:57 PM »

Chris,

It turns out that I have the same configuration in my master bath - heating element with Ditra on top.   I'd try a carbide or diamond rasp to knock it down relatively flat: http://www.amazon.com/Versa-Tool-Triangular-Universal-Oscillating-Carbide/dp/B002SHSGQI/ref=sr_1_fkmr2_2?ie=UTF8&qid=1264564340&sr=1-2-fkmr2 or  http://www.amazon.com/HARDIN-Diamond-Triangular-Concrete-Grinding/dp/B002SHP8FA/ref=sr_1_fkmr2_3?ie=UTF8&qid=1264564340&sr=1-3-fkmr2.  If that doesn't work, you might try a grinding cup with a grinder: http://www.toolplanet.com/category/Diamond-Concrete-Grinding-Cup-Wheels.   Then, finish it off with you're RO150.

FYI for the rest of the folks here...   It's the heating element that is the killer.   ONE slip and Chris can nick the heating element.  And if he nicks the heating element?   He rips it out!    Please keep the heating element in mind.

Having installed this myself, I understand his concerns.

Regards,

Dan.

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Michael Kellough

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« Reply #16 on: January 27, 2010, 12:09 AM »

If it really is a delicate job a multimaster type tool is best.

This belt sander is small and has very good dust collection
if you use the platen instead of the front wheel.



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Alex

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« Reply #17 on: January 27, 2010, 05:20 AM »

I would certainly give saphir a try. It is very hard paper, if you can call it that because it's more of a cloth, and will not tear like normal sanding paper. Another option would be, instead of removing the mortar, to add another (small) layer to level it out.
« Last Edit: January 27, 2010, 09:16 AM by Alex » Logged
steelydev

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« Reply #18 on: January 27, 2010, 08:30 AM »

hessec-

From setting tile for years, I've run into this before.

What are the concerns about the exact elevation of your finished floor?  I ask because we would not even attempt to remove the bumps.  Instead float more unmodified thinset over what you have.  Do one of the following:  If you are going with a small tile (less than 4x4) or mosaic, float smooth, allow to set firm enough to walk on then reapply thinset with notched trowel and roll in Kerdi.  you might lose a little in thickness.  If you are going with a larger tile, you could probably get away with floating the thinset with a notched trowel in a single pass and roll in Kerdi.  Always use unmodified thinset under the membrane.

You can easily make up for thickness with larger tile by switching to a 3/8 notch trowel. 

Otherwise, we've always used the Sandvik carbide scrapers to remove imperfections in thinset.  Work at a 45 degree angle to the ridges just like grouting.
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hessec

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« Reply #19 on: January 27, 2010, 08:47 AM »

Thanks,  I spoke to the schluter people (manufacturer of ditra) and they said that with what's left it will need to be ground down.  Why?  i'm not sure becuase it would seem to me that the leftover felt would just become part of the whole sandwich.......  The elevevation of the floor is not that much of a concern because as it stood before with the tile it was already a 1.5" step up.   This house is old old old 1870's and what's left of the original oak flooring (over the top of t & G pine) in adjoining rooms is about 1/4" thick or less therefore with the subfloor required for natural stone it would be impossible NOT to have a rise into this room.  If it has to be 2", then that's what it will be. 

My immediate thoughts were fill in the waffles with another layer of Self leveling compound or thinset and then just go to town again....and i'm still thinking about it!!  If you think that it will not fail in the future with this method I may  be willing to give it a shot. 

New tile will be 16x16" travertine  or 9 x 18" travertine. 

Schluter may be saying this to cover their butt in the event of failure. I don't really know.  I take my time to make things perfect but grinding this thing down is really taking it a  step too far.......  If there were no heat underneath- we wouldn't even be having this conversation, it  would be done.   

Chris
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tjbnwi

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« Reply #20 on: January 27, 2010, 10:15 AM »

I know I do not post here much, but I have to comment on this one. You are all working way to hard.

All you need to use is a rub brick;

http://www.marshalltown.com/Products.aspx?D=200&S=219

There are times power tools are not the correct answer.

Thinset is not as hard as brick mortar or concrete. If you wet to surface as you rub it will create a slurry that can be washed off. You can use the brick dry also, it will kick up very little dust. The dust it produces can be vacuumed up when you are complete. Also try wetting the surface and just use a scraper, thinset is not water proof, and will soften when wet. Do not soak the floor!!!!!!!!!!!!!!!!!!!!!

Either way you must wash the floor prior to any other products being used.

As for the mat it is repairable in place if need be. You should put a tatletale on the leads just to be certain it has not been damaged, it will alert you if you damage it during the next phase; (there are others on the market, this is the one I use)

http://www.nuheat.com/products/accessories/matsense-pro.html

On my installs, I always pour self leveling compound over the elements, then Ditra, then tile. Most floors need some leveling work and thinset should never be used as a leveling product. The SLC also protects the elements from possible trowel damage.

Two to three hours you will be done.

By the way there should be no power to the mat at this point, not enough mass to keep it from over heating.

Once you're done you will really enjoy the floor.

I'll go back to sitting in the corner now, soaking up all the [festool] knowledge that is presented here.

Tom 


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Holzhacker

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« Reply #21 on: January 27, 2010, 10:35 AM »

Stop wasting time and killing yourself. If the existing bed is sound, scrape off any high spots and fill the voids with a compatible leveling compound. Jifset or whatever you use in your area. You are talking about 1/16", there is no point to removing it, fill the voids and get the job done. I've done this job more times than I can remember. If the bed is sound, go forward, not back.
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hessec

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« Reply #22 on: January 27, 2010, 10:37 AM »

Thanks for the tip, I'll be sure to try that as well.   The elements are burried in SLC so there is some margin for error.   The margin gets smaller with the larger power tools.   I have 5 splice kits just in case.  The wires are hooked up to the loudmouth continuity meters and I check the Ohms readings religiously- i'm ok so far.   Do they sell rub bricks at any big box stores?
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monstrol

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« Reply #23 on: January 27, 2010, 11:27 AM »

I know you probably don't want to buy another sander but the RAS 115 with 36 grit or 24 grit might work.  It works differently than the Rotex.  There is a thread here somewhere about the RAS 115.
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JohnDistai

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« Reply #24 on: January 27, 2010, 04:43 PM »

Have you tried a floor scraper?  Not sexy, but it may do the trick.
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hessec

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« Reply #25 on: January 27, 2010, 09:33 PM »

The rub brick/stone is working!!! Can't tell you how happy I am. Thank you everyone!
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« Reply #26 on: January 27, 2010, 11:41 PM »

The rub brick/stone is working!!! Can't tell you how happy I am. Thank you everyone!

Awesome, I'm glad it's working for you.  Tjbnwi for President, good job sir.
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mhoy

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« Reply #27 on: January 28, 2010, 02:28 AM »

Congratulations on finding a method that works.  Reminds me of removing the old ceramic tiles from my concrete slab without the having to be careful part.  Grin

Mark
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« Reply #28 on: January 28, 2010, 03:53 AM »

Those stones are pretty amazing. I have one that I got from my Dad when he was still of this Earth. I used it as a kid on more than one project, including preparing a 2-stall garage for painting. The one I got from him is broken in half but it doesn't seem to have impacted its utility.

I have used it since to even out some green concrete when setting a tub. They require brute force but are totally controllable, work well, and don't raise a lot of dust - plus they are good exercise.


Tom
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