How to tell if dot and dab method has been used? - Tile Advice

[Mr S]

Hi All.

We have recently undertaken a major house project which included installation of under floor heating throughout the ground floor.

An incident last week revealed unexpected weaknesses in the kitchen floor which we have now found out (from our builder) is down to the method (dot and dab) having been used in that particular spot.

Despite assurances this is in an isolated spot, we remain concerned that dot-and-dab may have been used throughout, given the potential impact on the under floor heating efficiency.

Is there a simple, fool-proof way for us to confirm (or not) this? If not, is this something a third-party (e.g. surveyor) would be able to confirm?

Any help is greatly received.

Many thanks in advance.

 

[Old Mod]

Hi and welcome to the forum.

It’s a shame it’s under these circumstances.

It should be pretty easy to check to be honest.
Take a coin of the realm and gently tap the floor.
If the tiles change in tone when tapped, you’ll have your proof.
Typically dot and dab is fixed with 4-5 dabs.
One in each corner and maybe one in the middle, depending on format size.
So if they sound solid in the corners and hollow elsewhere, you can be pretty sure the ‘dot and dab’ method has been implemented.
This is a recipe for disaster with ufh, it overheats the free air and the tiles typically ‘pop’ off the adhesive.
It’s also an unacceptable way of fixing tiles to a substrate, be it walls or floors.

 

[One Day]

I like to use a clean, stiff bristle sweeping brush and by sweeping slowly over the floor, you can hear clearly the change in sound, revealing dabs.
Otherwise, sliding the edge of a coin across surfaces will also reveal dabs.
The only time this is unreliable is if the tiles are fixed onto insulation boards which can tend to sound hollow, even with proper solid bed fixing.
The most reliable method is to use a Flir infra red camera and lay heat mats on the floor to warm the surface before taking pictures which will clearly show the extent of dabs.

 

[Old Mod]

Never thought of that Mark, I’ve a camera, I’ll shall have to give that a go.

 

[Mr S]

The most reliable method is to use a Flir infra red camera and lay heat mats on the floor to warm the surface before taking pictures which will clearly show the extent of dabs.

Thanks for the detailed suggestions. Out of interest, is there a minimum spec/resolution of Flir camera I should hire for this or will a basic one (e.g. E4) do? Also, is this a specialist "heat mat" or the sort of thing you might use on stiff joints etc.?

Thanks again.

 

[Mr S]

Thanks all for your suggestions.

I tapped the extent of the surface(s) yesterday and (to my untrained ear) many sounded fine/consistent, but since some of the tiles are on different types of surface (e.g. plasterboard on the shower walls) it's hard to say for sure as they were definitely different (and a lot more "hollow").

(It may be the "techie" in me but the camera option sounds like the most foolproof).

Thanks again!

 

[Mr S]

The most reliable method is to use a Flir infra red camera and lay heat mats on the floor to warm the surface before taking pictures which will clearly show the extent of dabs.

Hi. In relation to the above. Could I please ask - Do you have a recommendation as to what type of “heat map” is best for such an experiment? I’ve decided to go down the FLIR camera route.

Many thanks!

 

[WetSaw]

Wouldn't using the camera with the ufh running show up the fixing method?

 

[Mr S]

Wouldn't using the camera with the ufh running show up the fixing method?

Yes. I did also think that. My guess is that you would want an even heat over the tile? With UFH would you not mostly highlight the outline of the pipes rather than be able to see where dabs are?

(And, I meant “heat pad“ of course, not heat map! (Darn phone typo!))