🤔Make it better, Every tile job needs this. Key, burn, coat, skim


if you ever install tile you need to see
this difference between success and failure so does this keying in your substrate
really make a difference so what”s keying in is well you get the backside of the
trowel if you’re going over plywood if you’re going over kerdi board if you’re
going over durock or cement board or whatever it is you going over is flat
siding the back with the back of the trowel to push the mortar into the
substrate really gonna make a difference on bond strength so I’m gonna do a
little test and we’re gonna I’m going to show you what the difference actually is
when you key in the substrate before you spread your thin set before you notch it
out and if you don’t key in the substrate so one side is gonna be key
it in with the flat side ust with a flat side and the other side I’m just gonna
leave the raw substrate and and and and do the test that way and then the next
day we’re gonna take those those apart and see which one actually held better
so this is very important if you before when you always should always key in
your substrate when you’re spreading your thinset so you get a superior one
and this is actually gonna let me show you what that difference is so that
piece of kerdi board here just plain old piece of kerdi board so I’m gonna key in this side just forcing the thinset this side is keyed
in and this side is just left alone I’m what i’m gonna do is get a blob of thinset and just drop it on and then I do the
same thing over here just drop it on and then let those set I’m not gonna touch
them I’m not gonna do anything to them I’m just gonna leave them like this
until tomorrow and then tomorrow we’ll test if keying in the thinset actually
makes the difference okay so this is the one that I keyed in and this is the one
that I didn’t key in now let’s see how hard it is get this off as compared to this one that’s
coming off in a million pieces it’s really stuck on there let’s try this one now see how this one comes off
that this one here I can’t it’s coming off it’s still the next day so it’s still pretty soft that’s why
it’s crumpled up like that but it’s stuck on there it’s really stuck on so this one here just popped right off
there okay so why does that happen well when you
key in your substrate what you’re doing is you’re forcing the thinset into all
the little cracks and crevices of the substrate whether it be kerdi board or
plywood or a cement board or whatever so you’re forcing this the the thinset the
mortar into that that surface so that penetrates into the substrate that
you’re gonna install the tile on so you’re pushing with the flat side of the
trowel you know mechanically pushing the thinset into that that area and then the
crystals can grow and and expand and penetrate deeper and deeper into the
substrate to get a really good bond when you just drop it on top you’re just
dropping it on on the surface and whatever adhesive strength it’ll gain is
when the crystals grow into the the substrate without having being filled
first to help engage the the adhesive quality of the thinset into the
substrate that you’re installing your tile on so that’s why it’s very important
to make sure that your surface is clean because you don’t want to want those
pores and all those those those places where the thinset has to penetrate you
don’t want that to be filled with anything else you want the thinset to
penetrate into that so you want it to be cleaned and then you also want it to be
if it’s a it’s a porous product you want it to be a damp so that it doesn’t pull
the moisture out of the thinset and cause it to stop curing prematurely if
you’ve got a porous substance the things that gains its strength by growing
crystals and interlocking and and getting harder and harder and
penetrating into the into the substrate and in the mortar itself as the crystals
grow it creates a strong material now this was just done one day after so it
was still fairly damp wasn’t that hard but you could still see the difference
between the one that I dropped on and the one that I had to that I know he
just you know that had had keyed in the surface first so that is very important
to make sure that you key in your substrate have a clean have a damp if
it’s porous so that the moisture doesn’t get pulled right out of the thinset and
it has the opportunity to cure and grow those crystals and get a great bond so
just in case you haven’t seen my videos before my name’s Salva Blasi being a
tile contract in the Boston area for over 35 years my youtube channel has
over 780 videos pretty much all to do with tile so leave your comments in the
comment section check me out on patreon if you can support me there that’ll be great
I’ll also leave a bunch of links to my favorite tools in the description and
don’t forget this right thanks a lot and also ring the notification bell so you
get notified every Saturday morning when I upload a new video thanks a lot

57 comments

I've always called it "skim or flat trowel " your substrate before your trowel scratch. I always look for any installer, I've never met, to do this when they start installing. It'll usually tell you all you need to know about the apprentice or installer.

