Any info on a moisture membrane under the slab - I have seen in other countries the use of plastic sheeting at the base of the slab - each strip of black plastic joined with a special adhesive tape - a bit like gaffers tape for those in the music industry. It is the standard approach in OZ and NZ for example and stops the rising damp as I understand. I asked today at Home Pro in Phi Mai and they could only direct me to a large roll of glad wrap - the sort used for wrapping furniture prior to storage or your suitacase at an airport as a security measure or for use as a painting drop sheet in Thailand. I have seen a lot of paint and render bubbling off walls in my own place and elswhere in Thailand (not related to plumbing problems) and was wondering if there were any first hand comments about this practie in LOS?

Phi Mai is outside of Korat, right ? You want to go and find a normal Thai hardware store, or someone that does agricultural supplies for the plastic sheeting. Perhaps around the market there. I bought 20 meters of the stuff last Year, on a roll - black, heavy grade, and folds out to a 4 meter width. I use it to dry out cashew nuts on, but could serve as the liner you're after. Round about 20 - 30 baht a meter. (1x4). I have heard, if you use the liner, your floor can 'sweat', depending on the climate you're in, but don't quote me on it - wouldn't waterproofing the concrete have the same effect ? I see a lot of paint bubbling off walls here, especially on a low level, in and outside houses that aren't raised up off the ground. I would imagine, a lot of contractors who do a job price for materials and labour don't waterproof their foundations, wait for long enough before painting new render - don't acid wash the render and / or use a priming coat for the paint, and use the cheapest paint. I'm sure there are some professionals on this forum who could explain it better than me.

Many thanks Ackybang - I found the black heavy duty plastic sheet on a 40 meter roll x 4 meters wide and the waterproof tape to join it together. Also found a builder that seems to know what to do about it - I did download pictures and photos (some from Thailand) putting the plastic down and then the steel reo up on supports for hopefully 100mm house slab. I got the plastic from Global House in Korat - 50kms from Phi Mai

cheers!

To enclose the ground floor [with non-loadbearing block walls i assume] later on is the stated objective in the OP, so concrete grade beams are necessary; dims & rebar depend on beam spans; use engineer's drawings. Kwasaki is correct, the slab thickness is inadequate; it should be 100-120mm, with a rebar grid held up off the bottom surface.

As to cost, they are ripping you off, assuredly. concrete is approx 2000 per cubic meter. steel is expensive so get a quote or receipt for payment. They can use conc blocks for formwork, at 6 bath per block. One week's work for four guys... do the math, ajarn.