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SPISurfer 10-14-2008 01:10 PM

Resurfacing Concrete Floor & acid stain floor
After tile removal, there were divots and mortar raised chunks in the cement slab. I ground down the chunks to be level. There was also black mastic under some spots.
1) Can I skim coat over black mastic?
2) What do I use to patch the divots? Will the skim coat be enough to cover the divots?

I have acid stained before in 1999. It held up great with the top coat sealant until our hurricane/flood this year. After being under 7 inches of standing water for about 24 hours, the sealant has started peeling.

3) Please provide any suggestion for removing the sealant - ammonia?
I used Behr Epoxy 1 coat clear for the sealer as the acid stain company's sealer was too expensive for me.

Now that I've removed the white tile (yuck) I'd like to do the whole house with acid stain. I don't want tile. The removal process was nasty, dusty. Plus some of my neighborhood who had newer installations were complaining for about 1 month about the squish they heard under their tiles.

I need to come to some floor decisions.

NOVA Pros 10-14-2008 04:42 PM


In my experience, working with acid stain and concrete, you should get up as much mastic as possible, by using a scarifier or such. After you get up the majority of the mastic, putting a skim coat over it would be fine. Then you could acid stain the skim coat. You can also fill in small divots with the skim coat material. If larger, just use some concrete patch, let set, then put skim coat over that.

To remove the sealant, you can use a grinder to scratch the surface, but then re-seal and all the grooves and scratches will be filled in and look smooth.

Let me know if I can answer any more questions. I use to work with decorative overlay (sprays and stamps), pavers, stamped concrete, and such.


SPISurfer 10-14-2008 07:27 PM

Thanks for the Reply

I was hoping not to have to grind. Late Night's Grinder Girl has nothing on me.

1) What would happened if I put the skim coat over the mastic after roughing it up a bit?
2) What do I buy for the skim coat? I found some self leveling stuff at HD in the tile section but it needs a liquid with it. I don't think I have the right stuff. I haven't found much help at the stores.

In 1999 I tried to remove the mastic in some parts of the house. I tried naptha and toluene (I'll probably die from chemical use) and an industrial floor sander. I couldn't get it up. The mastic would bind to the sand paper/ floor pad and continue to stick. The chemicals would make it somewhat of a gooey substance, but would not come off entirely.

3) What do you suggest for trying to remove the mastic?

Thank you for confirming my thoughts on tackling the sealer. I'm pretty beat down with house projects. I'll do a spot test in the closet of just plan ol' putting more sealer on top to see how it comes out.

Any suggestion are welcomed. I'll figure this out eventually.

glennjanie 10-14-2008 10:46 PM

Welcome SPISurfer:
The mastic should be completely removed. It will interfere with the bonding of any skim coat and will repel any acid stain.
See if the local rental store has a vinyl and carpet removing machine. It has an oscillating blade in front and 2 wheels on the back, electric powered. It will take some time but this machine will scrape the mastic off the concrete.
I would ask the skim coat supplier if it is stainable. Some skim coats contain epoxy (which may make it too hard) and some contain latex (which will make it repellant).

SPISurfer 10-20-2008 11:31 AM

Thank you much Glenn Janie --- I wondered about that latex. I've managed to stall on the flooring project and have gone onto plumbing and windows for now.

SPISurfer 10-23-2008 09:38 AM

Before Pictures
3 Attachment(s)
Here are some pictures: acid stain, divots in the concrete where tile was removed, painted concrete.

I'm still trying to determine what concrete/tile flooring we'll be using.

billy1955 11-27-2008 07:09 AM

remove black mastic
remove black mastic with soybean jell works great on concrete floors with out grinding the floor with all the dust.

If you can not find the product where you live let us know. I can give you the name of the company we buy from.

Thanks bill

PortlandTradesmen 11-28-2008 02:49 PM

First thing that stands out to me is that if you have a black mastic it would be prudent to have it tested for asbestos.

Next for the best look I always recommend grinding. I've ground floors myself and hired people that specialize in concrete grinding after doing both I'm definitely a fan of hiring out that portion of the job. A commercial grinding company will get it done quick and usually have excellent dust collection systems.

If your set on doing it on your own there are propane grinders that have a water feed so no dust but plenty of work cleaning up the slurry any way.

I find with a good skim coat product you may spend nearly as much on the product as you would hiring a grinding contractor.

As far as the sealers go as aggravatingly expensive as they are the good ones are their worth the money.

I've definitely done skimming, grind staining and repair so feel free to ask if you have additional questions.

yesitsconcrete 12-05-2008 05:27 AM

realize this was back in oct '08 but maybe some'll still read it:

nope, NO skim coat til the floor's CLEAN

patching the divots can be done w/patching cement ( we use sika ) & it can be colored to match the existing conc,,, ck w/sher-wms for some of their 877 tints & experiment,,, don't be discouraged if its not right in the 1st hr,,, no one ever got experience/technique/knowledge from reading labels, pamphlets, websites, or talking w/customer-no-svce personnel

the 'behr' name's a tipoff you got it at the apron store - not for pro's - had you used the right stuff, it wouldn't have been touched by the flood,,, next time find a urethane sealer & do a moisture test 1ST,,, strippers you can buy from apron stores, tho,,, did try the soy/citrus stuff once but a nitemare mess,,, we use ammonia only for neutralizing acid.

next time get dust muzzles to hook up to a wet/dry vac,,, we buy ours from dustless technologies { no financial interest },,, we use turbo diamond cup wheels in 12 & 24 segment style depending on whether we're leaving the floor stain-rdy OR prep'd for thin-cementitious overlays.

SPISurfer 12-08-2008 03:59 PM

Hey Yes,
Thanks for the reply! I want to make sure I get this correct.
1. Remove mastic/paint - ok ok I'm working on it - mineral spirits and a scrapper. As I said earlier the rented floor machine just gets gummed up with the mastic.
2. Patch with Sika
3. Grind with a diamond blade
4. Thin-cementitious overlay
5. Acid stain
6. Clean
7. Use a urethane sealer

I don't understand about the tint from Sherwin Wms. Are you suggesting a tint/floor paint from them verses using epoxy paint or an acid stain?

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