sanding/grinding down unmodified thin-set mortar

H

hessec

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Jan 26, 2010
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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]
 
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.
 
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
 
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
 
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
 
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.)
 
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.
 
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. 
 
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
 
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.

 
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.

371k.jpg


 
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.
 
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.
 
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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