I am looking to do a castle cake in a couple of weeks and I had read somewhere that you can use square cookie cutters to make the "Brick" design. I just realized how VERY time consuming (and probably not really all that reliable!) that is going to be... was thinking of perhaps using an impression mat.. my local cake store has the small 5x7 impression mat for the brick design.

Question... can I put the fondant on the cake and then use the impression mat on the sides?? (I don't want the top to have a brick design). sort of like this picture.... http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1708512

I've never used an impression mat before and was just wondering how difficult it would be... any tips or tricks are welcomed!

I really like impression mats because they are so versatile. If you will have enough room to get your hands around all the towers you can use the mat after the fondant is on the cake - the big trick is to get the impression evenly imprinted all over the mat. To do this you will have to be able to exert the same amount of pressure over each square inch. You might try the mat on a practice piece of styro or on just one tower before you get all the fondant on the cake. See if you like doing it that way. I usually just impress a large piece of fondant flat on the table and then wrap it.
Get a piece of thick upholstery vinyl from Jo-Ann`s or another fabric store. Make sure it has no fold marks in it. Lay the vinyl down on the table and place the impressed fondant pattern side down on top of the vinyl. Use the vinyl to carry the fondant to wherever you want it to be.
You may have to put a very tiny amount of water at the top of the piece of fondant to temprarily stick it to the vinyl - just don`t put much and put it on a place that will eventually be cut off or it will make a shiny spot.
Gently use your hands to smooth the fondant onto the cake so that you don`t rub out the impression. Voila!
If you find that you have obliterated the pattern in a spot or two, use a tool to remake the general outines of bricks. If it is not too obvious the eye will fill in the details and people won`t notice. You can also try to line the mat back up and re-impress the small section.