Author Topic: Oddly-behaving Old Paint (sanding/Rotex)  (Read 2036 times)

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Offline fdengel

  • Posts: 853
Oddly-behaving Old Paint (sanding/Rotex)
« on: July 19, 2017, 03:42 PM »
My mother is trying to remove paint from a wall using my RO 150 using some of the Cristal paper.  The paint has been on the wall for several years (so dry/cured); I think it might have been sponged on or something.  The paint is sticking to the paper in solid clumps - not the typical dust that gets stuck in the paper, but hard pieces of paint that we can kind of pry off.

Even more strangely, the paint was getting under the pad and sticking to the back of the pad in similar clumps.

I don't think we've ever seen this happen before,  but the clumps on the paper get so thick that I believe they are holding the abrasive away from the wall and slowing progress - for now, she is pulling it off once in a while, but why would it be doing that to begin with, and any ideas on how to improve on this situation?


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Offline Dovetail65

  • Posts: 4594
    • Rose Farm Floor Medallions and Inlays
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #1 on: July 19, 2017, 04:35 PM »
That's not odd, that is totally normal and I create garbage cans full off sandpaper like that every year.

It's the nature of the beast when removing finishes , the finish just wont dust up. If you think that's bad try poly or shellac and many other finishes.

Take the paper off and crack the clumps off and you can get more life out of the paper. I would need to see the wall, its a rare thing I would take an RO to a wall myself. I have every type and grit of paper, experimenting with that is going to help more than anything else

People are going to come on here and say change the suction, change the sanding speed, those things are only going to minimally help. This work is going to require gumming up a lot of paper at first, just write it off as the cost and part of this type of work.



« Last Edit: July 19, 2017, 04:39 PM by Dovetail65 »
The one who says it can't be done should avoid interrupting the person doing it.

Offline fdengel

  • Posts: 853
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #2 on: July 19, 2017, 05:01 PM »
The Rotex is the only large-pad handheld sander I have at the moment, and my mother has both asthma and allergies, so the dust extraction could (literally) be a life-saver (combined with a mask of course).  She is basically trying to flatten it somewhat before painting over it, so it is not necessarily a matter of getting all the paint off - the way it was painted before it wasn't quite flat/smooth and the objective is to improve on that.

Thanks for the input - we've done some other similar projects with the RO before but this is the first time we've encountered this particular behavior from the paint, so this was new to us.

Offline Naildrivingman

  • Posts: 289
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #3 on: July 19, 2017, 08:31 PM »
It may be easier for all parties to have a drywall contractor come in and do a skim coat /sand.  The cast in my area is about $0.50/sq ft.
Dance with who brung ya...

Offline Rip Van Winkle

  • Posts: 270
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #4 on: July 19, 2017, 09:30 PM »
As has been mentioned, paint clumps forming and clogging the sanding abrasives Is common.

A carbide tipped scraper like the ones made by Bahco or Hyde, with an improvised vacuum hose attached somehow can be used to flatten rough painted surfaced, but will require a bit if practice. It also won't clog like abrasives can.

Some painters and drywall installers would just install new 1/4" drywall board over the old paint.  It diesn't necessarily look great, but it might be less work.

If some of the paint is coming of in large chips then the surface is probably compromised anyway. Getting down to a non compromised surface will be a major pain, and will require a major amount of work.

If the paint removal is removing multiple layers of paint, there is also the chance lead paint is being exposed if the building is thirty years or more old.

A traditional method to deal with old cracking plaster, was to fill voids, remove high spots, and then glue a layer of canvas or other cloth over the whole wall, and then plaster and paint over the canvas. This is still involved, but doesn't have the thickness issue of the 1/4" drywall.

Offline tjskinny

  • Posts: 67
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #5 on: July 21, 2017, 01:20 PM »
When I have stripped some old paint and it was acting like that, solid clumps on the paper, I would turn down the speed to around 2.  The paint is getting soft due to the heat generated by the rotation and collecting on and under the pad.  Similar consistency as when you use a heat gun to scrap paint.