I just keyed in cause Joe my mentor or Sal continuing ed would slap me in the back of the head! 😂🤔
Love the detailed application at the end. That's how I sell my customer over the guy unlicensed at half my cost.

How thick of a layer should you have before laying down backerboard or the orange stuff? Should you back butter the backerboard as well? Before keying in, you have to sponge moisten the plywood or osb subfloor first, right?

Thanks Sal, great video to remind all us professionals out there to take the proper steps when installing. Short cuts will not save you time in the long run!
Rob Toronto

Sal I assume you would also do this with Cement board using a damp sponge first to wet it down then do a burn in coat first? Can you then immediately start to install your tile after the burn in coat? Thanks very much and always great stuff on your Channel Sal.

How about you do the test as you said you were going to. Key in one side and then spread the adhesive with the notched side of the trowel?

Keying in, notching ,back butter tile …..hard to disagree , its proper job but time consuming and joe the tile setter next block is lashing down his tiles making more money as he in and out fast and he gets loads work , I do it by the book and no appreciation or extra money and joe with his likes laughing behind my back and customers saying im expensive and slow , after 18 years of this im hoping to get out of the tile trade this year, I ve had enough

Well done Sal! I tell this to other installers, most don't know about it, but when they do they don't even care.

Anymore, as a commercial tile setter it seems the concrete floors are always less than desirable along with the walls. So I end up pulling everything off with edges first anyway just to get things close to flat.

Off topic but, since almost all tile varies a little bit in size, I'll have one role perfectly level and the next row using the same spacers will level which means I have to adjust my grout joints. Any thoughts?

Can you key in your substrate and let it sit overnight and get the same effect? Or do you have to apply your tiles the same day while the key in is still wet?

Hey sal I sent you a PayPal donation and an email question if you could read it when you have a moment. Thanks!

Great advice Sal. I have a question I have a bathroom that's 40 years old and the structure is good. could I just knock off the tile and paint a moisture proof and retile ? I pried off a few tiles and the walls still look good.

Let's see a video for adhering backer board to the sub floor (1×8) you had in this video. I am pretty sure there is nothing in the hand book for this type of install but you can correct me if I am wrong.

So great that you did this video. I deal with people daily that say industry standards are a tool against them. You’ve shown here at least that the installation standards of ANSI A108.5 are for their benefit. Keep it up.

I used to charge going rate in my area even though I properly set tile and knew I was better than most of the flooring guys setting in my area. one day I decided I’m charging more than going rate even though I was afraid I would go without work. four years later I have doubled what I make through a store and tripled what I make when I sale my jobs. my work has only increased and my reputation has grown in the area I live in as a top notch setter. And to be completely honest I’m not even close to some of the guys I follow online but because I listen to guys like sal I have gained confidence in what I do and know what I’m worth. People will pay enough to make it worth your time to do it right. Keep it up sal

Sal, great video as usual. I can't tell you how many bathrooms or floors I have removed tiles from where they pop right up because there was no back buttering, or keying in, or they failed to trowel the mortar with parallel trowel lines, and it never collapsed properly. I also find a lot of tile floors with 5 large dots of thinset, rather than full coverage thinset, so you have cracks and numerous hollow sounds under the installed tile floor.

Do it again, only this time leave them for 7 days…The one on the right may come away easier!

BUT…… why is dropping a blob of thinset and walking away a relevant test, no one does that. When you spread thinset with a trowel, aren’t you keying it in with pressure? For a test, I would spread the thinset with a trowel, then drop a blob on that and see how hard it is to pry off.. Either way, your the best Sal 👍

Although I know it is best to burn (key in) thin set into the substrate I had not realized how important it is before seeing your video. Thank you.

Not an accurate test at all. Do the test where you actually TROWEL both samples over the keyed and UNkeyed. The act of TROWELING is actually doing a good bit of keying and you did NO troweling on the unkeyed side……just a blob SITTING there. So the blob sitting on the unkeyed side has not been applied as TROWELED mortar would be. Your blob on the unkeyed has not been applied as would be in an actual installation. Mortar is to be TROWLED on……not just a blob loosely sitting there. I DO key in but this presentation does little to nothing to support that way of thinking.

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