Adhesion to painted concrete surface

Stan in Oly, WA

Well-known Member
My fireplace insert has a metal surround which overlaps the back hearth. On each side there is about a one inch gap between the edge of the surround and the edge of the tile, revealing a strip of mortared surface. The surface is about as smooth as you can get a vertical mortar coating with a trowel---good, but not glassy smooth. To keep this nagging detail for dragging on forever, my wife and I have decided that it might be enough to simply paint the narrow surface the same flat black color as the surround. Hopefully this will make it disappear, more or less. If it isn't good enough, and we decide to find edging tile to finish it, will thin set mortar stick to the painted concrete surface well enough to finish the job, or would I end up having to remove the paint?

Stan
 
If it's not an oil based paint, I'll vote for probably okay, provided you rough up the surface with sandpaper first. If it's oil based paint I'd say no.
 
I would think it would not bond or adhere. I'd try a test strip to find out. Its tough to coat existing cementitious materials with a parge coat of something like thin-set, more so if its painted. I'd venture a guess that you'll need to research some materials on this to find something that will bond both to the existing and the back of the tile. It sounds like the tile will be cut too, so you don't want to do this one over. I'd test the existing substrate with the paint, if the mortar is bonded well, then maybe all you need to do is prep the surface for something compatible, likely having to strip the paint. The bond of the paint and the bond to the pain with the thinset is the consideration here. Who knows, you might find an epoxy or something that works on this. One thing is for sure, bituminous, asphaltic, or oil based materials don't usually mix well with cementitious materials. Portland cement based materials applied to portland cement based materials, (existing) is kind of like a cold joint, and you know how thin layers can easily spall + you have a temperature differential being a fireplace, so that expansion can be a factor. Something heat tolerant and elastomeric that will bond may be what you are looking for, but there is a lot out there today. When I saw the subject I knew it was you Stan LOL ! Its kind of interesting as I used to go through this with sealants, with all the varying substrates, it was always a challenge to find/test materials to determine if they were suitable for the assembly or building components.
 
regarding paint, you might want to consider using high temp paint like is used on manifolds and bar-b-que grills in this application so heat from fire place does not cause problems
 
If all else fails, check with the thinset manufacturer. Here's a link to Custom Building Products, maker of the FlexBond, VersaBond, etc thinsets that you will find at Homer Depot. There's a technical data sheet for each of their products.
Custom Building Products
 
Thanks, Fred. While I was posting the question, my wife was out shopping for black foam board so that we could get an idea if we would like that look enough to use something black instead of tiling. I cut strips to size and it looks so good that my wife wondered why we hadn't done it a long time ago. I suggested a couple of ways we could get a more permanent fix, and what we decided on was to use strips of HardieBacker attached with some appropriate adhesive, then painted flat black to match the surround. I appreciate the link you provided.

Stan
 
Hi Billy. Thanks for responding. I sort of count on you to keep me from wasting my time in these situations. I just seem to have the hardest time remembering what materials will or won't bond well to other materials. Read my reply to Big Fred below about what I decided to do. I would expect to have good luck finding an adhesive to hold a 30" X 1" strip of HardieBacker to each side of the surround on clean, dry mortar covered concrete. Considering that there's no force working to move such a strip out of position, I'd almost expect to be able to accomplish it with double sticky tape. Just kidding. That kind of talk from amateurs probably makes you wonder if we're in the final days. Anyway, I don't foresee any major roadblocks with this course of action.

I often think about your advice concerning my raw concrete retaining walls. I probably would have parged them and hoped for the best if you hadn't warned me of what to expect. I don't like the look of them now, but I'd probably be a lot less happy if I was now dealing with a failing stucco-like coating. I've had a couple of ideas about what to do, but the truth is I'm running out of enthusiasm for labor intensive projects that I can't afford to pay someone else to do, and I haven't got enough working rotator cuffs left to do myself.

Stan
 
I've measured the temperature at different locations around the fireplace, and I don't think heat will be a problem where I need to paint, but I'll probably use the paint you suggested because I'll get the best match that way. I'm sure that the flat black face of the stove and of the surround were painted with high temp paint.

Thanks,

Stan
 
Stan:

I read your reply to Big Fred, . . . if that doesn't work out, you can buy pint cans of "Stove Black" (can't remember the name of the Mfg. as it's been many many years since I've used any), but Stove Black is used for RESTORING the black finish on old cast iron cook stoves. Wear rubber gloves and apply it with an old rag (a little bit goes a long long way) & DON"T get any on your clothing or anything else that you don't want to become PERMANENTLY black.

HTH

Doc :>)
 

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