Offline antss

  • Posts: 1277
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #6 on: July 21, 2017, 03:59 PM »
That is pretty typical for me when I've sanded latex wall paint.   Especially with lower grits.  In fact, I usually get more clumping than you show.

Offline Dovetail65

  • Posts: 4594
    • Rose Farm Floor Medallions and Inlays
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #7 on: July 21, 2017, 10:34 PM »
This is from last night, I ended up with about 10.




Today the kids will just clean them up by bending and crinkling  the discs to get the finish to pop off and ill get a little more use out  them.

The one who says it can't be done should avoid interrupting the person doing it.

Offline Pnw painter

  • Posts: 100
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #8 on: July 22, 2017, 01:02 AM »
Try switching to Granat abrasives. In my experience Granat tends to load less than other Festool abrasives when sanding painted surfaces.

I'm not sure what grit you're using, but try using 150 or 180. Some times the higher grits don't load like the lower grits.




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Offline aloysius

  • Posts: 165
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #9 on: July 22, 2017, 02:44 AM »
Nothing odd about it at all.  Quite normal for paint to clump that way.  Thick, multiple layers especially.  Friction from paint residues already on the pad melts the paint into clumps. 

Sometimes it's useful.  With a disc sander (variable speed grinder) , I've used this paint melting method for stripping exterior finishes.  A loaded abrasive disc melts the paint away through friction, leaving the underlying substrate not just effectively bare, but totally undamaged from the coarse grit's depredations.  Extremely messy (gobs of paint residue are flung off centrifugally), but remarkably fast & effective, & surprisingly dust-free.  The paint ends up in easily swept/vacuumed gobbets, not tiny easily inhaleable dust residues.

An alternative method is to use the tried & true technique of a hot air gun and 3" flexible scraper, finishing off with Rotex & Deltex type sanders with much finer grits (i.e. 80+). 
FOG-wit since '95:  Some say since birth...

Offline fuzzy logic

  • Posts: 336
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #10 on: July 22, 2017, 05:58 AM »
Hi fdengel.
(Off topic!)

Previous posts have fully addressed your query - so my post is to lament the
passing of the Festool Cristal abrasive (and Brilliant 2 come to that.)

I found Cristal great for this sort of paint stripping - not least because
clumps, for me, very easily popped off - though sometimes wanted
the backing 'paper' to be a bit stronger. 

Just out of interest, here is an old link, with some useful info' about
about the then available Festool abrasives. 
https://www.jamestowndistributors.com/userportal/pdfs/Festool/Festool_abrasives_brochure.pdf 

RIP Cristal and Brilliant2. 

Richard (UK) 
Decent people do the right thing - always?

Offline w802h

  • Posts: 202
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #11 on: July 22, 2017, 11:00 AM »
Yes, that kind of build up is normal and there are some finished surfaces that do it more than others.  Try moving the sander around to dissipate the heat.  Don't stay it one place too long. 

Offline Holmz

  • Posts: 3879
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #12 on: July 22, 2017, 05:54 PM »
If the paint is latex and is that gummy would a heat gun and a scraper be worth a try?
Or is the sander still the best option?

Offline Dovetail65

  • Posts: 4594
    • Rose Farm Floor Medallions and Inlays
Re: Oddly-behaving Old Paint (sanding/Rotex)
« Reply #13 on: July 22, 2017, 09:44 PM »
Hi fdengel.
(Off topic!)

Previous posts have fully addressed your query - so my post is to lament the
passing of the Festool Cristal abrasive (and Brilliant 2 come to that.)

I found Cristal great for this sort of paint stripping - not least because
clumps, for me, very easily popped off - though sometimes wanted
the backing 'paper' to be a bit stronger. 

Just out of interest, here is an old link, with some useful info' about
about the then available Festool abrasives. 
https://www.jamestowndistributors.com/userportal/pdfs/Festool/Festool_abrasives_brochure.pdf 

RIP Cristal and Brilliant2. 

Richard (UK) 

I was so aggravated when they stopped the Cristal. You are right for sanding finishes it was the best by far.
The one who says it can't be done should avoid interrupting the person doing it.