Any grout will do, but Polyblend is available everywhere and is of good quality. Get a light colored grout, white if you can, as it will be easier to dye a certain color. I personally use a mix of sanded and non-sanded, as sanded grout is much stronger, but non-sanded can be thinned down more. I start by using non-sanded grout in a soupy consistency for the first 2 layers. I then use a mixture of 3 to 1 non-sanded to sanded grout in the consistency of syrup. I only start adding color on the 4th layer, with a 50/50 mix of grouts. I personally use concrete coloring, as a little bit goes a long way. However, basic acrylic hoby paints will work, and there is usually a greater variety of colors. Some people paint over the grout, others just add highlights once its all done. Doesn't really matter either way, but if you paint over the grout completely, then a couple different sealing options are open to you.
To seal it, you have several options...and I am going way overboard explaining them here, but its something that comes up a lot. I'm sure there are more complete references on the net.
#1. Perhaps the safest and easiest to get is Mod Podge (matte or gloss). Durable finish, but it isn't water proof. Wiping with a damp rag is fine, but prolonged contact with water will break it down. Non-toxic at any stage, its a great sealer for cautious beardy parents. It's so cheap and it dries so fast, that resealing every few months isn't that big of a hassle. I've only ever needed to reseal my grout structures once in 2yrs, and that's with my dirtiest beardy. My clean beardy has never had his structures recoated, and they are still in great condition. This coats painted and unpainted grout equally well.
#2. Mod Podge also makes a "hardcoat" variety, and an outdoor version. The hardcoat is very tough, and its water resistant. A bit slicker then standard mod podge, but overall a nice product. The outdoor mode podge I haven't been able to find anywhere, but it claims to be very resilient to water, while still being non-toxic. If you can find this, that's what I'd use. Second choice would be the hard coat. A bit more expensive then standard mod podge, but if durability is a concern, this is the better product.
#3. Shields All #50 acrylic sealant. Available online, very water resilient, and non-toxic. Only available online, but if you don't mind the cost...a good buy. Coats painted and unpainted grout.
The above products cure very quickly and have no fumes. I'd say they are reptile safe after just 24hrs, but let the items cure for a few days to be on the safe side. Mod Podged items will stick to hard surfaces like tile if they don't have at least a day or so to cure. My vivs have tile floors, and I've had an item glue itself tot he floor on more than one occasion
. Hard coat mod podge seems to be a lot better in this regard. There isn't a lot of info on Shields All. But looking at its formulation, it should be pretty fast curing. Its a very safe product.
The products below have much longer cure times, and go up a couple notches in the hazardous scale.
#4. Shellac - the substance itself is completely inert and non-toxic. However, its the alcohol they thin it with that's noxious as hell. Shellac is moderately durable, but cleaning solutions will strip it away. It can also melt at high temperatures. I'd use this as a sealant for the cage walls of a desert viv, not high traffic cage furniture. It cures pretty fast, but I'd say at least 3 days until you put it back in the viv. Be warned, spraying the stuff in confined areas will get you higher then the goodyear blimp during the Superbowl (ventilated area a must!), and not in the good way (if there is a good way). Only thing I've ever used that made me more light headed was aerosolized acetone. Shellac only lasts a few months when mixed...you can order pure shellac chunks on the internet, then mix them yourself. Bullseye spray shellac is the brand you'll see in most hardware stores. They also sell brush on, but in large quantities you probably won't use. I'm sure it would coat unpainted grout, but I couldn't tell you how well it would adhere.
#5. Polycrylic and other water based wood finishes. VERY durable, but they take weeks to cure. 1 week minimum, but some people suggest a full month. You could also use traditional polyurethane, but its a 2 week+ cure time, and more troublesome to use. Extremely durable however. Polycrylic is the recommended viv sealer everywhere, and it will hold up to water and various cleaning chemicals better then most. Same as shellac regarding unpainted grout...I'm sure it would work, but I can't give you a definite answer.
#6 Epoxy based coatings - Epoxies are almost always inert and non-toxic when cured. Durability beyond the realm of any other finish, and are completely water proof. Because of the difficulties associated with their application, and long cure times, I'd avoid using them unless it was a semi-aquatic vivarium. People who make wooden fish tanks use various epoxies as the final sealing layer. There is even a brand of epoxy coatings marketed towards herp owners...but its pricey.
#7. Generic spray can clearcoat. If you give it enough cure time, it should be fine. But with the variability among products, cure time could be anywhere from a week to 3 months. So stick with known variables, and choose from something above. Nothing enamel based should be used, and oil based products should be passed on as well.
Anything you can't use? Yes, the stuff that might seem logical to use, grout sealer, is not actually a good choice. Penetrating stone and grout sealers are rather toxic, even when cured. Its not a big deal for a tile floor, as you aren't crawling on it belly first. But to a basking beardy, the prolonged contact might cause issues. Topcoat sealers, like those described above, typically cure to a PH balanced level...most penetrating sealers don't. Additionally, grout on its own is very caustic, and penetrating sealers don't seal the grout completely. Top coat sealers will create a physical barrier between the caustic grout and the skin of your animal. Its actually the cement within the grout that's caustic. Also, penetrating sealers don't protect against surface wear and obviously won't work at all if you coated the grout with anything, such as paint. There are non-toxic options in this category, but you'll be hard pressed to find them at a hardware store. Avoid oil based products.
It really comes down to this. Once cured, almost all hard coatings are inert and safe for direct contact (lacquers and enamels should be avoided). The biggest variable is how long they take to cure. Water based finishes would be ideal, as they are typically easier to work with. Most people would tell you to avoid oil based products...and I agree. Not worth the risk. I personally use Mod Podge for all my grout platforms because its cheap, easy to acquire, safe for my lizards, and most importantly safe for me. Given how many of these structures I make, the fact I can use mod podge indoors with poor ventilation and bare hands is a huge selling point.
