Technical Issues Q&A

Hey Riley,

I was sent an inquiry from one woman working in Mexico and another working on a wall in Wisconsin, which I fwd to Eric, 'cause I know he's worked in both places. I'm interested to know if your experience jives w/ his regarding sealant and use of latex-enhanced thinset. Are you familiar w/ the Laticrete 4237 plus sanded grout formula for thiniset/grout combo? Seems we've discussed it, and I've been using it for more than 10 yrs.



Gonna have to postpone our discussion of your repair pics a bit.


> From: Eric and Lindsay Rattan <>

> Date: Tue, 25 Jan 2005 21:07:41 -0600

> To: George Fishman <>

> Subject: Re: mosaic mural in cold climate

> Hi George,  Here are some thoughts on Wis. exterior mural.  Sealed 

> concrete wall. Yes,  ---scratch, sand or sandblast to insure mech. 

> bind, and make sure the mosaicist is using the word concrete correctly. 

> It is frequently used incorrectly. Signs of stress on wall may call for 

> and underlayment or reinforced mortar after sandblasting.  THINSET  be 

> sure exterior grade TILE Not all glazed porcelains are frost free . 

> Call manufacturer for tech. data. Call Eric for home test 608 231 

> 1883. Glaze fitting is a potential bomb here. (tech. ceramic term) Sanded GROUT 

> and a homemade course silica has some advantages. Call Eric to 

> discuss. No sealers. I don't recommend using a grout and additive for 

> setting tiles unless there is a real good reason, such as transparent 

> tiles where adhesive shows. 

SEALER  no! Stone /ceramic sealers are vapor 

> permeable which is a must but they hold as much moisture in as they 

> keep out so in the masonry trades sealing can be a cause for 

> failures.

CURING  The old standard of damp curing cementitious 

> applications  is still valid today except for many additives such as 

> latex. Latex additives can effloresce and most grout companies do not 

> want you to damp cure latex mod. grouts. The additive slows down 

> hydration so damp curing is redundant and often harmful.  If you feel 

> like you must seal (shower stall, soap scum ) for example, wait 30 days 

> minimum. Mosaic books are riddled with artsy craftsy info. I review the 

> tech sections of these books and am amazed at what I read. While I 

> appreciate the books and have purchased many, they are generally a very 

> poor choice for tech. info. That is the nice way of saying it. 

MEXICO wall.  30 days to let new stucco finish cure before applying tessarae. 

> In many cases this is impractical so it is generally safe to procede 

> after 2 wks. This is a good place to damp cure and use a reinforced 

> mortar. If you cannot find nylon or fiberglass for your sandmix use the 

> centuries old standby----  horsehair.  It is every bit as pemanent as 

> nylon or fiberglass. If there is a seismic factor here call Eric for 

> info. Because of the many many variables , I do not answer tech. Q's 

> from artists by email but phone only so I can get to the bottom of Q's 

> like. Is the wall really concrete?  Describe the wall. and so on and so 

> forth. I don't trust this machine so let me know if you rec. this   

> Thanks George.

> On Jan 25, 2005, at 9:19 AM, George Fishman wrote:

>> Hey Eric, regarding the Mexico project, if they put new mortar on the 

>> wall,

>> how long should they wait before applying thinset? Could you pls add 

>> that,

>> as well as any other suggestions for her.

>> Thx, g

>> -- 




>>> From: George Fishman <>

>>> Date: Mon, 24 Jan 2005 15:13:49 -0500

>>> To: Eric Rattan <>

>>> Subject: FW: mosaic mural in cold climate


>>> Hi Eric, if there's anything you would like to add...... (or delete!)

>>> All the best,

>>> g




>>>> From: George Fishman <>

>>>> To: "C. O'Malley" <>

>>>> Subject: Re: mosaic mural in cold climate

>>>> Date: Mon, 24 Jan 2005 14:44:16 -0500


>>>> Hello Carrie,

>>>> Congratulations on your new project.

>>>> For starters, I would suggest you read these and other publications 

>>>> of the

>>>> CTI.



>>>> Here's the general list:



>>>> 1. Be sure the wall is smooth and flat. Any bumps and dips will be

>>>> "telegraphed" to the surface of the mosaic, unless you're using 

>>>> mat'ls of

>>>> varying thickness, which will require a lot of thinset anyway. (thick

>>>> thinset!)


>>>> Verify that surfaces to receive mortar setting bed and tile are 

>>>> firm, dry,

>>>> clean, and free from oily or waxy films and curing compounds.


>>>> If the concrete substrate has a hard steel trowel finish or if curing

>>>> compounds were used, then the concrete must be heavily scarified. If 

>>>> sealant

>>>> was applied, I would do a test, because some sealants will tend to 

>>>> "shed"

>>>> thinset -- bad news.


>>>> 2. Don't use absorbent wall tiles or soft, absorbent stones (ask your

>>>> suppliers). As a rule of thumb, if water dripped onto the back of a 

>>>> tile

>>>> gets absorbed, don't use that kind of tile. Commercial floor tile, 

>>>> including

>>>> quarry tile, is generally non-absorbent, so are porcelains (glazed or

>>>> unglazed); glass is good too. Otherwise, moisture soaked into the 

>>>> tesserae

>>>> will freeze/expand and pop loose or pop their glaze.


>>>> 3. Use a latex-enhanced thinset (or epoxy, though epoxy is 

>>>> considerably

>>>> trickier). Laticrete's sanded grout can be mixed with their #4237 

>>>> additive

>>>> will create a colored thinset that can also be used for grouting. 

>>>> Mapei (and

>>>> probably other manufacturers) makes comparable products.


>>>> 4. Dampen, then cover work completed each day with brown Kraft paper 

>>>> to

>>>> control drying/curing.

>>>> This will help keep grout from developing a mottled appearance.


>>>> 5. Even after using the best setting materials, be sure to apply a

>>>> penetrating sealant (generally after a minimum of three days after

>>>> grouting). This is critical to keep the same freeze problems from 

>>>> occurring

>>>> with the grout/thinset. Normally, sealant needs to be re-applied 

>>>> after 6

>>>> months or a year.


>>>> 6. Some installers prefer working from the top down, so that thinset 

>>>> and

>>>> grout drips don't fall on the just-installed sections. Others prefer 

>>>> to work

>>>> from the bottom up, taking advantage of "stuck" sections to keep 

>>>> progressive

>>>> sections from sliding down. This is mostly an issue if you're using 

>>>> a face

>>>> or mesh mounting system. If you're not familiar with face and mesh 

>>>> mounting,

>>>> you need to buy one of the many recent books on making mosaics.


>>>> Another good source of information is the Yahoo Mosaic Artists 

>>>> Organization

>>>> newsgroup


>>>> Good luck!


>>>> So, here's my question:

>>>> I am going to be doing an exterior wall at a school (I live in 

>>>> Wisconsin -

>>>> lots of freezing and thawing in winter - and high temps and humidity 

>>>> in

>>>> summer) and would like your recommendations for products.


>>>> First, if the concrete wall is sealed, what do I do?  Any prep work 

>>>> that you

>>>> recomomend? Second, should I use thin-set as the adhesive for the 

>>>> tiles.

>>>> Thirdly, what tiles fair best in this climate outdoors?  I would 

>>>> like to use

>>>> glazed ceramic because it will go quicker (the wall is over 20 feet 

>>>> long).

>>>> Do you have a grout and additive that you would recommend?  Sealer?  

>>>> Any

>>>> other tips?




copyright George Fishman 2017