Yes it's acceptable as a substrate, however, the more important concern needs to be in the waterproofing of the grout and the sealing of the brick.

Wonderboard is a brand of fiberglass-reinforced cement backerboard. This material has little strength in bending so it must be well supported. It's advantages are that it can get wet and not deteriorate and cementitious mortar will adhere to it.

I would be cautious about using any kind of porous surface in a cooking area. IMO tile is a poor surface and brick would be worse. I would consider large pieces of slate, soapstone or honed granite and seal them well.

Snoonyb: thank you! Any special kind of grout I should ask for ( sealant, too) ?? I want to make sure everything is spelled out before we start.

Renovator8: Thank you for your feedback.
(This is an outdoor bbq and the brick top is next to it for placing food, utensils, etc).
When you say the Wonderboard should be well supported, do you mean there should be some kind of bar/wood etc beneath it? Please tell me.
I know the contractor did not mention any under-support material for the WB at all, just said the bricks would go over the Wonderboard.
What would a porous surface do in this situation - since you said the wonderboard would not deteriorate when wet, I'm assuming you mean stains/cleaning etc? Again, please tell! I am totally ignorant about anything to do with building materials and what I learn is from online sources only.

Also, if anyone can please tell me if the price quoted to me by the contractor is reasonable, I'd appreciate it - or at least, a ballpark figure, so I know.
Thanks!!!!

Is the structure of the BBQ wood or steel?
What's the area being covered?
Are you N, S, E or W of LA?

If he's self composing the grout the he needs to use Red Label cement for the mortar and grout.
There are premixed mortar and grout which are "modified" in that they contain a vinyl ad-mix.

Since there will be a food preparation area, the sealer must be approved for that purpose, as well as properly maintained.

snoonyb: Thank you so much for your kind help. We are northwest of LA in the San Fernando Valley.
I will post a picture later this evening of the bbq area.
The bbq from (Barbecues Galore) sits in a brick structure; the current tile has wood beneath which has deteriorated and caused the tiles to sink in, in one area.

Fiberglass reinforced cement board is a backer board for vertical and horizontal tiled surfaces. It will not deteriorate when wet like gypsum and wood backer materials. But it has little structural strength and should be supported every 16" on a vertical surface and fully supported on a horizontal surface. Basically the object would be formed with a structural material and the cement board would then be put over the surface of it so what is used for the base is very important.

The issue with porous surfaces in a cooking area is bacteria. In an age of increasing drug resistance of bacteria (23,000 people died of it last year) I would want something very dense and very smooth in order to reduce the chance of cross contamination. Meat is rarely an issue if it gets thoroughly cooked but it can contaminate uncooked foods if you prepare them at the same time on the same surfaces or with the same utensils.

Renovator8: Thank you.
Here is a pic of the bbq for you and snoonyb.
You can barely see where some of the blue tile has sunk in; we will be putting in a new ss bbq of the same dimensions and an ss door below. There is a natural gas connection beneath.
The existing brick structure below bbq grill will remain; only the surface will be re-done with used brick and we will have a 6 inch 'wall' ( ledge) running behind the bbq on top. ( am I making sense? ;-)).
The plug point on the right side wall will remain as well. To the left of the bbq there is a narrow tiled area.
The area is exposed to hot sun during summer ( no shade directly overhead).
Please give me your suggestions/advice and please also let me know what I should expect to pay( ballpark) for this job.
Thanks a lot! :-)

"(Barbecues Galore)" uses local subcontract vendors for their site installed BBQ's.
Another word of caution. When the existing tile and associated rough-top is removed, there may then be additional structure damage.
If you have not, you might want to do that first. For-warned is fore-armed.
I have not worked in your area for several years and no longer have any contacts to refer you to, however, you could try THEBLUEBOOK.COM, which is a self-policing listing of contractors by trade and geographical area.

"(Barbecues Galore)" uses local subcontract vendors for their site installed BBQ's.
Another word of caution. When the existing tile and associated rough-top is removed, there may then be additional structure damage.
If you have not, you might want to do that first. For-warned is fore-armed.
I have not worked in your area for several years and no longer have any contacts to refer you to, however, you could try, http://www.thebluebook.com/ which is a self-policing listing of contractors by trade and geographical area.

Snoonyb: Thank you so much for the heads-up and also for that link - very kind of you.

You are quite welcome, even of it doesn't fit.

I'm going out on a limb here. Given it's BBQ Galore, and having been exposed to their products, I would surmise that you may not have a brick BBQ, but a wood structure and faux or artificial brick adhered to hardy-backer or wonder board. Which, in my experience, has been a typical construction, mine were steel framed. and you may be able to tell by looking inside and doing some measuring.

Make sure you know exactly what you are getting estimates for, because faux used brick is relatively inexpensive.

Hi snoonyb,

Thanks for the info. We didn't use BBQ Galore for the construction - just bought the bbq from them and had the general contractor who did all the paving/brick /spa work in the backyard of our then-new home ( he did the work in 1991) also build us the structure and put in the bbq and connect the gas line.

I'll check inside anyway, by daylight tomorrow!

The info on faux used brick is very helpful - how does one know it is faux( if we use it now for the surface)? There I go again with another stupid question - sorry.

Depending upon the mfg. faux masonry products can vary from 1/4" too 3/4" thick, brick is usually 1/4".

That's a different story. Constructed by a contractor would indicate a better quality, however, as I mentioned earlier, when the top is removed you may find additional deterioration of the structure, so be prepared.

Faux masonry products are generally less porous than masonry products, because of their composition.

Because of the manner that tile counters are constructed
you will also need to replace the vertical trim tile.

There are numerous web sites which define and example tile counter composition.

Thank you, snoonyb! Yep, we will also be replacing the vertical trim tile.